Mid-lean, Fact, Fiction and Science.

[ScooterB]

When I started researching the problem of mid-tank lean almost a year ago I started reading posts and articles from many sources including this one and spent a lot of time talking to other enthusiasts as well as a couple educated and knowledgeable engineers to get as much information as I could get. This is a very debated topic and often touchy with differing opinions and observations. There are many opinions and a lot of misinformation running wild. My intent is to try to explain what I have learned objectively and scientifically as to what works, what doesn’t, and most importantly why.
Hopefully this will be informative and help some people understand how, what and why and even save them a little money and aggravation along the way.

One important point to note is that this problem is not limited to the Savage truck. Mid-tank lean is a common issue in the nitro rc industry. It is real and it is a problem. Although the Savage has a couple design issues that magnify this problem to the point it can become a real pain creating tuning issues and/or even engine failure. Most enthusiasts overcome the problem by running a little rich whether they realize it or not. I’ve also noticed that many enthusiasts don’t bother to check temps after their initial tune and run off and play blaming higher temps on run time. A properly tuned and fed engine will maintain a fairly constant temp throughout a run.

There are many issues that contribute to the mid-lean problem on a Savage, the first is what is referred to as head pressure. Head pressure is the weight of the fuel pushing on the fuel line. Obviously a full tank is heavier than an empty tank. The weight of the fuel creates pressure in the fuel line. Full tank = pressure, empty tank = no pressure. This is easier to demonstrate on a larger scale. Anyone who has ever emptied any container filled with fluid has probably noticed that as the level is reduced the flow slows down. This is a result of head pressure. Some good common examples would be emptying a large cooler through the drain hole or emptying an above ground swimming pool or water bed. The result is always the same, lower level = lower pressure and flow. Another important aspect of head pressure is that it is constant. It doesn’t matter if the body of fluid is an Olympic size pool or a fish bowl. At any specific depth the pressure will be the same. At 2†depth the head pressure in the pool is exactly the same as the fish bowl, or your fuel tank. Some will argue that the mathematic difference in head pressure is only .08 psi or something like that. The problem is that .08 is huge when you are talking about a system that runs at a peak of less than .25psi. That is a difference of over 30%. Combine that with the positive, negative siphon effects of the tank mounting height and the difference is astronomical.

The second problem is the pressure vs. siphon effect. Anyone who owns a savage has probably noticed that the seam and shelf in a savage fuel tank is just below the midline of the carburetor. When the tank is full the level is above the carb creating positive pressure and when low or empty is below the carb creating negative pressure or vacuum. Liquid will always flow to the lowest point in a siphon and if you raise the drain end higher than the supply it will stop and reverse the flow which is exactly what happens as the fuel level lowers in the tank. This combined with head pressure creates a significant difference in pressure to the carb. When the tank is full, fuel will push itself to the carb as in a siphon. When then tank is below half full not only does the fuel weigh less, it is also lower than the carb and has to be pushed or pulled up to the carb. Also keep in mind that in a nitro rc the fuel tank is effectively the float bowl of the carburetor without the float. Anyone who has spent any time setting up large scale carburetors properly understands the importance of correctly setting the float level. In a nitro rc setup there is no adjustment and the level varies as fuel is used.

The third problem is fuel slosh. In any moving vehicle fuel will slosh around in the tank. When the tank is full there is very little chance that the fuel pickup will be exposed to air. As the level decreases the chances increase. On a road car or boat this is not much of an issue, but in an off-road environment the vehicle is constantly being tossed around as well as the attitude being changed as it goes over obstacles or climbs and descends hills. And also in braking and acceleration. In aircraft, clunk lines are used to keep the fuel pickup at the lowest part of the tank regardless of attitude.

The biggest problems with the stock fuel tank are 1- Its mounting location relative to the carburetor. 2- Its height because it creates a greater difference in head pressure. And 3 the stone filter on the pickup tube as it allows air into the lines when exposed.

“But the exhaust system pressurizes the fuel system†Yes and no. Yes at mid to high rpm. No at idle to low rpm. Most nitro RC vehicles have fuel tanks mounted below the level of the carb. Something is needed to keep the fuel supply moving to the carb. Many have experienced running a nitro rc without the exhaust pressure due to a failure of the pressure tube or exhaust pipe while running and notice that they still seem to run quite well. The reason? The carburetor is doing its job. A carburetor creates a vacuum in the venturi which pulls the fuel in and atomizes it. All carburetors work on vacuum to pull fuel from a float bowl or source of fuel. With pressure applied the fuel will flow through quickly supplying the engine with the needed fuel. Although exhaust pressure can be quite erratic depending on how you are driving, bleed off is immediate and pressure builds as rpm and load increases.

What works, what doesn’t, and why.

ONE WAY VALVE IN EXHAUST PRESSURE LINE
Many have suggested and tried to install a one-way valve in the exhaust pressure line in an effort to store and hold the pressure created at high rpm and maintain a constant pressure. Initially this sounds like a reasonable solution, BUT. What happens is that the pressure is stored and pushes the fuel regardless of engine demand or even whether the engine is running. Remember that your engine will run without exhaust pressure. It does not need or have pressure at low rpm, The carburetor will draw fuel through the line.
The result is a flooded engine and possibly a hydro lock situation as the fuel is forced into a non running engine. As well as erratic tuning as the pressure may be high or low depending on how the car has been run.
RESULT; Does not work. Causes erratic tuning and flooding.

CLINE REGULATOR
How it works and what it is.
This is a fuel flow regulating device.
The fuel tank is pressurized from 2 to 12 P.S.I. by a unique one-way check valve with the pressure from the crankcase of a two-cycle engine or from the exhaust of a four-cycle engine. This forces the fuel to the controller under that P.S.I.
The controller is mounted either beside or directly behind the engine. The carburetor’s fuel line suction acts on the diaphragm in the controller causing it to open the fuel valve in the controller. It is a demand controller; thus as the carburetor’s fuel line suction increases, the amount of fuel the controller passes increases. When the engine is stopped, no fuel can enter the carburetor.
Links; http://www.billsroom.com/pcfs/products/CFS/fuelsysdescx.htm
http://www.billsroom.com/pcfs/products/CFS/pcfs_details.htm
Does it work? In theory it sounds great. Regulated fuel supply on demand. Controlled fuel delivery. Fuel cannot flow to the carb if engine is not running.
I have not tried this and have not found anyone who has on a car application. It is on the pricey side though at $60 currently and some people question the amount of pressure put on the fuel tank. Although 12 psi is really not that much. Also it requires a fitting to be drilled and tapped in the crankcase, which I have done, (for Perry Pump) and had absolutely no issues as a result. I am also wondering what the effect on the engine would be due to opening the cc up to such a large area as the cc pressure is what is used to force air/fuel into the combustion chamber.
RESULTS; this may work to provide constant fuel pressure and flow but will not do anything for fuel slosh/starvation

 

[ScooterB]

HEADER TANKS
A header tank is a secondary fuel tank mounted in a different location which is fed from the primary tank. (usually higher) The theory is that the smaller tank which maintains a constant level will provide constant pressure to the carb which will eliminate mid tank lean. Scientifically this is untrue as the header tank is essentially just a large cavity in the fuel line which is still affected by the head pressure and siphon properties of the main tank because it is fed and pressurized by the main tank. In order for a header tank to work as per theory it would have to be separated from the closed system. This would require a method to keep the header tank filled without being affected by the head pressure of the main tank either through a pump or some type of control valve/float valve.
Sorry guys. Although many have done this and claim that it helps, the only real benefit is that it would work as an air-fuel separator. Consequently it also complicates fueling up.
Scientifically it is unfounded. It does not work.

EXTENDED AND REROUTED FUEL LINES
Try this little experiment. Grab two identical pieces of fuel line, one a couple inches long and the other a couple feet long and blow through them one at a time. The difference is amazing. The longer tube has much more back pressure. The only thing this will do for you is add extra fuel lines and reduce fuel flow and pressure. In addition each bend reduces flow much more.

PRESSURE TUBE FROM CAP TO BOTTOM OF TANK
The idea here is to attach a small length of fuel line or rigid tubing to the bottom of the fuel cap exhaust pressure hole which runs to the bottom of the fuel tank. Initially I dismissed this idea as a great way to blow bubbles in your fuel and create foam. Although it may have some merit I am not sure to what degree. In actuality the weight of the fuel (head pressure) may act as a regulator to the exhaust pressure. When the tank is full and head pressure is high the exhaust would have to overcome this to pressurize the tank resulting in lower tank pressure when full. As the level lowers and head pressure decreases the exhaust pressure would increase. But if the exhaust pressure is much greater than the head pressure the effect is lost. Hmmm. Something new to think about. But does it mathematically balance out? The drawbacks are similar to the one way valve in the exhaust pressure line with the exception that excess pressure can bleed off although it would not be immediate and trapped tank pressure would force fuel back into the exhaust system at low pressures like idle and when the engine is not running. And the resulting bubbles could create foam in your fuel which would create a lean condition.
RESULTS; since the only way to bleed off excess pressure from the tank would be to force fuel back into the exhaust pipe I’m saying no. And IMHO foamed fuel can’t be good.

FOAM INSERTED INTO FUEL TANK
This is a simple method of inserting open cell foam into the fuel tank.
Well this one does help one aspect of the problem and that is fuel slosh exposing the fuel pickup. But does absolutely nothing to overcome head pressure effects. One of the main problems is fuel slosh, I have experimented and proven this to be true. The fuel pickup is located at the rear of the tank so that when accelerating or climbing a hill the fuel will flow to the rear and cover the pickup. In theory this is great. The problem is that if you go up a hill you also have to come down. On a road car or boat this is not so much of an issue but with a savage or any off-road vehicle the rough terrain also causes the fuel to slosh around which momentarily exposes the fuel pickup.
RESULTS; This will help minimize the problem of fuel slosh but does nothing for head pressure or the pressure/siphon effect.

AFTERMARKET TANK IN STOCK LOCATION
Many people have installed aftermarket fuel tanks and modified them to mount in the stock location with most people being satisfied with the results. Why it works and why it is not a complete solution. In my research the tanks being mounted in the stock location are 1 smaller (less fuel weight = less head pressure) and 2 shallower than the stock tank, (less head pressure and less variance in head pressure). The relationship in mounting height to the carb center also plays a role. The downside to these tanks are reduced run time due to smaller capacity. Although scientifically it is not a 100% cure it does reduce the effects to a more manageable level which many are able to tune and run successfully. Some have theorized that the shelf in the stock tank affects tank pressure. This is not true. In actuality the stock tank design effectively funnels fuel to the pickup. The height of the stock tank (head pressure) and the location of the tank in relation to the carb center (pressure vs. siphon) combine to create the problem. Also the stone filter in the bottom of the stock tank allows air to enter the fuel line as the level becomes lower and sloshes around because it is easier to pass air through the filter than fuel. This creates air bubbles and a lean condition.
RESULTS; In my opinion it would be much easier and safer to run with the stock tank and only use the top half above the seem refilling before the level falls below the shelf.

MID-TANK CONVERSION
A mid-tank conversion mounts an aftermarket fuel tank in the area where the radio and servos are located in stock configuration. This requires relocating the throttle servo to the area next to the engine and relocating the steering servo underneath the new tank and relocating the radio gear and radio batteries to other locations on the truck. Locations vary due to personal preferences but are usually located outside the frame rails or next to the new tank depending on tank size. The tanks used for these conversions carry up to 250cc of fuel and move the weight forward on the vehicle which many prefer and claim improves weight balance and handling as a result. Obviously the much larger fuel cells offer extended run times. These conversions are becoming increasingly popular and have some pretty obvious benefits, and are felt by those who use them to be the ultimate cure. Usually the tanks being used are shallower than the stock tanks which most likely plays a large role in the success of the system. (Lower head pressure and less variance) Although scientifically speaking they are still subject to head pressure, exhaust pressure variances, and fuel slosh. The result from a scientific standpoint is that although highly successful there would still be a fuel line pressure drop as the tank level decreases. Also from what I have observed the fuel tanks appear to be mounted slightly higher than stock and in relation to the carb which would in theory promote fuel running into an engine running or not.
Because this system does not overcome head pressure entirely, from a scientific standpoint in my opinion it cannot be called a 100% cure. Although in real world use it may be good enough.
RESULTS; This is an improvement to the stock configuration. It may work to a very manageable degree. Although scientifically it is a remedy not a 100% cure.

FUEL PUMPS
Perry Pumps brand fuel pump. In the case of a fuel pump, a small pump is used to feed fuel to the engine and carburetor. These have been used in rc aircraft for many years and have been used in rc cars with varying degrees of success. Although these require a little skill and thought to install for the most part they can be done with basic mechanical knowledge. Installation is fairly straightforward requiring a hole to be drilled and tapped into the engine crankcase to provide the pulses needed to operate the pump and another hole drilled and tapped in the fuel tank to provide a return line for excess fuel and pressure. Other than that the fuel goes in one side and out the other to the carb with a T fitting routing excess fuel back to the fuel tank. And another tube on the bottom of the pump running to the crankcase tap fitting for the pulse waves that power the pump. This creates a constant flow system. With this pump installed it is not necessary, and discouraged, to connect the exhaust pressure line to the tank. Instead a one-way valve is installed to the tank fill cap in a way as to let air vent into the tank but prevent fuel from running out in the event of rollover. Why it works. The pump completely isolates the supply to the carb from the variance of head pressure, pressure vs. siphon effects, and exhaust pressure fluctuation. Remember back to the header tank issue of not being able to isolate the header tank from the main tank? This system creates the correct situation by isolating the fuel supply from the main tank, but an extra tank is not required. The fuel line creates the equivalent of an isolated header tank or float bowl with plenty of fuel delivery and excess fuel and pressure returned to the main tank. What doesn’t work? The stock fuel tank pickup. In the event of rollover the pump moves fuel so fast that it is likely to run out of fuel and stall and the stone filter in the bottom of the tank would rather allow air through instead of fuel creating air bubbles in the fuel line when the tank is low. As a result a clunk line is recommended to cure both problems. The other limiting factor in my testing seems to be high rpm functionality. Aircraft run rpm’s in the low 20k range whereas car and truck engines run up to 40k rpm.
http://www.perrypumps.com/nitro_page.htm
http://www.perrypumps.com/prod02.htm
RESULTS; Works great to a point. The limiting factor seems to be RPM as the pump seems to lose effectiveness and efficiency at high RPM

 

[ScooterB]

CLUNK LINE
This device does not address the issue of mid-lean but it does address the issue of fuel slosh and starvation. The stock pickup is a stone filter designed to keep large debris and dirt particles out of the fuel line. It is rigidly mounted. Funny thing is that its almost exactly the same as the air stones used in an aquarium to make tiny bubbles which is exactly what it does in the fuel line when exposed to air which is what happens as the fuel is sloshed around. A clunk line is a small weighted fitting which is free to move around the fuel tank falling to the lowest point with either gravity or g-force. Ideally the clunk would move to the front of the tank while braking hard or descending a hill and move to the rear of the tank under acceleration or while climbing a hill. It would also fall to the top of the tank in a rollover ensuring a constant supply of fuel. The stock savage fuel tank has too many ribs and obstacles to allow the use of a clunk line as the line would get caught or tangled in the webbing. But, with an aftermarket tank?

IN SUMMARY
In a perfect world we would all be running electronic fuel injection or carb’s with float bowls, but in the world of rc where packaging and cost both play major roles in the end product we have to make do with what is available.
An ideal system would provide constant unchanging pressure and prevent air from entering the fuel supply line.
The current system of using exhaust pressure to help push fuel to the carb is the industry standard. It is cheap and simple and works well enough for the manufacturers and most users. The problem is that it is not very accurate at compensating for variations in fuel level. Its not perfect but it works.
So what should you do? Well the simplest and cheapest thing to do is nothing. Use the stock tank but refill it when it gets to the seem. This actually means you’ve already used 2/3 of the fuel or around 110cc. The mixture settings should be fairly consistent as the fuel at this level is above the carb centerline and the chances of air entering the lines due to fuel slosh is minimal.
If you want more then consider all the options and the cost vs. benefits. Gather facts and ignore opinions then make an informed decision as to what you are willing to do.
What not to do. NEVER run the tank empty. This goes for all tanks. This is a guaranteed way to run lean and damage your engine. The stock pickup is partially exposed when the tank level is at about 3/8†from empty. (Sitting still on level ground) Refill well before it is empty.

Hope this helps explain how things work and why. Good luck.

 

[frddyj]

how did the perry fuel pump end up workin out for ya?

 

[Pope]

Great write up.

 

[Bankrupter]

didnt you start a thread like this last year ? perry pumps have been tested a few times fred . .. they are good for adding a smoke system to the exhaust but thats about it on a screaming 28

 

[Shaun]

nice writeup!! some interesting reading there.............

 

[frddyj]

perry pumps have been tested a few times fred . .. they are good for adding a smoke system to the exhaust but thats about it on a screaming 28

yep, true.

last year scooter was onto the perry pump hard & strong & then vanished before giving a review after a lot of running with it.

the time of putting this thread together makes me wonder if he got the pump to work or not, wasnt pleased with the results or just wanted to find out more to keep researchin like this.j

 

[Purenitro]

Great writeup and for a lot of it you are correct, there are however some discrepancies in the info, it's just so big lol, I'll read the other half later.

 

[Bankrupter]

yep, true.

last year scooter was onto the perry pump hard & strong & then vanished before giving a review after a lot of running with it.

the time of putting this thread together makes me wonder if he got the pump to work or not, wasnt pleased with the results or just wanted to find out more to keep researchin like this.j

the man above this post used them and told me they don't work on .28's way back then.. I almost put the info in that thread but I just left it alone ...

 

[ScooterB]

Sorry about vanishing like that guys. It was a rough year.

As for the Perry Pump, It is a great little product but I found that for this application its drawback seemes to be that it loses efficency at High RPM.
The exact cause is hard to know but could be one of three things. Either the diaghram cant vibrate fast enough or the check valve inside the pump cant open and close fast enough or the fuel itself may be foaming inside the pump. I don't know but it drops off at the upper RPM of this engine. You cant tell unless you do a long high speed run and it runs out of fuel after sucking the fuel out of the return line.

But from idle to around 7/8 throttle what it did for the engine was amazing. Smooth idle, instant throttle response, smooth consistent power, instant starting. It seriously made the engine run like it had fuel injection, it was very promising. Runs were consistent in tuning and temp throughout a tank which was the point to begin with.

It was a great experiment though and helped to positively identify the issue of fuel slosh. While running the trucks up and down the face of a large dune. They would literally run out of fuel on the way back down if the tank was 1/2 full.

I'll definitely be using a clunk line in any setup I use in the future.

I have a couple ideas I want to try before I give up on these pumps but I'm looking at all the options right now.

 

[Bankrupter]

Scoot don't forget the pick ups location and orientation when you talk about head pressure. it is a factor but with the outlit above the fuel level it is much less. also motors send less pressure at RPM as well (pipe feed) they have more pressure off idle / low rpm then they do as they spool up..

 

[ScooterB]

Sorry Bank I respect you a lot but according to the engineers and science behind it. The pipe bleeds off most of the pressure at low rpm and it does nothing more than send week pulses to the tank. Each pulse is positive followed by negative. At high RPM you may be right I wont argue that one as the pipes flow and scavenging may pull the pressure waves away. Regardless either way the pipe pressure is inconsistent.

As far as head pressure to the carb the engineers also say the pickup location is not a major player as they all pickup from the bottom. Whether the fitting is at the bottom or the top of the tank makes no difference, the actual pickup location is at the bottom. Its a siphon. If the carb is above the fuel level there is no pressure. If it is below then it does have pressure. The pressure to the carb has to do with the level of the fuel in relation to the carb level. As soon as fuel is pushed into the tube it becomes a siphon.

If you raise the entire tank above the carb then the carb is subject to the full head pressure of the tank (the weight of the fuel) If the tank is in the middle of the carb the carb is subject to only the weight of the fuel above the carb. If the tank is below the carb the carb has no head pressure. It doesnt matter how much fuel is in the tank.

This is simple to prove. Grab a fuel tank and fill it. attach a line to it and prime the line. If you hold the line below the fuel level the fuel will siphon out. If you raise the line above the fuel level it will stop. Simple.

See pics.

 

[Bankrupter]

head pressure is if it were to start w/o priming it .. that is a siphon. the head pressure on its own is zero to start the flow

Call dave a buku. He has studied the pipe and tap pressure more so then a engineers book smarts tell him. I come from a long family of engineers. they can tell you many things that in a lab make sense. But practical science is not the same.

Look up buku. his number is listed and Dave will explain tap flow to you -=as tested=- over a wide base of motors. As he did me years ago.

Purenitro will also agree with my statements and redesigns these motors to work to peak performance.

 

[Bankrupter]

that is why the ofna 250 tank mod works as well as it does. (head pressure/ siphon) Once primed that tank will supply nito with no tap line and barely lean out at all till 1/2 tank tanks point. At that point the tap pressure is good to run a full race tune till 1/8th of a tank where it still wont lean a mill past its allowable limits if you know how to tune. I have had mtl with other mid tank set ups over time.

get the tank above the carb in any set up and you will not see MTL unless you are tuned to lean to start with

 

[ScooterB]

Bank I believe you on the pipe. different pipes and motors will have more pressure at different rpm. There is no point in arguing. The main point is that it is inconsistent.

I'm sure that Buku has the equipment to do the testing which I do not. I am going off of information from an engineer who builds scale V-8 model engines who has also done a lot of testing.

I think we are missing the main point of how the fuel pressure varies to the carb due to different influences and how it affects tuning. That is the whole point of this write up.

 

[ScooterB]

that is why the ofna 250 tank mod works as well as it does. (head pressure/ siphon) Once primed that tank will supply nito with no tap line and barely lean out at all till 1/2 tank tanks point. At that point the tap pressure is good to run a full race tune till 1/8th of a tank where it still wont lean a mill past its allowable limits if you know how to tune. I have had mtl with other mid tank set ups over time.

get the tank above the carb in any set up and you will not see MTL unless you are tuned to lean to start with

Thats the whole point.
Wouldnt it be nice if the tune didnt change at all?
Perfect tune from start to finish.

 

[ScooterB]

the man above this post used them and told me they don't work on .28's way back then.. I almost put the info in that thread but I just left it alone ...

Isn't the whole point of a forum to share information? I remember asking if anyone else had tried these back then. Sure would have been nice to have some of that info and compare notes.

 

[Bankrupter]

Isn't the whole point of a forum to share information? I remember asking if anyone else had tried these back then. Sure would have been nice to have some of that info and compare notes.

It is... my bad I didnt want to cut your wings as you had already tapped the mill when I got that info and was waiting to see what you found too

Thats the whole point.
Wouldnt it be nice if the tune didnt change at all?
Perfect tune from start to finish.

Electric fuel pumps FTW ! lol but a good mid tank helps more then mtl alone so it is a 50/50... I had mtl on 2 150 cc mid tank set ups with my strung out modded stuff ... 250 no issues

Bank I believe you on the pipe. different pipes and motors will have more pressure at different rpm. There is no point in arguing. The main point is that it is inconsistent.

I'm sure that Buku has the equipment to do the testing which I do not. I am going off of information from an engineer who builds scale V-8 model engines who has also done a lot of testing.

I think we are missing the main point of how the fuel pressure varies to the carb due to different influences and how it affects tuning. That is the whole point of this write up.

yea bukus full pipe design works on that pressure. with out it at the right RPM the design would not work at all. I have spent hours on he phone with him chat him up great guy !! he can help you more so with the glow as its his focus. He has big buck test equipment just for these lil suckers. no cheapo x dyno stuff. that man has a 30K brake dyno that test so many parameters its just flat stupid... he is a wealth of info as well as Robin "purenitro" (we are good friends). He would be glad to talk your ear off for hours as well. Well worth the time with what you can learn about glow from him...

 

[ScooterB]

For the record I have been studying and considering the 250cc Ofna setup but also considering one other option and that would be the Cline regulator. My big concern with the cline is opening the cc up to such a large area but then again I already have the fittings in place and cline offers a money back guarantee so if it doesnt work I can return it. Might be worth a whirl since I already have the cc tapped and ready.

The only thing I don't like about the Ofna setup is its height relation to the carb. I would rather have it all above or all below the carb line so that the pressure doesnt go from positive to negative as the level lowers. Seems to me there would be less tuning variance going from + to 0 or 0 to - than + to -.

In a perfect world where I could have a perfect setup I would use the 250 ofna mod with a clunk line and the cline regulator as it has the benefits I'm looking for. But if it doesnt work. I think I can live with the Ofna setup.

That setup covers all of the fuel supply issues as well as increased fuel capacity and weight balance. Yeah I'm a perfectionist. I want it perfect all the time. If there is a better way I will find it. 🙂

 

[Purenitro]

I have tried the perry pump and found the same issues as you, the parts just aren't capable of operating speeds these nitro's reach. Depending on where you come though the block you can run into problems, if your in line with the counter balance of the crank, it will block the hole for the negative pressure stroke. it has a bad effect, the best place is the center of the back pate but obviously that's not an option. I never stopped you on your quest because when I saw it, you already had the holes drilled, damage was done. You have done a lot of research, I bet you learned piles along the way, if I had said to give up, you just might have, and that's not good for learning and gaining knowledge.

Here is a small video which will help you see what happens across the rpm band, internal exhaust pressure drops as rpm increases, this fact alone is what limits any modification to the perry system as you can't get away from the loss of pressure pulse, that's when I gave up lol.

If it's info your still seeking, I could share some with you lol, shoot me a pm.

http://www.bukupower.com/videoPop.html

 

[Purenitro]

Electric is the ticket if 1) you can find a small enough "nitro proof" pump, 2) it doesn't kill your run times of receiver packs. I just run 90% of my tank under the carb and have no issues.

 

[Bankrupter]

Electric is the ticket if 1) you can find a small enough "nitro proof" pump, 2) it doesn't kill your run times of receiver packs. I just run 90% of my tank under the carb and have no issues.

and I run 90% of my tank above same result smooth tune


But if your looking for perfection and instant power on demand give up the dinosaur age and buy some lipos !!! lol MMM rocks

 

[ScooterB]

Now that what I'm talkin about. Sharing info!

One of the other reasons I wrote this up was because I see too many people taking advantage of people who don't know better with false gimmicks.
This hobby should be fun for all and a lot of people get frustrated with the hassles and give it up.

 

[ScooterB]

I have tried the perry pump and found the same issues as you, the parts just aren't capable of operating speeds these nitro's reach. Depending on where you come though the block you can run into problems, if your in line with the counter balance of the crank, it will block the hole for the negative pressure stroke. it has a bad effect, the best place is the center of the back pate but obviously that's not an option. I never stopped you on your quest because when I saw it, you already had the holes drilled, damage was done. You have done a lot of research, I bet you learned piles along the way, if I had said to give up, you just might have, and that's not good for learning and gaining knowledge.

Here is a small video which will help you see what happens across the rpm band, internal exhaust pressure drops as rpm increases, this fact alone is what limits any modification to the perry system as you can't get away from the loss of pressure pulse, that's when I gave up lol.

If it's info your still seeking, I could share some with you lol, shoot me a pm.



http://www.bukupower.com/videoPop.html

Thanks Nitro.
That video is perfect.
Yep I learned a ton and glad I did it. As for the holes in the cc they are easy to fix with a 6-32 set screw and locktite. I drilled through the motor mount as recommended by Perry and positioned it toward the rear of the cc just in front of the starter plate so that it would have the least amount of obstruction.
One thing I have thought about trying was to run the return line to the bottom of the tank and reattach the exhaust pressure line. With that setup I was hoping the exhaust pressure would then force fuel instead of air back through the return at high rpm. Maybe it wont work since the exhaust drops right off at the top end. Might be worth a try if I can find a fitting to modify the tank with. But if that wont work I'm pulling the pumps.
On the other hand It would also make me wonder if the Cline system wouldnt also have problems at high RPM. If the pressure drops off that much then that system wouldnt have the pressure to operate properly either.

Again I'll ask if anyone has tried that system?

 

[ScooterB]

Electric is the ticket if 1) you can find a small enough "nitro proof" pump, 2) it doesn't kill your run times of receiver packs. I just run 90% of my tank under the carb and have no issues.

Any electric device especially a motor will shorten run times. Also they are not engine demand driven. Just seems to complicated and troublesome. You'd probably need an extra battery pack and a place to put it along with a switch to turn it on and off. More weight and more trouble.

I hate batteries thats why I have nitro's. I can run all day without having to recharge anything. LOL

 

[Purenitro]

I hate batteries thats why I have nitro's. I can run all day without having to recharge anything. LOL

NO argument there bud, none at all, nope........umno

 

[JargonBomb]

Old but very educational post. I didn't know MTL was a thing until I started to notice it myself. I have adjusted my SavX to run a little more on the rich side to compensate for MTL.

 

[GAJ]

Very interesting read.