1/2 Lean Cure

[ScooterB]

I know this topic will definitely arouse interest. I hope I don't offend anyone.
While I have read and read differing theories and expanations it seems that this is a common problem in Nitro model engines of all types. The lower the tank gets the leaner the mixture and is not simply a savage problem. (although the savage seems to have a more severe case than most.)
While reading up and researching I kept thinking that there had to be a better way to create a contant and consistent pressure and flow. I thought about my waverunner which had a fuel pump operated from the exhaust pulses. I did some searching on the web with no results. And then I talked to a very helpful salesperson at my LHS who directed me to Perry Pumps.
At Perry I found the following:

VP-30 Regulating pump

The VP-30 regulating pump is capable of performing like no other fuel delivery system. It delivers an ideal .25 PSI to any model carburetor from a .15 to a 3.0 cu.in. engine. The pressure remains constant throughout the entire speed range, making the carburetor adjustment easy and simple. Once the needle valve is adjusted, the mixture will not vary regardless of how low the fuel or the attitude of the airplane, thus eliminating rich/lean runs altogether.

Price: $41.95

Diameter: 1"
Length: 1.5"
Weight: 23 Grams
Flow Rate: 3.5 Oz./Minute

This description says airplane but it is the same pump that Perry offers in their systems for Nitro cars and trucks.

for more info go to Perrypumps.com and navigate to the rc car and truck section.

While engine size is limited to 3.0 the salesman who I talked to found that you can run two of these (increased fuel flow, same pressure) for larger engines.

I'm ordering two. (CLARIFICATION: 1 FOR MY TRUCK THE OTHER IS FOR MY SONS. 2 Trucks 2 Pumps.)

 

[frddyj]

when you get the pumps can you take some pics as you install them? what powers the pumps?

seems like a lot of money & additional hardware to mount & deal with vs. getting a mid tank.

I'm curious about it & hope it works out for ya :resp:

 

[ScooterB]

More thoughts on the subject.

More theory for those interested.
First subject; Vacuum vs pressure. Not to get too elaborate but without one you cannot have the other. They are entirely relative to each other. In a RC Nitro setup the fuel tank is pressurized which causes fuel to flow to the carburetor (Vacuum). Now the experiment. If you fill a 5 gallon bucket with water and then take a wet dry vac and put the hose at the bottom of the bucket and turn it on you will notice that as the level gets low it will start to suck air long before the bucket is empty. In an RC environment you would add bouncing and vibration to the equation which causes the liquid (fuel) to slosh back and forth. I believe that this is part of the problem due to my own observation on temps and fuel levels and the fact that I have observed temps increase dramatically as the level is lowered (Below the level of the shelf and not just at the shelf level)
By using a fuel pump the vacuum vs pressure difference is reduced due to the fact that the tank would no longer be pressurized.

Second subject fuel volume vs level; If you go back and fill the 5 gallon bucket used earlier with water then empy into your bathtub and then again using the vacuum to suck it out you will notice that the vacuum starts to suck air even quicker. This is because the same volume of water is spread over a larger area and the pickup is closer to the surface. (Large flat bottom fuel tank)

Fuel systems, Carbs, Injectors and RC; In our closest cousins (2 stroke carbureted motorcycle engines) fuel is fed by gravity to a carburetor float bowl. In this case the float operates a valve which regulates and controls the fuel level in the carb, the fuel is then sucked through the jets and into the airstream. The float bowl also has the ability to seperate any air which may flow through the line very quickly as this bowl is vented and has an abundant supply of fuel. As long as the correct level is maintained the engine never starves for fuel.

Fuel injection systems feed fuel to the engine using a high pressure constant rate fuel pump. The system consists of a supply (tank), pump, regulator and injectors. The regulator keeps constant pressure and supply and excess fuel is returned to the tank. As fuel demand rises the regulator maintains pressure and more fuel flows to the injectors. the injectors regulate the flow of fuel into the engine by the amount of time that they are open.

Why bring up injection? Because the carburetors in RC cars are fed in a similar manner. They do not have float bowls and rely on pressure to maintain a steady flow of fuel to the engine. Much like an injection system, if that pressure fluctuates the fuel air mixture will be affected. What about the air in the lines? First without a pressurized tank there is less vacuum vs pressure and less likelyhood of pulling air into the line. Second because air (a gas) will compress and also very quickly flow through the jets the fuel flow is restored much quicker. And because this pump system is regulated the drop in pressure due to the air will quickly be restored.

So why not a simple electric pump? Simple when the engine dies there would be nothing to stop the flow of fuel. Remember this is a carburetor not an injector. Crash it, walk over to get it, and the crank would be full of fuel. As well as size, packaging, and power issues.

With the pulse powered pump, when the engine stops so does the pump.

Why don't the oems put pumps on? Cost. For many years they have been building small engines which have worked just fine with the pressurized fuel tank method. But with the advent of the newer larger higher reving and thirstier engines the problem is becoming more prevelant.

Feel free to dissagree with me. I am certainly open to learning.

 

[ScooterB]

when you get the pumps can you take some pics as you install them? what powers the pumps?

seems like a lot of money & additional hardware to mount & deal with vs. getting a mid tank.

I'm curious about it & hope it works out for ya :resp:

They are powered by crankcase pulses instead of the exhaust because these pulses are stronger.

I will post pics of the install and an update on how they perform.

 

[ScooterB]

As far as price, it seems to me that $48 is pretty reasonable considering the cost of a midtank conversion and the fact that it should eliminate the tuning hassles and increase engine life.

 

[ScooterB]

Pics and specs

Here are a couple pics. I hope I did this right.

 

[Bankrupter]

As far as price, it seems to me that $48 is pretty reasonable considering the cost of a midtank conversion and the fact that it should eliminate the tuning hassles and increase engine life.

I don't think 96 bucks plus shipping is worth the benefits of the mid tank. If anything Id run them with a mid tank. Adding them to the build cost. Doing a mid tank was more balancing a brick that it was about the lean issue. But two birds with one stone was worth it to me. Also the price of my mid tanks set up was well under 96 bucks. With CF parts. That's just my 2 cents :resp:

But on the oter hand I am very interested in seeing this on any rc!

 

[ScooterB]

I'm ordering two because I have two trucks so it is $48 each. It would be $96 if you have an engine larger than 3.0.

 

[Bankrupter]

I don't own anything other then .28's

 

[HopIt]

I'm ordering two because I have two trucks so it is $48 each. It would be $96 if you have an engine larger than 3.0.

Do you mean .30 CI or like you wrote it, 3 CI ?
or does this mean you have to fit two pumps to any engine bigger than .30 CI ?

+ I gave you rep, whatever the outcome, this is very interesting !

:resp:

 

[frddyj]

Do you mean .30 CI or like you wrote it, 3 CI ?
or does this mean you have to fit two pumps to any engine bigger than .30 CI ?

+ I gave you rep, whatever the outcome, this is very interesting !

:resp:

thats the way i read it also; meaning if i have a 4.6, then i would need two pumps? is that not the case?

also, when you install, can you snap a pic of the the crankcase under that plate where the tube comes out? I'm wondering if you have to make a hole in the c.c. to get the pulses that drive the vacuum. thx bro :resp:

btw scooter, don't think we're rippin on you, just haven't seen anything like this before and I'm interested to see how it works & how you have to fit it into your r/c. and of course if your happy with the results vs cost & effort eace:

 

[ScooterB]

The manufacturer lists 3.0ci. So your 4.6 is actually .28ci. Am I wrong?
I am waiting for more info from the manufacturer so I hope to clear that up.
There is a post that has a pic from their site of the install on an engine and a pic of the specs and pricing.

You do have to tap the CC for the pressure pulses. The pulses in the case are stronger than the exhaust pulses. See picture.

 

[ScooterB]

Pump specs

Here are the specs from the manufacturer site and links to their site.

VP-30 Regulating pump

The VP-30 regulating pump is capable of performing like no other fuel delivery system. It delivers an ideal .25 PSI to any model carburetor from a .15 to a 3.0 cu.in. engine. The pressure remains constant throughout the entire speed range, making the carburetor adjustment easy and simple. Once the needle valve is adjusted, the mixture will not vary regardless of how low the fuel or the attitude of the airplane, thus eliminating rich/lean runs altogether.

Price: $41.95

Diameter: 1"
Length: 1.5"
Weight: 23 Grams
Flow Rate: 3.5 Oz./Minute


http://www.perrypumps.com/prod02.htm
http://www.perrypumps.com/nitro_page.htm

 

[frddyj]

The manufacturer lists 3.0ci. So your 4.6 is actually .28ci. Am I wrong?
I am waiting for more info from the manufacturer so I hope to clear that up.
There is a post that has a pic from their site of the install on an engine and a pic of the specs and pricing.

You do have to tap the CC for the pressure pulses. The pulses in the case are stronger than the exhaust pulses. See picture.

lol, yep, braincramp bro youre right. don't mind me, I'm a bit --> :retarded: i saw the pic & read what you said before about the pulses from the CC., just wanted a look under that plate if you get the chance to do it.

 

[X25]

This is interresting. But I'm not sure that i want to go drilling a hole into a $200+ CC hoping not to screw anything up. So i would have to say this mod is not for everyone. But i do find this interesting. I am also wondering if this is the direction that the hobby is going to go one day. Think of it an EFI savy. More ground pounding hours of fun with less fuel. LOL its a nice thought

 

[Bankrupter]

How are you going to set up the bypass?

 

[ScooterB]

From what I have read the bypass returns excess fuel to the tank.

If your scared to drill the crankcase they will do it for you for $20.

They've been building these for 20 yrs so I think they just might know what they are doing.

Still waiting for their reply to my email. Hope I hear soon.

 

[Bankrupter]

From what I have read the bypass returns excess fuel to the tank.

If your scared to drill the crankcase they will do it for you for $20.

They've been building these for 20 yrs so I think they just might know what they are doing.

Still waiting for their reply to my email. Hope I hear soon.

Yea thats my question how will you do it w/o their carb?

 

[Trixter]

FLM and ofna mid tank no drilling no leaning. you can do the mid tank, throttle mod,all for under $55.00 at SMF

 

[ScooterB]

You don't need their carb. this is a fuel supply to the carb. It is regulated and gives a constant perfect .25 psi pressure of fuel at a rate of up to 3.5 oz. per minute. Regardless of fuel tank design, size, position, mounting, or engine fuel needs. And remains constant throughout the engine RPM range.

Costs $48 which where I went to school is less than $55 and this will work without having to refab half the truck. It mounts nice and neet in a 1 X 1 1/2" space. with one fuel line coming in, one coming out, and a line to the cc.

Ive talked to others as well as reading here who have done the mid tank conversion and they said it helped but didnt completely cure the problem and it makes sense to me that it wouldnt cause this is a Nitro RC industry problem not owned by the HPI Savage. It happens in airplanes, helicopters, boats, and cars. And they all have one thing in common......exhaust pressurized tanks.

Another theory of mine and maybe the most important is the exhaust pulse vs tank area. If you know anything about tuning exhaust, speaker enclosures, or anything with soundwaves and volume you will understand this.
With any stock fuel system which is feeding pressure waves into a closed chamber the resonant frequency is changing as the fuel level decreases. When the tank is full and it recieves an exhaust pulse the area in the tank is small and the pulse wave inside the tank is therefore strong. As the fuel is used and the tank empties the area is large and the pulse wave is more easily absorbed by the area in the tank. Remember that your exhaust is not pushing a steady stream of air, instead it is delivering pulses and in between each pulse there is a gap which bleeds off pressure. And possibly even creating a vacuum, (that is if your exhaust is scavenging properly) Larger empty area = less pressure.


This may be a simpler way for everyone to understand and you all have the means to perform this little experiment.

Take a shock absorber and extend the shaft all of the way out and fill the shock as full as possible with oil (or any fluid, this is an experiment) so that there is as little air as possible left in the cylinder. Now cap it off and compress the shock. You will feel resistance and pressure and the shock shaft will rebound back to the extended position. Now uncap and pour half or more of the fluid out, recap and recompress. You will notice little or no pressure. Hmmmm. when you compress the shock this is equal to an exhaust pulse. when the shock is empty there is plenty of compressable air which easily absorbes the volume of the shaft with very little change in internal pressure. When the shock is full there is very little compressable air and the pressure builds very quickly.

Like I said before bigger engines need more fuel which leads to bigger fuel tanks. Bigger fuel tanks in turn create more empty space as they are emptied, which creates more problems with fuel slosh and pickup starvation, and pressurization problems.

The only real cure is a fuel pump which doesnt care how big the tank or how full it is.

 

[Bankrupter]

my only question is why you would want a tank hanging on the side of your tvp? that the only part of this I don't get..

BTW I have a 250 cc tank on a modded novarossi 528. Two extremes.. Huge tank and one of the most powerful mills you will find and no mid tank lean issues at all.. So not all your sources are correct. But that is not the point I'm dieing to see this. How long do you anticipate till you even buy the pump.

 

[ScooterB]

don't get me wrong, I'm not saying a mid tank is not a good thing, I think the midtank has other benefits such as weight balance and I do believe that it helps with the midlean problem. I just don't believe that it is a complete cure. Too many repeat stories industry wide. Besides I guess I'd rather have a $12 tank hangin off the side than a $75 radio. Somethings gotta be out there.
:resp:

 

[Bankrupter]

don't get me wrong, I'm not saying a mid tank is not a good thing, I think the midtank has other benefits such as weight balance and I do believe that it helps with the midlean problem. I just don't believe that it is a complete cure. Too many repeat stories industry wide. Besides I guess I'd rather have a $12 tank hangin off the side than a $75 radio. Somethings gotta be out there.
:resp:

I pick the RX lol So when ya gonna order?

 

[ScooterB]

Wanted to order today but didnt get a break at work so hopefully tomorrow.

I hope everyone will be patient and wait for them to ship, then I'll need to probably go to an indoor track unless I get some warm weather. I'd prefer my local const site but I hate mud.

I will do a complete write up with pics.

 

[Bankrupter]

don't forget the vid!

 

[frddyj]

The only real cure is a fuel pump which doesnt care how big the tank or how full it is.

fuel pump may be the only cure if your tank is lower than the carb cuz you gotta get the fuel uphill & youve got gravity working against you.

mid tank is also a cure because it significantly raises the height of the tank which allows a huge amount of gravity feed. much like when you siphon gas from a car, you do not need a pump so long as the tank you are trying to fill is lower than the source tank, the fuel will 'gravity feed' downhill
got a good demonstration of this when a dude i bash with (wears an orange coat btw) lost the pressure line from exhaust & continued to burn through 1/2tank of fuel before realizing it. the 250cc midtank gravity fed the mill.

so its really a matter of choice, looking forward to seeing your build bro, sounds like its gonna be pretty kool :jamout: rockout

 

[X25]

I agree with freddyj i have done this when i rip a exhaust coupler my truck with a stock tank mind you still runs with no pressure line on it. Not to say that i don't like or support your fuel pump build I'm just wanna make sure i can see both sides of it. also most of use who have mid tank mods don't hang our radio gears out to get hit. My servo is on the inside of my TVP'S and my RX is in the rodio box with my tank my hump pack is on the front bulkhead protected by the bumper and body.

 

[ScooterB]

Update

Just to keep everyone informed on the status of this thread. I have been in contact with Gary Conley and have some new information. I will share his comments. Also I have oredered 1 system through my local hobby shop, not because I have doubt but because theyre supplier had only one in stock. (They are looking for another. Or I will buy direct from Perry.)

Gary Conley is a model engine builder who builds 1/4 scale V8 engines and is the owner of Perry Pumps a subsidiary of Conley Precision. See link to video http://www.conleyprecision.com/online_videos.htm
Gary has also built a 1/4 scale replica of the Dodge Viper V10 which was contracted by Chrysler. (you'll have to do your own research to find out what happened to it)
These engines startrockoutrockout around $5300 and up.
He is very knowlegeable about model engines.



" I am sorry it took me so long to respond to your request. I sell a pump and bypass system for cars, which is a #300202. It is $54.95 plus $5.50 shipping and handling. You can check it out on my web site www.perrypumps.com. The intercooler, which is no longer available, isolated the carb away from the heat and gave a ram effect to the fuel. I am working on a new version of the intercooler, but unfortunately do not know when they will be available. The reason for your engine running lean is because of something called “head pressure†which is the weight of the fuel. On a full tank the weight is heavier than at half tank. Also muffler pressure is never constant. At idle there is no muffler pressure that is why the fuel pump is a great idea. My system allows the pump to run all the time and bypasses the excess fuel back to the tank. You will need to drill and tap a 6-32 hole in the crankcase of the engine. This is a very simple operation. You may want to give me a call to discuss the options.



Best regards,

Gary L. Conley

www.conleyprecision.com"



"For what it is worth, I have sold thousands of pumps for car applications. Head pressure has nothing to do with muffler pressure. Head pressure is the weight of the fuel. If you take the muffler out of the equation, as the fuel level get lower in the tank the head pressure is less. That is why you are constantly adjusting the needle valve. Keep in mind that you need to be very careful about running too lean. That is why “hot restarts†are so difficult. All of the fuel has vaporized and any incoming fuel, depending on the temperature of the engine, will also turn into vapor. Once again, you are adjusting the needle valve for low fuel level. Add muffler pressure, which is NEVER constant and another needle valve adjustment is needed. The object of the fuel pump and bypass is to stop the constant adjustments. There will always need to be a small adjustment because of fuel, weather, barometric pressure, humidity, glow plugs, etc, but nothing like what you are currently doing. It does not take very many lean runs to do damage to the engine. Once again, it will be much easier to discuss this over the phone. I do not know if your local hobby shop will have this system. You can, however, purchase it direct from me. Good luck.



Best regards,

Gary L. Conley

www.conleyprecision.com"

To reply to those who have run without the exhaust line connected I never said they wouldnt run without exhaust pressure. Its the fluctuation in pressure that is the problem. (There was another post here about a racer who does this to mellow the power build.) A carburetor creates a vacuum which will draw the fuel into the engine the same as it would with a float bowl carburetor. As well with a mid tank the fuel is flowing down hill. (How do you stop the fuel from running into the engine when it is not running?) The difference is having enough fuel for a sudden burst of throttle and having a steady flow and pressure regardless of fuel level.

 

[ScooterB]

Parts are here

The parts have arrived for the first truck build. Attached are a couple of quick pics from my preliminary mockup. I will be fabricating a bracket to mount the pump. Should have it installed within the next couple days depending on my schedule. You will see in the pics the fuel line routing and notice that the fuel tank has a new fitting. This fitting is for the fuel return. I am considering attaching the one-way valve to the air intake so that it will have a filtered air source for the fuel tank vent. The one way will not allow the fuel to flow into the intake but will allow air to flow into the tank.
Also I have learned that the recomended location for the CC tap be on the right side of the engine to reduce the chance of extra oil or fuel entering the pulse tube
Enjoy the pics.

 

[Bankrupter]

So what is it a lil diaphragm pump? It looks to be in a smash zone ATM. Id rethink its location a tad bit. Maybe a mid tank and put it on the left of the mill? lol jj there... But for real I would get it a lil lower if you can. or behind the tower. don't know how limited you are as to how far away it can be. FLM ext would be nice for it 4 sure. It could mount behind the mill.