Engine tuning

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Harrington81

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Hi there everyone.I'm having a problem with tuning my 4.6 engine.I'm trying to get the wheelies on command thing going.I turned the hsn about a full turn a 1/8 at a time from flush and the lsn almost all the way in.If i adjust the lsn about a full turn from flush it still bogs off the line with no wheelies.how much do u turn in the 2 needles generally to get bottom end power and top end power?Also idle screw.I herd u take the air filter off and adjust it to a 1mm gap with no throttle....is this true?After running for about 10 minutes the temperature raises to about 250F and i can't tune it to have power without it overheating.I hope someone can help me.Thanks for having a great site.
 
Yes the 1mm gap for the idle screw on a stock engine is correct. I usually play it by ear. If it idles nicely and the wheels aren't turning I just leave it alone. But if you are bogging off the line you might have it too rich.

If you are only getting 10 minutes of run time before you are overheating you are running way too lean. I would suggest returning the needles to factory settings and go from there. Keep in mind that weather plays a role in tuning. Air temp, humidity, and even altitude can play a factor (thinner air = less oxygen). Also be sure to adjust your high speed needle before you adjust the low speed needle.

Good luck!!
 
Hi there.What does the idle ajustment screw do anyways?If i have the gap at 1mm it dosn't idle properly so i have it about 2mm.How much do u generally turn in the hsn and lsn anyways to get good performance.I wanna get wheelies without overheating.lol.Thanks for the reply.
 
Hi there again are u talking about adjusting the lsn or idle screw if i'm bogging off the line?U said it's to rich so i think your talking about the lsn right?
 
If you are bogging at take off try leaning the idle adjust screw to a 1mm or less gap. My O.S. says the gap should be .5mm By opening it up more it is in essance "flooding" the engine with a less than ideal mixture.

As far as the high needle and the low needle, adjustments will vary. Typically I only adjust the high needle unless I know I the performance is strongly lacking. Try going back to factory settings and get the idle screw set, then the high needle and then the low needle. Don't look for wheelies right away. Get your mixture right so that the engine is running efficiently then find the sweet spot that gives the power you are looking for.
 
Dragin is correct with the order of adjustment : idle, hsn, lsn. If you try to do the lsn before the hsn is done tuning you will run really lean. Return all needles to flush and set the idle needle so there is 1mm gap inside the carb. Then tune the hsn at 1/8 increments clockwise until you lose performance, then back it off until its good again. Then turn the lsn needle clockwise at 1/8 turn increments as well.
 
Also what breakin did you do for your engine (I'm assuming it was new)? This can affect the tunability and life of your engine if its not done right.
 
Alrighty, here, hope this helps a little.

Idle Adjustments :
Low: Engine struggles to idle, very hard to start
High: Engine revs during idle, and the model attempts to move
Key spot: Find a good mix between the two, afer tuning, it may be necessary to retune the idle adjustment screw.

High Speed Needle:
Rich: Engine bogs during acceleration, doesn't seem to run to it's ability, and pours the smoke from the exaust. Sometimes, being too rich can cause the RPM of the motor to stay under the shiftpoint of the transmission.
Lean: During full throttle situations, it may bog out and jitter. Also, being too lean can cause extremely high performance during medium throttle positions. A key factor to remember, the leaner you run the motor, the quicker it's going to wear out.

Low Speed Needle:
Rich: A rich low speed needle will show signs of a "hesitation" at the first second of a full throttle take off. Sometimes, this needle can be so rich that it causes the engine to stall from an idle to full throttle situation.
Lean: If the low speed needle is to lean, the engine may actually "act up" and jitter on take off.
The key: Find a spot where you get nice off the line performance, and a nice stable idle. Making sure to get a good LSN setting can be the maker, or breaker, of pulling those nice off the line wheelies.

I usually run my motors at these specs, and how I test them.

I run around 230F after three full speed runs, tested by a temp gun.
The LSN, is right off of stock, and here's how I test that.

I pinch the line about 3/4" from my carb. It revs up barely and dies. If it runs for more than a few seconds, or it revs up a good bit, it's to RICH, and if it dies immediately, it's just to LEAN.

Remember though, almost everything can play a factor in tuning your engine, air temperature, altitude, type of fuel, glow plug, air filter type... Almost everything. That's why, before each long bashing session, or race, I end up tuning my motor first. That way, I'm getting the best performance for the motor on that specific run.

I hope this helps out man, and I want to say, "Welcome to the HPISF Forum!!!!" It's a pretty cool place, and there's a ton of very smart people who know these things inside and out. 🙂
 
Last edited by a moderator:
Harrington81 said:
After running for about 10 minutes the temperature raises to about 250F and i can't tune it to have power without it overheating.
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This part of your post also leads me to believe that you may be experiencing the real pain in tuning called the half tank lean. If you're running a savage, with the stock tank, then most likely you're having this problem.

What is half tank lean? Well, due to the shape of the fuel tank, there's a point where the pressure return actually gets restricted, and cannot push the fuel to the carb with the same force. This is due from the tank size change about half way down. There's some physics involved that I'm not going to get into, but it's been a major pain in the rear for me.

Currently, I'm waiting on a midtank mod, that uses a better fuel tank that doesn't have a size difference like the stock one. But I'll tell you how I got around the problem myself.

I only tuned for performance AFTER it passes the half tank spot, so I'm getting the tune correctly for that period of time. Where, at a full tank of fuel, it's running extremely rich, both high speed and low speed needles are running rich. Once it hits the half tank leanout spot, it's ready to really rock.

This problem, as I said before, comes from the stock HPI Savage tank. There's quite a few other options to fix the problem, but the best way around it, is probably a different tank. That's why I'm getting a midtank mod for mine. The half tank lean is such a pain in the rear to work with, specially when trying to tune and not knowing it's happening.

Try tuning with only half of a tank of fuel. See how that works for you. It may solve your problem for now, but remember. If you tune at that spot, then run a full tank, the first half of the tank will run rich, maybe even to rich for the engine to reach a shift RPM. I'd personally look into getting a different tank, midtank mod, or maybe even header tank. You can find MANY threads on here about the problem, and their fixes.
 
well i have the .28 axial ans its sweet spot is around 265 to 270 degrees.
also you might have to run a few tank of fuel before you really see what the mill has to offer.i did with mine.
 
AoD said:
I pinch the line about 3/4" from my carb. It revs up barely and dies. If it runs for more than a few seconds, or it revs up a good bit, it's to lean, and if it dies immediately, it's just to rich.
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AoD,

I thought if you pinch and it dies quick then it too lean and if it revs up alot then it's rich?

If not then I've been screwing up, so let me know

Tobias
 
I'm sorry texas, thanks for pointing that out for me. I've written them backwards. I must have been typing the words before my brain was processing them.

If it runs for more than a few seconds, or it revs up a good bit, it's to RICH, and if it dies immediately, it's just to LEAN.


If it's running lean, cutting the fuel off will immediately kill the engine, since it's pretty much starving for fuel anyways. If it keeps running for a while and/or Revs up a lot, it is to rich, as the motor has too much fuel in it as is.

The LSN only effects the low range from IDLE to the first couple seconds of throttle. The LSN will have almost no effect for top end speed performance, but can make or break a wheelie.

Thanks again though Texas, I didn't realize I typed it wrong, fixing it in my post now. 🙂
 
AoD said:
I'm sorry texas, thanks for pointing that out for me. I've written them backwards. I must have been typing the words before my brain was processing them.

If it runs for more than a few seconds, or it revs up a good bit, it's to RICH, and if it dies immediately, it's just to LEAN.


If it's running lean, cutting the fuel off will immediately kill the engine, since it's pretty much starving for fuel anyways. If it keeps running for a while and/or Revs up a lot, it is to rich, as the motor has too much fuel in it as is.

The LSN only effects the low range from IDLE to the first couple seconds of throttle. The LSN will have almost no effect for top end speed performance, but can make or break a wheelie.

Thanks again though Texas, I didn't realize I typed it wrong, fixing it in my post now. 🙂
Click to expand...


Ok cool, I just woke up and thought my brain was still sleeping at first. :sleeping: Glad I could help

Tobias
 
ya engine temps vary alot!! i've seen people here say there sweet spot was running temps of 300 which i thought was really high but apparently it still had a trail of smoke and stuff so i guess it goes to show you every engine is different!! my savage x runs 230-240 and wheelies with ease but another persone with the 4.1 said his ran at like 275-300 so go figure!! but never tune by temps anyway as theres just to many variables to concider!!
 
NITROADDICT said:
but never tune by temps anyway as theres just to many variables to concider!!
Click to expand...

That's right! The temperatures are a good way to determine how the motor is running. But there's many different things to look for. An engine might be running at 200F, but running extremely lean, or it could be running at 270 and really rich. The temperatures range widely from engine to engine. The most important thing to remember is that the cooling is different on each motor. So, even though you're running 230F, you might not be running where the engine needs to be. 🙂
 
I have an RB modded STS D30M which runs best around 300 degrees. Every engine is a little different, this is why you tune for performance.
 
Yes I know everyone says to tune for performance but I hate it when I see my temp gun read out above 270 degrees....kinda wish I didn't have a temp gun because with my very first nitro motor (Nitro Star .25) I never did have a temp gun until I got my STS .28 and the NS25 ran perfect at 6 gallons when I sold it, yet now I am always checking my temps and worried, lol.
 
Yeah, owning a temp gun is almost asking for stress lol. I've ran 3 motors without one, and they all seemed to run rather well. Now that I have a temp gun, it's "STOP AND CHECK!!!" every five minutes lol
 
Alright i'll think about getting a midtank for it.I've just fixed my overheating issue but still experience bogging from a stand still at wot.I know my hsn is set correctly.I try to lean out the lsn but it still bogs know matter what i do.The car has so much more power at a half a tank that it's almost imposible to adjust the needles.I know there's something wrong somewhere.Anyways thanks everyone.
 
I also found it wierd that when i filled it from half a tank to full it would slow the idle down.It's almost like there's not enough pressure coming from the exuast pipe.thanks.
 
That's because it's going from low amounts of fuel to heavier amounts of fuel. I had all the same problems before, and I went with a midtank. More than happy that I did. Even with the tank up front, I still flip it on command. 🙂 No tuning issues now either. I was ready to throw my savvy a couple times because of half tank lean!
 
its cheaper and faster to buy the tank from new era, no modding a tank just buy and put it on, ive had mine for a couple months and now leaning problems
 
Thanks for the input guys.Hey ohu8mine2 is the tank your talking about (fuel tank 125cc w?stone filter rear mounting and where does the long screws mount onto on the bottom of the tank?thanks
 
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