Going lean after high speed run.....

[chrisexv6]

Starting to tune my STS 28 a little. The only issue I have right now is that I keep getting the "high RPM after backing off from high speed" issue. You know, when you back off the throttle and the RPMs go high like the engine has an airleak, then settles back down.

I started with the needles at factory again. Its really rich on the low end but seems OK on the high end. I've tried leaning the LSN even though it seems contradictory to what I'm trying to do, but I can't see richening it as its already smoky burn your eyes rich.

Temps are always in check, in fact they are probably a little low (barely over 200, around 205-210 or so) after a few high speed runs.

Is it possible that the LSN being so *rich* could cause the RPMs to go nuts after a high speed run? The theory makes sense in my mind, but then again lots of things do

Thanks in advance.

-Chris

 

[Brushlessboy]

The LSN wont be doing that. It has NO effect past say, 1/5th throttle. I would imagine, though could be wrong that its not an airleak because you should notice that across the board. Is it possible that you're tuning it without high speed runs everytime, and you're getting a false reading from unburnt fuel in the crankcase?
Other than that, check your exhaust for split seals and such, maybe your backpressure is gone, which although seems like nothing, makes it mighty hard to tune....

 

[chrisexv6]

It was suggested on another forum that the HSN is too lean and needs to be richened. I've also read the stock STS exhaust gasket stinks (along the lines of your backpressure suggestion), but I'm pretty sure I used the HPI one I had on my old engine.

Ill try the needle settings first, as its easier than trying to locate a new exhaust seal. Incidentally, I ran the truck a little later in the day and ended up richening the HSN (was running in grass and trying to keep the temps down) and the issue seemed to improve quite a bit, albeit not completely disappearing. I think the HSN may have been masking the issue, as I had to lean the LSN a little after richening the HSN, so I might have just had the wrong HSN setting and "fixed" the LSN to that incorrect setting.

-Chris

 

[olds97_lss]

Any time I've had that, it's usually the HSN that is a bit lean. 1/16-1/8 turn normally calms it down really good.

Might not hurt if you give these a read:
http://www.nitroreview.com/hintstips/ParisRacingEngineTuningTechTips.pdf
http://www.rchobbies.org/cars_eng-tuning.htm

Might help you understand what the engine is doing a little better.