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Revo 3.3 won't stay tuned after warm-up

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M

mooseheadluke

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Vernon, BC, Canada
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  1. Bashing
Hello there. I have been bashing nitros for well over a decade now, and I have extensive knowledge and experience with all types and sizes of nitro engines...but I am baffled by this problem I am having. I have a fairly new Revo 3.3, I did the proper run-in on it and it ran great for a long time. Then one day I found it would not stay idling, so...Yes, I just had to start playing with the needles and the idle. Well it turned out that it was just a slice in the pressure hose coming from the exhaust to the gas tank. Now that I have fixed the hose, I cannot seem to get the engine to tune in correctly again. If I start it from cold, it runs good, idles a little fast (creeps forward) but doesn't stall. Once it gets up to running temp (220-250F) I find that it stalls whenever I hold it with the brake for more than a couple of seconds. If I do get it to stay idling long enought to do a low-needle pinch test, it comes out fine, with a 2 second delay followed by an increase in revs, and then a stall. The High speed needle seems fine, good smoke, good temps, quick off the line at full throttle. I have good glowplugs, good, new, fuel (33%). Like I said, it runs great, but it just wants to stall when braked. If I set the low needle or the idle set screw higher, it, of course, wants to creep waaaay too fast. Has anybody had this same problem with the 3.3? Any suggestions? Also, does anybody know what the stock setting on the idle set screw is, or how open the throttle slider to be at stock setting? :\
 
First, you should ONLY tune an engine when it's at the temp where it's expected to run.
Your idle needs to be reset AFTER you turn you throttle trim knob all the way down. Set the idle screw while holding the brake in the full 'on' position.
 
Thanks Rolex. Yup, I only do any changes once its all warmed up. Like I said, the problem is that once its up and running, and the HSN is set fine (I really never have to change it) I never have time to set the LSN or the ISS because the bloody thing stalls before I get a chance to test/set it. I know its not running hot and stalling because its hot temp never gets past 270-280 and its blue smoke is fine and it never stalls under load...only when I brake. By the time I get to it to try to hold the brake on and set the idle screw, it stalls.
 
Once the LSN is set you probably won't need to adjust it unless you change fuel content. The HSN needs to be tweaked almost every time you run it, to compensate for humidity and ambient temperature.
Raise the idle still it starts to creep, then make your final adjustment with the brake applied.
 
I had a similar issue that kicked my butt and it turned out that a faulty OWB on the starter was intermittently grabbing every once in a while during idle or coasting around corners.
Not saying that is the problem ....but it could be.
I changes it out and the problem went away.
 
Thanks Dougrevo33, I will check that out also. Rolex, I do tweek the HSN every day, but only a 16th or so...its very stable. Since I cannot seem to get it to not stall when I stop it to check it, how do you suggest I go about this? Should I just set the ISS high, or the LSN high, or both, so it won't stall when I pull it in to check it. I would think the ISS, that way I can at least do a pinch test on it and get the LSN good first. I have to try to isolate whether its the LSN is causing the stalling at idle.I think I might also change the long looped fuel line, just in case it has a small crack. There has to be something strange going on to make it run so well at load but stall at fast idle, and not stall at idle when cold.
 
It's the clutch, or the OWB, or the engine has simply lost compression.
 
Most likely it did not lose compression he just has to get the low speed set right mine did this all the time till i got the lsn right.
 
Thanks Scrogg. I am going to try that. I still have not been able to get the tune just right on the 3.3, and I have had a couple of other people tell me that the stock clutch is a bit 'catchy', so I am going to get an after-market one.
 

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