Idle prob. after high speed run

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machinist45040

RC Newbie
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Location
Southern Ohio
RC Driving Style
  1. Bashing
My problem is that when I come to a stop from a high speed run I have a very high idle that last from 5 seconds to a minute. I've haven't been able to find any air leaks and have tried every possible tuning combination with no luck. I've also tried new glow plugs. Temps are always good. 240 after high speed and 210 at idle even when it's idling high. I'm not really sure what else to try. :\ Any ideas would be greatly appreciated.
 
You are a tad lean on the HSN and a little rich on the LSN.
Richen the HSN, then start leaning the LSN in 1/12th turns until it takes about 5-6 seconds for the idle speed to drop after a WOT pass. Now your LSN is set correctly and you can adjust your idle speed down. Make sure you have linkage working properly. The linkage not closing the carb all the way will cause the issue you are having as well.
One other thing... if the engine is still being broke in, this could be detonation from excess compression. Time and more fuel thru the engine will remedy it.
 
Today I tried to richen the hsn and to lean the lsn in small incements which just made things worse. If i lean the lsn any more at all it starts to idle extremly high all of the time and even higher after a fast run. Then takes about 40 sec. to come back down. I backed off the idle speed screw as far as it can go with these settings and it still idled high. The engine was broken in properly and has over a gallon run through since. Could it still be making enough compression to cause detonation?
 
Sounds like an air leak... they are tricky little buggers and almost imposible to find sometimes.

They have tortured me for months. I think I got them all,, but still I have a high idle... the idle screw seems useless to me. The only way to get the idle down is to richen up the LSN which then causes me to have lots of run-on after I get off the throttle, but atleast it will idle and not creep forward...

I'm almost Fed up and ready to go electric... Anyone want to trade ?
 
The Revo exhaust gasket and pipe coupler are very prone to leaking. Take the exhaust off and inspect it.
Revo fuel tanks like to leak at the fuel tank O-ring. Check that.
If all that is good then richen the LSN back to flush, set the HSN to 4 turns out.
Before we go any further, what fuel and glow plugs are you using? What airfilter and exhaust?
If you are using Traxxas fuel it's time to switch. That stuff is garbage.
The engine will tune 10X easier with good fuel. I suggest Byron's Race, O'Donnell's or Trinity Monster Horsepower, Sidewinder.... all are way better than Traxxas's poor excuse for fuel.
 
I've already checked the fuel tank for leaks and it was in good shape. The air filter and exhaust are still stock but I don't think i've ever checked the exhaust for leaks. I'll take a look at it this week. I've tried both Patriot and O'Donnell's fuel which have both worked great in the past. As for glow plugs I used traxxas brand in both medium and hot. With the hot plugs it starts very easy and runs smooth. With the medium plugs I have to set the lsn very lean just to get it to start which just makes the idle 10X worse.
 
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Check out the exhaust and stick with the hot plugs.
 
I may have a little leak in my Main bearing..... I have a very small amount of spray on the inside of the Body and I have to run the LSN rich (2 turns out... or a little past flush) to keep the revs low enought to stop the truck. If I pick the truck off the ground and let it idle away (no thottle input) it will start to rev,, then rev more and more.. kinda doing a ringggg ding ding ringggg (like my sound effects ?) If I hold the brakes it stops, but you can tell its still trying to rev up..

I have my temps back down from the 300°+ range like I had before, but this revving is annoying... Its a new engine with less than 3 quarts of Sidewinder 20% through it.... Is there any way to seal the main bearing without replacing it. ???

Oh by the way... I researched Electric in my frustrations... Holy Crap are the batteries and Chargers WAY over priced... I'm going to give this Nitro stuff another chance...
 
Wow Scrogg you got your hands full, 2 newbs to 1 green guy! :hehe:

Let me jump in and see if I can help a little. My first 2 questions are :

Have you checked the trim knob on the transmitter and actually looked in the carb throat to verify throttle position/idle gap? (ok that's sorta 2 questions in one so I have 3)

Do you have throttle return spring on the carb?
 
I've checked the gap. the throttle is returning fine, and I have the spring.
In my case I think its the main bearing but hate like hell to tear apart a NEW engine... I was hoping to just seal it somehow...
 
I had a leaky bearing on a trx 2.5 a while back. It was spraying a good bit of oil and would have high revs at idle. I ended up buying a new block of ebay that had the bearings preinstalled for $20. Once I put that in it was back to running like new. Far as I know the only way to seal a leaky bearing is to replace it.
 
i have the same problem except i just broke in my engine and set it all back to factory......:(
 
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