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Aug 28, 2021, 10:37 AM
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Traxxas 2.5 will not tune

I have new traxxas 2.5 I am trying to break in. I can't adjust the idle down. The high speed needle is out 4 turns from full in. I added 3/4 turn more rich because I am using 25% nitro fuel. Low speed is flush at factory setting. The engine speed is very erratic it will suddenly lean out and go max RPM with the throttle barrel closed. When I pinch off fuel line at idle it over speeds. It must be pulling air from somewhere. So much for proper break in. I have many years playing with nitro engine. Have never seem this. Any help would be appreciated.
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Aug 28, 2021, 12:45 PM
GloBroz PowerLab
1QwkSport2.5r's Avatar
Check your idle gap. It should be 0.5mm-0.7mm. If it’s not in that range, set it to 0.6mm for breaking in. Next, set your high speed needle to 1 turn leaner than factory setting. Set your idle mixture 1/2 turn leaner than factory setting. Use a long reach HOT plug for the first quart or so. At this point you will need leaner settings and a medium heat plug.

You must set the engine so it builds enough heat - 200F is the minimum. When you have the settings correct, it should idle at around 190-200F and after a couple WOT runs maybe 230F. After half a gallon, lean it down a touch more so it runs clean from idle to WOT after a 5-second idle period. It should be slightly loaded up after 10 seconds of idling.

There are heaps of threads about air leaks and such... Don’t go out and put silicone on everything to fix “air leaks” because it’s highly unlikely there are any. Traxxas engines aren’t top notch race engines, it they aren’t rubbish either. If you’re an experienced Nitro tuner, then you should not have any issue.

What brand and kind of fuel are you using?
What glow plug brand and heat range number are you using?
Aug 29, 2021, 10:36 AM
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Thread OP
The glow plug is Traxxas came in the engine. Fuel is Torco 25% I went with the air fuel for brake in because their car fuel has no castor oil. I have always believed ABC type engine should have some castor oil. There are few Hobby shops in my area anymore. Its hard to find fuel or parts. I took the carb apart and found the idle adjustment screw was stripped. I am awaiting a new carb. I am old school when the carbs where made out of metal. It may have air leaked from there??
Aug 29, 2021, 10:50 AM
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Thread OP
PS The idle gap was almost 1/8" out of the box. Also the engine was seized in the pinch right off. I worked it free with WD40 and oil carefully by hand. These was brand new TMAXX in factory sealed box. I did take the engine apart today. I could not see any damage. After the engine ape sh#@t fast RPM on it's first start I needed to check.

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