PSD

trying to tune but it won't hold consistent idle. when it does idle it ramps up in rpm like crazy, the clutch engages and wheels spin. but when i try to test drive the engine cuts out.
I'm using base settings, 4 turns on the high needle, low needle even with the housing, idle gap adjusted anywhere from 0.5 to 1mm.

tried the 3oclock test, engine will hold for a few seconds then drops to 6.

FWIW, car is Jato3.3

1995 Monster T

Start with high 4-1/2 turns out low ..024 in from flush and the idle 1mm gap. Use fuel with at least 14 oil lube. You want the low even with the throttle barrel. The ball link adds .024 in depth. Use a fuel filter.

RazorRC

iTrader: (5)

Best advice I can give you is to throw "base settings" out the window and learn how to tune a nitro engine. JQ's video on YouTube is the best I've seen.

There are too many variables (temperature, fuel, nitro %, glow plug, elevation) to be able to use any sort of hard & fast setting.

Roelof

Check the throttle link/servo if it pulls the carburettor open. Like if the idle goes up, activate the brake to see if the idle lowers.

PSD

throw the base settings out? then what do you use for a starting point?

I figured the linkage needs a little clearance to keep from messing up the idle gap, confirmed that from JQ's video.

I'll try the 4 1/2 .024 1mm settings, thanks. BTW, fuel is Traxxas 20% nitro, new purchase from hobby shop, couldn't find any info regarding oil percentage.

some back story- car was given to me by neighbor who someone gave to him, no information available about run-time or care. only thing i did was tear the engine down, replaced crunchy bearings with new from Amain.

I'll try more tuning when time permits, thanks for the help.

1995 Monster T

My recommended settings work every time I have ten t maxx trucks. and the setting for the 2.5 and 3.3 are the same. Those vides on the web are total garbage. The traxxas fuel is 14% oil lube. If engine dosen't stay running with my recommended settings I would suggest a new block engine. $100 3.3 Same as replacing just the piston sleeve. Just swap the carb starter and header and clutch.. Break in engine 6-8 tanks at idle then drive slowly. Tune high speed another 3-4 tanks. Don't go past 4 turns on high. Use a fuel filter.
NEW TRAXXAS T-MAXX 2.5 4910 COMPLETE ENGINE MOTOR RUSTLER REVO 4-TEC STAMPEDE | eBay
For Traxxas TRX 3.3 Nitro Engine NO Carburetor Revo T-maxx Jato Slayer Pro 4-Tec | eBay
i suggest you use a separate glow plug ignitor. As the wand one will die and you will have to have one anyway. Once tuned you can use the wand glow driver but I find it better with the separate glow ignitor.

PSD

thanks, I've had my eye on that 3.3 engine. I've bought from that seller before with good results.
hope the tune works but my pessimism is leaning towards compression.
i tried new TRX glow plug, no difference. did get the dynamite lipo wand DYNE0201, it works good.

1995 Monster T

If the truck was passed down several time? I to expect the compression to be bad. when you had the engine apert did you notice if the piston went part the top of the sleeve? I have had some luck with poor compression engines bringing them back to life. you have to toon rich and use more oil lube 18% and they will work again. Stay away from that race fuel with 9% oil nothing but trouble. 14-18% is good enough for back yard bashing.

PSD

put a new carb on today, tried base settings, suggested settings, small changes both ways, no difference, ran like crap.
will not idle long without glow driver hooked up, will die instantly on snap throttle, or any throttle input really..

new engine ordered.

Roelof

Get a new glowplug.

1995 Monster T

Did you note the new carb settings? The low and idle are usually close. The high starts @ 4-12 After broke in stay above 4 turns on high.
Thats usually the last thing to try. The piston and sleeve is worn out. Take your time break in in new engine.

PSD

this was an Ebay kit breakdown, but I don't think the seller would mess with the settings.
the high was only 3 1/2 turns and the low was even with the inner shoulder.
pic is the old carb with low adjusted even to inner edge, same as the new carb delivered today.
So for low setting I should be .024 further out then the picture?

Re glow plug, I changed it, no difference.

1995 Monster T

The high should start at 4-1/2 turns on a new engine. After break in no less than 4 turns and the low should be .024 in from the throttle linkage. When the ball linkage is removed the low needle should be flush with the throttle body .+ or - 1/8 turn max. for adjustment. Just measure from the throttle linkage in .024 depth. Looks close.

PSD

new engine is here, i pulled the glow plug and added some 2stroke oil. also put some in the intake port.
with the glow plug out engine is very hard to turn over, to the point i need a shop rag on the flywheel.
might be "pinch" but it feels like binding. i wouldn't know, never had a new nitro engine before

Bud

Heat it up to about 200 Degrees f with a heat gun. Should turn over easier. It'll loosen up some when it gets broken in. Always good to preheat it when it's new.