View Full Version : TRX 2.5 Running Terrible and Erratic, Can the engine be shot?
02-03-2006, 03:48 PM
It got really nice out now so I decided to run a few tanks
Last week it overheated maybe 3 times after a few tanks of fuel and running it full throttle around a 1/4 mile paved track for over a hour.
Running 30% Trinity Race
I adjusted this carbs setting over and over again.
If I run it rich the thing bogs and is so slow.
My idle is eratic and the idle screw works but the engine just doesnt respond
Low speed needle lean it has good power, rich it bogs and dies.
What keeps happening is that is is stalling at full throttle.
If I make a long stretch pass 500 feet then hit the brake the thing just stutters and dies. Adjustments to the High speed needle have not corrected this.
starts back up easily so It is not running hot.
I am starting to think the motor is fried or the carb.
I pulled the air cleaner off for a few passes and it had even more power but still idled and died.
If i lean the low speed needle to mich the engine shuts off, if i richen it too much it dies too.
I took 4.75 turns from closed on the HSN, what traxxas recommends.
the HSN was 3.25 turns it ran great but this is really lean for 30% fuel.
Any thoughts or suggestions?
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02-03-2006, 06:09 PM
Okay here's what I'd do,
I think the LSN is your problem. It may be too lean. Set everything back to factory settings, that's 4 turns out from close on the HSN, and in my estimate 1.8 turns counterclockwise on the LSN. Look in your carburetor and make sure there's a 1mm gap for the idle screw.
It's critical that your LSN be on the rich side, because if you try to tune on the lean side your HSN will not produce good results. A couple months I had extreme temps because my lsn was too lean.
Now follow the instructions again in your manual for the fine tunnig adjustments. PLEASE when making adjustments especially to the LSN turn in 1/16 increments because this is a lot more sensitive than the HSN, and don't tune the LSN until the HSN is giving you engine temps around 240-270 and blue smoke is visible.
Now if that doesn't work take your engine to your LHS and check it's compression. I have a feeling that due to the sustained periods of high RPMs that maybe your engine is worn out, but hopefully that's not the case.
OOOHHHH and that's a big no no!!. I hope you're talking about something else when u said u pulled the air cleaner off and did some high speed passes. If you did pull off the air filter, u're in trouble because any minute, small, piece of dirt that gets into the carburetor has gr8 potential of destroying your piston and sleeve fit.
02-03-2006, 08:27 PM
Also - high nitro race fuel is probably not the fuel to use if your tuning skills are not "spot on". Fuels like Traxxas Top Fuel have the proper blend of lubricants to provide protection even in the event of an occassional lean run.
Because it restarts readily, the piston/sleeve fit is probably okay. A "dead" engine will not restart until it cools down and the sleeve contracts a little.
Try some Traxxas Top Fuel 33%, and a fresh Traxxas 3232 Super Duty plug and report back.
02-04-2006, 12:51 AM
Hey I started from the begining again tonight just for 10 minutes.
This engine was tuned perfect for 3 months, not a single problem
I have used 3 plus gallons and only 4 glow plugs, the glowplugs are lasting really long and not burning up. I would have kept the original if Traxxas didnt tell me no too thats how good it was running.
Im using MCOY plugs
This last gallon of fuel is when I noticed some changes, Pink Trinity Race 30%, 1 quart from empty when these syptoms occured.
I previously was running Odonell and Byron, all race blends because the thing was tuned spot on every run.
It almost apears as if someone in our shop has messed with it because its kinda crazy how it ran 100% and stronger than ever until a few days ago.
Compression is perfect, only other conclusion can be a worn out or damaged carb.
I worked on the LSN and the Idle earlier and i got the car to stay put without racing forward again, had decent power but not perfect and I will spend some time getting it right.
Car is slow and I know something is not right.
I did open the motor after break in and did a few modifications which may have weakend things
lighten the crankshaft and polished it,
bored the carb intake a few thousanths
Engine ran so STRONG it was faster than a few OS 21 I raced on the same on road paved oval track in their Ofna buggies.
Having a machine shop makes you play more.
I wish i did the NOS injection then I would blame it on that, I still may make my own version to end the TRX final misery and get a bigger better engine.
02-04-2006, 08:40 PM
I think you might be running the truck wide open too long. You said you were running it on a 1/4 mile paved track for like a hour. 1/4 mile is extremely huge and I'm guessing you were probably let her hammer a bit. Maybe it is a fried motor. Just my 2, Jeremy
02-04-2006, 09:03 PM
Good Point I dont run it on the 1/4 all the time but when I do it is WOT and Ill run over 1 quart of fuel that day.
Today i got some more fuel 30% Odonell, I had a quart not too long ago and the car ran it's best but was always out of stock.
Today I got a gallon.
I tossed the remainder of the Trinity fuel and ran 1 tank of the Odonell today and it seems to be running good again, the tune is 90% perfect.
In the LHS today a few guys said this Odonell is the best and the Trinity fuel was harder to tune with.
I didnt know fuel choice has alot to do with it but I guess it does.
When the weather clears up I will go the track again and see if I can get this thing up to speed again.
02-05-2006, 04:13 AM
if you ran it WOT for more than 30 seconds, you most definitely have a stretched con rod...
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