Weird T-Maxx Issues - Hard to Start, Unstable Idle, Impossible to tune

[Dr. Bogger]

Hi Everyone!

I have a T-Maxx 2.5 (With a TRX 2.5R).

It was given to me for free due to the problems it has.
It does run, but not very well.

When I start it, i have to prime the hell out of it just to get it to stay running.
(It's hard as hell to get it to start and stay running (and I have the EZ-Start System)).

Once it does start, and even after the engine warms up, it just has a very unstable idle. It'll speed up, slow down, and die, in no specific order.. just randomly.

When it is actually up and running, and warmed up, the engine is virtually impossible to tune. I have reset it to factory settings, prolly 100 times over again, and it just always wants to overheat. I measured temps of upto 380 degrees F with the HS needle set at almost 5 turns out. (Which should be very rich, but for whatever reason, its still running lean)

Heres what I've replaced so far, in this order:

1. Replaced all the Fuel Lines
2. Replaced the Glow Plug
3. Replaced the carburetor
4. Replaced the Glow Plug again
5. Replaced the entire Engine (Carb and everything)
6. Replaced the EZ-Start (Because I broke it by mistake... Whoops!)
7. Replaced the glow plug again (they all were working, just replaced it to rule it out)

It is NOT a tuning issue, and it's not a carburetor issue.

Its gotta be something else, because it'll run, just very unstable.

Any suggestions as to what could be the cause?
This thing is just driving me crazy! I hope someone can put an end to my misery.

Please everybody! Put in all your efforts on this one!

 

[zrock]

Did u replace the engine as one unit carb and engine? Usually that is signs of a air leak. Mine used to overheat to the point of shutting down and I had to reset low and high speed back to factory and adjust the gap. Then all was good. Have u checked for any binding in the linkage? Also I have read posts where the clutch caused some strange engine issues

 

[chickenman242]

have you replaced the fuel tank or checked it for leaks cracks or maybe a blockage at the outlet

 

[Phins Fan]

I would look at this to start with:

[ame="http://www.youtube.com/watch?v=6xwDy-I0Z4I"]How to seal an RC engine from air leaks - YouTube[/ame]

If you still have issues than go onto what chicken said. Its a process of elimination but typically airleaks are responsible for all of your issues

 

[Dr. Bogger]

Did u replace the engine as one unit carb and engine? Usually that is signs of a air leak. Mine used to overheat to the point of shutting down and I had to reset low and high speed back to factory and adjust the gap. Then all was good. Have u checked for any binding in the linkage? Also I have read posts where the clutch caused some strange engine issues

I replaced the Carburetor on the Original Engine, and i sealed the original carburetor before i replaced it.

Then, after all that didn't work, I replaced the entire engine (Brand New) (with a new carburetor already on it)
Still didn't fix the issue.

If you still have issues than go onto what chicken said. Its a process of elimination but typically airleaks are responsible for all of your issues

I already did seal the original carburetor (before I replaced it with a new one).

have you replaced the fuel tank or checked it for leaks cracks or maybe a blockage at the outlet

Yes, i checked the fuel tank for leaks, and didn't find any.

Nothing I've done has solved the issue at all.
Any other suggestions?

 

[2revo1maxx]

Yeah, richen the high speed needle and wrap the cooling head with something to keep it from over-cooling in the cold weather.

 

[Dr. Bogger]

Yeah, richen the high speed needle and wrap the cooling head with something to keep it from over-cooling in the cold weather.

That's irrelevant to my problem....?

 

[2revo1maxx]

If you have a new engine overheating in NY weather then you most likely have a LEAN engine. It could be an airleak, but it's rare on a new engine.
Have you taken anything apart on this new engine?

 

[Dr. Bogger]

If you have a new engine overheating in NY weather then you most likely have a LEAN engine. It could be an airleak, but it's rare on a new engine.
Have you taken anything apart on this new engine?

lol, I live in NY, but i am currently on vacation in South Carolina.

The engine is not lean.. if you read my post above, i had the HS Needle set at 5 turns out, and it still reached temps of over 300F.

I know how to tune an engine, I have a RedCat Caldera 3.0 that runs perfect! 100 times better than the Traxxas. It never overheats and holds a perfect tune.

Its not the tuning.. i can guarantee you that. Its something else, and i don't have a clue what is causing the problem.

 

[2revo1maxx]

Then it must be an air leak. Have you had this new engine apart?

---------- Post added at 8:55 AM ---------- Previous post was at 8:53 AM ----------

lol, I live in NY, but i am currently on vacation in South Carolina.



I know how to tune an engine


and i don't have a clue what is causing the problem.

Btw, I just think this is funny.

 

[Dr. Bogger]

Then it must be an air leak. Have you had this new engine apart?

No I have not. I replaced the engine thinking it would solve the issue, but it did not solve anything. So the engine it's self is eliminated as the cause of the problem. It must be elsewhere.

 

[2revo1maxx]

Are you running it too hard?

 

[Dr. Bogger]

Are you running it too hard?

Nope, it had nothing to do with that.
It wouldn't have anything to do with running it too hard.

Do me a favor, and re-read the original post.

 

[2revo1maxx]

Do me a favor and quit being so stubborn.
Your engine is running lean, from an air leak or bad tuning etc. Look for exhaust or fuel tank problems, then check your engine for air leaks.

---------- Post added at 9:48 AM ---------- Previous post was at 9:46 AM ----------

Are all four screws in your fuel tank? Or is it missing one?

 

[Zdragon71]

Check your exhaust boot for splits or holes also check your fuel tank lid seal. When you open the lid and close it you should feel suction. Check your header for cracks as well. All of these thing will cause the problems your having.

 

[alpinehyperlite]

I know how to tune an engine, I have a RedCat Caldera 3.0 that runs perfect! 100 times better than the Traxxas. It never overheats and holds a perfect tune.

Best/worst. Post. Ever.












EVER!

 

[zrock]

you said you replaced the entire engine complete with carb. You did not say you sealed the new engine.. Start with the basics seal the engine completely... Takes 10 min and then you have eliminated the air leak possibility completely... Just because its new does not mean its totally sealed

Also check your fuel tank o ring if that is leaking you will never get a proper tune

 

[frickenjoey]

I know this may be a silly question to you but, when you put the "New" engine on it did you break-in the engine?
It really does sound like you have an air leak on the engine. Do you see bubbles in the air lines? If so are they coming all the way from the tank or starting some where in between?
What fuel are you running, howabout what temp of glow plugs? Does the engine still have good compression?

 

[Phins Fan]

All honestly it would appear you DO NOT know how to tune an engine as there has been plenty of solid and legit suggestions by quite a few seasoned members who have not only helped me with my tuning incompetence but others as well. I agree with 2 Revo. QUIT BIENG SO STUBBORN!!! You can't start a thread asking for help and then tell everyone they dont know what they are talking about or that they are not helping your situation. The best way to get help around here is to not shoot down everyone elses suggestions but rather take them with pride and thanks.

Good luck with your tuning situation..

 

[mrbones]

Check the nozzle on you exhaust pipe where it goes to the fuel tank and make sure it's not plugged up. I had one plug up on me and I had to drill it and run a wire through it to get it clear.