Newbie nitro owner having issues.

[Davidwebb911]

Hey everyone, new nitro car owner in need of desperate help. I just bought my first nitro car, built it and now in the break in procedure with my engine, which is an FX engine. I start the engine and itll idle fine for 5 to 10 seconds and then with ZERO throttle input, it'll rev to the max and stay there. If I put the car on the ground, it'll take off with me giving it ZERO throttle input and won't return to idle.

The engine is preset from the factory for break in, i havent touched anything on the motor. The throttle linkage doesn't move, neither does the carburetor. While in the idle position, It'll literally just rev up to the max until i pinch the fuel line and kill the engine

I am a newbie and this may be something simple, driver related or something else, but i have absolutely no clue why its happening and what to do. Can someone help me out or at least point me in the right direction?

 

[fstnd]

Welcome to RCT!
Play with the needles. Just don't forget the standard settings.
I'd try richening (turning counter clockwise) the low speed needle (LSN) by a quarter of a turn and see if it helps. If not, you can screw it back in (leaning). Then, you should richen the high speed needle (HSN), which should help.
Of course, check your fuel lines, check for any leaks and make sure no oil is being spit out of anything but the exhaust.
When the engine runs away, it's safer to block the intake with your finger then pinching the fuel line. If the engine keeps running, that indicates a vacuum leak.
A video would be very helpful

 

[9x19]

Welcome to RCT

I'm strictly an electric runner, but there are lots of nitro fans here that will likely try to help you out!

 

[332_RC]

Welcome to RCT!

 

[Chubaka]

Welcome to the site. In addition to the above, what's the idle gap look like. Should be around 1mm

 

[CertifiedMike]

Welcome to RCTALK.COM!!!

Everything that was suggested are great places to inspect. Also, just verify that your linkage and everything including the carb itself are operating as intended.
When the linkage does move, does the carb too or is there a loose screw or some other issue thats preventing proper smooth operation of the carb itself.
Have you adjusted the linkages properly?

Curious if you removed or loosened, adjusted the orientation of the carb when it was installed.
Carb oring leaks are very common and can act similarly to your runaway issue.

This sounds like an air leak to me.

 

[Davidwebb911]

I've replaced both fuel lines and it didn't change anything. I've made the LSN and HSN more rich and it didn't change anything. I've checked all the screws of the motor and everything is tight and snug with no fuel leaking anywhere.

The carburetor idle setting has only a sliver of an opening per the instruction manual. I haven't removed, loosened or tightened any component of the engine except the needles to richen the mixture.

The linkage moves freely and correctly per the instruction manual and doesn't move at all when throttle/brake input isn't given.

Really at a loss here...... should have just stayed electric lol.

 

[Davidwebb911]

Here are some pics of my setup for reference. You can see the sliver of a gap in the carburetor which the idle its set at

 

[CertifiedMike]

Did you start it and then try to choke it out with your finger blocking the air inlet? Just because YOU didn't mess up the orings doesn't mean they aren't messed up. It is fast and cheap to replace them. Be sure to use green slime or similar silicone based lube or you're wasting your time.

You aren't going to see an airleak. You are unlikely to tighten up a screw to fix one too.
You can put some superlube at the base of the carb to make a temporary seal to test.

Your issue is an airleak somewhere.
Your engine needs to breath which clearly it is, no exhaust issue, and fuel which it also clearly getting.
Since your motor would choke out and die if it was getting too much fuel, that is not the issue either.
You need to be looking for an air leak. Unregulated air is getting past your carb idle gap and letting your motor run exceptionally lean at very high rpm by the sounds of it.
Don't let it run like this for long at all!!! Chances are very good that its running very lean if its doung whaylt I think it is. Not good for nitros.

Try replacing the orings.

Fixing a nitro is far easier than most ppl think. They are VERY simple.

They are easier for me to understand than brushless, lipo...

I can not see your idle gap pic. My phone sucks. I'm hoping someone can chime on to verify but it sounds like its set correctly to me.

 

[Littlemotor]

What fuel are you running? That engine is setup for 16% nitro. Also are you heating the engine before starting?

 

[Davidwebb911]

What fuel are you running? That engine is setup for 16% nitro. Also are you heating the engine before starting?

The manual says any fuel between 16%-30% and I'm using Traxxas 20%. I preheat the engine with a engine heater and a heat gun as I've come to find out an engine heater alone is insufficient with this engine to get it to not stop TDC.

 

[Littlemotor]

The manual says any fuel between 16%-30% and I'm using Traxxas 20%. I preheat the engine with a engine heater and a heat gun as I've come to find out an engine heater alone is insufficient with this engine to get it to not stop TDC.

The manual can “say” that all it wants-there is a HUGE difference in PTH clearance, and necessary shims(s) stack height required between those (5) fuels sir… Also you could not PAY ME to put Traxxas fuel into one of the highest end engines available..

You need to verify your PTH clearance, and shim accordingly before you go any further. That is detrimental, and also absolutely has an effect on your RPM.

Also-I would be INCREDIBLY surprised if there were ANY defects, or issues with that FX engine.

 

[Davidwebb911]

The manual can “say” that all it wants-there is a HUGE difference in PTH clearance, and necessary shims(s) stack height required between those (5) fuels sir… Also you could not PAY ME to put Traxxas fuel into one of the highest end engines available..

You need to verify your PTH clearance, and shim accordingly before you go any further. That is detrimental, and also absolutely has an effect on your RPM.

Also-I would be INCREDIBLY surprised if there were ANY defects, or issues with that FX engine.

Forgive my ignorance as I genuinely don't know, what are you referring to by "PTH Clearance" and to "shim accordingly"?

 

[Littlemotor]

Forgive my ignorance as I genuinely don't know, what are you referring to by "PTH Clearance" and to "shim accordingly"?

Piston-To-Head clearance. This is the measurement in thousandths of an inch (0.0xx”) from the piston face @ top dead center, and the closest point to the piston face from your head button’s fire deck. You must also keep in mind that these are often tapered in onroad engine’s (as well as in many high end off-road engines these days), and will there by yield different values at different locations, so it’s a very big deal to know exactly what you’re doing, or you can “measure” all day long, and not get the correct numbers as you are not in the correct location to begin with.

You absolutely 100% risk damaging your brand new engine if this process is not done correctly-let alone; skipped all together because “the manual says it’s good for 16-30% fuel”…

I’m getting the impression that you’ve never done this before, is that correct?

 

[Davidwebb911]

Piston-To-Head clearance. This is the measurement in thousandths of an inch (0.0xx”) from the piston face @ top dead center, and the closest point to the piston face from your head button’s fire deck. You must also keep in mind that these are often tapered in onroad engine’s (as well as in many high end off-road engines these days), and will there by yield different values at different locations, so it’s a very big deal to know exactly what you’re doing, or you can “measure” all day long, and not get the correct numbers as you are not in the correct location to begin with.

You absolutely 100% risk damaging your brand new engine if this process is not done correctly-let alone; skipped all together because “the manual says it’s good for 16-30% fuel”…

I’m getting the impression that you’ve never done this before, is that correct?

Correct. I did my research before buying, watched tons of vids on youtube about nitro rc and found nothing to what you are referencing and I don't even see it in the manual. if I have to do what you just explained to me (thank you for that) I'll stick to electric.

I don't know how to check that and adjust it properly and in all honesty, I don't have any desire to. Everything i read and watched before I purchased anything, in essence just said buy the engine and all required pieces, break it in per manual, tune it to optimal settings and go.

I hoped the issue with this engine would be something simple, but it doesn't seem that way. Thanks to everyone who suggested things and tried to help me. I'm going to sell this thing and stick to electric lol.

 

[Littlemotor]

Correct. I did my research before buying, watched tons of vids on youtube about nitro rc and found nothing to what you are referencing and I don't even see it in the manual. if I have to do what you just explained to me (thank you for that) I'll stick to electric.

I don't know how to check that and adjust it properly and in all honesty, I don't have any desire to. Everything i read and watched before I purchased anything, in essence just said buy the engine and all required pieces, break it in per manual, tune it to optimal settings and go.

I hoped the issue with this engine would be something simple, but it doesn't seem that way. Thanks to everyone who suggested things and tried to help me. I'm going to sell this thing and stick to electric lol.

It IS simple if you know what you’re doing, or if you don’t have the experience; are willing to take the time to learn. Like anything else; we crawl before we walk.. There are absolutely aspects of electric that are no different-LiPo management, knowing how, or learning how to solder correctly, understanding voltage, motor kV, gearing, routine care, and maintenance, etc..

Just because you can’t “find anything about it online”, doesn’t mean it’s not crucial to success.. There are many members here who are willing to help you learn-including myself. Sounds like you’ve made up your mind already that “nitro is too involved” though.. could you solder proficiently the first time you picked up an iron?

 

[CertifiedMike]

I will confirm, Traxxas is not good fuel. Also, this guy @Littlemotor is seriously smart. He knows an awful lot about nitro. Way more than I know.
You took the time to go thru some basics. Pulling a few more screws, learning a different power system seems like not much more effort. Running your own nitro is very rewarding. Well worth your time.
It s not too hard. I can do it and I'm not that smart.

You are talking with likely the most knowledgable nitro guy on the site. You should take advandage of this opportunity to learn.

 

[Littlemotor]

@Davidwebb911 /Jason-dammit-Bourne, should you change your mind, start here-very detailed, and will tell you what to expect, and very close to everything required to set that rowdy little FX up properly for success:

Post in thread 'Project “Old School”. A Littlemotor Jammin’ CRT.5 1/12 nitro truggy build for 2025!!! '
https://www.rctalk.com/forum/threads/project-“old-school”-a-littlemotor-jammin’-crt-5-1-12-nitro-truggy-build-for-2025-.145261/post-1523796

Just trying to help a brother out, and would love to see ya not throw in the towel just yet.. Gotta be determined, and resilient in ANY form of RC-not just in nitro..

 

[Davidwebb911]

It IS simple if you know what you’re doing, or if you don’t have the experience; are willing to take the time to learn. Like anything else; we crawl before we walk.. There are absolutely aspects of electric that are no different-LiPo management, knowing how, or learning how to solder correctly, understanding voltage, motor kV, gearing, routine care, and maintenance, etc..

Just because you can’t “find anything about it online”, doesn’t mean it’s not crucial to success.. There are many members here who are willing to help you learn-including myself. Sounds like you’ve made up your mind already that “nitro is too involved” though.. could you solder proficiently the first time you picked up an iron?

It's funny you bring up soldering cause I knew since shop class in high-school, I was never good at it. LoL. Every time I get a new battery or ESC for my cars or helis, I just take it up to my hobby store and have them do all the soldering lol. I know my limitations .

truth be told with this nitro thing, having issues with everything from the moment its brand new, is enough to turn me off with it. This was just something I wanted to try and for me at least, turned out to be a waste of $$$$. Live and learn, but I'm glad that people in the community reached out and tried to help me. That's why I love the RC community

 

[Davidwebb911]

@Davidwebb911 /Jason-dammit-Bourne, should you change your mind, start here-very detailed, and will tell you what to expect, and very close to everything required to set that rowdy little FX up properly for success:

Post in thread 'Project “Old School”. A Littlemotor Jammin’ CRT.5 1/12 nitro truggy build for 2025!!! '
https://www.rctalk.com/forum/threads/project-“old-school”-a-littlemotor-jammin’-crt-5-1-12-nitro-truggy-build-for-2025-.145261/post-1523796

Just trying to help a brother out, and would love to see ya not throw in the towel just yet.. Gotta be determined, and resilient in ANY form of RC-not just in nitro..

PLEASE don't do the JB thing lol, I get harassed by that dailey lol