Tuning help
 

Need help in regards to a trophy truggy. Having trouble with the motor stalling at around half throttle. Have returned all the needles to factory settings and have slowly been leaning out the high speed but the problem is still present. What am I not doing, what should I be checking?
Thanks in advance.

try changing the glow plug and change all your fuel lines, then I would make sure none of the needle o-rings are bad. start there and report back

Have changed plugs and fuel lines. Will have a look at the o-rings. Thanks mate

I the o-rings have shrunk, the needles will screw themselves in or out - rarely if ever do they leak air. Try driving the truck around with the glow driver attached. If the engine doesn't quit with the driver attached, the needles are still too rich. Also keep in mind - the idle needle controls fuel mixture up to about 60-70% throttle travel and while the main needle controls fuel mixture above that, it controls overall fuel flow too. If the main needle is too lean, it will interfere with the idle needle. Generally you set the main needle (high speed) first and set the idle mixture second, but only when the idle needle is "in the ballpark". If the idle is way too rich, often you will get too lean on the high side. It would also be a good idea to ensure the idle gap isn't too large. Many manuals spec a 1mm gap and 99% of the time that's way too big. .5-.6mm is a good starting point. Make sure the throttle linkage doesn't bind at all and the throttle closes against the throttle stop easily and quickly when the trigger is released to the neutral position.

Cheers for the info. Will try this out.

did you break the motor in right? or has it been running for a long time and just now developed the problem?

I bought it second hand for a flat out deal. The chassis looked very much untouched as far as scratches etc go. Figured even if it needed a new motor it's still a bargain.

could have a bad piston and sleeve, i bought a savage 5.9 one time that idled fine and was good for about 60 percent throttle travel but thats what it ended up bein. does is run better when its cold or once it warms up?

Idles a lot smoother once it's warm. Seems to my untrained eye to run very rich regardless of where the needles are set. Not sure if this is a symptom or sign.

Clean the air filter?

Worn out piston/liner sets will start and run when cold, but as soon as the engine warms up enough, the engine will overheat and quit and not restart until it's cooler back off. An engine that runs rich no matter where the needles are set usually indicates an air restriction causing the engine to draw more fuel.

Gave the filter a clean and fresh oil when I done the fuel lines.

have you adjusted the low needle as well? the one in the end of the slide? Whats your idle like? will it idle well or does it have to be given continuous gas to stay on?

Stalls a bit when it's cold but once warm the idle seems fine maybe a bit high. Has quite a bit of oil coming out the exhaust when at idle. Am I able to post a video?

Sounds like the idle needle is still too rich. Post links from YouTube in your thread. Uploading to YouTube works best usually.

Awesome thanks for the advice. Will get onto it tomorrow after work.

Went to get the video this afternoon but my glow igniter was flat so I'll try again tomorrow.

Here's vid 1 of two:
https://youtu.be/yFg3gCO60Z0
Here's vid 2:
https://youtu.be/Wjdpjl7OybA
Temps when idling away were up around 92deg Celsius. Hopefully you can see the amount of oil coming out the exhaust. I also had the filter off and quite a lot of fuel was splashing out from the carby.

Did you try driving the car with the glow driver still attached like I suggested? It sounds sloppy rich and loaded up.

Yeah I did but it still stalled. Which needle would be the first to lean out? Would it be possible that one of the needles is letting too much fuel through even after moving the needle settings?

id there is fuel actually splashing outta the carb, i think something is wrong with your high speed needle. a oil dripping from the pipe is normal, since the fuel does have oil in it, just a byproduct of a nitro engine.screw the high speed needle all the way out and inspect it and its bore. some way or another its gettin too much fuel.

Then it's flat out too rich. Lean the idle needle 1/4 turn and try to rev it up and clean it out. In extreme cases, you can lift the car off the ground and rev it up to clean it out. Don't rev it hard for long, just enough to burn off what's in the crankcase. If the engine still is quitting, lean the idle needle more until it will rev without quitting. Once you're there, tune the high speed needle for best performance (revving cleanly and not cutting out), and then go back to the idle needle and adjust in small increments until it will rev up to WOT cleanly. After you think you "got it" let it idle for 10-15 seconds. If it quits when you throttle it up, the idle is too rich still. If it's a little burbly and smokey at first but cleans out and revs up nice, you're pretty much where you want it to be. Ideally you want it to ever so slightly load up after a long idle (10-20 seconds). If it doesn't load up at all after 15-20 seconds, it will end up being too lean at the bottom of the tank and probably run pretty hot. Another way to tell how the engine is running (mixture-wise) is to pull the glow plug and look at the base of it. Shiny metal means rich, brown like maple syrup is perfect, and black is lean. Ideally you want it to look brown. If you have an infrared temp gun, hit the cylinder head heatsink with it to see what temp its at when it quits. If it's below 150F, it's just way too fat and needs to be leaned down.

What at fuel and glow plugs are you using?

FWIW - if the settings are too rich, it's not uncommon to have raw fuel coming out of the exhaust at idle. It's common to see the carburetor spit fuel too in overly rich conditions, but it's usually not noticed since ground based engines really shouldn't be run without an air filter for any length of time. Airplane engines will spit fuel at WOT when set to a "perfect setting" and it's visible with a good camera. It happens due to a phenomenon called fuel stand-off or carburetor stand-off.

Wow this is great information. Very much appreciate it. I'll head home from work and get testing. I'll let you guys know the results. Thanks again.

Would it be worthwhile replacing the needles?

I don't think it is because they're not something that usually wears out. If the engine is really old, the o-rings can shrink over time, but if they don't unscrew themselves, the o-rings are fine. Contrary to what some guys say, bad o-rings will not cause an air leak except if the o-ring under the carburetor is bad or missing.

I think 90% of your problem lies with the needle settings.

What at fuel and glow plugs are you using?

Sweet. I'm running an LRP r5 medium cold plug on 20% nitro mix. It's our weekend here in aus so I'll have some time to play and hopefully get it running.