r.c truck running weird

[johnrodgers]

i have myself a savage xl two speed but i imagine the problem i am experiencing isnt make or model related. i basicaly had my engine tuned fine and was hitting some jumps and it had excellent top end, but after a few tumbles it always runs like it is lean with the throttle chopping out at full throttle and terrible top end. i tried adjusting the slow speed and high speed adjusters to make it run richer but to no avail. I'm wondering if my engine has worn or if it have to do with the throttle servo? also i swapped out the air filter but it seemed to only have momentarly releived the issue to a small degree. any suggestions of what to do are welcome. thanks in advance.

 

[ThunderTiger]

Just a thought, but try swapping out your glow plug. Also, check your fuel lines and tank for air leaks. Check your engine for air leaks too.

All of the above can induce hot running and "lean" running conditions through more air getting in than is required.

Also, go back to factory settings on you carb needles (HSN & LSN) and work from there.

 

[johnrodgers]

just last night before bed i thought it may be the glow plug. ill check all of the above though, thank you for the tips.

 

[bigjay]

Sounds like it could have an air leak.

 

[johnrodgers]

i un assembled the engine today and noticed there was quite a bit of debree around the cylinder head, i imagine it was from not tightening the 4 bolts that hold the heat sink and cylinder head on enough but was not sure, so this time i made sure to tighten it up good. also i think i may have lost the tube that connects from the gas tank to the pipe, i think it is some sort of overflow vent but not sure. is this tube crucial? would it have any effect on how the engine performs if it was not there?

 

[Amoeba]

The tube from the exhaust to the gas tank is necessary. It provides pressure from the exiting exhaust gases into the tank to push fuel to your engine. Nitro engines don't "suck" all that well so a positive pressure in the tank is required to keep the fuel pushed into the engine.

 

[AxialLST]

If it is the tube I think it is, it provides pressure in the tank, forcing fuel to the carb. This is a very critical tube, without it the engine will run lean due to the engine not being able to draw enough fuel at higher RPM. Basically that tube regulates the fuel that is sent to the carb based on the RPM and exhaust output of the engine. I would replace that tube, make sure the cylinder and wall arent scored by any of the debris you found, re-tune, and run it. If you have the cylinder and sleeve out while you check them (really the only good way to do so unless theres obvious damage to the sleeve) check the pinch as well to ensure that the engine didn't sustain any damage while running too lean.

Disclaimer: I am not an expert, but I did stay at a Holiday Inn last night...

-AxialLST

 

[johnrodgers]

thank you guys so much, i think the tube fell off when i was hitting a drop, i have already had to replace my fuel tank and the primary fuel line and it took quite the while for delivery. any recommendations as to were to get silicone tubes?

 

[AxialLST]

Unsure if the ones they carry at hardware stores can withstand the stuff in the fuel and the heat, but you might try that route. All of the LHS carry fuel tubing. I would check your local hobby store first, if there isn't one near you check the hardware store, just be sure to ask if its fuel and heat resistant, or the package it comes in may say.

-AxialLST