Engine help, its going crazy!

[thenameskam]

Posted in stadium trucks, but doesn't seem to be to much activity on that sub forum so ill post here!

I have an hpi mt2, just got it from a friend and i ate up the spur gear, got a new one and replaced it and tried starting it, and the it would idle for 1 second and then shoot straight up to full throttle and hold there then cut off. did it every time i started it, so i noticed that the car's servo in the "neutral" position was almost full throttle so i adjusted it back to the neutral position. Now when i start it, it idles fun but as soon as i hit the gas, the engine starts to climb to full throttle on its own, and I've watched the servo/throttle in the carb and its not moving at all. I tried to tune it and see if that helped but i noticed it wasn't at all. so i turned the car ALL the way lean, and it ran and did the same thing, but it was spitting fuel right out of the exhaust a good foot. turned the car all the way rich and it was doing the same thing. i tried tightening the carb down to make sure i didn't have a leak, but nothing is working. Any ideas anyone? I'm about to just buy a new engine and be done with it! any help much appreciated!

 

[Assassin]

Posted in stadium trucks, but doesn't seem to be to much activity on that sub forum so ill post here!

I have an hpi mt2, just got it from a friend and i ate up the spur gear, got a new one and replaced it and tried starting it, and the it would idle for 1 second and then shoot straight up to full throttle and hold there then cut off. did it every time i started it, so i noticed that the car's servo in the "neutral" position was almost full throttle so i adjusted it back to the neutral position. Now when i start it, it idles fun but as soon as i hit the gas, the engine starts to climb to full throttle on its own, and I've watched the servo/throttle in the carb and its not moving at all. I tried to tune it and see if that helped but i noticed it wasn't at all. so i turned the car ALL the way lean, and it ran and did the same thing, but it was spitting fuel right out of the exhaust a good foot. turned the car all the way rich and it was doing the same thing. i tried tightening the carb down to make sure i didn't have a leak, but nothing is working. Any ideas anyone? I'm about to just buy a new engine and be done with it! any help much appreciated!

It sounds like the little arm on the throttle that the servo moves to activate the throttle is slipping. There should be a nut surrounding it to keep the plastic arm moving the throttle opening. Adjust all your servos and arms etc to 0 input, including the carb gap, then tighten up that nut to secure it better.

 

[thenameskam]

but i have no air filter, and the carb is not moving up at all, and neither is the servo? possible air leak?

 

[TaterX]

What do you mean by no air filter? Whats there?

 

[Assassin]

but i have no air filter, and the carb is not moving up at all, and neither is the servo? possible air leak?

Is there a little plastic arm that opens and closes the carb when the bar attached to the servo pushes or pulls it?

 

[TaterX]

Is there a little plastic arm that opens and closes the carb when the bar attached to the servo pushes or pulls it?

I don't think it will ever tune again without a complete overhaul if he's been running it with no air filter.

 

[Assassin]

I don't think it will ever tune again without a complete overhaul if he's been running it with no air filter.

Depend on if hes just tuning it with the filter off only, and not running it around with it off.

 

[thenameskam]

i was just running it without an airfilter to watch the carb and see if it was opening/closing etc. but as the engine kept climbing the full throttle neither the carb or the servo was moving

 

[TaterX]

Depend on if hes just tuning it with the filter off only, and not running it around with it off.

Your right didn't think about that.

 

[Assassin]

i was just running it without an airfilter to watch the carb and see if it was opening/closing etc. but as the engine kept climbing the full throttle neither the carb or the servo was moving

Then the tune is lean.

Reset the needles to factory spec specified in your manual, or online PDF manual, tune from there.

 

[thenameskam]

will try and tune tommorow, but for tonight i can't seem to get my servo with the linkages setup correctly? everytime i would hit the breaks it would cut out. so I'm trying to adjust them so that when i hit the breaks on the servo, it doesn't pull the carb in at all and cut air flow. but with my idle screw all the way in, it only leaves a VERY time amount of space and if i loosen it just a 1/4 turn its completely closed and if you continue to loosin the idle screw it just keeps turning further back after its already fully closed. is something wrong with my idle screw that why it keeps cutting out? i can't seem to adjust the servo to where it wont move the throttle back at all.

 

[Assassin]

will try and tune tommorow, but for tonight i can't seem to get my servo with the linkages setup correctly? everytime i would hit the breaks it would cut out. so I'm trying to adjust them so that when i hit the breaks on the servo, it doesn't pull the carb in at all and cut air flow. but with my idle screw all the way in, it only leaves a VERY time amount of space and if i loosen it just a 1/4 turn its completely closed and if you continue to loosin the idle screw it just keeps turning further back after its already fully closed. is something wrong with my idle screw that why it keeps cutting out? i can't seem to adjust the servo to where it wont move the throttle back at all.

That is step 1

You need the gap set around .5 to 1mm, so that it will stay open that amount when pushed closed.

With your transmitter trim set to 0, make sure when you hit the brakes the gap doesn't close at all it holds your .5 to 1mm gap from 0 input to full brake, and as soon as you apply throttle, it starts to open. Also make sure that when you hold full throttle, it opens all the way. Do this and reset the needles to factory settings before running the truck. Then follow any tuning guide

 

[thenameskam]

but isnt there something wrong with my idle screw? there is really no adjustment at all in it. maybe 1/4 turn and the carb is fully closed. i think thats why I'm having and issue with the cutout, because when i adjust it per waht you said. when i break, it still causes my carb to move towards close just a tad more

 

[Assassin]

but isnt there something wrong with my idle screw? there is really no adjustment at all in it. maybe 1/4 turn and the carb is fully closed. i think thats why I'm having and issue with the cutout, because when i adjust it per waht you said. when i break, it still causes my carb to move towards close just a tad more

Then like I said earlier your plastic bar that moves the carb open and closed has slipped.

Easy fix, loosen the nut that secures it, reposition the arm where your idle screw has more room for adjustment of the gap, then tighten it back down. Adjust your linkages from there.

 

[thenameskam]

I will try that today when i get home!