I can't get my idle down!

[scootr]

Hey lads. So have broken in a new 3.3 motor in a tmaxx I've had for a couple of years.
But I can't get the thing to idle properly!
I've down all things needle related and it still idles high. I've even back the idle screw all the way out (yes all the way!) while the high and low needles where on stock settings.
I have changed the front bearing too, and checked for air leaks, and can't find any.. I've also tried a revo 3.3 pipe.
Running out of ideas..?

 

[SMaxxin]

I've always had problems with new traxxas engines leaking around the carb neck and back plate, and don't forget to check the o rings on the needles. If your idle screw is closed and it's still has high idle you have to have an air leak. You best bet would be to seal the engine, once they are sealed they run great.

 

[griff7373]

With the idle screw all the way out is the slide closing completely in the carb, your linkage could be off or binding causing the slide not to close enough.

 

[Rolex]

Stock setting are not for normal running, just for starting the break in. If the LSN is too lean that would also cause a high idle.

 

[scootr]

Yea I'm thinking air leak too.. But just can't find it!
I don't think it's the lsn. I've screwed it in, in increments until it runs too lean.
Best stuff to seal with?
Thanks guys. Anything else?

 

[olds97_lss]

With the idle screw out completely, you may be causing an air leak just from that. That said, when the idle screw is out, can you look down the throat of the carb and see that it's completely closed? If not, does it close completely when you apply the brake? If it doesn't, then you have something binding causing it to not close which is also causing your high idle.

 

[Rolex]

I don't think it's the lsn. I've screwed it in, in increments until it runs too lean.

Screwing it IN is what causes it to run lean. That in turn also causes the idle to rise. It also causes it to overheat. You need to adjust the LSN as WELL as the idle screw till it idles properly.
As others have mentioned, does the carb opening change while adjusting the idle screw or hitting the brake?
If not, there's the possibility that you have backed the idle screw out of the groove in the carb slide and now it does nothing.

 

[scootr]

Looking down the throat I can see it close. As I unwind the idle needle, the throat closes all the way.
Re the lsn, I have gone from blubber rich to lean and back again, at the same time monitoring and adjusting the idle needle, in order to determine its not the LSN.

 

[olds97_lss]

If it were me, I'd pull the engine, clean it, reseal it with RTV. Check the engine for excessive leaks first to see if maybe your front bearing is a bad source of an air leak. Can usually tell by seeing oil/gunk all over the bottom of the engine. Then again, I keep my stuff relatively clean so it's easier to see issues like that. Not @Rolex clean, but clean'ish.

If you can determine if the bearing is leaking badly or not, and it's not, then clean it really well and inspect the crank case for cracks. I busted 3 or 4 TRX2.5 crank cases, all along the engine mount flange. They run like crap and will not idle or tune at all when there's a crack in them. I have proof:
https://www.rcnitrotalk.com/forum/threads/rough-day-for-my-jato.75027/

 

[scootr]

All sealed up and have also experimented with a different carb. Problem still exists. Looking to try a new header next.
Funny thing is, that is runs excellent. Good launch, good top end, runs tank till empty (ofna tank), idle all day too. Just idles high, which is annoying, especially when my 3.3 revo is running perfectly next to it.

 

[olds97_lss]

You didn't find any cracks in the crankcase anywhere?

 

[scootr]

I'll have another look and report back.