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Idle Speed

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NitroRider

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  1. Racing
How do I know if I have the idle speed set right on my TMAXX 2.5 engune?
I think I have it cuz when I turn the Carbartor all the way closed the motor keep going.

Not sure about this tho.
Thanks
 
The idle gap should be about 1 mm at most. Take the air filter off and see how big the idle gap is.
 
I never touched the carbartor adjustment to get it to run that way. I had someones else break it in when it was a new truck. I had to rebuild the motor.

I got it set that way with the high speed needle. I think I need to adjust it just a tad bit more its spitting out a little gas. It well even start up with the carb closed. When the truck starts this way it wont even move forward or backwards untill I give it gas. When i did give it gas look out I thoght it was going to do a wheelie. Seems to have some tork.

Sorry for some of my words. I am not the best in spellig. if there is anything else you guys can tell me on how it should act when set right please post it.

Thanks
 
the carb should NEVER close completely or it will stop the engine.....just like cupooter said the gap should be about 1mm......there is a 3rd screw on your carb that sets this gap...usually right near the throat of the carb....remove the airfilter and look at the carb barrel when you close it all the way....there should be a small crack opening at this point..as you turn the idle screw in it will make this gap increase.....if the gap is set right you should be able to pinch the fuel supply line going into the engine and get about 3-5 seconds before it sputters and soon after that die out......good luck and let us know what's happening...
 
Here is where the idle screw should be:
2007-1212-2.5IdleScrew.jpg


and here's a link if you can't see attachments:
http://home.comcast.net/~98gmarquee/pics/misc/2007-1212-2.5IdleScrew.jpg

Please note, I borrowed this image from olds97_lss.

Try the pinch test:

Pull a couple high speed runs to clear out any excess fuel from the engine.

Pull it in and pinch the fuel line right next to the carb.

If it dies immediately, richen it 1/8 turn.

If it speeds up then dies after 4 or more seconds, lean it 1/16.

If it speeds up slightly then dies in 2-4 seconds, then you're right on target.

After you do the test and get your needle set, THEN you adjust idle speed. A common mistake is to use idle speed rather than needle settings, which can give you bad bottom end.
 
Ok here is what I have come up with. I do see the gap in the carb. I am getting blue smoke and all. But its stuck going backwards. I tryed to change it to forward by hand but it still didnt change anything. I read somewhere that it could be that the idle was to high.

whats next?

One more thing it would run a little then click and shut off. I had it out side it seemed to be in high gear. I couldnt hardly control it.
 
Cupooterluvr said:
Please note, I borrowed this image from olds97_lss.
Click to expand...

Thought that looked familiar.

As for it not shifting out of reverse, are you sure your reverse servo is working as it should? Is it moving the shifting rod completely? Does the entire truck seem to jerk at all when it's at idle?

The old t-maxx trans had two pawl type clutches in it. One in the two speed and one in the forward/reverse portion. The one in the forward reverse portion is what makes the truck jerk/shudder when you apply gas from standing still. Once it fully engages, it doesn't shudder again until the truck stops.

If your idle is too high and the truck is jerking at idle, then you need to lower the idle so it stops jerking.
 
If the idle gap is very small you might have an air leak which will make it be extremely hard to tune and give an erratic idle. I fixed mine with some new fuel lines and teflon tape on the fuel filter. You should also make sure the tank lid and exhaust pressure lines are air tight as without fuel pressure it'll be hard to tune also. If this doesn't fix it, then you need to check all the screws and seal up the engine with some gasket compound (like permatex engine sealer). Cinch some cable ties around all the joints in the fuel and pressure lines for that one bit of extra seal.
 
Ok the pinch test passed. So the idle is right. It dont seem to be stuck in reverse now.
I have had a lot of trouble with it getting stuck in revrse tho.
 
With a high idle, the clutch (or optidrive, I don't know which is on the 2.5 maxx) won't disengage so you can't shift. With the right idle it'll shift every time.
 
If your spur gear is spinning then your idle is too high. I usually hold the brake down when shifting. Also it just acts funky sometimes (doesn't mesh right inside?) and you have to go try shifting a few times while moving the truck back and forth. It's not a perfect system.
 

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