Engine Trouble

[speedingbulletbp]

have recently bought an XTM 457 Pro race engine, but I'm having a slight problem with it. At first I put it into my Losi 8T and I have just finished switching it over to my XTM Mammoth ST and I continue to have the same problem.

The problem is that it wants to drive itself at WOT. The low and high speed needles have no effect on it even when I switched it back to factory settings. The temps run about 130F-140F. It did this in both trucks and I am clueless why it is.

Also since I put it into my Mammoth ST, if I touch th brakes at all it kills the engine. I'm guessing I need to tighten the spring on the throttle servo to fix that problem.

ANY HELP WOULD BE APPRICIATED. I need to get this thing on the track before the next race.
Thanks

 

[AxialLST]

Killing the engine when you touch the brakes is an idle adjustment screw problem. I would set your trim for the throttle servo to neutral, adjust the linkage, then turn in the idle screw a hair (Not sure which direction it is on your mill but I know mine you have to tighten to adjust idle speed up). As for the WOT issue I have no idea about that one, but 130-140 degrees is way too low. Does the engine accelerate smoothly or bog?

My best guess would be the throttle linkage is set incorrectly causing the engine to run at a higher throttle, and the idle is set too low, causing it to die when you hit the brakes :\

-AxialLST

 

[speedingbulletbp]

it has a very snappy acceleration no bog at all. I'm supprised it doesn't do wheelies. Ill have to see where my idle screw is because now that you say that it sounds like the problem. It has a very high idle I'm guessing that might be my problem. the linkage was my guess on killing it with the brakes, so should I just tighten the spring to fix that?

 

[AxialLST]

No, basically if it's set up correctly idle speed should not change at all when you hit the brakes. This is regulated by the idle screw keeping the plunger from being pushed closed in the carb. This is the steps I would take to fix it:

1. Disconnect all the connections from the throttle servo.
2. Push the plunger in gently as far as it will go and look down the barrel of the carb, should be about 1mm opening, if the isnt the case, adjust the idle screw until it will stop there, and this gives you a good starting point.
3. (Be sure the throttle trim on your radio is set to neutral for this step) Re-connect the throttle linkage, and turn everything on. If the plunger moves open from where you had it set, adjust the linkage to where it should be, and using your radio, open the throttle to make sure it opens fully.
4. Now, fire the engine, you may have to give it a little throttle as it will be cold, but dont turn any screws on the carb until it is warmed up.
5. After the engine has idled for a few min and is nice and warm, adjust the idle screw to the highest point you can go without the truck moving, then back it off a hair. You should be able to now give it throttle, and brake without the engine dieing. Do not run the truck yet, the brake still needs to be adjusted!
6. Turn off the engine, and push the truck around with your foot or w/e and apply the brakes, if it stops, good, if not, adjust the spring tighter until it will.
7. I like to adjust mine where the truck will stop hard while pushing it, and making sure it rolls freely with the brake off, then fire it up and make some low speed passes and adjust to your liking.

Hope this helps, I am no expert by any means but I did stay at a Holiday Inn last night

-AxialLST

 

[speedingbulletbp]

I noticed when I turned on the electronics it opened up the carburetor halfway in result giving itself gas. I havent started it yet because its about 100F outside right now so when the weather cools off ill try it out thanks for the help I appreciate it.

 

[AxialLST]

No problem, glad I could help