ORIGINAL: Varad

Your probaly running with a bad plug. Ive had that happen to me and a fresh plug seemed to fix it.

ORIGINAL: charlieboy

For some strange reason i can't seem to keep my 2.5R running. It will start run for a few seconds (10-13sec) and then die.
I've taken the whole engine apart the motor has still pretty recently broken in but i'm not exactly sure how many tanks.
Bought the truck from a guy who said he had it breakin at a hobby store.

Anyway i think i have made every possible setting on the HS needle and low speed needle and still the same results, apart from sometimes when it does not start any at all.
I'm suspecting its the carb because the engine seems still new, my exhaust is securely fit and all the fuel lines are sound!!

ORIGINAL: dight1

Well then you just suck at tuning rc's. Get a easier engine to tune and check the engine compression. If the compression isnt the problem then you must of put something together wrong in the engine.
My truck didnt start at all and the problem was the HSN spot was dirty. I cleaned it out and then it worked like a beauty.

ORIGINAL: 89ram

get the guy you bought it from to help you get it started and tuned. you never had it running good since you got it, right? did this guy sell you his lemon? might be worth checking out.

ORIGINAL: Quickywd01

How is you fuel? It could be old or new that has evaporated some so there isn't enough nitro. But if you think you have an air leak:
"Try to do a little research next time." By Mr.Caveman. Find you leak if suspect a leaking carb.

"Airtight is Right
In order for an engine to idle, transition and tune consistently it must be airtight- airtight meaning that no air can enter the engine except through the carburetor intake. Surprisingly, even brand new out-of-the-box high-end engines can have air leaks and until these leaks are found and eliminated, the engine won't run consistently and cannot be precisely tuned. The good news is, several years ago I figured out an easy way to check for and fix air leaks. You'll need the following:
• A small glass of soapy water
• A small brush
• About a foot of fuel tubing

Step 1. Be sure that the high-speed needle is open at least two turns out and the throttle is at fully open.
Step 2. Install one end of the fuel tubing on the carburetor nipple. You're going to be blowing into the other end of the tubing to pressurize the engine crankcase.
Step 3. Place your thumb over the carburetor intake to prevent air from escaping, then blow into the fuel tubing while brushing soapy water around the base of the carburetor, on both sides of the pinch bolt, around the fuel fittings, at the high and low speed needle valves, around the front bearing and even around the back plate.

If any bubbling occurs you've got an air leak. But don't be alarmed. Fixing the leak is easy and your engine will run remarkably better and more consistently when you've eliminated these leaks.


The Fix


Brushing soapy water around all possible air leak points while pressurizing the case will easily identify air leaks.
The most common air leaks seem to occur around the pinch bolt. Applying a dab of RTV (or silicon) over both exposed sides of the pinch bolt will fix this type of leak. RTV is also great for sealing any leaks around the base of the carburetor. Simply remove the carburetor and run a small amount of RTV around the base of the carb where the leak occurred. Reinstall the carburetor and allow the RTV to ooze out between the crankcase and the carb body. For leaks around the high-speed needle valve fittings, usually retightening the high-speed needle assembly will take care of these. Leaks directly at the high speed or low speed needle usually means there's a damaged O-ring that must be replaced. Many racers don't realize that the front bearing can leak air. That's why nearly every high-end engine uses a rubber sealed front ball bearing to not only keep out dirt, but also air. If your front bearing leaks air, it's time for a bearing replacement.

This simple leak check can easily be done even when the engine is installed in a car. After you've done this test on several engines you'll be surprised of two things: first, how often unwanted air leaks occur and second, how much better your engine runs, idles and tunes when it's airtight. To run right it must be airtight!

Airtight Fuel system
The Fuel system must also be airtight. If the fuel tank, tank lid, fuel lines or filter has a leak then the same kind of tuning issues as described above will occur. While you can check the fuel system by using the same method of brushing soapy water onto the suspected offending area while blowing into the tank, I generally find it better to simply remove the tank from the car and submerse it in a sink of water while blowing into the vent line and plugging the fuel line. If bubbles are present you've got a leak.

An engine at full throttle produces about 6 to 8 psi in the vent line and conversely in the tank. By blowing really hard you're also able to produce about 6 to 8 psi for a couple of seconds. If you're able to blow hard enough to cause the tank lid to open slightly and leak, it's time to replace the tank lid spring or bend more preload in the spring. The entire system (fuel tank, fuel filters, fuel lines, tank fittings, etc.) must be airtight to achieve consistent repeatable performance. I always that my fuel system is airtight when it's new but also recheck it every time I rebuild a car after a race. It easy insurance plus soapy water is a good way to thoroughly clean the tank. Just be sure it's totally dry before using it by flushing out any water left in the tank with fuel before installing it in you car. " By mr. apollo And if you need pictures of how to do this let us know.