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Nitro blues

Nitro blues

Howell, John

YOU’VE GOT PROBLEMS? WE’VE GOT FIXES.

I need help with my 1/8-scale buggy. My car has been running funny lately. After I start it, the engine keeps revving up high, and I have to kill it because I’m afraid it will blow up! I run a brand-new O.S. .21, and I bought it because I thought it was a high-quality engine. I have only a few tanks worth of fuel through it. What’s the deal?

Josh Livery

Josh, you didn’t give me much information, so I’ll run through the most obvious causes and hope to get you looking in the right direction.

First, check your throttle linkage; it is the most likely cause of your problem. When the throttle trigger is in the neutral position, the carburetor should close as far as the idle-speed screw will allow. The carb should consistently close to an approximate 1mm opening. If your linkage and throttle-trim settings on the radio check out, it’s time to take a closer look at your mixture settings.

An excessively lean fuel mixture commonly causes the condition you describe. A lean fuel mixture causes the engine to race even when you’re off the throttle, so check to make sure that your carb settings are in the ballpark. Refer to the owners’ manual to set it to the factory-recommended settings, and then tune from there.

Another potential problem is “false idle.” It’s when you’ve set the mixture too rich (either on the high-speed needle or the low-speed needle), and to compensate for that, you set the carb’s idle screw to open the carb more than it should, e.g., it’s now open 3mm instead of 1mm. Basically, the engine now idles at around 1/4 throttle! If, for some reason, the engine has cleaned itself out or it has been leaned out, the idle is now set way too high and has to be readjusted.

If all else fails, look for air leaks. The high revs you experience could be happening because too much air is getting into the engine. Check for a leak around the base of the carb and for a hole in your fuel line; check that the head is bolted on properly, etc. Check all these things before you start the engine again.

Copyright Air Age Publishing Aug 2003

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