Re: Help with GMS 76 tuning.

Using 15% Wildcat (18% oil) with added 2% castor.

From what you describe, your low end adjustment is to lean. Back it out 1/4 turn at a time, making sure to readjust the high end at every step too. Another way to get your low end in the ballpark is to let your engine idle for 10 seconds, and then pinch the fuel line. If the engine slows down and dies quickly (2 seconds or so), then it is to lean. If it speeds up quite a bit, then it is to rich. Ideally you want the engine to run at constant speed and then after 5 seconds or so die.

YOu may want to run a few more tanks through the engine too. However, if it sustains the full throttle setting, it should be good to go!

sounds like the low end is too lean. Typically, you will have to lean the low end when the weather is warmer and richen it for colder weather (for what it's worth) IF that engine even has a low needle.......it may be an air bleed carb for all I know.......anyway, usually you can make adjustments to the low needle then set the high needle while running, bring the engine to idle for 30 sec or so and punch the throttle.......if the engine "burbles" lean the low needle, if it just goes "blah" and dies, richen the low needle.

Brad L.

Until you get about 60 minutes run time on a ringed engine, you are wasting your time trying to get the carb tweaked, IMHO. Once you get there, then setting the carb up tends to be quite easy.

Keep plugging with the rich running until you have at least 60 minutes - preferrably 90. On a .76 2 stroke, probably 1 gallon of fuel before it is ready to fly, still slightly rich though.

David

REduce the nitro to no more than 10%. These engines are designed for lower nitro and run great on 5%.

Also, 2-3 clicks from peak is too lean! Keep it about 1/4 turn from peak and things will last a lot longer. If transition from idle is bad, check the idle mixture setting. The low speed needle controls mixture up to around 2/3 throttle.

This is the first ringed engine that I ever ran that would idle perfectly right out of the box. I had one ticking over at 1800 RPMs with an APC 13X6 on the first tank. 5% nitro Excalibur fuel.

What he said. Mine runs primo on 5% Powermaster.