Derag2

I keep getting backfires through the pipe, with my STS .30 i put an OS 8 plug in it and it runs okay, but it backfires alot. What do you guys think is the problem, So far this motors been a pitta... but im gonna run it some more in the morning.

Thanks in advanced.

bennyblanco

what fuel % you running and how many head shims you have on it?

JayC1968

My Feedback: (3)

Backfires are actually preignition. If you are not shimmed right and or using the right plug for the percentage fuel you are using it will ignite too soon and throw the piston down again before getting to top dead center where it should ignite.

I am pretty sure the STS 30 comes with a .20 shim. I would add a .10 and see if that helps.
Also keep in mind the fuel/plug rules

10-16% fuel= a HOT plug
20%= Medium/HOT
25%= Medium/COLD
and 30-33%= COLD

ALSO when using 30% and up fuel you NEED to add a .10 shim to the head.

If you use the wrong plug with fuel it will cause firing trouble. ALOT of people think OH CRAP my engine is running hot and throw a cold plug in while using 20% and then complain because it won't run right... That's not the case. Temps in all my years of nitro are nothing but tuning issues. providing you're using the right plug for the fuel being used. There are alot of factors in temps and can be easilly resolved with proper tuning to ambient conditions such as..........
Altitude
ambient temp
humidity
and so on

There is a reason why there a different heat plugs and that is based on the FUEL percentage, NOT running temps

Hope this helps

Derag2

I running stock shims, 20% nitro and OS #8, which i was told is a medium hot........

bennyblanco

you need a hot plug!!

Derag2

I put in an OS A5 and so far the backfiring is gone but temps are still up there in the 260-270 range..... Any richer and the thing doesn't wanna run worth a crap.... I pulled the plug and there no friction with the piston hits TDC so i'd assume the "break in" is done. I know its gonna take alot of fuel to competely get it broke in but I just don't understand how anybody gets this thing to run right at those temps....... It smokes like there no tommarow, its just a haze when im running around it smokes so much......

bennyblanco

if the temps are still hi the break in process is not completed give it some time don't lean it out yet!!!

Derag2

Where do you guys get shims from? Im gonna put a .10 shim in and see what happens, The backfiring is back again.....

bennyblanco

i order my shims from http://www.racernine.com/