I mount the engine on a bench and fire it up...everything seem to be fine.Well, something worry memost is the carb.When I open to full throttle fuel start spraying out in mist as do the engine couldn't consume all the fuel when WOT.At first I thought it is on the rich side and when I lean the high needle it doesn'tmake much diffrent.So far the engine had consume about 1 gallon of fuel all on the bench,still haven'tmount it on a airplane yet.What worry me is the firewall is going to be soak in fuel when it fly.Is it the motor or my tuning that causes it?[]

Normal for a GT 80. A v-stack MAY help, also try a smaller prop and let the engine rev up more. Or maybe it needs to be a little more lean.

The mist is caused by carb blow-back. This is caused by the inlet port closing too late, and mixture strength has nothing to do with it.
A carb stack increases air inertia, and thus may reduce the blowback problem, certainly when combined with higher rpm.
At higher rpm (smaller props) the engine will be more happy. You are now running it lower than the speed it was designed for.

Thanks for the help on this matter,I am currently running Top Flite 24 X 10 prop do you think this is too much prop for a GT80? As I mention earlier so far it had only consume about 1 gallon of fuel.Is it Ok to run a 22 X 8 Zinger prop? Which is the correct way follow the recommended prop from the manufacturer or prop to run at a certain rpm.

I would keep running it with the 24x10. I ran mine with a Bolly 24x12 and it did well, though a 24x10 would have been better. My engine also sprayed fuel on throttle up. What I did was glue a piece of foam behind the carb so the foam would absorb the fuel instead of the fuselage structure. The foam eventually gets eaten away but costs very little to replace on occasion.

A rich mix makes the engine run slower making the problem worse. Use your smaller prop for bench running, just dont use full throttle very much.

Opinion.... Best for breakin is a light load at normal RPM. in this case you should be running over 7000 rpm

Hi
Way don´t you try this?
This is the solotion on this problem, and you also save fuel. (smaller tank)
It is available to all Zenoah engine.

Jonas

Thank you all for the advise.Frankly speaking I don't have much experience in gas engine.Thank you all again.