zul_cessna

Hi, Last month I tached my engine with JXF 22 x 8 and I got 6800 rpm, but 2-3 day ago I tached again and I only have about 6000 rpm, I try to tune back the engine and cannot go higher. Any idea what went wrong ?

pe reivers

To be honest, no.
Loss in power can have so many causes you could fill an encyclopedia with it, and it is not possible to diagnose over the 'net with such meagre data as you provided.
My advise: If all the obvious, like carb setting, fuel supply, clean exhaust system etc. seems OK, send the engine to MVVS for maintanance.

zul_cessna

thanks pe

zul_cessna

Hi pe, i just wondering any possibility cause by the ignition ? my ignition produce only little spark.

pe reivers

That would be guessing. Like I said, too many reasons can cause this.

zul_cessna

Take out the plug and saw inside, carbon build up almost 1mm thick

pe reivers

In that case, you probably had:
set the engine too rich, maybe even on the wrong oil.
you need to clean out the engine, best done by running carbon remover mixed in with your gas. This is sold in the better automotive shops
Fit a new plug.
You also need to clean out the muffler, which probably is coked up. Oven carbon cleaner may do a good job there.

zul_cessna

thanks Pe, will do things that you mention and hopefully will gain back the RPM

zul_cessna

Open and fond piston ring stuck, try to remove and it was broken, already change to new piston ring, should I break in the engine again ?

pe reivers

With the ring broken, you also should have noticed a sharp drop in compression.
Yes, please run in the engine again with a bit of extra oil (like 3%), but not too rich! The plugh must not be black.
Running in a new ring may take a bit longer than in a new engine, so be patient. Change throttle settings frequently, and avoid prolonged full throttle running for the first gallon.

k_jitsu

Why?

zul_cessna

Pe, can the ignition battery effect the RPM, I was using 5 cells previously but now change to 4 cells, will this makes major effect ?

pe reivers

because now all rubbing surfaces are smooth and shiny, and have work hardened slightly, especially the lower ring land in the piston.
Probably not, if the engine runs OK. It depends which type of ignition you have. Vlach ignitions run very well on 4 cells.

k_jitsu

Thank you, Pe