skydiverken Posted June 29, 2021 Share Posted June 29, 2021 Hello A very strange thing occurs to my Vittorazi moster185. During my last flight, my max RPM just decreased to 6400rpm instead of 8400rpm. Also have a CHT gauge, max temp is +/- 205°C. Engine starts after 1-2 pulls, idles great, reaches max rpm but after about 30seconds, the rpm drops at wide open throttle. I guess there is some kind of leak when the engine gets warm. I still haven't found the cause, the things I checked and changed: - fresh fuel (2,5% oil/fuel) - new spark plug - swapped carb with a 100% working Walbro WB37 carb (pop off pressure is good, new membranes,...) - replaced the coil (with 0,45mm gap between flywheel and coil) - fuel system is ok (replaced fuel lines,fuel pump and filter) - fuel tank valve is ok - brass weight at bottom fuel tank is ok - replaced al the gaskets between carb and reed valve - reed valves are ok - replaced exhaust gasket - motor has 130h, put a new piston, piston rings, needle bearing Has enyone encountered the same problem? I am running out of ideas Best regards, Kevin Quote Link to comment Share on other sites More sharing options...
admin (Simon W) Posted June 29, 2021 Share Posted June 29, 2021 I would have put my money on the coil TBH, but the only thing that is not on your list would be the primer bulb.... SW Quote Link to comment Share on other sites More sharing options...
cas_whitmore Posted June 29, 2021 Share Posted June 29, 2021 Does it have a foam filter in the air box , Not a moster but mine has one Quote Link to comment Share on other sites More sharing options...
skydiverken Posted June 30, 2021 Author Share Posted June 30, 2021 Hello Thanks for the replies. Also changed the primer bulb (forgot to mention), there is a foam filter in the airbox but it's clean... Quote Link to comment Share on other sites More sharing options...
Steve Posted June 30, 2021 Share Posted June 30, 2021 I had a similar issue, check that the primer bulb isn't drawing in a tiny bit of air. The engine copes and runs normally until it goes wide open for a while. I had that problem even on a brand new primer bulb - some types of retaining clips cause the pipe to slightly distort on the connection to the bulb. Quote Link to comment Share on other sites More sharing options...
Ganbatte Posted June 30, 2021 Share Posted June 30, 2021 Can you make the problem appear while on the ground, so a friend can watch for bubbles in the fuel line? Quote Link to comment Share on other sites More sharing options...
skydiverken Posted July 2, 2021 Author Share Posted July 2, 2021 I Found the problem. The internal structure of the silencer was broken. Those pieces and some sound absorbing material caused a partial blockage... 2 Quote Link to comment Share on other sites More sharing options...
admin (Simon W) Posted July 2, 2021 Share Posted July 2, 2021 Good find! Thanks for sharing. SW Quote Link to comment Share on other sites More sharing options...
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