screaming 91SZ

[R-4-L]

this is a non pupmed engine.,

with MPII, on a TZ90 machine, new clutch and clutchbell liner is fine.

needles on 1.5 for high, 1.5 mid. idle a hairline rich.
pitch -10/0/+10

symptom:
as the heli spools up, the rpm gets extremely high, the engine is literally screaming, and I had almost no control on the cyclics that I almost crashed.

so I tried to lower the throttle's hover point. I kept doing so until the rpm was still high but managable.. I look at my radio to find that the throttle curve on hover point was 30%.. and the linkage setup was a perfect 100% travel:carb barrel. so literally 30% throttle meant 30% barrel open.

I opened the head, everyting clean and shiny.
opened the backplate, all new and not a scratch.
opened the needles, they are clean and the grooves look clean.

i ran out of ideas! any suggestions please?

[DavidH]

Things to check.

Make sure pressure nipple on muffler is open and not clogged.

When you say 30% barrell opening. Where exactly is the carb barrel in regards to the marks on the carb body?


David

[R-4-L]

there are three marks on the carb's case, the barrel's mark is below the first by 3-4mm.

I didn't check the muffler's pressure nipple... i'll do that right away..

[DavidH]

I would also see if the carb is seated good in the crankcase. Sounds to me like the motor is definitely sucking air from somewhere and this is why it is leaning out and speeding up. Does the motor get excessly hot when this happens.

David

[R-4-L]

yes david, it gets hot as if the needles were half a turn open only! .. I thought the heat was ok as it was a hot day anyways.. just didn't fly for more than 5-10 seconds sessions coz I was worried about the engine.. good thing I was using byron fuel that had lots of oil.

nipple is not blocked by the way.. leaving only one thing,, as you said, air is getting in from somewhere... I just checked the big O-ring on the backplate.. looks fine..
I'll eyeball the o-ring on the carb later.. its a new engine by the way.

[DavidH]

Well Byron fuel really has no more oil than any other brand fuel.
Did you check the engine before you installed it? Take off the back plate and look and see if any debries were in it left from the machining process?

David

[R-4-L]

i don't know why i got the impression that byron had like 24% oil! my bad, just read the sticker,, 20% just like others..

thats what I'v done david.. checked inside and out, looks soo clean and new.. I didn't disassemble the whole engine. probably that'd me my next step.. I don't know why I keep suspecting the carb.. any special places on the carb I should look for?