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HELP serious rich running problem

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HELP serious rich running problem

Postby Pops » Wed Jul 04, 2018 5:43 pm

Had to divert into Rochester Sunday due to major power loss which looks like serious rich running - ignition and compressions have been eliminated and its pouring out black smoke and miss-firing and won't rev past 2100 with things being worse on large throttle openings.

All the basic mixture stuff ruled out ie air filter, collapsed scat hoses,, main jet or needle dropped out, cold start jammed on, Carb heat stuck in etc.

My engineer stripped the carb with me today and apart from a little bit of debris in the cold start chamber it appears to be fine.

We refitted the carb, ( new inlet rubber as well because I had one) and its just the same.startes straight up,ran rough at all revs and really bad at higher revs and throttle settings

Any ideas? Mine is an early 2200 SK with the 32 mm carb. I've had it for 11 years and its up to 1200 hours and has never missed a beat before. currently unflyable and stuck at Rochester.

not been on the forum a for a few years - sorry folks
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Re: HELP serious rich running problem

Postby Steevo » Wed Jul 04, 2018 8:09 pm

Was this something that happened all of a sudden or something that got worse over time?

A carby doesn’t usually just go bang all of a sudden. In-fact, other than a blockage, there isn’t really that much to go wrong especially all of a sudden.

When you say compressions and ignition are fine, what were the compression figures. I assume it was a leak down test and not a normal compression test.

If the timing was out, this could cause this kind of behaviour but that would show up in a compression test and other symptoms, but that would be something serious to put the timing out such as broken flywheel bolts.

The carby could be flooding. I have recently had a few issues with my carby. This turned out to be a float issue. It was not immediately obvious but due to the issue, the float was floating low so raising the fuel level in the bowl causing a rich mixture. But even with that, all I got was lumpy running and black spark plugs.
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Re: HELP serious rich running problem

Postby Pops » Fri Jul 06, 2018 2:14 pm

Looking back I would say it’s been starting to run richer over past 4 or 5 hours but
Then got a lot worse. It’s definitely rich running not timing / flywheel etc
Had a message from Gary Cotterell who is now in NZ with a few pointers. Apparently engine
Breather problem or blow by pressurisation of crankcase a can cause the fuel pump to over pressurise. He says carb / engine very sensitive to this and can even stop the engin. Also he has advised that there
Is an airway that leads to the atomisation jet that blocks easily especially if carb heat is open

So things to look at

Pops
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Re: HELP serious rich running problem

Postby Steevo » Fri Jul 06, 2018 3:27 pm

Well Gary knows what he is talking about.

If the fuel pump was to over pressurize, then it would force the float needle valve to stay open creating a very rich mixture and flooding.
Jabiru J160 & Jabiru SPL-450
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Funke ATR833 OLED/Dittel KRT2
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Re: HELP serious rich running problem

Postby Matt » Mon Jul 09, 2018 11:28 am

what were the compression reading? If the compressions are good like you say then you don't have to worry about blow-by over pressurizing the crankcase. A blocked breather wont take five minuets to sort out. Have you checked the carb floats for sinking? You should perhaps check the output of your fuel pump. It will require a pressure gauge plumbing into the system. Could be over pressure as mentioned.
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