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Old 11-19-2012, 04:29 AM   #1 (permalink)
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Backfiring thru carb

I am Helping a friend who traded for an 02 883. The bike had been sitting for awhile and the previous owner rode it a considerable distance with it back firing thru the carb. When I looked at it the First time the Carb was gummed up. It has been gone thru several times and is in good shape at this point. The intake gaskets were also changed.

The Problem: the bike will start and idle perfectly, even for extended periods. When you give it any throttle the accelerator pump will shoot the steam of fuel, the slide starts to rise and the RPM starts to come up. At this point the engine will not come up on RPMs and the carb slide will start to rise and fall a small amount but rapidly. THEN the engine back fires thru the Carb, Flames coming out of the carb.

The Compression is strong and every this else seems to be working good, The engine will not come up on RPMs without the severe back fire and then it will eventually die.

Any thoughts on what it could be would be greatly appreciated.

Thanks,

Al
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Old 11-19-2012, 07:42 AM   #2 (permalink)
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I am taking it your working with a stock carb, I would first unscrew the carb top & check the vacuum piston, it could very well be damaged from the history of backfiring. It is in alot of cases a lean mixture that causes premature firing.

Doesnt sound like ya have an intake leak, I would be pulling the carb apart to check for varnished fuel which will give you all kinds of trouble. A can of carb cleaner works wonders, let it sit awhile then finsh off with a quick spray of brake cleaner.
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Old 12-02-2012, 07:47 PM   #3 (permalink)
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I had the same issues with an 883. The problem was due to a damaged crank position sensor.
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Old 12-04-2012, 06:11 AM   #4 (permalink)
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What else can you tell us about the bike, (what pipes, what jets since you said the carb has been gone through already)?

I don't think those years have a crank position sensor like the 04'~06' or I would check that out as palemeat said.

If you pull out the choke/enrichner some can you ride the bike with minimal carb farts?

On my wifes 05' I took off the carb disassembled it and let it soak in a cleaning bucket for a couple of days. When I put it back together I bumped up the needle valve by one line. Then went through the air/fuel mixture setting and she doesn't fart once.

Get us the jet(s) size maybe they are to small.
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Old 12-04-2012, 10:39 AM   #5 (permalink)
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intake leak or the carb is lean
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Old 12-04-2012, 08:52 PM   #6 (permalink)
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The backfiring through the carb is most likely caused by a lean mixture, as the previous posters said.

The lean fuel mixture burns very slowly (relatively) in the combustion chamber, so slowly that it is still burning when the intake valve opens to let in the next charge of air.

Make sure it is squeaky clean inside (sometimes fuel hoses start to deteriorate and can send bits of rubber into the carb you just cleaned) and inspect the rubber diaphragm as Rollmeaway suggested.
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