I had a set of plug that constantly collecting heavy black deposit on my 89 GSX-R750. It ain't bother me 'till I found that the bike power is decreasing and I experienced heavy abrupt carburetion and the engine hardly keep rotates.
Seems like there's a problem with the carburator so I brought it to a mechanic. He clean it with an air compressor and everything is normal again. The bike runs smoothly. Next weekend I try to ride the babe but it shows same symptom. I checked the plug, black deposit on all four. I thought that the mixture is too rich so I've tried to move the needle circlip one slot upwards. The bike pull not as hard as before on the mid but it felt good at hi rpm. A week after that I tried to ride again but the abrupt thing re-emerge. Checked the plug and it was black, again.
Do I have to set the screw below carburator's outlet (is this the air screw??) or what? The black deposit is easily removed and the exhaust (it's a free-flow) fart black smoke, it also shows same deposit.

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[ 10-21-2002, 09:30 PM: Message edited by: Simon Orttan ]

have you checked the air filter(s)? if they're dirty they could cause a rich condition. also i'd check to make sure that your choke circuit is closing fully, as that would cause fouling too.

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http://www.geocities.com/batty718/bike_small.jpg

sounds like you may have plugs that are way too cold in heat range as well as possibly poor ignition coils and too rich in the carb department could be jetting and or float level lots of things to check, good luck.

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86 totally non stock

Don't forget the basics...run a compression test to be sure the motor is in good condition before spending too much time on all the other possibilities.

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Rbike
92 GSXR 750 for the track
86 BMW R80 for the street

I don't have any factory info so to avoid lot of guesswork could anybody suggest the factory standard plug number for NGKs, plug gap, float level, compression number?
Is there any easy way to check whether the choke circuit stuck?

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JR9C is standard. JR8C is a hotter plug. Gap should be factory set around .028. Compression should be around 150 or so I think but I'm not real sure on that one. Don't know if this is any help or not but around here they add 10% ethanol to the gas during the winter. Ethanol attracts water and is an added variable into your fuel mixture. Probably don't have to worry about that in CA. Maybe that's related to your problem, don't know.

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'89 750---Factory ignition advancer and shift kit, Barnett Kevlar Clutch and springs, Goodridge SS brake lines.

[This message has been edited by Umf (edited 02-04-2001).]