CB650C 1980 rich plugs need help

If it's broken or just needs tweaked

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CB650C 1980 rich plugs need help

Postby TurtleSniffer » Thu Aug 03, 2017 8:57 pm

So I have been working on this bike for almost two years bringing it back. Right now my problems is the plugs are a sooty black which is running rich. Since I first got it to run a year ago it has been rich and Ive made numerous adjustments since then like float height, valve gap, clean gas tank, 90 main jets, and multiple Pilot screw adjustments. It seems better and runs nice but plugs are still coming up black after a quick 15 minute ride. Iturned the screws out 2 1/8 like the book said still rich, choke would bog it down til it died. Since then I decided to go the opposite way and turn em in since i realized it was on the gas side and it feels better and choke no longer kills it but its still rich.

My carbs are PD50B with the adjustment screw on the engine intake side, so I've

Turned pilot screws 1-1/2 - 2 turns in
Set valve gaps at the hondaman measurements i found somewhere long ago
Use 91 gas as the Clymer manual reccomends
Set float heights to proper level
Rebuilt all four carbies $$$
Verbally abused it many late nights
Put new D8EA NGK plugs
Installed a new stock emgo paper air filter ( missing air filter cover from PO) :|
Stock 4in4 pipes

Im not sure really what to look for to try and solve this problem. Should i just leave it kinda rich? Its nowhere near as bad as before and has good power but i don tknow if the plugs will eventually carbon foul to death after repeated use or overheat my bike. I live in CA btw

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Re: CB650C 1980 rich plugs need help

Postby tario » Sun Aug 20, 2017 12:34 pm

If you ride with spare plugs and a socket set it shouldn't ruin the bike. It just runs a little dirty. Going too lean can heat up and cause more problems from what I understand. Im running d7ea plugs and can get 5000km or so with no problems. Did have one or two fail on me eventually. I use premium gas(which is 91?). I'd look at new plug wires and making sure all ignition system connections are sound and clean. You could be getting weak/intermittent spark and it only fires every second shot. It sounds like you are doing the right things if all the pieces are doing their job.

Are the plugs getting oil fouled from blown rings or an internal oil leak? A compression test might shed some light on this.
1979 cb650
1980 cb650

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