Topic: #2,3 Plugs keep fouling?

[cb750fjoe]

I have a 77' CB750F that the #2,3 plugs keep fouling on me. They seem to have been doing this since I rebuild the carbs about a year ago. After rebuilding I bench sync them. I bought new coils for them after this started thinking I might have a weak coil since #2,3 run off the same one. No Change. Made sure my pilot screws were turned out to correct setting. Even adjusted them several times to get a difference, still no change! I kept cleaning the plugs and would last for a few days then foul again. Bought new plugs last week. Rode to the mountains and pushed it pretty hard most of the day. On the way home it started running on what felt like just 2 cyls. Got it home and cleaned the plugs and now its still running on just two. Anyone got any suggestions as to what might be my problem?

[upperlake04]

 Welcome Joe.  Are the 2/3 points and timing spot on?
 I had the same problem and after many passes at eliminating electrical/carb possibilities found that the slow jets in carbs 2/3 had been drilled to a larger diameter    It is unlikely to be your problem, but plug fouling was the result.

[gerhed]

Had a similar problem recently with my 75 F.
Ran fine for a while with new plugs then 2 & 3 started missing badly.
Didn't change the plugs, but
Put in a new points plate.
Problem appears to be solved

[goon 1492]

almost smells like a points prob, have you cleaned them lately, use some emery paper inbetween the points when they are closed... gently... and it will give you a new surface to work with. Or just replace them

[cb750fjoe]

Points aren't the problem since I've changed that to an electronic ignition about 10 yrs. ago.

[Cvillechopper]

Check the wires running from your elec ignition unit to the coils.  I've found a couple that had some damage and were shorting to the frame intermittently at first, then badly as it burned off more of the insulation.  Take special notice of any area the wire is crimped or clamped.  Fixed a friend's bike and found the plate had been installed pinching the wires.  Fried one lead completely.

[Jeremiah]

Have you checked choke linkage?  Make sure all 4 open up the same amount?  I had that problem recently on a 750...    Also, people sometimes mess with the middle 2 carbs trying to make them a hair richer than the outer carbs like on a modern inline 4.  May want to double check all your jet sizes

[TwoTired]

Why don't you vacuum sync your carbs?

[cb750fjoe]

Well at this point I think I need to check my ignition wires to make sure nothing is shorting out since it's only running on two or 3 cyls. then I'll do the vacuum sync.

[Cvillechopper]

I'll throw this up for you.  One of the most knowledgeable members on this board mentioned vacuum synching the carbs, I'd go with that if I were you just to rule it out.  I hadn't noticed that you only bench synched.  That'll get you started up, but it won't get you riding.  Starting to put a load on unsynched carbs can foul plugs, no question.

It also would get worse when riding for longer periods as the carbs need less fuel once they're properly warmed up which would take longer without proper synch. 

Throw the gauges on and see how far off you are.