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Hell spawn carbs

motogtp

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Making progress on my '78 SS. Before - plugs completely fouled in less than 5 miles. After rebuilding the carbs (new floats, float needles, 105 jets, O-rings & gaskets, but not the needles) it runs nice now, idles well, runs hard. Except that now the plugs foul up completely in about 40 miles. I'll be riding along and it will suddenly start running rough, loose power, and then dead in a 1/2 mile. Pop in a new set of plugs and off she goes like nothing happened. I found out from the PO that he had CycleX rebuild the carbs a little over a year ago. Said it still didn't seem to run right so he had another shop that specialized in 4 cylinder Japanese bikes tweak it. The exhaust pipes at the head are perfectly chromed like the engine has never run lean in its entire life (6100 miles). So here is my question...if two "pro" shops can't seem to make these carbs work are they the seed of hell spawn? Should I cut my losses and get a different set and rebuild them?
 
Trawling around the web while researching my build I've read people mention the Iridium plugs are supposed to solve fouling issues.
Not sure what plugs you are running or if your issue is so severe even the Iridium might foul.
I have no personal experience as I've still to get my bike out on the road and find out when my plugs foul.
 
The problem isn't your carbs but the heat range of your plugs. If your plugs are the wrong heat range they will not keep fouling burnt off and will foul out.
 
What color do you get on the fouling? Could it be it's burning oil? Just a thought, since Ken at CycleX knows his shit around these scoots. I don't think he'd mess up your carbs.
 
Thanks for the feedback. I did run Iridiums but that was before I rebuilt the carbs. The fouling is black and fluffy (all 4 cylinders) but I suppose it could be burning a little oil. When I rev it I do see little bursts of what looks like diesel smoke. I assumed that was unburned fuel.

I am running (stock spec) NGK D8EA plugs. I might try a D7EA set and turn in the idle adjustment (they are at 1 1/2 out now) a bit. I agree about CycleX. That's why I am thinking these things are "unfixable" because the PO didn't think it was running right after CycleX cleaned and rebuilt them. When I got the bike it had 115 jets and the floats were upside down so who knows what the second shop did.
 
Black smoke is unburnt fuel. White/blue-ish is oil. Are your points/timing set 100% correct?
Stock heat ranged new plugs, points/timing set to specs. Only after that is checked and cheked again I'd dive into the carbs. And I would first double check the float level (since you just rebuilt the rest of the carbs).
What air filter are you running? Stock?
 
If it is running fine except the plugs fouling I'd try the D7EA plugs first without adjusting anything else. Only change one variable at a time. If all else is fine it could be that simple. Dialing in the air bleeds isn't going to affect anything at cruising rpm's and that seems to be where you're fouling out. If the hotter plugs don't fix it then go from there. Iridiums won't fix anything if the heat range isn't where it needs to be.
 
Stock airbox and filter. CycleX ignition, I have checked the timing twice. I dropped the float levels a little (18mm instead of 15mm spec) just to try something. If the idle circuit isn't really affecting the fouling then I must somehow still be getting too much fuel via the main jet. How sensitive are these carbs to the needles? I haven't changed them yet but they look good. I have the stock spec 105 main jets in now. Seems silly to go smaller than stock (size 100) but would that help?
 
Do you know if the needles have been shimmed? Might want to take a look, it would richen it up if they are shimmed...this takes the place of the grooved needles in the older carbs. Just so you know...yes the needles do wear, mostly on high mileage carbs though. I would keep a look out for a different set of carbs...you can all ways resell what ever set you dont use.
 
Black plugs

Needles don't appear to be shimmed. I think I may have misdiagnosed the plugs (picture attached). These are D8EA plugs after only 5 miles. The manual says rich running shows the insulator tip as black. In the pics the entire plug is black, including the insulator and bore. I think I am burning more oil than I thought. Might be rings or valve seals but either way its probably time to pull the heads. With only 6,000 miles it's possible that it sat for a long time and the rings may have been compromised. Crap!!
 

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Extreme rich will cause the whole plug to be black like yours. The F2 head is bad for wearing guides very quickly though.
 
Extreme rich will cause the whole plug to be black like yours. The F2 head is bad for wearing guides very quickly though.

Yep, that's been the struggle. With the changes I've made I can't figure how it could be running even slightly rich much less extreme rich. Plus I don't really want to tear the top end down but it is probably inevitable. I think I have a combination running a little rich and burning oil. As luck would have it I followed a '77 SS in traffic yesterday. His was smoking more than mine and it ran great. Bastard! ;>D
 
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