Honda CB750 Rebuild - Bikes Running Decent But I Have Some Real Concerns

Posted by jsmits on
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Honda-CB750-Rebuild-Bikes-Running-Decent-But-I-Have-Some-Real-Concerns-tp4050853.html

So i've been working on a 78 CB750 this winter, and I've finally gotten it close to being able to take for a ride. It's running pretty good, I just need to get a few more things back in place and do a run through on some bolts before I take it for it's first cruise. I have a couple of questions as I'm sure I do not have the carbs just right yet. I have a few symptoms that I want to run by someone whose been around the block on these things.

The biggest thing I'm concerned about is the first carb on the left side. I've been having a hell of a time with this one as the needle seat is pushed in further than the rest. I don't know if this is standard from the factory, but it seems to cause a lot of problems with the gas level in the bowl and I've had trouble with it overflowing. I can sort this out by playing with it a bit once the carbs are back on the bike.

So the bike is running pretty well. I have it idling good once it warms up for a bit. Slight, fast blips of the throttle cause it to bog down still but I should be able to work that out with some more idle and timing adjustments. Here's my main concern though, that first carb has far more air suck/blowback than the rest. You put a piece of paper in front of each carb intake and while the paper is mostly stable on 2, 3, and 4, the 1st carb the paper really dances a lot. You can feel air coming back out when you put your hand near it. Could this be an issue with one of the valves on that side? Also, if you cover that carb, the engine shuts down completely, while the others it only drops a bit. And one more odd thing, spraying carb cleaner into that carb also kills the engine.

Is this normal or do I have a real problem that needs to be addressed?

Also, the outside cylinders run much hotter than the inside. I have a laser temp reader, and pointing it at the exhaust right near the flanges, the outside 1 and 4 are around 450-500 at idle while the inside 2 and 3 are around 275-350. Is this normal or could this be a symptom of another problem?

Thanks in advance for any help or insight duders.