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-tp4050853p4050860.html
Thanks for the very detailed response Re-run. I'll run through your response bit by bit.
The plugs are D8EA and they seem pretty healthy from what I can tell. I know the bike needs more idle adjustment.
I was refering to the float needle and the pressed-in seat that it slides up and down in. On the 78 carbs, this 'seat' is pressed into the carb. The first carb's float needle 'seat' is pushed further in, so the float tab that the needle sits on needs to be bent way further down than the rest for the float to be set at the proper level.
The bike has low miles on it and the carbs are spotless. Accelerator pump is working, all the jet passageways clean and I have 120 mains and #42 pilots to help it run better with pods (the last owner put them on and I do not have an airbox). The next carb pull I'm going to shim the slide needle to further improve it's pod performance.
I did bench sync the carbs, and the floats were all at 14.5 mm exactly. This was fine until after a few pulls of the carbs, that troublesome first carb started overflowing. I ended up adjusting its float height a bit with the carbs on the bike to get it to stop.
I then synced the carbs with a set of gauges after I had it idling well. The bench sync got them pretty close, but that first carb needed to be raised a bit to get it in-line with the other gauge pressures. The bike ran much better after this.
I have one of the
Pamco ignition systems on it. The points were really weak when I first got it and decided to go with one of these. It's got brand new coils and spark plug harness as well. I advanced the timing on it a bit last night as it felt a little too retarded, and the bikes idle performance improved some more.
I'm wondering if the heat difference has something to do with the new 4-1 exhaust as thats where I'm taking readings from. Maybe the outsides don't get as much flow as the other two and theres more heat buildup on the outside two? I'll try heat readings off the cylinder head directly next time.
My main concern is that extra air suck/pull on the first carb. To me it feels like possibly a valve issue on that cylinder. Is it something to worry about or something that can be lived with until I decide to pull the engine again? I'm a noob (web developer's first real forray into mechanics) and this project has been my first real learning experience with a SOHC system. Is it possible that one of those valve springs went back on too tight after I lapped and did the seals? Or maybe one of the rocker arms is out of adjustment, allowing a bit of air in and out of the cyclinder at the wrong part of the stroke? And this is causing some back pressure during slower engine revs?
I just want to be sure these problems aren't going to be catastrophic if I put some miles on the bike before I pull the engine again as the bike is running pretty good. Better than my friends old 350 I used to ride ever did at least lol.
I'm going hard on this thing this weekend and getting everything back together and wired up before I take another run at the carbs. Thanks for the reply and I look forward to additional insight!