Hi to all,
I'm a new CB owner, after a long venture in the world of dual-sporting, and am already truly impressed by the immense knowledge and dedication of CB riders, especially on this forum. I'm hoping you all will be able to help me out, though, with a nagging problem I'm having with my bike. Here's the deal:
The Bike: I bought a 1978 CB750F from its second owner, who was given the bike by an old man who had left it sitting for fifteen years or more. The second owner rode it only once, around the block, said it "ran terribly," then sold it to me for 400 bucks.
- We're looking at 17,000 mile on the bike.
- There are air pods instead of an air box.
- There's an after-market Kerker exhaust, which kicks ass.
- I've also put a '78 750K tank onto the bike, since the original tank was rusted through. Not the most elegant solution, but it works for now.
- Everything else appears to be factory.
The Problem(s): although the bike starts and idles (though I had to spray a lot of carb cleaner into the air intake to get the thing going, but after much tinkering I seem to be able to get it to idle without any special help), it sometimes stalls when I open the throttle. More importantly, exhaust pipes on
cylinders 2 and 4 are not getting hot, even after spraying the intake on those cylinders with carb cleaner and running the bike for a long time.
What I Have Done So Far:
- I did a valve job, and everything is adjusted to spec.
- I pressure checked the cylinders, and they're all reading at relatively normal levels. Some slight discrepancies, but nothing to cause this problem.
- Contact points are adjusted.
- There is enough fuel in the tank.
- All four spark covers are getting a good spark, and all the spark plugs are new.
- All jets are clear in the carb, and they are not after-market or readjusted.
- The float bowls were all at different levels, so I readjusted them to 14mm. Spec settings are 16, I think, but I'm compensating for extra air from the air pods. I should mention that most of the floats had to be adjusted by 10mm or more, and the levels were quite uneven. But I was able to get the bike to idle before this adjustment, which is curious. It still idles now, after the adjustment, as well.
- Ran some Sea Foam through the tank.
- I've tried the pilot screws at one-and-a-half turns, at 1 turn, and at half a turn, with no difference.
What Happened:
- The first time I ever started the bike, it idled reasonably well, but Cylinders 2 and 4 were not getting hot.
- I checked the bowls on all four carbs, and all had fuel.
- I did the valve adjustment, points adjustment, and re-checked the jets.
- I fired her back up, but the bike at this point would not idle at all, unless I was spraying carb cleaner into the carburetor intake. There was plenty of fuel in the tank, and there was fuel in all four carb bowls.
- I took the carb off, at this point adjusted the floats to 14mm, then re-checked the jets, cried a little, and put the carb back on.
- At this point, the bike started to idle, but cylinders 2 and 4 were still not heating up. Water thrown on the exhaust pipes does not evaporate for several minutes.
- Again, there is fuel in the bowls, and there is spark on all four plugs. The plug covers are not crossed or misaligned.
Here Are My Thoughts- I almost certainly do not have an ignition problem.
- Fuel is getting through from the tank to the bowls, so that's good.
- Maybe there's some kind of vacuum or air issue. The boots have a lot of gunk or sealant of some kind on them, as though they've been screwed with in the past.
- The carb gaskets had silicone sealant on them, leading me to believe that someone was either being enthusiastic when re-sealing the carbs, or they too suspected an air leak.
Now What?I feel stuck. I'm really unsure of where to go from here, and I've kind of reached the limit of my mechanical creativity. I hereby submit myself to the genius of the internet, and ask you all for your help.
Many many thanks!
