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CB750 Project 1978 K8 looking for some tips

tdubsy

CB750 Enthusiast
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Hey Everyone,

I've Been working on my CB750 for a few months now and have found a pretty decent amount of help on the forums.

Before the bike was barely running and wouldn't idle below 2000 rpm, Now its quite better but still a ways away from running well. I'm not a mechanic so don't be surprised if i've missed something even if its very simple


These are the current symptoms

- Bad/slow throttle response (very slow or bogs down if under 2000 RPM) Deosn't return to idle the fastest
- Small but consistent backfiring cylinder 1 (out of exhaust) - started after adjusting valve spacing (too tight?)
- not enough power to be able to roll around with just the clutch and not applying gas
- Plugs coming out sooty telling me it is running rich
- I have the stock 4 to 4 exhaust. pressure out of 1/4 is noticeably higher compared to 2/3. Can tell by holding hand near muffler


This is what I've done so far.

-Rebuilt Carbs (accel fuel pump was clogged)
- New Carb boots (old boots had vacuum leak)
- Installed dyna electronic ignition and coils
- static and dynamic timed ignition
- New spark plugs/boots and wires
- adjusted valve spacing to OEM specs
- Synced carbs

https://www.youtube.com/watch?v=dhGfIRxR9kE


Does anyone have any idea what I should be focusing on next? Did I maybe tighten the valves too much on cyl 1 to cause the backfiring?

I am also very curious about the cause of uneven exhaust pressure
 
Have you checked your ignition coils to make sure they are in spec? I did not see that you changed them. Also are all the pipes hot to tell you they are all firing. I had an issue that mine would run but had no power. It ran on one cylinder as coils were bad.
 
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