CB750 K1 with 400 miles on rebuilt top end. Cylinders had virtually no wear (have it written down but off the top of my head I want to say worst was shy of .0015" and the rest were significantly less) so just honed and new rings, head ported, seats cut, polish chambers, new guides, new exhaust valves, lapped, etc... Reused springs. 90% of the time 1 kick to start and I'd attribute the other 10% where it fired second kick to operator error. This morning and this afternoon it was hard to start, maybe 5-6 kicks. This morning it seemed slightly less smooth and slightly lower idle after it ran a few minutes before I headed out, I adjusted idle stop just a hair tighter and it seemed fine, and later adjusted it down just a hair once it was warmed up since it was idling higher than I had it previously. Starts fine one kick when hot, say 30 mins or less since at full temp. I want to say it took a few kicks to start yesterday when leaving work.
I thought maybe plugs were fouling or something simple. What do you guys think of these plugs? I'll withhold my thoughts for now... Those are 1-4 left to right. #3 is a little oily because the tach drive started leaking down on it this week. Ordering a DOHC seal since reports here are they seal better.
After cleaning these with brake cleaner and a soft brush it fired first kick on only 3 cylinders (forgot a wire!). Didn't seem any smoother though. I had idle mixture screws about 3/4 out with slight variances, It seems to idle a little better with them 1/2 out so that's where I put them. I understand they should be set approx 1 turn out, which this engine does not like, too lean and will increase RPM as choke is nearing closed. I'll probably repeat carb sync since I changed them.
Engine makes great power. Last night I went for a long ride and hammered on it quite a bit. I got carried away one time and very briefly hit 10 grand or just shy of, snuck up on me as the clutch is slipping if accelerating hard over 7k or so. New clutch is on the way to fix that. One other time I had it up to about 9k for a split second. I'm wondering if it's feasible I may have bent a valve and that may be causing the hard start or slightly less smooth idle. I am regretting not changing the springs for stiffer, I did not expect it to be so rev happy with a stock cam as my previous stock 750s were more or less signed off in the neighborhood of 8000-8500. After going to 10k last night I noticed no change for the next 20 mins or so home. Smooth idle and pulled hard. It still pulls hard. No backfiring intake or exhaust. What are chances I bent a valve?
I think I'm going to adjust the valves again. I adjusted them initially cold then again after 100-150 miles with the engine somewhat warm. I've since read they should be adjusted HOT. I had them set to .002" IN and .003" EX. My compression tester does not fit these threads so I'll pick up another or a fitting that does and check that as well. Timing again too and probably a carb sync, again. Also I did not rebuild the carbs after doing the engine. They were supposedly rebuilt a couple years ago. Looked clean and ran well enough prior to restoration and I was impatient so just sprayed all passages with cleaner and threw them on.
