I've had a '74 750 for a couple weeks now, I've run thru a few things and she's much better but not all the way home yet. Before I take any shots in the dark thot I'd ask the experts
As far as I know everything on the bike is stock. Carbs, airbox, cam, bores, etc. When I got it the bike:
1) Will not idle at start for 4-5 minutes. Idle is rough at all times and can't be left unattended no matter how warmed up.
2) Hunts for idle as warming continues. Shoots from < 1K to >2500K. Must use idle speed set screw to adjust - constantly.
3) Low power thoughout throttle curve.
4) Bike is WAY to tender at low RPM. Will not even take off at < 2500 RPM - stalls. Cruises @ 3.2k so 25K way to high for starting out.
5) Pinging in exhaust note of #3 or #4.
6) Varnish on both sides of engine - gas leaks.
I did this:
1) Set valve clearances. Cyl #3 slightly intake out, not much ~.002". #3 exhaust out about the same amount. #2 intake out .001".
2) Set point gaps (both sets). Points OK, but 2-3 gap out .003"
3) Set timing (static). 2-3 was out 8 degrees, 1-4 fine. Did not do dwell or dynamic timing.
4) Changed plugs. 1 & 4 looked lean. 2 looked normal. 3 looked unused - ouch didn't like that. Piece of carbon between electrode and conductor otherwise very clean - TOO clean.
5) Rebuilt carbs with full kits, set floats. The kit included all factory needles and jets btw. I did a bench sync only, but ordered a four place sync tool.
Number 3 did turn out ot be OK btw.
After that she idled steadily but still roughly, started hard but did not leak. She had much more power, but had some large flat spots going from mid-high speed.
So I...
1) Moved the needles to 2nd from the bottom, off of the middle (factory) position. I found them in the second from bottom btw, but thought with the rebuild they should go back to factory.
2) Used my new sync tool.
After that she started and idled great but I had to have the airscrews at 1/2 turn at most and she would have liked them all the way in too. I was uncomfortable running her with that thin a "potential" mixture, wanted here closer to the factory (1 turn) setting. Also the flat spots were better but not gone. I don't think there was any stumbling. The reading for #3 cylinder on the sync gauge was troubling. She would sync fine at idle with the others, but goose the throttle and the others vacuum readings went up, but 3 didn't.
At this point I gave a serious eyballing to the boots and clamps. The boots did not reveal any leaks at idle and were nice and supple. But... they appeared to be somewhat loose on both the head and the carb side (the airbox boots too btw). The clamps were all maxed out but I could still wiggle the boots on the engine. I thought it was enough that some leakage could occur, especially at high RPM, like my flat spots.
So off came the carbs again
This time I put the needles back to factory and then used regular (radiator type) hose clamps to hold all the boot joints. It is as beautiful as you'd expect, but I have NO leaks I'm sure of that.
What I got was:
1) #3 vacuum readings match the others now (yay) she was just leaking at the boots it's seems.
2) Hard starting.
3) Very litle reaction to airscrew settings. 1 turn out is fine, 1/2 turn maybe a titch better if at all.
4) Sensitivity to starting at lower RPM is back. Wants to start out at 2.0K. I like to roll out from 1.5k, all my other bikes do.
5) Mild flat spots @ around 45 MPH and just the slightest hesitation when gunned from there.
6) After 5 minutes of driving it runs/idles steadily, with the above notes tho.
That's where I'm at.
The bike has the original 4-4 pipes on it (yay) but the innards are toast on at least some of them I'm sure. I covered some rust thrus on the exteriors with metal tape just to help the back pressure some, but it's not like having the baffles in good shape.
I'm sure tuning would be easier if the pipes in new, but can I work around them somewhat? Are there tuning tricks I can use to simulate full, stock back pressure? Am I mising something else I should be looking for?
I'm considering taking the carbs BACK off and going to the bottom needle setting, probably keeping my scenic radiator clamps unless someone tells me that movable boots are fine.
Thx in advance guys!
