Topic: 76 CB 750 hard starting - cold blooded.

[gears351]

Hi, just joined - I'm trying to fix a bike for a friend, a 76 SOHC. The local shop did it for him about 2 years ago and now that he's racked up some miles we've unearthed a few problems (they put the tapered steering head bearings in without the lower spacer, this summer it started grinding the lower tree against the frame tube) along with a few other issues that had us questioning their attention to detail.

Anyhow, it's been hard to start and really cold blooded. I went through the carbs and couldn't find anything (no dirt, debris, corrosion, shellac) but I noticed that the air screws were cross drilled and hollow! I haven't been able to confirm from anyone if these were in fact stock - the stock setting is 1 turn out but these were set at 1/4 (so the cross drilled passage is lined up with the air passage in the carb body). Lastly, fuel seeps from the carbs if you leave the gas on while it's parked.

My questions are:
1.) will a weak battery cause hard starting? (it turns over and eventually starts but won't hold an idle on it's own - even on choke - for the first 40 seconds or so.
2.) anyone familiar with these air screws?
3.) will the float level affect starting (No, stupid me didn't check it the first time I had the carbs out)?

[andy750]

My questions are:
1.) will a weak battery cause hard starting? (it turns over and eventually starts but won't hold an idle on it's own - even on choke - for the first 40 seconds or so.
2.) anyone familiar with these air screws?
3.) will the float level affect starting (No, stupid me didn't check it the first time I had the carbs out)?

Hey welcome and you came to the right place. First dont let anyone tell you these are cold-blooded - they are not. Its all to do with how it is setup. Answers to your questions:

1. Yes a weak battery will not help starting. Get an AGM and never look bacl...if not then charge your battery  or replace with a fresh one so you KNOW its good. If it dosent hold charge after that then look elsewhere...

2. Air screws - should be ~1 turn so Id pull them and make sure you have the little spring that they seat into. Sounds like you should replace yours....

3. Float level will affect starting if too low or even too high. 26 mm is the correct setting...best pull those carbs and check or pull the bowls and measure amount of gas in each to see if they are even ....kind of a measure of float height but not so accurate. Pull the carbs and check all settings...needle height, jets, float height etc...

good luck!
Andy

[gears351]

Thanks Andy, I was afraid you'd say that.....
The battery holds a charge for a few days, the exhaust valves were too tight (couldn't get a .002 feeler in - so I've set them all at .003") the points and dwell and timing look good, plugs are good (NGKs)... I was REALLY hoping I wouldn't have to yank the carbs again.

What about those funky drilled air screws? The springs are there. I have not checked the carb synch.


 

[gears351]

nobody's heard of these drilled air screws?!