I touched on this subject in another thread, but wanted to solo it out for more discussion here - i'm one of the lucky ones with the bill blue burnout so i had to rebuild my 351...

The first go 'round, to start the bike all i had to do was twist the throttle a few times, and the bike would start instantly on the button; no choke. After the rebuild, its back to the way it was stock carb - choke, turn it over for a while, finally start, let it warm up on the choke, turn the choke off and let it run a little more before the idle finally settles.

So what could have changed? The mix screw is in about the same place it was, and i've tried adjusting both ways as needed.

I adjusted the idle screw up a bit, which improves cold starting, but then once the bike warms up it idles too high - is there some potential interplay between the idle and mixture screws that i need to know about? is there a spec for the initial setting of the idle screw? perhaps i need to bump the idle up but adjust something else?

Last but not least - is it possible that my timing may be a smidge off - could that cause these symptoms?

 

The timing is virtually impossible to change, IMO.
Did you do any carb work?
I would look for a leaking intake boot between the carb & head.

 

Bill sent me a one size larger jet with the new kit to try. in the end, i was unable to tune it - it was just too rich at all settings. so i put the old one back (which was working perfectly before the rebuild)

I went thru and made sure the intake boot was properly installed (airbox to carb). i replaced the O-ring on the carb to head side, and the throat is seated as far as it will go. when the weather clears a bit, i will try the WD40 test to check for vacuum leak.

Anything else i can check? thoughts on about where the idle screw should be for starters (i moved it around a good bit while messing with that other jet)

 

I did the wd40 test and as far as I can tell no vacuum leak - although I’m no expert on the matter. Any tips on that?

still hard starting and slow to warm up. Even warm I have to pulse the throttle to start it. Baffles me bc before the rebuild it was eerily easy to start even without choke

 

FWIW hard starting and slow warm up is usually a sign of lean at the pilot and choke circuit. Same as with the CV. Totally unrelated to main jet. Don't know if that helps. Idle mix should give a hint too. If you open up the idle mix and it keeps gaining rpm past 3 rotations, that is a sign of too small a pilot jet. I think the same would be true on the pumper. If you mean twist the throttle to get a squirt from the accelerator pump when you say "pulse" that is richening the mix at start up and idle temporarily.

 

Yes that all makes sense.

Somewhere just past 3 turns out on the mixture screw it starts stuttering and will die. The magic setting for me before was about 2 turns out. The exhaust smells on the rich side of healthy to me at idle.

I've got a call in to Bill to see if he's seen this scenario before. Puzzling..

 

Lets talk about this some more. It got up in the 70s here on sunday so i fired up and rode. I noted that when engaging the 'choke' it actually leans out (the rpm goes down and it stuttered and died - should raise the rpm slightly). Making me wonder now if i have an issue with pilot/enrich circuits. Perhaps a blockage? Once i warmed it up manually via the throttle, it settled in and rode fine.

 

How do you know it isn't flooding out?

 

well....good point.

whats next steps to investigate?

 

What does your spark plug look like after riding?