Starts w full choke but won’t idle - GS750C

[KiwiGreg]

Reliving my youth I’ve purchased an exceptionally clean 1977 GS750 that has had an 850 kit recently installed. The bike starts immediately with full choke & no throttle, but I can’t get it to idle. I can control the revs by adjusting the choke, but without choke it cuts out. Apparently the carbies have been cleaned and have new needles/jets. So I’m thinking the issue is points, timing or carbies. Any advice please ?

[KiwiAlfa156]

What carbs is it running? Standard carbs Mikuni VM26 or something else?

[zed1015]

I'd first ensure that the pilot circuits are clean, that there's no blocked pilot jets and no broken fuel mixture screw tips blocking their outlets in the venturi floor before going any further.

[unfocused]

If you have Suzuki VM26's, listen to Zed however, make sure you remove both idle circuit screws and check for broken tips. One in the rear and one in the front. If it runs on the choke circuit don't go chasing an ignition problem. Also, you mentioned the big bore kit. You sure it still has points?

[rphillips]

He didn't say, but wondering if he can keep it running with the throttle when choke is off. Maybe at 1500 or 2000 rpm. Or is it he's just turning choke off and it dies... Hope he comes back.

[Syd]

Hi KiwiGreg from another Melbourne dweller - Welcome to the Forum.

[KiwiGreg]

Hi all - sorry, I can’t work out how to reply to individual messages - maybe I can’t? Any help on this front appreciated.
To KiwiAlfa - Kiora. I’m running standard/original Mikiuni VM26.
To Zed - thanks. Hoping I don’t have to, which probably means I definitely will.
To Unfocused - appreciate the advice about Zed and will take it. Still running points, though fairly new sets looking at them.
To rphillips - it was cutting out as soon as the choke was off of a fraction on. And any throttle would just kill it immediately, irrespective of the choke position
HOWEVER READ ON.
To Syd - Thanks for reaching out. I’m in Clayton & Oakleigh, where are you?
AFTER SENDING MY FIRST MESSAGE I SPENT ANOTHER HOUR PLAYING WITH THE BIKE.
After keeping the choke on (but low at under 2000rpm) for a good 5min, I finally managed to keep the bike idling (a little rough) with no choke.
I then slowly increased the revs up and down in a roughly 1000-3500rpm range. That seems to have fixed the issue - whether temporarily or permanently, I have no idea.
Today - 24 hours later - I started it on choke, let it warm up for a minute or two, shut down the choke completely and now it idles nicely. Took it for a 500m run down a long service driveway and shifted through the gears and accelerated smoothly.
Maybe bad fuel (only a few months old), maybe gum in the carbies (despite new needles and gets in the last 2 years).
who knows?
I’ll keep playing for another week or two then hopefully a Roadworthy and Club Rego.
Thanks all for your help and advice.
Cheers Greg

[rphillips]

Try a shot of the best fuel additive ya'll have over there. Around here Seafoam seems to be the one recommended most often. May or may not help, but never heard of it hurting anything... Glad it's doing better.

[KiwiGreg]

Will do thank you