Cannot use choke even when cold

[kev edwards]

I have refurbed 28mm pumpers, plungers done bt Z1015, jetting is stock , will fire up on choke but have to turn off immediately, if I keep it lifted it stops the motor, once warmed idles and runs perfectly with light tan plugs, seems it does not like choke even if I only have it partially on, stumped by this.

[zed1015]

Pilot mixture is too rich.
Lean it off on the air screw and if that isn't enough then fit next size smaller pilot jets.
Getting it off choke asap is a good thing but an over rich pilot will cause lumpy running and plug fouling at low revs and when in traffic so watch for that as an indicator.

[kev edwards]

Took the carbs back off after trying with air scews 2 and 1/2 turns out, did not realise I had weakened it off that much, still sooting up, for some reason I had put 17.5 pilots in, probably because I had the same size in the 26 pumpers I had on, so back to 15 pilots, air screw 1 and 3/8th's out fired straight up, choke off immediately and off for a 20 miler, pulls like a train, got back idled for a couple of minutes , plugs out tan colour with a touch of soot on the plug threaded part, I haven't even put the vac gauges on these yet, and am very pleased as they are at the moment.