KZ440 cutting out

OK, it’s becoming more and more apparent I don’t know shit.

I’ve been playing with the primary main jet size on my KZ440 since I went from 2 into 1 to a 2 into 2 exhaust. The bike was running lean so I’ve gradually gone up in size from the stock 68’s now up to 100’s and now the engine starts cutting out at about ¾ throttle and the plugs are still as white as they’ve been. I can’t see how going up 13 sizes in main jets isn’t making a difference? Especially since my experience with kart racing showed me the cutting out was usually due to a lean jet.
When I had the 72’s in there it didn’t cut out but it ran super hot and the plugs were white. Now it runs super hot, the plugs are white AND it’s cutting out.

I have checked for air leaks and I can’t find any so now what?

I’m truly lost here. Can someone steer me somewhere in the right direction.

Is the 2 into 2 stock? Are u running the stock airbox? If so return to stock jetting and leave it alone if it runs ok.bj

Nah, BJ, the headers are stock but the mufflers are emco shortys. I am running a stock air box. I had the stock 68's in and it was lean (running super hot and the plugs were white as snow). I went up to 72's and still the same. I went to 90's, nuthin. Up to 95's and then to 100's and still the same white plugs but, as mentioned, now it's cutting out at 3/4 throttle.

If not already done, would assure that the ignition timing is correct, and that the advancer is properly functioning and not stuck or hanging in its retarded position.

Best to check the advancer operation with a strobe-type timing light by watching the advancer quickly move back and forth as rpm is varied by blipping the throttle.

The advancer might need lube or both cleaning and lube.

Good Fortune!

Thanks Patton.
Yes, the timing is good and I lubed the advancer about 2 weeks ago so I think all is well there. If I replace jets going up or down it has an affect on the cutting out so I feel safe in saying it's not an ignition issue, not that that isn't important.

These are CV carbs (36mm Keihens) and they are fickle little bastards. I'm learning that the secondary mains are more important to jet properly first, then move on to the primary mains. Or so that is what I've read. I can't see the engineering sinse in all this chaos. Carbs shouldn't be this difficult! I know they were made to run lean because of all the emissions crap that was going on in late 70's to early 80's but this is ridiculous. Is there a 1980 KZ440 on the planet that has anything other than bright white plugs? Is it possible to run these things any other way other than lean?

If anyone has any experience with these carbs and can recommend a good baseline for a two into two exhaust, stock airbox, I'd sure appreciate it. The mufflers are emco shortys with stock header pipes.

If not already aware, there's some good info in the FILEBASE about Keihin CV carbs, as well as other brands of CV carbs.

May go into FILEBASE. Then "Non-model specific" category. And do a "Search Document" with "CV" as the keyword.
The search will bring up the following topics, plus others.

www.kzrider.com/filebase/doc_download/47...-shop-manual-via-omr

www.kzrider.com/filebase/doc_download/474-keihin-cvk40-via-omr

www.kzrider.com/filebase/doc_download/135-cv-carburettors

www.kzrider.com/filebase/doc_download/19-cvcarbs

Good Fortune!

Some more potentially helpful links regarding CV carbs:

www.thegsresources.com/gs_carbrebuild.htm

www.drpiston.com/Cvcarbs.html

www.factorypro.com/tech_tuning_procedure...igh_rpm_engines.html

Good Fortune!