KZ440 cutting out

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09 Jul 2011 18:25 #461913 by Mickey356
KZ440 cutting out was created by Mickey356
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.

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09 Jul 2011 18:45 #461915 by hocbj23
Replied by hocbj23 on topic KZ440 cutting out
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

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09 Jul 2011 20:34 #461930 by Mickey356
Replied by Mickey356 on topic KZ440 cutting out
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.

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10 Jul 2011 01:50 #461976 by Patton
Replied by Patton on topic KZ440 cutting out
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! :)

1973 Z1
KZ900 LTD

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10 Jul 2011 20:15 #462138 by Mickey356
Replied by Mickey356 on topic KZ440 cutting out
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.

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10 Jul 2011 23:31 - 10 Jul 2011 23:33 #462160 by Patton
Replied by Patton on topic KZ440 cutting out
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! :)

1973 Z1
KZ900 LTD
Last edit: 10 Jul 2011 23:33 by Patton.

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10 Jul 2011 23:36 #462162 by Patton
Replied by Patton on topic KZ440 cutting out

1973 Z1
KZ900 LTD

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