carb HELP!!?!?

First off i would like to say hello. I have been lurking on this site for a while and have found a lot of useful information regarding my bike. I have a 1979 kz1000c2 that i have been having problems with. The previous owner 'rebuilt' the carbs without using a kit and they leaked fuel all over. I bought a set of carb kits and that cured that problem but now i have another...

For some reason the bike absolutly will not run without the choke on. When the choke is on the engine will race, and if i turn the throttle it immediatly dies. I have no idea whats going on with the thing. Also, there is a vaccum port on the fuel petcock that is not hooked up. Would that have anything to do with this running condition, and if so where would i run the hose for vaccum for it??

Thanks for your help!
Regards, Brent

I had a couple of things wrong. First off, I did need to hook up the vacuum line to the petcock (duh on my part). Second, There were vacuum caps on the two right side carb vents (who the previous owner and I both thought were vacuum ports). That and a little bit of tinkering fixed the problem! It now runs wonderfully at low rpm. I still have a problem though. At mid throttle while cruising I lose power. It will accelerate slightly just starts stuttering and stalling if I keep on the trottle. I'll do a little more research on the message board, but if anyone has any ideas I would appreciate your input. By the way, when I had the carbs apart I replaced the main jets with 105s (were previously 102.5) to compensate for the pods, but left everything else the same. I have the pilot screws out about 2 1/2 turns.

Regards,
Brent

Post edited by: bdecho, at: 2007/09/17 14:43

Anyone have any ideas??? I pulled the plugs after driving it around for a while and it looked like it was running lean so i put 107.5 mains and 17 pilot jets in it. It did nothing to cure my problem... now i can't get the thing to idle off of choke again either. What gives? I still have the same mid throttle stalling problem!!! I'm starting to think that its an electrical problem after all. Could it be possible that its just not getting a hot enough spark? Any ideas would be nice...

bdecho wrote:

... At mid throttle while cruising I lose power....

Might be obstructed fuel tank vent. Test by running with fuel cap loosened.

bdecho wrote:

... I have the pilot screws out about 2 1/2 turns....

For OEM carbs, FSM says 1 1/4 turns out from lightly seated, so 2 1/2 would seem much too lean for pilot circuit. Would re-set to 1 1/4 turns.

I thought that turning the screws out would richen the mixture not make it lean... are you sure? I turned them in, then back out to 1 1/4 turn and it didn't change a thing. I still can't get it to idle, when i rev the engine it still cuts out about 1/4 throttle. The gas cap didn't change a thing either. The only thing that i haven't tried so far is replacing the accelerator pump, and i'll have to order one, but I doubt thats the source of the problem. Any ideas??

sorry double post:whistle:

Post edited by: bdecho, at: 2007/09/18 17:51

bdecho wrote:

I thought that turning the screws out would richen the mixture not make it lean... are you sure? I turned them in, then back out to 1 1/4 turn and it didn't change a thing. I still can't get it to idle, when i rev the engine it still cuts out about 1/4 throttle. The gas cap didn't change a thing either. The only thing that i haven't tried so far is replacing the accelerator pump, and i'll have to order one, but I doubt thats the source of the problem. Any ideas??

Was looking at the FSM covering 79KZ1000 showing side pilot air screws on A1 and D2 (unscrewing allows more air for leaner). Re-read your post and noticed C2 (cop bike), so checked parts diagram which shows both side pilot air screw and bottom pilot mixture screw and no accelerator pump.

So am befuzzled. Are carbs OEM? Do they have BOTH side located pilot air screws AND bottom located pilot mixture adjustment screws (unscrewing allows more mixture for richer) AND accelerator pump? If answers are "YES" -- then sorry I don't know about these carbs with dual pilot adjustment screws and accelerator pump.



Post edited by: Patton, at: 2007/09/18 19:23

Perhaps the parts diagram is indicating that some 79KZX1000C2's were equipped with side located pilot air screws and others with bottom located pilot mixture screws.

Am sure that unscrewing side located pilot air mixture screws allows more air into the pilot mixture which leans the pilot circuit fuel mixture.

Am also reasonably certain that unscrewing bottom located pilot mixture screws allows more fuel mixture which enrichens the pilot circuit fuel mixture.

Others more knowledgeable about your particular carbs will render better advice.

I finally figured out the problem! After fighting with the carbs to no avail i checked into the ignition system one more time. I set the points gap and the timing, but apparently it wasn't advancing right. I cleaned the thing up and the 1/4 throttle problem went away!!! I'm sorry to get everyone scraching your head when it wasn't even a carb problem after all. For the record the carbs have only one pilot screw on the side of the carburator and it does have an accelerator pump. I guess that means that they aren't the origional set of carbs... So in any case unscrewing the pilot screw leans the fuel mixture correct? I didn't mean to disagree with you Patton but the results i was getting seemed opposite from the plug readings and i just wanted to make sure. Now i have to take the carbs out one more time and put the 105 mains back in because i have a little backfiring on deceleration :blush: I think i will put the 15 pilots back in too since it seemed to idle better with them. I was so sure i had the igniton buttoned up... :S Thanks again for your help!

bdecho wrote:

... carbs have only one pilot screw on the side of the...unscrewing the pilot screw leans the fuel mixture correct?... have to take the carbs out one more time and put the 105 mains back in because i have a little backfiring on deceleration...will put the 15 pilots back in too since it seemed to idle better with them....

Thanks for the report.

Yessir -- unscrewing the side located pilot screw leans the fuel mixture (by allowing more air into the fixed amount of fuel being drawn up into the pilot jet).

But thinking size of main jets is unrelated to backfiring on deceleration. And that smaller pilots might possibly increase the backfiring. Believe the backfiring is being caused by some other reason.

Per FSM, the A3 and D2 standard pilot jet is #15 for OEM Mikuni VM28SSx4 carbs (but as noted, maybe not the stock carbs).

When people disagree with me, it's usually because I'm wrong. But at least I smell bad. :lol:

Good Luck with the tuning!

A Dyna S ignition is the best investment you
can make.Finding some smoothbores or 1978 Z1R
carbs will be the second.I threw away my points
in 1978,never looked back.The 1979 pumper carbs
were hard to adjust,I bet Sudco sold a ton of 29s
in 79.