SOLVED! 650 w/750 juggs. Runs on choke only.

Had an assortment of goodies and I did a little reading and figured it "could" work. Here's what I have.

A 78 KZ650 bottom end all fresh. KZ750 cylinders with good compression. 650 heads but with the 750 cams. KZ900 A4 26mm carbs (jetted as stock for a 900 and airscrews 1-1/2 turns) with matching 900 intake manifolds. Kerker 4 into 1 pipe. 4 individual K&N's.

Put it all together and fired it up tonight for the first time to see what my baseline "behavior" would be. Didn't want to start just on choke so It got a squirt of gas in each carb and fired up on the choke only. Ran a bit fast but not scary. Maybe 3000 RPM's. Warmed up a little bit and took choke off and died instantly. Needed the same procedure to restart.

Oh and stock 650 ignition. Points are low mileage and set to stock spec. The bikes in decent general shape.

I'm not asking for a miracle setup (unless you happen to have one but I'm no 4 stroke expert. All my jetting experience is with big bore 2-strokes so I do know the language but not the bike. Any help establishing a good starting point or any general advice period much appreciated.

Thanks Much!

it sounds to me like you have plugged pilot jets. the choke is not an actual choke it is an enrichner it dumps raw fuel into the throat of the carb to assist in starting. if it runs to long on the enrichner then you will begin to get into a lean situation that's why it is reving high like that. clean your pilot circuit out and your problems should go away.

Thanks for the quick reply. I cleaned them thoroughly when I got them. Good soaking. Blew out all passages etc. but they sat up for quite a while before going on the bike. I'm going to pull em this weekend to take a look at everything and make sure it's still clean but they were tip-top and I'd be really surprised if jet blockage is the problem.

Make sure you can blow carb cleaner through all the passages in the carbs as well. Stock main jets for the 900 carbs should be #115, but with individual K&Ns you will probably have to go richer than that for it to accelerate crisply.

You never mentioned if you tried to rev it once you turned the choke off. Maybe the idle screw is set too low, see if you can get it to maintain a decent idle speed by holding the throttle open a little bit. I have my idle speed set to around 1200 rpm when the engine is fully warmed up, but when it's cold, even after running on choke for a minute or so, it will still idle very low, to the point of dying if you don't keep it running with throttle.

clogg idle circuits....final answer.....they can get missed by a scinch...you'll get it...

Check for clogged idle circuits as suggested but you also need bigger pilot jets. Bump them to 17.5 instead of the stock 15. With vm26s on my stock 650 motor with k&n pods and 4-1 I was running 17.5 pilots and 117.5 mains to get her running like a bat outta hell.

Well it was driving me nuts last night so I stayed up too darn late pulling the carbs and doublechecking the pilots and mains. They are as clean as can be. Every jet blown throught with carb cleaner and air. I could see light through every pilot. All back together and nothing new. Big squirt of raw gas into every carb. Full choke and it'd take some winding up but it'd start. Reved it up to about 4000 RPM and held it there for a second and backed off on the choke and straight to zero. Tried it again at lower RPM and same deal.


26mm (VM26SS) KZ900A4 & A5
Main Jet 115
Air Jet 1.0
Needle Jet O-6
Jet Needle 5DL31-3 (last number is the clip position)
Throttle valve (slide) 1.5mm cutaway
Pilot Jet 17.5
Air Screw setting 1 3/8 turns out

Here's the stock jetting #'s from Z1 enterprises page for the 900 carbs I'm running. I'll up the pilots and main I suppose but before I do, everything else is going to get a once over from points to pilots. This is always the most frustrating part of any build. In the meantime I'll drop the 650 carbs I have back on there and see where it takes me as at least a benchmark.

Thanks for the help everyone and keep it coming if you think of anything.

are u 100% sure that the pilot passageways, in the carb, are clean.the air passage must be free to suply air ,or the jet will not get fuel.
no point messing with the mains yet. u are only useing the pilot at this stage.
it is certainly a good idea to double check the timing, as u have mensioned.
good luck.

You do mean the air passages that lead to the jet. The ones metered by the air screw. It was late and I was tired so I'll go back and check them one more time tonight.

those passages are the most important areas to go after use carbleaner and compressed air the passages are very small and easy to gum up if you can't get any flow thru them try torch tip cleaners or pieces of copper wire and try to get them all the way thru the passage that usally frees things up.just be patient and take your time depending on how long these carbs have set some of that varnish can be pretty stubborn go until you get air flow thru all the passages and jets.

I have had to drill out the brass bead that plugs the OEM hole before. I can’t remember if that is necessary on that model, but it is an easy fix. Just plug the hole back up when done. This can be done with a small round lead fishing sinker weight, or whatever u have on hand.

i had cleaned my 29 smoothbores with spray and air,because of dirty running and changing idles...and somehow clogged the idle circuits,,,while cleaning em!!!!!....and was sure i had em nailed...but my symptoms were as you describe to a word....i posted and was told what t.b said and others......i re-did em once more with fine wires to pass through all removable parts in a dish of carb cleaner,, and was extra, extra picky, and looking for missed fittings or holes/passages,of which a found an area that i had missed beofre,tiny passage ports....the guys were right!!! and it now idled perfect once set...pulled clean like never before...and did not pop and crackle as before under a load in downshifts.....so to repeat...you'll get to em i bet....and be soooooooo happy when you do...imo...