jetting 81 kz250 single

I've finally got my KZ250 81 running and I can now throttle it/rev it nicely since cleaning the main jet that turned out to be blocked causing it to stall as soon as you give it throttle.

The only problem now is that it will only run and rev with the choke on (which was also the case before I fixed the throttle problem). If I turn the choke off even when warm, it stalls.

I'm running a pod filter which I know will make it run lean. But I would have still thought that it would idle and rev even on stock jets with a pod?

Does anyone know where I can buy the correct jets for a pod filter and what sizes I should get?

Also, does anyone know what the correct mixture screw setting is in this situation?

I can tell you what type jets to use if you explain what type carburetor is on there and what the current jetting is. I don't have time to do research.

thanks WG, you have a very good point. It's a CV32 Kiehn. I've got two of these carbs second hand (one that I've fully rebuilt keeping only the origional jets, the other I've just used for test parts (these carbs are specified as the standard ones for this model). One of the main jets looks like it says 98 on the side but it's hard to tell (which is odd as I didn't think this carb took 98's as standard, thought it took lower). All the other jets have any markings worn off. It seems to be running lean.

Keihin does its business in two ways... rich mid-range with smaller main jet and leaner mid-range with larger main jet. Most of the CV Keihins have TWO main jets. One is called the main and the other the secondary main. The secondary main is usually the REAL MAIN JET. I am going to be forced to look at the parts fiche to determine if I can figure out what type situation you are in...

OK... you have #98 secondary main, #68 main and #35 pilot. The N05A jet needle is one I don't list for the KZ750 CV34s so I am not sure what profile it has. there is no marking on the needle jet so that is another spec that can't be determined...

I would guess you have a richer mid-range and smaller main type assembly based on the larger #68 main. This is the barrel shaped jet offset from the secondary main. Since you can't buy larger pilot jets for this carb, I suggest you bump the secondary main jet. As a guess, I would start with about a #130 Keihin main... you might want to have a #125 and #135 on hand as well... in other words buy three mains (secondary mains) and do some experimenting.

Put the #130 in. I think it will be the right one... Try and pull to redline in 4th or 5th... If it pulls cleanly, your jetting is right. If not, pull up the choke lever a bit (not all the way) and see if it runs better or worse. You have a true choke system so if you choke air and effectively richen the mixture, this will tell you whether to use the larger or smaller main. One of them should be about right. If you run better with the choke actuated, use the larger; if worse, use the smaller. In the odd event that my guess as to the correct range of mains (secondary mains) is messed up, you may need to buy one more main; say a #120 or #140 to get the jetting zeroed in. I think your "main" jet #68, should allow you to use pods without too much fuss but if you feel the bike isn't starting and running well at lower rpms and through mid-range, you may have to buy a large "main" jet... perhaps a #70 or #72. These are harder to find.

Very greatful for your time indeed WG.

Do you have any recommendations as to where I can buy a selection of these jets from? - don't worry if not, but I thought I'd ask first. - Do you sell them?

If you call my friends at z1enterprises.com and ask them, they can supply what you need I think. I doubt they will have what you need listed on their site but they either have it in stock or can get them quickly.

Ok, I've got a set of 115 - 135 jets on order to replace the stock 98. Will post the results after some testing.

I've tried a 115 through to 130 secondary main jet tonight and I have the same problem with all jet changes.

It revs OK, if I apply throttle while backing off the choke (I have to do this at the same time) - Revs best around the 130 jet. But...

The bike will only start with the choke on (which is probably normal) although it then won't idle with the choke anything but fully on (no matter how warm). - Even then, it stalls more easily under a 130 jet, than it did with the stock 98.

Something doesn't add up, as there's another guy on here with the same type of bike who simply changed to a 130 and the bike ran fine with a little popping when decelerating.

The jetting suggestions were not intended to "fix" the idle issue you describe. What you describe is a situation where the bike will run with the enrichener circuit all the way on which is providing gas to the bike at idle... the idle circuit (pilot circuit) needs to be cleaned as it is very very likely plugged somewhere.... most likely in the internal passageways carrying gas OR the slow jet itself.

Thanks WG, it's definitely sorted the revving issue.

Is the slow jet the one that can't be removed without drilling out and melting some glue etc? I took the Main 68 jet out tonight and it wasn't 100% clear. I blasted it through with carb cleaner then air and now it has a cleaner bigger hole showing when held up to the light. It hasn't solved the problem though so I guess it's the pathways to this jet that are clogged up. - Although when I blast air through this jet while it's fitted, I can feel a good clean stream of air coming out a hole near the pod filter end of the carb.

- When trying to run the bike, it often makes a huge clank then stalls and smoke filters out of the carb, near where the pod filter is connected. I guess something is igniting in the carb? (It scared the hell out of me when it happened) but the bike started again after.

I have a shop near me that offers sonic cleaning, do you think this is worth paying for or is it a waste of time?

We use an ultrasonic cleaner in our shop as well.

Happy daze........

It's only on the paddock stand and I haven't run it through the gears yet but the bike now sounds like a bucket of angels! (compared to before anyway).

The pilot adjustment screw is backed out two and a half turns, the idle screw is set so the bike idles at around 2500 rpm (if I back it off any more it hardly lowers the idle speed).

It revs cleanly to red line.

I have to have the choke fully on to start the bike, it then idles with short waves for a few seconds, then it revs to 2500rpms and stays there. after about 30 seconds, I can back the chock all the way off without any negative effect.

This is also in a garage that's just under room temp.

It will be interesting to see how it runs through the gears and on the road, when I fit the new chain and sprocket kit in the next week or so. It will also be interesting to see how it starts and runs in different weather conditions.

But for the most part, I think it's 80% there.

(Part of the solution, I think, (along with copying your settings Dave (you know who you are mate!) and using the 130 secondary main recommended by yourself and WG) was cleaning out the pilot jet which was less than clear!).

Many thanks to WG, Dave and all who've got me this far.