1/4 throttle lean spot

Not sure exactly how to tackle this issue, so I thought I'd ask the Gurus.

The bike is a kz650 with suzuki VM22 carbs. It had pod filters until recently when I put velocity stacks on. I now have a narrow lean band around 1/4 throttle. Every where else is perfect according to the AFR.

According to the VM carb Manual i need to swap the needle jet or the slide for a different cutaway size. According to partzilla, the suzuki carbs have a smaller cutaway (richer), so that is helping me. But the needle jet probably flows 5-20% (depending on exact part number) less than the 650 needle jet size around 1/4 throttle.. I have some kz650 vm22 carbs for parts ( pilot fuel needle seat damaged), so I could transfer over those needle jets.

Am I on the right track here? How do i press the the needle jets out without damaging them?

The carbs in your picture look like Mikuni carbs that would have come on a Kawasaki rather than a Suzuki. Take a look at the link below to see what Suzuki VM22carbs look like. Ed

www.google.com/search?q=suzuki+mikuni+vm...EAE&biw=1366&bih=616

pretty sure they're from a suzuki.
www.partzilla.com/catalog/suzuki/motorcy...rburetor-gs550b-c-ec
www.motorcyclespecs.co.za/Gallery%20%20A/Suzuki%20GS%20550.jpg

Also, they have pilot air screws and fuel screws which the kawasaki ones dont.

But thats all beside the point. either way I need different needle jets.

Thanks for the pics! I stand corrected. Ed

No eBay APP ID and/or Cert ID defined in Kunena configurationThese will cure your 1/4 throttle lean spot and are suitable for your Z650 carbs.
Fitting different slides or needle jets will only mask the flat spot and also richen the entire rev range and decrease your gas mileage.

Installed those correctors today and they dont really work as advertised. I had to drop from 1.05 mains to 0.95 because the AFR gauge was pegging rich at WOT after installing these. They did help with the 1/4 throttle issue a bit, but it still sputters while warming up but doesnt anywhere else in the throttle range ( i can "skip" 1/4 throttle and go straight to 1/2 from idle and it wont sputter). Once warm, it doesnt sputter and feels better than before, but the AFR is still lean.

I also tried my needle jet and jet needle adjustment idea and that ended badly. 1/4 was more lean than before. I really need new slides with a different CA, but those dont really exist

Needle jets are pressed in from the bottom of the carbs. To remove them go in from the top (pull out the slides) with a long blunt rod narrow enough to fit over the needle jet (and inside the opening) and tap lightly. The jet should pop out easily and be retrieved at the bottom. To install new jets just put the jet in from the bottom and press firmly on the end to push it into place.

Thanks, i already sorted that out though. Shame it didnt change the fuel curve like i thought it would

All this is a lot of faffing when all yoou need to do is swop out 22's for 24's. I have tried numerous times to get any set of 22's to run correctly through the revs range and failed, swopped in a set of 24's and 20 mins jetting corectly and perfect.
As I understand it the only reason 22's were ever used was to satisfy stringent emissions which can only be detrimental to performance.
No UK 650 came with 22's on it from khi.

good to know.

I tried to buy 24s, but the seller had it listed incorrectly and i didnt know how to spot the difference back then. Its just a dirty commuter bike so im trying to not get too crazy, but i may have to hunt down some 24s


Edit: were you putting velocity stacks or pods on those vm22/24s that you had issues with? otherwise its irrelevant. I had no issues before stacks/pods.

Over the years I've worked on dozens of 650's, so everything from stock to highly moded. First thing I do if a impoted bike has 22's is swop in 24's. I've learnt that the cost of a set of 24's, approx £100 here in the UK, is less than the unproductive grief and pointless cost of parts in trying to get a set of 22's running correctly with the added bonus of more power.
I personally have a stock bike and a highly modified bike with velocity stacks and a 4 into 1 amongst other things and both pull cleanly through the revs. Only difference in the carbs is tne second bike has pilots 2 sizes bigger and mains 1 size bigger.

Saablord wrote: Thanks, i already sorted that out though. Shame it didnt change the fuel curve like i thought it would

I would be surprised if the needle jet was the fuel restriction at 1/4 throttle. I would expect the pilot jet to be the restriction, or perhaps the needle itself if it's adjustable.