TOPIC:

Hey gang,

Before I tore the carbs apart this winter, my KZ650C2 started and ran fine except the carbs were a bit gassy (like its owner), and I thought I could get more power out of the bike (don't we all?). It has a Kerker 4-1 and an opened up airbox.

I got the K&L Rebuild Kit for these carbs and cleaned out the carbs, replacing everything that came in the kit:

- All gaskets
- Float needles
- Air Screws
- Pilot Jets - I couldn't read a number on the pilot jets so I assumed they are the stock #15

- Jet Needle (changed clip from 3rd posn to 4th posn)
- Main Jet - The kit came with a #95, 97.5, 102.5, and one marked "102". I assumed this was the "105". So I increased my main jet from 102.5 to the "102" marked, #105.

I took the opportunity to clean out the choke plunger as well as replacing the airbox rubbers. I also synchronized the carbs.


Results:

- More power from 1/2 throttle to WOT (hooray!)

- On cold starts, engine bogs and complains for the first 5-10 minutes at under 4000rpm. This thing used to love cold starts (rode all winter near freezing temperatures).

- air screws had to be set to 1 turn out instead of the 1 1/2 specified, plugs still a touch too white for my taste.


Question:

Is it possible the K&L pilot jets are leaner than the original #15 pilot jets I pulled out of the carbs?

This is the only thing I can think of. I replaced the coils and plug caps without effect on this problem (improved responsiveness though).

If the K&L jets are a touch leaner, my theory is this is affecting the cold running as airflow to atomize the fuel has been reduced by the turned in air screw. Idles fine when its warm.

Note that I rebuilt another KZ650B2 set of carbs this winter, replacing only seals, and that bike runs like a top with the original carb jets.

The "102" marked main jet really cast the quality of the K&L jets into question.
I'm just looking for some opinions, I am thinking of ripping the carbs open to reinstall my original pilot jets. I'm not sure if going to 17.5 pilots is the answer either.

Geesh... where to start... First, I am a K&L dealer but don't sell their stuff retail; I use their parts and occassionally, their carb kits. Their jets are pretty easy to read so I don't understand not being able to read the 15 on the pilot jet. Their numbers are about twice as big as Mikuni numbers.

If you can pull redline, leave the main jets alone. You should have about #107.5 mains with your setup in my opinion. The jet needles are good on 4th clip. Now... the K&L pilot jets. At some point in the past, they had a bunch of pilot jets that were junk. The drilling or beveling process used (beveling around the jet hole) was poor and the gas didn't flow through the jets as it should. When you take a can of carb cleaner and spray through a Mikuni pilot jet, it should result in a tight stream... not a slobber of cleaner. The bad jets slobbered and were basically junk. K&L has since corrected this issue, near as I can tell. I got into the habit of testing each pilot jet with carb spray whether it is new or not. You MIGHT have bad jets. I have seen this problem mostly with the VM26/28 carb type jet and not the VM22/210 type pilot jet used on your VM24s and the VM29s but it is possible. Next, with your setup, you SHOULD be using #17.5 pilots. This size isn't a bad idea for even stock airbox 650s as it allows easier starting, quicker warm ups and takes some of the cold-blooded nature from those bikes. I bet you have #15 pilots and I bet they work fine but are just smallish. Contact www.z1enterprises.com and order some genuine Mikuni #17.5 pilots (don't forget to tell them VM24 carb type) and I bet that fixes your issues. Turn your airscrews out to 1.5 turns when you get them installed... this should be close.

Thanks wg, carb tuning is fun thanks to you!

It is having a bit of trouble getting to redline so I'll up the 105 to a 107.5.

Have you ever seen K&L mis-label a main jet like that? It is stamped "102" and there is a "102.5" in the kit. You're right that these were stamped really big!

I'm looking forward to getting this carb dialled in just right - I'm going to be grinning from ear to ear and hugging the bike and stuff when I do...

I buy jets in BIG BAGS normally... not in kits. I haven't noted any that were mis-stamped in the past. They mostly don't stamp .5 on the end of any of their sizes... they will send 102 for 102.5. Not sure what to tell you have the numbers. I have a bench mount magnifying glass just for these situations bwhahaha...

heh.. speaking of magnifying glasses, I put the original #15 pilots back in and eliminated all the cold starting problems.

I also put the original #102.5 jets back in, and now run to 7000rpm before the bike coughs out. Do I need bigger main jets to get to redline or is this an ignition issue?

Anyways, it was obvious that the air holes in the K&L pilot jet were smaller than stock. It's impossible to say if the main hole is smaller, and the same went for the "#102" main jet I had in there.