650B running very rich. Starting point for jets?

I'm a new owner of a 77 KZ650. It is running very rich to the point of thinning the oil with gas, I took the carbs off last night and bench sync'd them, measured the floats and noted the jets but didn't touch anything. I believe I set the air screws to 1 and 5/8 turns? Whatever was printed under the seat.

After searching around, I get the feeling that my jets may be too big. I have 107.5 mains and 20 pilots.
I didn't check the needle position.

I probably should do a more thorough check and clean of the carbs, but I want to make sure I have reasonable jet sizes before I start.
I almost considered finding an airbox and going back to the spec'd jet sizes, but I think I'd rather work with what I have. Though an upgrade to K&N pods is not out of the question.

77 KZ650B
Chopped 4-2 stock exhaust
Cheap pod filters (unbranded)
Mikuni VM24: 27mm float height, 107.5 main jet, 20 pilot jet

If you have fuel in the oil, jets are not the cause. The problem is a failed petcock and at least one failed needle valve.

Adjusting the floats to a particular height will only get you into the general neighborhood. To properly set the fuel level, the clear tube method is your best bet. The Kawasaki factory service manual and several dozen posts on this forum describe the procedure.

With your setup, I'd be surprised if a 107.5 is too big, but everything else needs to be sorted out before you will know for sure which size is right.

Some cheap pod filters make dialing in the mixture next to impossible. If your carbs have an air jet in the mouth, near the edge, the filters may be covering them.

Using the search function, you should be able to find some discussion threads particular to your setup.

Thanks Tex,

I just checked and I don't believe my carbs have an air jet. They have two round passages which makes them VM24 as opposed to VM22.
The pod rubbers aren't interfering with the openings, but perhaps I should upgrade for peace of mind,

I have a gravity petcock, and with the tank removed it doesn't leak (off position, of course) so I assume the petcock is ok.
How else could it fail? Other than fail to open, of course.

When you say failed needle valves, those of are the valves which the floats push on, correct?
All four move freely and spring back. I suppose I need to remove them and check for wear?

I should mention that compression, leak down, valve clearance, spark and timing have been checked and I believe are within spec,

Do the clear tube test. Also check the Valve adjustments. Common issue for Po's not to adjust them. Also timing. If all correct, then look at the jets.
Steve

I made a very crude fuel level fixture when tracking a problem with a non-firing cylinder.
I'm now understanding that this is a way to check the operation of the needle valves, correct? And the levels relation to the float height.

I'll search for threads on a more robust fuel service level gauge.

Thanks!

It's not complicated and it is the only way to see the true levels. Take a piece of tubing and screw it in the drain hole till it stops leaking and you gave a gauge. You can even heat it and the threads will stay. This is for my 33's. The attachment is off a mini mag light I made 20 years ago.
Steve

The stock pilots are 15s so 20s sound a little rich............. 17.5s are what most run with pods and a header maybe 110 - 112.5 mains too... nettle on the 4th clip (stock location)......like stated nettle valve and level sorted first though.

cjaldous wrote: Thanks Tex,

I just checked and I don't believe my carbs have an air jet. They have two round passages which makes them VM24 as opposed to VM22.
The pod rubbers aren't interfering with the openings, but perhaps I should upgrade for peace of mind,

No blockage is good. I suppose you could get everything else up to snuff, and if those pods work, use the savings for a celebratory steak dinner.

I have a gravity petcock, and with the tank removed it doesn't leak (off position, of course) so I assume the petcock is ok.
How else could it fail? Other than fail to open, of course.

If the petcock does not leak at all, then the next suspect on my list would be the floats and valves. Fuel level is way too high or valves leak. Typically what happens is that the petcock leaks, one or more needle valve is nit closing (dirt, corrosion, wear, gross maladjustment), thus allowing fuel to over fill the carbs, slowly running into the engine, past the rings and into the crankcase. In extreme cases, the entire engine can fill up with fuel, from bottom of the transmission to the carbs. An in attentive owner attempting to start the engine can bend connecting rods and do other serious damage.
Did you ever imagine so much activity in your garage at night? :woohoo:


When you say failed needle valves, those of are the valves which the floats push on, correct?
All four move freely and spring back. I suppose I need to remove them and check for wear?

Yes, wear, dirt and corrosion can prevent them from creating a perfect seal. Sometimes a good cleaning or light polishing can fix yhe problem other times, replacement is the only good option.

Ok, so regarding the internal carb bits.

What I was calling pilot jets, I realize are the needle valve seats. So here where the jets stand.
107.5 Mains, 15 Pilots, and 2.0 needle seats for cyl (1-3) and a 2.5 needle seat for cyl 4.
Cyl 4 plug always has more carbon. I will change this to a 2.0.

Some of the pilots needed cleaning. The air screw seals could be replaced, the needle bodies were missing sealing washers, and some of the needles had a wear-ring starting. Also, cyl 1 needle had a different spring needle and longer travel on the spring compared to the others.

I will replace some of the seals, the 2.5 needle seat, and all the needle valves.

How do you position the bike for fuel level reading?

The factory manual shows the tube being held near the airbox edge of the carb, with the bike in a "true vertical" position.
I've been taking readings with the bike on the center stand, shimmed under one foot to level the bike, at the rear edge of the carbs.
Should I be taking the reading with both tires on the ground instead? I noticed the 2.5-4mm spec is very sensitive to the bike's position.

Also related, I bought these to make a fuel level tool. I was tired of my jammed-in hose solution leaking gas all over the ground.
www.mcmaster.com/#1105k16/=xxpb38
Using a 3mm drill, I drilled out the end of the zerk which let me remove the ball and spring, turning it into a small tube fitting.

When the FSM says "secure the motorcycle in a true vertical position," I'm guessing that means both tires on the ground, not on the center stand, held upright and level. Correct?

I haven't found any discussion of float needle sizes. I've got some float needle wear, and mismatched seat sizes (three 2.0s and one 2.5). So I was going to order new ones, but realized they came in a bunch of different sizes. I can't find any reference to the stock float needle seat size for VM24SS on a KZ650.