KZ550-F1: Running Rich and Poor Fuel Mileage

In my fun with the KZ550, I've discovered my fuel mileage is pretty bad, We're talking like 25 MPG on average. In addition to that, it seems to be running quite rich, noticeable from the smell of the exhaust and blackened spark plugs and exhaust.

Unfortunately I have no idea if the thing has been rejetted. It came with pod filters installed and based on it not being lean I can only assume they were.

Is there anything I can do to try and determine what would be causing it to run so lean, and if jets are needed, is there a way to determine which ones I'd need short of throwing random jets at it and hoping I get it right?

Thanks!

Before ripping out the jets, I would check the service fuel level in each carburetor using the clear tube method described in the fsm.

When was the last time the valves were adjusted?
Steve

Would check for gasoline having entered the crankcase and contaminated the oil.

Do the "sniff" test and carefully examine condition of the oil.

Do not run the engine when its crankcase oil is diluted with gasoline.

Good Fortune!

First I'd make 100% certain you are running on all four cylinders. I've gone to work on many bikes that were only running on two or three without the owner knowing it. You can use a water spray on the exhaust pipes to check that.

Tk26 carbs do not have a safety overflow so the gas could just go into the motor if the floats and petcock are faulty.
As Patton and Texas suggest, fuel level (and gas in the crankcase ) would be the first thing to check. That can done without removing the carbs as long as you have a centerstand. The fuel level (bottom of meniscus) should be about 7mm below the bowl gasket surface.

The next thing I might check is the enricher circuit. There is a ball-detent that is supposed to hold the enricher valves shut. People often lose the ball when they pull the choke rod out. The ball and spring reside inside the diaphragm chamber of carb #3. If the choke rod doesn't positively hold fully in with a click, then the ball may be missing, and you may be using the enricher unknowingly. When the rod is in all the way, each of the four enricher plungers are held in with spring preload. There is a small spring on each plunger rod to hold them in with tension.

Then I'd inspect all of the diaphragms. If they are torn, they may not rise, and that will behave similar to a choke.
I'd also check the needle to see what it is. If it's adjustable, it's not stock, and you should note where the adjustment is, and if any shims are being used, Take really good photos of the needle.

Then finally, when you open the carbs, look for the jet numbers. And take photos of the jets too so we can identify if they are from a jet kit.
The pilots should be 32 and the original main would be something like 110, 116 or 120.
The parts fiche shows 120 but the chain drive models show 110. It's hard to see why there would be such a large difference on two motors with the only difference being the output drive system.

Alright, I finally got around to tearing stuff down and seeing what all is up. Here are some answers to the questions:

1.) All four carburetors have a Keihin #128 primary jet. Flat head slotted and the "K" on the side. The other jets look stock but have no markings that I could find. Sorry for no pics, I used my last set of gloves on the teardown and didn't want to get gas all over my phone.
2.) Diaphragms aren't torn but a bit wrinkled. I've had them work fine like this in lawn equipment, but, this isn't a lawn mower. Does anyone even sell these anymore? Can't seem to find any for the TK-26.
3.) Floats are not full of gas which would cause them to stay open.
4.) The level seems about 7mm using the clear hose test. All are pretty much the same height eyeballing it, I didn't do 100% precise measurements.
5.) It is running on all four cylinders. None of the four pipes on the manifold are cold or cooler than the others.
6.) Vacuum petcock is working as intended. Verified this when taking the tank off to get at the carbs easier.


So, at this point I'm thinking I need to replace the diaphragms. The jets may or may not be an issue, if a 120 Teikei is the same as a 120 Keihin, I can't imagine a 128 would be causing too many issues especially with pod filters.

Diaphragms won't cause you to lose 20 mpg. The problem is something else, most likely running rich.

Not sure if this applies but sometimes when the petcock fails fuel back flows down the vacuum line and into the carbs that way.

Compgeke wrote: Alright, I finally got around to tearing stuff down and seeing what all is up. Here are some answers to the questions:

1.) All four carburetors have a Keihin #128 primary jet. Flat head slotted and the "K" on the side. The other jets look stock but have no markings that I could find. Sorry for no pics, I used my last set of gloves on the teardown and didn't want to get gas all over my phone.
2.) Diaphragms aren't torn but a bit wrinkled. I've had them work fine like this in lawn equipment, but, this isn't a lawn mower. Does anyone even sell these anymore? Can't seem to find any for the TK-26.
3.) Floats are not full of gas which would cause them to stay open.
4.) The level seems about 7mm using the clear hose test. All are pretty much the same height eyeballing it, I didn't do 100% precise measurements.
5.) It is running on all four cylinders. None of the four pipes on the manifold are cold or cooler than the others.
6.) Vacuum petcock is working as intended. Verified this when taking the tank off to get at the carbs easier.


So, at this point I'm thinking I need to replace the diaphragms. The jets may or may not be an issue, if a 120 Teikei is the same as a 120 Keihin, I can't imagine a 128 would be causing too many issues especially with pod filters.

The original main jet would have been a Tk and marked 120. The TK jets are numbered by diameter of orifice in hundredths of mm. So if the Keihin is numbered similarly, it should at least be close.

The stock pilot jet would have been marked 32.

As long as they are not torn, the diaphragms are probably ok. It is normal for those diaphragms to come out wrinkled.
I don't think you can get new ones.

7mm below the bowl surface sounds right.

Do you know what needles you have? With Dynojet needles, the main jets should actually be smaller than stock.

Just to be sure, you should not have an intermediate jet circuit, and no caps over the pilots, correct? If you do, the carbs are from a different bike.

Here is a TK26 page describing the Gpz version of the TK26.
s3.amazonaws.com/gpzweb/TK26mainPage/TK26mainPage.html

Also, have you checked the ignition timing with a strobe to Mae sure its advancing? You should at least make sure the advanced moves freely. You dont want get too deep into carb issues without verifying some basic things about the motor and ignition.

Finally got a day off to tear stuff off the bike again.

So, here's the rundown:

First off, Needles are not adjustable, they're the stock 4A02 needles.

Main jets are the 128 Keihin across all four.

They screw into stock bleeder tubes it appears.

Pilot jets are nowhere near the correct shape but are a #30, smaller than stock. I'm probably going to have to swap these out.

Should look like this:


And finally, the whole thing. No intermediate, no pilot plug.

I can't see the photos so I'll check back later, but the main jets should be #120, and your version of the TK26 carbs should have no intermediate jet and no pilot plug.

Your pilots are wrong, as you said. But the one you show as the correct one is also wrong. That is for a Tk22 carb. The Tk26 carbs use a shorter head pilot.

You can see the correct pilot here, with the bleed holes.
s3.amazonaws.com/gpzweb/TK26mainPage/TK26jets/TK26jets.html

Without a jet kit for pods, you will have to play around with jets for quite awhile, not to mention possibly shimming the needle. Either way, you probably want to get a baseline with the correct style pilots. Jets R us (linked in the link above) has 32.5 which are probably closest to stock 32. I would try those.

The jet kit for the early Tk26 (gpz550) carbs uses the stock pilot jets.

I'd realized later on that I linked a pic of the wrong jets there. At least I haven't bought anything yet.

I'll grab some 32.5s next pay cheque and see what improves. With any luck that'll be a big help and from there just minor adjustments to figure out what's needed for the 4 into 1 and the pod filters (that I'd love to swap to an air box...if an unshattered one existed).