One cylinder running rich

I'm having trouble with the number 4 cylinder on my 77 KZ1000. The sparkplug in #4 is black. It's not oil, it's definitely rich. The other three cylinders are a nice clean, tan color. I have adjusted valves to spec. The compression is equal on all cylinders. The bike has a Dyna S ignition and coils and I just put new Dyna plug wires on. The ignition timing has been checked.

This bike starts great and has excellent throttle response until it warms up, then it has a slight stumble coming off of idle. Any rpm above idle, it runs great.

I pulled the float bowl off of the number 4 carb and it has a 107.5 main jet, which my clymer manual lists as stock. Any ideas on what I should check? I'm thinking about putting a rebuild kit in as soon as Z1enterprises gets them back in stock.

Almost forgot to mention, the bike has a K&N air filter (which is clean and oiled) and a Vance and Hines 4-into-1 pipe with baffle.

Thanks

Sounds carb related. Sorry you gotta wait for the rebuild kit to come in. Good luck.

Has one of the adjustment screws been tampered with? I would check that the mixture screws are adjusted the same as the others.

A couple of thoughts..is the #4 cylinder firing? Does water sizzle when dripped on the exhaust header pipe for that cylinder? Did you check the plug wire/plug cap to make sure they have the proper resistance? Try swapping the 1/4 plug lead and see if the problem moves from the #4 to number #1 cylinder. Did you check the level in the fuel bowl using a piece of clear tubing ? Are they all within spec? A float that is not adjusted properly or sticking can cause too much gas in that carb. Let us know what you find out.

Al

Ditto on checking the bowl fuel level with the clear tube. This could definitely be caused by having the fuel level too high.

I would also drop the bowl and clean the heck out of everything in the bowl and the float and seat.

I made a stubby screwdriver to get to the bowl screws so I can drop the bowls without removing the carbs. Smartest thing I ever did. If this is an "outboard" carb you should be able to get to it.

Thanks for the advice. I set all mixture screws at 1 1/4 turns out, then fine tuned to get the highest rpm. They are all within 1/4 turn of spec. I will double check them though. I pulled the float bowls off of #1 and #4 and the float height measures the same. I know this isn't the correct way, but I hate to spend $70 for the adapter that screws in to the drain hole. Is there a cheaper way to attach the clear tube for measuring float height?

Number 4 cylinder is definitely firing. It runs great above idle. Also, the plug is not wet with fuel, just black. It did this before I put new plug wires on, so I'm sure it's not electrical.

Thanks again for the advice. If you have any more ideas, please let me know.

fordtruck wrote:

...Is there a cheaper way to attach the clear tube for measuring float height?...

Just "thread" clear plastic hose into the drain hole opening. Usually doesn't leak, but a slight seepage won't affect the measurement.

Could use the "Search Forum" box (see in above horizontal ribbon) to find many links with detailed instructions about the clear plastic tube test.

Just type "clear plastic tube" inside the box and click the "Go" button. (Choosing some other search phrase might also be okay or even better).

As known, the "testing" is fun quick and easy, carbs on the bike with no disassembly required. While the "adjusting" involves much more careful effort.

Good Luck!

I used aquarium clear vinyl hose. It was a little too fat to thread into the hole, so I melted it with a candle while stretching it to both narrow and harden the vinyl, then cut it with snips.

Worked great, but hated that whole process. :lol:

Qdude wrote:

I used aquarium clear vinyl hose. It was a little too fat to thread into the hole, so I melted it with a candle while stretching it to both narrow and harden the vinyl, then cut it with snips.

Worked great, but hated that whole process. :lol:

Smells like . . . victory!

Thanks for the info guys. I'll try and check the float level this weekend.

Another possibility could be a too tight valve clearance on #4 which might be sealing okay during engine compression test but failing to seal when engine reaches normal operating temperature. If not already done, would check the clearances.


Edit -- Oops, now see this was indeed already done.

There is always the chance that the main jet needle is a different height than the others.

Too true, good one !