running lean

my question is--how do you know when the carbs are running lean? my pipes are black so i can't tell if they change color drastically. they engine seems normal and looks normal. i changed the float height on my vm29's, not sure i did it correctly, seems to run o.k. thanks for the input.

Generally if it is running lean the spark plugs will be white instead of the normal tannish color. Black means you are running too rich.

Soot can mean a rich air/fuel mixture but can also mean incomplete combustion caused by wrong heat range plugs, use of too high an octane gas, poor spark, etc.

It is a better idea to check your plugs although sooting can mask how they really are burning for the reasons above.

How did you set the fuel level on the 29s? What type bike do you have, do you have a stock airbox or pod filters and what exhaust?

wiredgeorge wrote:

Soot can mean a rich air/fuel mixture but can also mean incomplete combustion caused by wrong heat range plugs, use of too high an octane gas, poor spark, etc.

It is a better idea to check your plugs although sooting can mask how they really are burning for the reasons above.

How did you set the fuel level on the 29s? What type bike do you have, do you have a stock airbox or pod filters and what exhaust?

i have them on a 1976 kz900 with a 1075 wiseco kit. i turned the carbs over and adjusted them with the floats resting lightly on the needle. i adjusted them to 24mm. it solved the overflow problem and the sputtering, but not sure if i went too far. they had velocity stacks on them, no filters. the bike has points, and original coils.

Check voltage to your coils with the bike not running. Put a positive lead from a multimeter set to 1x VDC scale on the lug on your coil where the yellow/red wire connects and the other multimeter lead on the frame. Then switch the power on via the key. Check both coils. If you have less than ~12.4 VDC then the problem is poor power supply to the coils.

The smoothbores present some tuning problem; especially with no airbox/air filters. you didn't mention compression or cams but if you have a bored out engine, and no air filter, then you could be up near #130 main jet I suspect. You will have to ask someone who has more experience with performance mods, like Jeff Saunders, on what main jet. The pilot system will also be tough... the pilot system tuning is complicated (over complicated) by the adjustability in the smoothbores. The little holes in the tips of the air screws are the problem. I would buy a NEW set of air screws and fill them in with JB Weld and adjust the idle. Otherwise about a #20 or #22.5 pilot would be OK depending on which slide cutaway you have. The Suzuki variation of the 29s used much larger cutaways which means a lot more air at idle and much larger pilot jets are needed.

This is USUALLY where fouling comes from using 29s. Find out which pilot jet you have, which slide cutaway and then buy a second set of air screws and experiment.

With your set up, honestly, I think doing the main jet plug chop to determine the main jet, then doing some roll ons to set up the clip on your jet needles and then working out the pilot circuit as I already mentioned would be the way to go... the burn on your plugs doens't mean much as the bike may be right in one or two areas but rich in the third and you might be complicating the problems with poorly powered coils.