TOPIC:

Hi all,
Have put about 500 miles on my shaftie, and it's been fun. However, I've noticed it's been getting considerably "richer". It puffs at idle, and smokes when I hammer on it. It will clear up if you stay in it, but it's getting to the point where cruising isn't easy. It seems like it will load up, then start to miss. If you downshift and crank up the R's, it cleans out and is ok for a little bit. Plugs are tan after a hard run, however VERY sooty after a easy cruise.

It starts great. I mean when it's cold, it will start as soon as you hit the button. I mean, RIGHT NOW. I NEVER have to choke it either.

The iginiton is good. I know for sure.

The mods are K&N pods, 4-1 open pipe, aftermarket ignition, accell wires, B7es plugs. Air pipes on the valve covers are just connected togather with a piece of hose.

The carbs are off of my '76 chain drive 900. They have the stock jets in them. I don't remeber what the jet sizes are, but I do know when I had them out I looked them up and they were stock.

The bike ran great at first, this richness problem seems to be getting worse.

Any ideas?
Thanks

Post edited by: high toned son of a bitch, at: 2006/08/18 21:02

anyone? help please?

give the air filters a good cleaning and try that first,
then check voltage at coils and see that your geting good spark, then timimg (agian)
im going through alomost the same deal, cant seem to lean my bike out any!!!

Hey HTSOB. Sounds like you have to narrow down your problem and a plug chop might help.

Here is what wiredgeorge recently described. You might consider following his advice from 2005/11/04 08:52

You asked for help on a plug chop. I suggest you buy a new set of spark plugs. Drive the bike to a road where you can run at higher speeds without endangering anyone or losing your license. Pull to the side and put the four NEW plugs in the bike and then run at wide open throttle in 4th or 5th gear for about 1/2 mile. Hit the kill switch and coast to the side of the road. The burn on your spark plugs will reflect ONLY main jet air/fuel mixture burn. If you warm the bike up with the plugs in it, you won't know if the condition reflects idle circuit, mid-range or wide open throttle. It won't hurt the bike to do this test. Anyway, remove your plugs and examine them after doing a "plug chop" and you will KNOW if your main jets are too small, correct or too large. The plugs will be white=small, tan=correct or black=too large or somewhere between. The secret to doing a meaningful plug chop is to NOT RUN on the plugs till you are ready to do the actual wide open throttle run.

wiredgeorge Motorcycle Carburetors

As George described, give it a try. Might be helpful.

Cheers-Colin Firth-Ontario Canada
1977 Kz650 Custom, Wiseco 810 and lottsa go-fast goodies.
www.wgcarbs.com

hi
no plags B7ES,that`to coold.i`m running with champion
N3C(also NGK B8ES).speed running N2C (NGK B9ES).
the jet needle :the main jet can be replaced with a smaller or larger one.your mixture is leaner.the groove number "4"is better for K&N.(no."4"is a richer mixture)
greetings achim

Did the plug chop and all 4 are golden brown. Like I said before, when I stay on it, it will clean out and run awesome.
It is the worst when I am just cruising around. You ca hear it drop a (random) cylinder, then if I run it up, it will pick back up and be ok.

After cruising around, the plugs are black. After ideling, the plugs are black. After a hard WOT run, the plugs are tan.
Air filters are new K&N pods, cost about $75 for them.
Any further ideas

Remember, I never have to choke this bike. Last couple nights it's been in the mid 50 degree range. I have gone out at 2-3 a.m. and it fires up and idles great, about 1000rpms, NO CHOKE. I bet it doesn't even crank for a full second.

Post edited by: high toned son of a bitch, at: 2006/08/21 21:23

So it sounds like the jetting is good, given the nice tan color from the chop.
And it sounds like you soot the plugs up at lower idle.

I'm no carb expert, but don't your carbs have a pilot adjusting screw like others? The screw that adjusts the fuel mixture at low idle while the pilot system is in use? Have you tried setting them at the factory setting and work from there?

It was recommended that you check coil voltage. I was waiting to see this addrssed before saying anything. I would do that before mucking with the carburetors. I would also check valve clearances. I would also actually look inside and record the jetting (main jets size, pilot jet size and jet needle position) before asking for help and also positively ID the carbs as jetting will be relevant to the original jetting which is different for the different types of carbs. I would also describe at a minimum the intake (airbox, pods?) and pipes on the bike a bit. There isn't sufficient info in this thread to even hazard a guess as to why you have incomplete combustion during some ranges of operation of the bike.

wiredgeorge wrote:

I would also describe at a minimum the intake (airbox, pods?) and pipes on the bike a bit. There isn't sufficient info in this thread to even hazard a guess as to why you have incomplete combustion during some ranges of operation of the bike.

high toned son of a bitch wrote:

The mods are K&N pods, 4-1 open pipe, aftermarket ignition, accell wires, B7es plugs. Air pipes on the valve covers are just connected togather with a piece of hose.
The

Coil is fine. I have checked the spark. By the 1" arc it will produce, I'd say I've got spark. Spark is NOT the problem.

Again, the bike runs awesome under a load. Idles fine other than puffing a bit of black smoke. The worst is at cruise (light load). Starts fine.

At minimum description the modifications are:

4-1 Kerker header & pipe, No baffle
K&N Pods that are new
Accel wires
Valve clearence from what I can remember was .007" I will have to check the papers to verify.
I will pull the carbs off and get the jets. I am currently in Cincinatti for business, so won't be able to do that until Friday night.

The original carbs on this bike are now on my shelf. They had the SINGLE fuel inlet with accelerator pump. The Carbs that are on the bike now are off of my 76 900. They are a dual inlet type.

This problem has gotten worse. I guess the problem area (cruise) is getting worse. Still starts fine, still WOT fine. Smoke will clear up after a short burst.

The carbs have a screw on the side of each that I presumed to be the idle mixture. They were at 2 turns out. I turned in until the bike started to sputter, then back out until it evened out. Which put them at about 1 1/2 turns out.
Carbs have been synced, I may pull the cover off and see if any of the set screws have came loose.
Thanks

Missed the pods/pipes thing. Unless you have owned the KZ900 since new, I suggest you verify the type VM26 by checking the ID mark on the flange of the carbs. Check the current jetting. The air screws on the sides of the 76 VM26 aren't particularly helpful adjusting; that is, they don't do all that much. Get the jetting in there and we can probably figure this out. The OEM jetting is #115, #17.5, 5DL31-3 - With pods/pipes on an ST, you should probably keep it the stock jetting EXCEPT for the mains and then go to #120s. I am not going to argue about spark as I have heard that MANY folks have hot spark but when they check the voltage at the coils, they find that they have 9 or 10 volts. The valves lacking clearance can also cause the symptoms you noted. Most folks think their bikes are running like jackrabbits when they operate at only a fraction of their potential. I don't mean to doubt anyone's self assessment but I hear the same things over and over. When it doubt, and you are fouling plugs, check coil voltages, valve clearances and jetting/carb type.

Will do, wiredgeorge. I will recheck the voltage, and pull the carbs to verify jet numbers.
Report back friday night.
Thanks for the tips