78 KZ1000 sooty plugs, popping exhaust

Hello, I recently picked up a 78 kz1000A. Before I bought it, it was sitting for 4 years. However it's in nice shape, and after new gas, plugs and a battery the bike fired right up. So far I've been really happy with the bike. Except for when it idles it pops in the exhaust, and when ridden at low rpms (under 2500) it stumbles like the plugs are getting fouled.
Otherwise it runs great, it revs nice and smooth and has a lot of power. But the bike still isn't right, the plugs are coal black and sooty, the blackest plugs I have ever looked at. They aren't wet with gas, just that sooty black stuff.
The bike is stock except for a vance and hines 4 into 1 with a baffle, K&N pod filters, and a dyna ignition with coils and accel wires. It doesn't have points, so I guess it's the dyna S? It has the green coils. Anyway it has the stock carbs with 120 main jets, 20 pilot jets and the needle in the top position with a little washer underneath it. The fuel system itself is clean, the tank is like new inside, the fuel lines and filters are new and the carbs are spotless inside, and only required a quick cleaning after I got it, since the fuel system was drained prior to storeage. I was thinking the pilot size was the problem so I messed with the pilot screw (they are underneath the carbs towards the front of the bowls) so screwing them in makes it leaner. No matter where I turn them the problem is still there. I read up on repowering the coils. I checked voltage at coils it was 10.5V, battery voltage was 12.4V. So I thought for sure that was the problem so I repowered them as per the diagram I got on wiredgeorge's website. I now have 11.62V at the coils when battery voltage is at 12.02V. So I still have a .4V drop. I still tried the bike to see how much better it would run. Still no different. It is a little more responsive, but it will pops in the exhaust, and new plugs were black within a minute. the plugs are B8ES gapped to .032. I checked compression and all are right around 140. I didn't check the valves, since the compression seems so good. So I didn't know if anyone else experienced a problem like this and what did you do. I've been searching for a while on here, but it seems like I checked everything unless I'm missing something. So let me know. Thanks alot

Check float heights...

How do I know what to set them at? I am not exactly sure what to measure. Thanks

NewKZguy wrote:

How do I know what to set them at? I am not exactly sure what to measure. Thanks

Here's a link to one of several informative threads about this. Easy to find more help and pictures by doing a search for "float level" or "clear plastic tube."

float level

It's a quick easy check without removing anything from the bike. But the adjustment, if needed, is more involved.

Might also try running through a few tankfuls with Seafoam or similar carb cleaner added to the fuel. However, odds are that carb overhaul is indicated.

Good luck with the repairs.

I'm going to check the float level tomorrow. I don't think the carbs need rebuilt. They have new needles and seats, new gaskets, and everything looks like new inside. The o-rings on the pilot screws are also new. The carb boots are new, and the exhaust gaskets are new. I'm really leaning towards an ignition problem, but I don't know much about the dyna ignition. Is there anything I should check related to the dyna ignition?
thanks

Also do a compression test.

I checked compression and all were right around 140

checked the float level, and it looked right, but I still lowered the floats just slightly, still no difference. What else could it possibly be? I'm about out of ideas

Where otherwise running well, but seriouly over-rich at low speed with adjustment screws ineffective, and float level okay -- casts heavy suspicion on carb pilot circuit. Particularly clogged air passages, clogged pilot air jets, and/or clogged pilot jets. Realize carbs were drained before long time storage and look really clean, but the symptoms nevertheless point to problems within the pilot circuit.

Where pilot screws turned all the way in to maximum lean, but still leaving pilot mixture far too rich, logic suggests insufficient air combining with fuel in pilot jet. Air must get through the air jet and air passage to pilot jet, and the pilot jet must allow the air to intermix with the raw fuel (via the lateral holes in the pilot jet) coming from the float bowl up through bottom of pilot jet. This air/fuel combo leaves the pilot jet and goes to the bypass outlet and to the pilot outlet (the pilot outlet being governed by the pilot screw).

Insufficient air combining with fuel in pilot jet likely results from clogged air passages, clogged pilot air jets, and/or clogged pilot jets. IMO it's best to install new pilot jets.

Suppose it's also possible the starter plungers are worn or stuck open (i.e., not completely closing), which could cause an excessively rich mixture.

Having said all that, perhaps a poor spark for whatever reason at lower RPM could be causing the problem. Incidentally, if not already tested, battery voltage across the terminals should be 14-15 volts at 5,000 rpm.

Hoping for you an early and successful resolution.

Post edited by: Patton, at: 2007/06/11 17:38

Thanks for the reply. I am going to go through the carbs again. I used a lot of carb cleaner through the pilot circuit passages, and it would spray through the pilot screw passages and the air passage at the back of the carbs. The chokes aren't stuck already checked that. The charging system itself is not charging correctly. It is however at idle and low rpm. At idle it charges 12.6V and charges 13V by 4K. However it runs fine after 2500 rpm. So I really don't think the charging system is the culpret at the low rpms. I have a rectifier in the mail which will hopefully correct the charging problem, but again I don't think it will fix this problem. It also looks like the top end of the motor was taken apart at one time, maybe the cam timing is off??? Not sure if it will run as good as it does from 2500rpm up to 8500rpm, but it's a possibility. I think I'm also going to check the timing, maybe the advance is locked in the advanced position. I am still leaning towards an electrical issue.
thanks

NewKZguy wrote:

...still leaning towards an electrical issue....

Recall reading the Dyna igition system at lower rpm operation requires more electrical power than stock points system. So perhaps a good fully charged battery is even more critical with Dyna ignition at lower rpm.

Would also assure good ground wire connection from the negative battery terminal.

With plugs removed and grounded against cylinder head, wires connected, ignition on, transmission in neutral, and using starter button to spin engine over, do the plugs produce a good fat spark? Thinking this spark is applicable to lower rpm operation. Weak spark could mean incomplete combustion due to some fault in the electrical system resulting in an ignition problem. Good fat spark mitigates against an electrical issue at lower rpm.

Would also double-check ignition timing with a strobe light (NOT the static timing method), both F marks at idle and advance marks at increased rpm.

Also -- assure the pointed tips of the pilot mixture adjustment screws are not damaged from being overly tightened in the past (as this could prevent proper leaning adjustment).

Just some random ideas as food for thought.

Keep the faith!

Post edited by: Patton, at: 2007/06/12 20:07

More thoughts -- are the pods overly oiled? Have you tried temporarily operating the bike with the pods removed?

And if going back into carbs anyway, would install new pilot jets -- there're not expensive and would assure allowance of air into the fuel before moving from pilot jets to bypass and pilot outlets. Thinking the precise orifices in the pilot jets may have been damaged incident to prior cleaning efforts.

Not giving up yet.
But may have to call in the BIG GUNS (that would be Wired George)