1977 KZ 750 Twin // Any genious mechanics?

Got a problem...I guess. I have a Mac 2 into 1 and some cheap pod filters. The carbs are clean, floats set, syncronized, rebuild kit and I had my carbs C-clip(?) set 1 below (richer) the middle setting on the needle jet and I have 135 main jets. I was using B8ES plugs set at the correct gap. And the pilot screw was 1 1/4 turn out. I have good spark. Everything was running awesome for a few months and then one day it crapped out on me. Well it was due to fouled plugs. So I changed them to the exact same plug with the correct gap. While I was at it I changed the C-clip to one above the middle (or 2 stages leaner) and I went with some foam pod filter without any oil for now. And changed the pilot screw to 1 turn out. Why in the hell is it fouling these plugs sooner than the last? Thats even with no oil on the filters. And these are the kind that require oil. Heck, I even took my filters off and ran the bike for 10 minutes at idle and my plugs where still jet black. How is this so damn rich? Shouldn't I be able to whiten the plugs with a 10 minute idle with no filters? Is my main jet too big?

I'm confused. It like the bike ran leaner before this change but thats impossible.

DOES ANYONE HAVE 2 125 MAIN JETS (MINE TAKE THE SMALL DIAMETER KIND)

*** ALSO, SMITHGPZ GIVE ME A U2U. WHEN THIS PLACE CHANGED IT DIDN'T SAVE MY U2U MESSAGES FROM YOU AND I NEED YOUR PHONE NUMBER AGAIN ***

Post edited by: shawntmartin, at: 2005/11/16 14:27

Shawn, I think it is unlikely that carburetor settings changed suddenly and your started fouling plugs because of a rich mixture. Possible, but not likely unless you were mucking with the carburetors and THEN the fouling happened. Sounds like you have tried making them leaner since the problem started. With no effect either...

Evidence points to another cause for the problem...

If you had changed plugs and used the wrong type or heat range, that would do it but sounds like that isn't the case.

If you had over-oiled some air cleaner elements, that would have done it but that doesn't seem likely.

If something is blocking the air intake somehow... like running with the choke on... that would do it; something to check here.

If you float height changed for some reason... allowing too much gas in both carbs? Hmmm, not likely if you didn't muck with the floats.

If you started having electical problems on your coil... Something that effects both plugs firing and they aren't firing as hot as they should. This would leave you with soot on your plugs. Try checking voltage to your coil first.

Valves out of adjustment can cause plugs to foul. Have you check valve clearance?

I guess timing being off might cause sooty plugs as well... Check the timing...

If you are running points/condensor; the condensor may be shot or malfunctioning.

Lots of things can cause fouled plugs but in your circumstance, it sure sounds electrical...

Check your pods, Shawn. There was a post up awhile ago about the pods blocking the inlet.I always use the rule of going up a jet size for every mod(1 for aftermarket free flowing pipes, 1 for pods) but the weather has gotten colder which would make it run a little richer. When was the last time you changed your points and condenser? How's the shim size for the cams? I would leave the "e" clip at 1 above and the idle jet at 1 1/4 out. But the mains shouldn't be fouling it out at idle.

WG! You beat me to it! But then again he was calling for genious mechanics and I wasn't gonna answer:silly:

WG, the only thing I changed was the needle position and the pilot screw. I did take the bowls off but was careful not to disturb the floats. I'll reinspect things. The ignition is a fairly new Newtronic electronic ignition and I saw plenty of spark. The UNI foam filters are new and they have a wire that wraps around in a spiral so that the foam doesn't clog the inlets. I was going to try some brand new plugs but go hotter (B6ES) and see what happens. When I ran the bike at idle with no filters it would stumnble a pop a little which I thought indicated a lean condition but the plugs where jet black. I don't know if the plugs would've changed to white in just a 10 minute time span at idle. I'll check the timing and see whats up. I still would like to tinker with 125 main jets if any one has an extra set that they don't need...

Post edited by: shawntmartin, at: 2005/11/16 15:55

Post edited by: shawntmartin, at: 2005/11/16 15:56

Post edited by: shawntmartin, at: 2005/11/16 16:08

I'll see what I've got at home and let you know

It takes a lot more voltage to fire a plug under compression that it does to fire it in open air, so you could see a really nice fat spark but still have a bad plug cap or wire (or even a coil).
The only way to tell for sure is to measure the resistances with a meter, check the wires, plug caps, and the coil, and make sure you are getting 12 volts to the coil.

I had the same problem on a twin, and it was bad plug caps. I guess after 25 years it's reasonable to expect them to go bad

shawntmartin wrote:

... The ignition is a fairly new Newtronic electronic ignition and I saw plenty of spark....

Hmm. Sounds kinda familiar. Please see this...

kzrider.com/component/option,com_joomlab...atid,2/id,3882/#3882

I forgot to mention that the bike runs pretty strong after about 1/3 throttle. Its the 0 to 1/3 that has the stumbling....then all of a sudden POW!. I don't know how much of the potential problems stated in the earlier posts can be eliminated with this info??? Sounds like the plug caps and wires could be eliminated. Sounds electrical...but I don't know for sure.

Did you have the idle jets out at all where they could have been dropped or bent? On the electrical side, It sound like it's acting like mine did before the reg/rect went out. You will know when that happens!

shawntmartin wrote:

I forgot to mention that the bike runs pretty strong after about 1/3 throttle. Its the 0 to 1/3 that has the stumbling....then all of a sudden POW!. I don't know how much of the potential problems stated in the earlier posts can be eliminated with this info??? Sounds like the plug caps and wires could be eliminated. Sounds electrical...but I don't know for sure.

Again, this is *EXACTLY* thye same symptom I had until I changed the timing like described in the link to the post above....

I know all of the other stuff makes sense, and I spent a whole riding season troubleshooting all of those correct things. Hey, I'm not really complaining, I have everything perfectly adjusted now...

I'm only driving this point home because you have the same bike, the same ignition, and the exact same (former) problem/symptom....

Post edited by: biquetoast, at: 2005/11/17 19:26

Thanks. I'll tinker with the timing and see what happens. The bike used to run great. I've never adjusted it since then so I didn't know that the timing could change over time.