1978 KZ-650 runs bad when cold

Hi all, first post, hope I get this right.

I have a 1978 KZ-650. I think its a B model, or D, can't ever keep that straight. For the last 2 years it's been getting worse and now I can't ride it unless I have at least 15 minutes notice!

This is what I mean: Until its been idling 10-15 minutes and it completely warmed up, it only idles, and idles a little rough. If I try to open the throttle a little, it sputters and misses like crazy and will die. Oddly, when you first hit the starter, it zooms right up to 5000 rpm if you want but you can't hold it for more than 20-30 seconds because it will die at that throttle opening until warmed up.

Once its a little warmed up, it still stumbles around for the first few miles, at low throttle openings. If you can get the throttle opened up without stalling it, it roars and takes off like a banshee. It can jerk you back in your seat.

Even when I've been riding an hour, it still runs much better at wider throttle openings.

What I did before this: Tore down all 4 carbs and stood over a parts washer for days, with a toothbrush. Seemed like it was running very rich before I did this, so I moved the clip on the needles to lean it out a little. After that, the low-opening problem was still there, and it ran noticeably hotter.The plugs came out whitish-tan.

Since I still had the issue, I tore them down again, cleaned them on a bench (no parts washer at hand) with carbo-clean and put the clips back where I had them at the start. I haven't looked at the plugs after that. There's little change in performance except that the gas milage is way down- from about 40 to about 33. I have a new air filter, and new plugs.

I often smell gas but can't find and liquid gas puddling anywhere on the bike or floor.

I'm wondering about fuel flow-- why would that be related to temp?

Help!

Welcome. B models have spoked wheels, and C and D models have Mag wheels.

Check your carb manifolds for cracks, or even the caps on the manifold nipples.:laugh:

You can spray some WD40 onto the manifolds while your bike is running. If you get a rev surge, there's a leak or crack in the rubber.

Try a search on cleaning the carbs, including blowing compressed air through the passages. Never done them myself (paid a shop) but remember past posts on the subject.

Post edited by: rstnick, at: 2006/08/09 22:25

I have spoked wheels, so it must be the B model. :ohmy: Was there a B2? I might have that.

I had used carb cleaner to check for leaks on the manifold boots. Can't detect any change in sound or idle speed when spraying around there. I had cracks in two of them ten years ago and replaced them-- had to extract some of the screws. The top ones are blind holes and all came out easily. The bottom ones are through-holes and all had some rust. Broke one off. Retapped the hole bought new screws, they fit very well.

Haven't tried the WD-40 leak test lately- I should do that again. I did it after the first carb job and didn't find leakage.

Could this be a timing issue? I felt real uncertain when setting the timing after the first carb job and wasn't sure I had it right.