'77 KZ650 B1 Mysterious Carb Issues.

I'll apologize ahead of time if my question is duplicating something already asked in the past.

I'm hoping that my mysterious carb issue isn't so mysterious to a few of you on this forum.

A little back ground. I bought my '77 KZ650 B1 last summer. The bike was built sometime in '76. I can't currently make out the month. Only the year. The bike had been sitting for 2 years but started right up after a little fiddling with it. I drove it 40km home on what I found out later was only 3 cylinders (bad coil). The throttle would stick and the bowls would over flow onto the motor at stop lights but it got me home.

I had the carbs cleaned and rebuilt using Keyster carb kits. Part #KK-0041. Main jet #102. Pilot jet #15. I also adjusted float levels. The only adjustment screw on the carbs is the pilot screw. As a side note I replaced the bad coil with a Boyer Bransden Micro Power digital ignition kit (KIT00287). To insure good power to the coils I ran the ignition relay setup and replaced the regulator and rectifier with units from Oregon Motorcycle Parts.

Now my issue(s). The bike is difficult to start especially cold. Even warm it has you wondering if it'll start at all. Once running after a cold start the bike runs great and has amazing throttle response. When warm and still in the driveway occasionally giving it a shot of gas will stall it. Nothing odd yet you say? Well, I'll get on this bike with the great throttle response on my driveway and drive it to the end of the road. The moment I try to pull away from a stop it stalls it self every time. It loses all power. The further I drive the worse it gets. Once it has stalled and I restart it, I need to give it a minute for the idle and power to build back up again. Then, if I'm lucky I can baby it though the intersection and get the revs up. Once past 1/8 to 1/4 throttle (2000rpm) the bike rides and accelerates like a dream. It absolutely loves the highway. So do I because the moment I have to stop again getting going is a nightmare. Some intersections may take 2 or 3 starts.

I've had everything done by a journeyman motorcycle mechanic. We synced the carbs and tuned everything on the lift. I've checked the timing on the Boyer Bransden kit countless times to insure it wasn't a timing issue. It idles and revs great... until you drive it.

I'm hoping some one knows what I'm talking about because I'm running out of ideas. Is this something that's associated with these early carbs? Should I be looking for replacements and if so what's the best plug and play for the buck?

Thanks in advance for your help.

sounds like you mechanical advancer is sticking not to familuar with the 650s but its behind the points or pickups on the 1000s on the right hand side,

jeffasaki wrote:

sounds like you mechanical advancer is sticking not to familar with the 650s but its behind the points or pickups on the 1000s on the right hand side,

Yes.

And would also assure correct valve clearances and perform a compression test.

Good Luck!

Open the CD sized cover on the right side of the engine, inside you should find the mechanical ignition advancer.

It works by the use of weights and springs and was used a lot in the 70's and 80's Kawasaki's.

It retards/advances the ignition depending on rpm's. Some light oil like 3-in-one or sewing machine oil is about all you will need once in a while.

The advancer is held to the crankshaft by a fastener. Make note of how it's put together as it can be re-assembled 180 out having you scratch your head as to what's wrong.

I think I may have your answer, I rebuilt my carbs awhile back and had similer problem. On another site (KZ650.info) I posted this problem.....

"Hey guys, my turn with a problem. I've had a Kerker on my bike for the last 28 years but lately I've been wanting to put a stock exhaust on the old gal. A couple weeks ago I picked up a free '78 KZ650 parts bike. The factory exhaust is in 7 out of 10 condition. Pretty excited to say the least. Installed exhaust last weekend and bike ran good but I know it should be running a little rich with Kerker jetting (105 mains, no number on all pilots, whatever rods clipped to 3rd slot,K&N in stock airbox) So, yesterday I pulled carbs and swapped in brand new 102.5 jets (not going back to the 90 something jets it came with), new 15 pilots and new rods (clipped to 4th slot) that came in kits (Keyster) that I installed a couple years ago. Now the bike starts fine, idles better than before, has better throttle response and pulls hard up to 9-10 grand. BUT, when you let the clutch out and go to take off it runs like it's starving for gas and feels like a cylinder or two is not working but once you hit about 4 grand the bike smooths out and flat takes off. Cruising on the freeway at 70 is fine with plenty of power and coming to a stop it idles perfect and has great throttle response. It ran OK before jet swap so I know all passages are clean. Jets, pilots and rods are all I changed. So what to you guys think as I'm getting tired (and good at it) of pulling these carbs."

The response that solved my problem was as follows....

"John: Where did you get the new "rods" and jets ?? Are they Keyster ??? If so, you'll want to bin the "rods" (jet needles) and put the stock items back in. When you compare them side by side you'll see the Keysters are usually far thicker than the stockers. This will give you a lean condition all the way up to about 1/2 throttle.
Keyster only has one size of needle for all their carb kits, apparently, and no one has been able to find out, yet, which bike that needle is SUPPOSED to fit.
As well, I would NOT use their jets. Their quality control sucks big time and so you can't be guaranteed that all 4 jets have exactly the same hole size. IMO, you should get the correct genuine Mikuni jets if you're mad to have new jets."

A little long but I think you have the same problem I had, my bike runs perfect now with the old rods and the Keyster jets are working fine.

short story put some oil on your advancer work it into shape the end

I really wish it was as simple as oiling the advancer jeffasaki. Problem is in order to oil the advancer I'd have to install one lol. Everything was removed from the ignition when I installed the electronic ignition kit (Boyer Bransden).

Thanks Bluemeanie. You've given me a solid point to work from. I'll be sure to let you know how it turns out. Thanks again.

Are you sure the rubber carb mounting boots are not cracked or causing a vacuum leak? Sounds like you have checked all of the usual suspects.

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