Running rough and now won't start

Hey guys, although I've been using this site for tech help and research, this is my first post.

Here's some background on the bike. I have a 77 KZ650 B1 that I purchased last spring. When I got the bike, I had the valves done by a local shop as well as some new electrical, points and the carb synced. Since then the bike has been running pretty good (despite running a little rich - but that was solved). The other day I was out for a ride and all seemed well until after hitting highway speeds the bike began to struggle, hesitate and backfire. I swapped the plugs but that didn't solve the issue.

I checked compression (all good), checked spark (all good), pulled the carbs and cleaned everything, checked air filter and even auto adjusted the cam chain tensioner according the the clymer manual.

Now, when I kick the bike over it won't start and it produces black smoke from the left pipe (shifter side) followed by a nice big backfire and flame. Nothing from the right side, at all.

Any ideas? I was told to check the points but I'm still getting a good spark across all plugs.

ps sorry for the long explanation, I just wanted to make sure I provided as much info as possible.

Thanks,

Well check the points.
Steve

I had a kz900 with points. Was going on trip to Niagara Falls and figured to avoid the walk if shame I'd put new points in before I left. Bike ran great until about 20 miles from falls. Brand new condenser went bad. From your description I'd about guarantee it's points or condenser.. I wound up putting old set on after arriving home backfiring and top speed of 55 whole way home. If it winds up being points and condensers I'd consider putting a Dyna S ignition on it.

You will get good spark because your not firing under engine pressure. Spark on mine looked great to.. Bad condenser..

Sorry this is such a late reply.. between waiting for parts and traveling, I haven't had much of a chance to finish the repair.

I finally had some time and I installed a Dyna S ignition and although the bike fires up beautifully, I'm still experiencing the same problem.. low power, hesitation and the inability to get up to higher RPMs. if I try to crack the throttle, after I let off I get a backfire from the left pipe.

Any thoughts?

Thanks,

Is the advancer stuck in closed (idle) position, or possibly re-installed 180° out ?

Good Fortune!

I'll jump in here and follow along. My 79/650B3 just started doing the same thing last week, Although she fires up and revs all day long - that is until I put her in gear and start rolling it stutters and doesn't want to find power/backfires. My initial thought is the timing advancer as Patton pointed out. And since I never pulled it out to clean and lube, will start there.

The other thing I noticed were my plugs went black/fouled and I could smell a rich fuel mix - so something tells me there isn't enough juice getting to the spark plugs under load. From what I know and what information is in the FSM: the timing advancer is based on "speed"... (please correct me here). I am also looking to replace the 36 year old coils and not wait for failure but keep the points. If the timing advancer checks out I will order coils and take it from there.

Thanks for the response, guys.

The timing advancer is moving freely and everything seems to be installed correctly. My original problem is still the same, this issue came out of no where. The bike was running great and during a ride, after hitting highway speeds it started to behave this way. It was thought that my points/condensers were bad, so I swapped for the Dyna...unfortunately, I'm back at square one.

My coils are Dyna as well, they were installed last summer by a local shop. After LineArtist's comment, I wonder if that's where the fault lies? Do you have any advice on how to test my coils?

Thanks,

Depending which Dyna coil you have (5 or 3 ohms), you can test the coil with a multimeter set at Ohms using the leads/connection found under the tank. My 79/650B3 wants 3.2-4.8 Ohms for the ignition system. That's a broad range. New coils are light years better made than in the 70's but they are subject to the same problems caused by heat. I test my coils with them off the bike and apply a small amount of heat gun heat to the surface that normally faces the engine. If the Ohms drop there might be a crack in the case casing the winding to generate less current.

I'm asking several people about coils these days but 3 ohms Dyna coils are not recommended for a points ignition (you want the 5 ohm coils). And for the Dyna S ignition the 3 ohms are recommended - but I don't know why the 5 ohms are not (maybe someone can provide the reason).

Depending on your bike, my KZ and other 650's came stock with 4.0 ohm coils (someone please verify this statement).

I posted here a few days ago to diagnose my problem:

Check the air box, sometimes a work rag or paper towel gets in there, sometimes a mouse - make sure it's clear. Then clean and gap the plugs and turn her over... Sounds like she isn't getting enough air - also check compression.

I'm sorry...sometimes I have to chuckle to myself when I read about all these problems everyone has....
I understand that many here do not have as much experience in trouble shooting as others do but....it sounds like a simple fuel flow issue.
As in very little.... super lean with an open throttle setting.
Think simple.
Even though I think you went the wrong way from the get go.... if you've done all this other stuff, as previously described.. what ever that is left over, regardless of how improbable it seems to you, must be the truth.

IMHO: Fuel mixture is not getting into the engine off idle or very slow speed... or roaring in.

Have you looked at the spark plugs to see if they are black and wet or very light colored and dry?
Have you checked to see if you have a good fuel stream flow from the tank to the fuel lines, and on to the carbs?
Have you even looked to see where the fuel level is in the float bowls?
Have you had the carbs off and looked at the insides, checking the needle and seat for debris holding the floats up and needles closed?
Have you or anyone else "cleaned them" recently and possibly messed that up?

All this should be "Trouble Shooting 101" stuff...

MaxKZ wrote: ... issue came out of no where. The bike was running great and during a ride, after hitting highway speeds it started to behave this way....

Fuel starvation may result from a clogged air vent in the fuel tank cap.
Could rule this out by test riding with the fuel cap ajar (loose and not snapped down), which assures more than ample venting.

Fuel starvation could also result from clogged screens on the petcock tube located inside the tank, or crud inside the petcock mechanism.

Which type petcock is fitted -- manual operated or vacuum operated?

Good Fortune!

Thanks Patton, I'll check that tonight! I believe the petcock is manual.