TOPIC:

I'm experiencing a very odd problem with my 1978 KZ650:

About 2 weeks ago, I started experiencing what I thought to be a lean fuel condition caused by a faulty petcock. The petcock was replaced yesterday with a brand new manual unit from Z1 Enterprises. Needless to say, that did not resolve the issue.

Here's what the bike is doing:

The bike cold starts fine when choked - normally when cold started the idle would be high, and it would require fine choke lever adjustments to avoid a very high idle condition. Now the idle is much lower, even under full choke conditions. Even under the cold start conditions, the bike seems fuel lean.

The bike now never seems to reach a smooth running condition after warm-up. Once warm, the engine will rev, but it seems starved of fuel and not normally as responsive to throttle input - nor will it reach the higher RPMs when revved without bogging. I can keeped the bike revved fairly high (still seems lean), but when I start driving from 1st gear it just falls on its face. It takes everything that its got to take off.

Then, once riding, the bike seems to surge. You must use hard accelleration to even begin to move, and its seems to cut in and out, sometimes beginning to accellerate correctly (seeming like its finally getting enough fuel).

It spits, and sputters, and surges, then without warning - it runs like a friggin' top again. It's so odd - it seems like if I really get on it, it just works itself out and runs great. Here's the clencher though: after running great for 15-30 minutes, it starts right back with the same problems. Lean, no power, cuts in and out, sputters, backfires a little, and just falls on its face.

PLEASE HELP!!!

If I can't get this resolved, the bike is going up for sale. This bike is MINT, and has always ran flawlessly like a new bike until the little issue came up. I even tried Seafoam and new gas, even though I know it didn't need it.

I would check out the ignition system first.
Condition of plugs, coils and wires
Primary wiring to the coils.
Points for gap and burns if you still have original igniton.
Timing advancer for smoothness while turning and/or sticking.
And all wiring.
Ride safe,
Les

The Milkman wrote:

I would check out the ignition system first.
Condition of plugs, coils and wires
Primary wiring to the coils.
Points for gap and burns if you still have original igniton.
Timing advancer for smoothness while turning and/or sticking.
And all wiring.
Ride safe,
Les

So, this intermittent problem could be ignition related? I'm totally lost now. Damn that sucks!

del

The starting and idle is normal. The idle will be high unless you adjust the choke lever down just a tad right after starting. Your real problem them becomes that the bike "falls on its face" when you start off. Does the bike have pilot mixture screws or air screws? Sounds like the pilot system is not adjusted properly as in, not enough gas. The surging is most like a clog or kinked gas line or the carbs just need to be properly cleaned.

I just seems odd because this bike ran like a top, and I mean perfectly - then one day, it just started with this crap.

The fuel filter/petcock is new. The tank is spotless. The bike was very well maintained and this just came from nowhere.

By any chance did you fuel up at a different gas station and just get a load of bad gas???

chopstar wrote:

I just seems odd because this bike ran like a top, and I mean perfectly - then one day, it just started with this crap.

The fuel filter/petcock is new. The tank is spotless. The bike was very well maintained and this just came from nowhere.

Believe it or not I just typed a long reply and lost it due to hitting the "back" button accidentally. Arg!

So to be extremely brief, please try the things that people here suggested and report back in this thread so we can keep track. What has been suggested so far if I am correct is:
1.) Run the bike with an open gas cap (to verify the cap vent works)
2.) Check your carb pilot screws according to your manual (make sure they have not vibrated out or something)
3.) Check the color of the plugs after the failure (watch for white=lean)
4.) Check the ignition settings in general according to the manual (points settings, auto-advancer lubrication, timing)
5.) My addition, check for newly cracked carb manifolds.
6.) Also, you might want to check and make sure your floats are workign correctly if the above doesn't help...

Please let us know the results...

I really appreciate all of the help. I'll go through the manual tonight. Check the carb settings. Check the tank vent. Check everything that I can. Hopefully I'll get lucky. If not, she'll be up on the sales block - I just don't have the time anymore.

del

The bike has the petcock (brand new manual unit) fuel filter only. Gas was completely new yesterday - drained old before petcock replacement. Plus I added Seafoam. Bike exhibited this condition before and after petcock/fuel change.

I once had a 900 that ran like that after a jet had vibrated loose. Screwed it back in and she ran fine. Hope you get so lucky.