KZ750 CSR: No start and backfiring

Hello everyone. Its spring now and everything that has gone wrong (which is a lot) has been corrected as far as I know and I need to get out and RIDE! Hopefully you guys and help me figure out whats going on.

So, the problem is that the bike WILL NOT START. Its a 1982 KZ750 CSR twin. Its got electronic ignition as standard and it seems to be working fine. I have checked spark and its a decent blue one on both sides. Advancer is lubed and installed correctly. Compression is stong (160 lbs both sides) and valves have recently been adjusted to spec. I have ridden with the new valve job so that does not seem to be an issue. CARBS. Boots are fine and dont seem to be leaking. Bench synched and very clean. Float level set and not leaking. Everything SEEMS to be perfectly fine.

When I try to start, I get a really good crank but backfiring through the exhaust. Plugs are WET with fuel. No work was done with the cams so timing should still be set and good to go. And thats it. Nothing else. Im just stuck with a non running, seems-to-be-fine sort of deal.

What do you think could be the issue. I am sure I left some things out so feel free to ask. Thanks

bpchura wrote: Hello everyone. Its spring now and everything that has gone wrong (which is a lot) has been corrected as far as I know and I need to get out and RIDE! Hopefully you guys and help me figure out whats going on.

So, the problem is that the bike WILL NOT START. Its a 1982 KZ750 CSR twin. Its got electronic ignition as standard and it seems to be working fine. I have checked spark and its a decent blue one on both sides. Advancer is lubed and installed correctly. Compression is stong (160 lbs both sides) and valves have recently been adjusted to spec. I have ridden with the new valve job so that does not seem to be an issue. CARBS. Boots are fine and dont seem to be leaking. Bench synched and very clean. Float level set and not leaking. Everything SEEMS to be perfectly fine.

When I try to start, I get a really good crank but backfiring through the exhaust. Plugs are WET with fuel.

Check fuel levels with a clear tube.

bpchura wrote: . Its a 1982 KZ750 CSR twin. Its got electronic ignition as standard and it seems to be working fine. I have checked spark and its a decent blue one on both sides. Advancer is lubed and installed correctly.

I would still suspect the advancer or maybe that the timing is off. My 750 twin doesn't have elect ignition so I am not an expert on that.

Plugs are WET with fuel.

Shooting from the hip here: make sure the plug is not wet with fuel and OIL. These twins do have the valve seals go bad and the oil can run down from the valve shaft through the opening and onto the plug (guess how I learned about that).

It fouls the plug which on a twin means NEITHER plug can fire (they are wired in series) so they don't fire and the cylinders flood with gas.

Sometimes the plug would clear and you hear a loud POP backfire but it doesn't start. Made mine and absolute beech to try to start, constantly fouled plugs.

Something to check.

Levels are good. About a half inch below the carb body. Measured the gap also on the float. 18mm

I am sure that it is fuel. Actually had that happen a few months ago. Got to change out those seals. SO fun

bpchura wrote: Levels are good. About a half inch below the carb body. Measured the gap also on the float. 18mm

Measuring the mechanical gap won't work. Not sure what carbs yours has: on the BS-38, the fuel level is supposed to be 4.5mm down from the lower edge of the carb's upper.

It couldn't be too far off. I just changed it less than a mm. Would that cause it to flood immediately?

Tried using starting fluid spray?

Good Fortune!

I sprayed some carb cleaner fluid which usually ignites into the air box while cranking. There wasn't any response. No pop or anything.

Could it be something with the ignition? Shouldn't it pop or start up for a sec with some carb cleaner in the air box? This model does have the electronic ignition so there is no way to set it and I didn't mess with anything before it ran last. I changed out the coil with one I got online from a salvage shop that looks a lot better than the one I have. I tried to check resistance on both of them but the multimeter was showing some pretty whack readings and I don't think i was doing it correctly. But both cylinders give a nice spark and there should be no reason why it wouldn't be firing correctly.

bpchura wrote: I changed out the coil with one I got online from a salvage shop.

Same thing I did, gave me a nice batch of misery. Z1 sells a good replacement coil for $36.

I don't under stand this:

It couldn't be too far off. I just changed it less than a mm. Would that cause it to flood immediately?

Are you checking with a clear tube to actually read the fuel level or just measuring the float> If not using clear tube, it could be way off. On my BS-38, the spec is 5.5mm +/- 1mm so a 1 mm change is a big deal.

Are you saying that you are seeing flooding?

If so, it will never start.