KZ 750h Runs perfectly for the first hour, then...

Happy 4th everyone! I need some troubleshooting insight. I purchased this bike in March. 1980 750 LTD h has been a work in progress. New chain, sprockets, clean tank, fuel filter, rebuilt petcock, plugs, all filters synthetic oil. Ignition wires look fairly new. I brought bike in to have carbs cleaned and jetted. Bike starts without choke and pulls like a freight train up toward 9K. What has been happening pre and post carb work is that after an hour and a half or so of riding around, back-roads or highway or city streets, the bike will start hesitating, bucking, losing power and exhaust smells like gas. The mechanic also checked the carb boots. Bike has original air box. I will be bringing the bike back this week. Any insights? Sincere thanks for your help.

Assuming that the charging system is ok and the battery is retaining charge it sounds like it could be the ignition system or the power to it breaking down with the smell of unburnt fuel in the pipe.
Usual suspects to check first are the ign coils , condensers or pulsar coils and CDI if not on points .
These can develop intermittent faults or shorts when hot and create the symptoms you describe.
This is best done by substitution with components which are known to be ok.
Obviously it will be best to check all the electrical system for bad or broken connections etc .

The problem could be the ignition coils as they can get hot & fail under load. A simple test is to ride the bike at highway speeds, then stop & feel the coils --- press hard with your fingers: they should be warm, not hot. Mine were getting very hot, so I installed the green Dyna 3.0 ohm coils & spark plug wire set from Z1Enterprises.com. The grey 2.2 ohm are supposed to be a better match for the stock electronic ignition, but I got the green in case I had to get the Dyna S.

Also, you could try redoing the spark plug wire connections. Unscrew the ribbed compression boots at the coils to redo those connections. If there's the white crusty oxidation, nip off the ends of the wires a tad. Or go ahead & get new. I used dielectric grease on the connections.

So you're taking it to a shop. Did they adjust the valves? If the didn't even check them, I'd be wondering what other routine maintenance they didn't do.
Steve

What was your finding?? I am having the same problem.

If not already done, clear-tube testing should help determine whether fuel levels are within spec.

Too high fuel levels may allow seemingly good performance until the plugs load up and combustion gets progressively weaker due to an overly rich fuel mixture.

After correcting the mixture, would also install brand new spark plugs.

Good Fortune!

The clear tube test is critical, as is all the other various maintenance tasks as outlined in the factory service manual. Valve adjustment being at the top since so many people neglect this task until the engine misbehaves and burns it's valves and seats.

Was going to suggest coils till I noticed this is 9 months old and 8 months ago he figured it out as bad coils :laugh: .... then 2 months ago he put it up for sale as a perfect running bike so the coils musta helped.