Kz750 twin

I am beyond frustration with my bike. 1977 kz750b twin. Running the stock carbs, stock jets, stock airbox, stock rubbers in good shape. Only thing not stock are some open slip on mufflers that came on the bike. Bike generally starts good and run goods, well not anymore. Bike will not restart when hot, will not reliably start when I want it to, has stranded me twice in two days. I'm about to go grab a trailer to bring it home again and it's only 20miles away. 

I'm fed up with these carbs, no matter how much I clean them, adjust them, mess with them, I can not get this bike to run reliable and it's all in the fuel delivery. I'm almost ready to scrap the thing and say good riddance. Spark, compression, valve clearance, etc are all within factory specs. 

Seems to me the only option for replacement carbs are through speedmotoco, has anyone used them on a kz750b and was it worth the investment? I generally love how this bike rides but if I can't take a 30min trip without fear of being stranded by a carb issue this thing is dead to me.

Any suggestions, experiences, or ideas? 

Not starting when hot is almost always an electrical issue. I would first suspect the battery. A dead cell will cause this problem. It may show proper voltage at rest, but under load will show a dramatic drop.
Next I would suspect the coil. When coils reach the end of life, they will often overheat and fail to provide strong reliable spark.

My bike is kick start only due to a dead starter, not sure if that would still make the battery suspect but I will check for sure.

Next, I will go through the manual and see what checks are available for the coil and do that too, wouldn't surprise me i guess, looks original. 

As a New issue, it has always started when cold, now this morning after sitting overnight it won't start and that's new, so once home in gonna check through the battery and coil. Any other ideas? Keep them coming, anything to help get past this frustration block 

A clogged tank cap vent can create a vaccum and disturb the fuel flow. 

What do your spark plugs look like?
Do they smell like gas?

A truly dead KZ starter is pretty rare, which makes me think something else is afoot.

I will be checking everything out tomorrow, I decided to step back from the bike today and start fresh tomorrow calmly instead of today while I'm frustrated.

Thanks for all the ideas so far, I will be updating with what I find along the way. 

I already tried with the gas tank cap open to see if the problem is cured and that was not the case, vent seems clear. 

And my starter is not the bad part even though I state the starter is bad. The starter  spins with power directly applied but some previous owner removed the chain between starter and starter clutch so it really doesn't do anything, just spins freely. I really don't mind the kick start so I'm not gonna approach that issue till much later down the road when doing other work inside the covers.

When the bike is running well and starting like I want it usually starts first or second kick so not an issue for me with the starter. 

So the starter motor problem is previous owner inflicted, not electrical. Many previous owners should have their toolboxes welded shut.

Stepping away when frustrated is always a money saver and sometimes prevents gushing blood and broken bones.

TexasKZ - thanks for the help so far, the previous owner was somewhat of a hack, happily would have his toolbox welded if I could have lol. 

I'll start fresh tomorrow morning and go through this methoidcally. looking forward to getting some testing done and reporting back so i can solve this. Thanks again. 

Alright so, I started by checking voltage and load testing my battery, the battery checks out fine.

Spark plugs didn't look great, so i put a fresher set in for the continued testing. Plugs I pulled out .....
 

I then moved onto testing the coil per my sevice manual. The manual says to set my meter to rx100 for the primary but my meter only goes to 2k ohm. When I tested that I got .002 for my range
 

I then tested across the secondary using the plug leads and my reader didn't seem to show anything.....

 


So should I assume the coil is bad even though it started a few times before i began my testing. It still wasnt a reliable start and shut off at idle a few times and still struggled to restart when hot 


Now for a twist, after reassembly the bike starts easy. Gonna go out in a few and run it till the motor is hot and park it and try the restart

Your primary reading is 2 Ohms ( it's on the 2k scale so you need to move the decimal point) as the meter only has a 2k scale it can't measure he secondary at 10k

Awesome, thank you for clearing that up, I will look for another meter for the secondary, I was getting between .003 and .004 after I checked again, so I'll assume that's OK now that I understand the meter better