BS38's work on a CSR engine?

I am more or less throwing a bike together from a few bikes i got on a deal. The CSR engine was the way to go as I love having a electronic ignition and not worry about the points.

I have the BS38s from a 78 KZ750 twin that had a bad engine. I have cleaned them very well and did a bench sync. Running premium gas from a clean gas source. I am asking for help because I can get it to fire and almost run but it just wont fully start. If I play with the choke it seems to have a sweet spot that it wants to run, but as soon as I touch the throttle back to nothing.

The air mix screw has been set from 2 turns out to 3 1/2 with no change in results.

Does this CSR engine kx770BE059679 need to have BS34 carbs to run? I can't think of anything that is holding the bike back from running besides a correct blend of air and fuel.

Thanks in advance.

Compression, fuel, spark are all you need.
Have you checked ....
oil in the crank case?
compression test?
nice blue spark at the plug?
If that all checks out clean and rebuild the carbs.


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Thanks for the advice and I will do a compression check, that is the one thing I have not done.

Still looking for a little more info on these two different carbs thought. the BS38s that I have look like this:



From what I can tell the bike came with carbs that looked like this:



Can I make this work with the normal jetting from the BS38s?

Thanks to wgcarbs.com for the pics

There may be problems with fitting the carb holders & airbox ducts, especially the ducts as the airboxes are different.
Performance-wise, I would think you could use the carburetors from any 750-Twin.

Did a cold compression check L125/R130. that had me smiling.

Took carbs back off again found the left carb bowl jets did have some stuff in them.

As most of the folks on here keep writing about, I put the air box back on and gave it a try. Sure enough, she fired more or less right up. I have a small shed and as it is 1 degree out today and the wind is 15 mph, that was good for me. At least now I know she runs.

So yes the KZ750M1 can run with the KZ750-B1 carbs.

After looking over the engine and feeling around, I could feel a little air rushing out of one of the cylinders while she was running. She was running really ruff and throwing blue smoke out the #1.

Ended up changing out the head and valve cover off of the blown 1978 KX engine. Took the valves off and did a okay job on the valves and lapping them. New head gasket and snugger her all up.

Turned the gas on had the choke on and hit the starter, she started up after just a few turns and what a difference. The blue smoke was gone and no longer having any other running issues.

Took her out for a little ride and wow need to rebuild the forks. I think adding another couple inches to the spacer on top will do it, along with new oil and seal kit. I am using the old CSR forks I think as they have the air caps on top. I have never opened a set of forks and not have the cap try to take my hand off. There was little or no pressure on the spring, just different I guess.