Carbs popping on acceleration, etc. 83 KZ750 Twin

Ok, I have an '83 KZ750 twin. I just need to verify some things before I go digging in to this.

It will only idle with full choke on after warming up. If I spray carb cleaner around the manifold it will sputter and die. If I use the throttle to rev it and hold it at 3k rpms, push in the choke, rev it more, it will pop through the carbs. So this means I most likely have a lean condition? And probably leaking air around the manifold?

Other possibilities?

Thanks all.
Mark

sharkmonkey wrote: ............... If I spray carb cleaner around the manifold it will sputter and die. ...................

No doubt about it - the carb holders are leaking and should be replaced. That needs to be done BEFORE fiddling around trying to tune the carbs. Otherwise you not only are wasting your time but you may mess up what are already perfectly tuned carbs that cannot operate properly until the leak is eliminated. Ed

Definitely check the things that affect the carbs before blaming them.
The carb holders (manifolds) are crucial. Even a tiny leak can cause mixture and running problems. Also be sure that the carb to air box tubes are flexible and well sealed. Be sure that the air filter is clean and properly installed, and even the air box lid itself needs to be properly in place.
You should also insure that the valve clearances are within spec, as badly out of adjustment valves can give the carbs confusing vacuum signals. Clean fuel is also important.

Good information. Unfortunately the previous owner cut out the air box. I would LOVE to find an original air box and carb to air box tubes.

I guess you will be using individual filters. One of the 750 twin guys here can get you started on the right jetting path to get it running better. Running without filters and with stock jetting will give you a very lean mixture.

Those use 34 mm cv carbs. It is important to get pod filters that do not block the ports on the bell mouth of the carb. Cheap pods usually block these

Will the carb holder manifolds from a KZ750 four fit the KZ750 twin?

Nope. To my knowledge no other bikes are similar. You'll probably have to hunt around for a better used pair. Then a very light bead of Honda sealant around the rim on the block so you get a good seal. There are aftermarket snorkels for the airbox but since you don't have one... If you do score one of those though keep it in mind.

the 81+ 750 twins have a separate carb setup specific to those years. Parts will be very hard to find as they were made in limited numbers. If you're desperate you could get brand new K&L carb holders for the 76-80 750 twin and run the early model BS38 carbs.

It make be possible to retro fit another carb boot by filing out the bolt holes. I have done this on a KZ400, but it will take some guess work to see what might fit.

You might message Mike and ask him what will fit.
Steve
jetsrus.com/mounting_flanges/mounting_flanges.html

I took the carb holders to the parts shop and they were impressed by the good condition they are in. So we used some sealer and put it back together. I also sprayed carb cleaner all through the carbs. Now I can't accelerate at all! It kills the engine when accelerating.

It could be a timing issue. Check your advancer to see if it’s rusty