Mid range sucks

My slow acceleration (or lean as my tuning guide calls it) is good, starting from 2000rpm and accelerating up 1000rpm at a time to 50% full rpm range, no hesitation or surging. Mid range sucks, starting from 2000rpm, give her half throttle and she "sucks" for something, gas or air I don't know. Heavy acceleration is fine, full throttle from 2000rpm, slight hesitation through the mid then accelerates fine up to red line. Tried moving the pin e-clips to a richer setting (3 to 4), same problem. Try leaner maybe???

What kind of carbs? CV or VM?
Steve

Mikuni Slide carbs on '78kz650sr

Are you using pod air filters? Ed

Not anymore. Two owners ago it had pods, Then the guy I bought it off put the original air box back on (which I prefer looks wise) but didn't set the carbs back to factory. All the jets should be right now.

Seems like the problem is in the transition from the pilot jet to the jet needle. I wonder if the PO changed the needles and the taper is too abrupt for the stock setup?

That's possible, the needles are the only thing that I haven't swapped out completely.

mackinnon0909 wrote: Not anymore. Two owners ago it had pods, Then the guy I bought it off put the original air box back on (which I prefer looks wise) but didn't set the carbs back to factory. All the jets should be right now.

Good!
The 1978 KZ650-SR came in two flavors – the KZ650-D1 and the KZ650-D1A. The D1 came with the Mikuni VM24SS carbs (24mm) and the D1A came with the Mikuni VM22SS carbs (22mm). The first image below will enable you to positively identify which carbs your bike has. It shows the extra orifice that the VM22SS carbs have and that the VM24SS carbs do not have.

The second image below shows the stock carb jetting data for the 1978 KZ650-D1 and KZ650-D1A carbs. This assumes your bike has the stock carbs without the accelerator pump. Ed

Brass one I just removed and is stamped Y63, steel one was in a bag of spares that came with the bike and has no markings. steel one is a smaller diameter at the tip. Carbs are vm24ss.

Raising the e-clip will lower the needle and lean out the mixture and visaversa.
You might want to check your needle jet.

According to the chart the nettle clip should be in the 4th position (not the 3rd) from the factory (like shown on the brass nettle).... whats the main jet if pods were installed it could be too big ..... chart calls for a 102.5 for a stock exhaust and air box. Mine needs at least 4,000 or just over for it to really start getting on the pipe..... might be a little of what your feeling.

Swapped out the needles and moved the e-clips to the 2nd position and she seems to be running correctly now, thanks all for your ideas and tips! Now just need to figure out what happened to all my lights...