1976 KZ750B Mikuni jets

Ok, so I'll be rebuilding the original Mikuni carbs on a 1976 KZ750B project I acquired. Bike has a 2into1 header with a wide open chrome pipe as a muffler. Yup, it's loud. Also has pod air filters. I got K&L rebuild kits that come with 125 & 45 jets and a needle with 5 slots. I know opinions will vary but can someone suggest, at least a good ballpark, the following?

What size jets?
Needle position?
Air mixture turns?

Oh, and I'm in Phoenix, maybe 1400 elevation.

Thanks!!

Start with 50 on the pilots and probably 130 - 135 ballpark for mains. The stock needle clip position is #3 (center) but the needles in the kits usually don't match the stock ones. Hold them up side by side and check. If they are like the ones on the 79 750 twin, the slots are about .020" apart so you can get a "1/2 slot" adjustment" with a 4-40 stainless flat washer that's about .010" thick.

The pilot jet screws on the side of the carbs run about 2T out from all the way in.

I recommend buying a used air box it will probably save a lot of wasted time.

If you have the carbs torn down, check the diaphragms carefully for slits or air leaks. You have to hold them up to a light to see them. They will screw everything up.

find out whats in there now.

how does the bike run currently? if you dont have any idle issues i would leave the idle jet alone size wise. are you having flat spots in your power curve? if so, up the main jet to what you feel is right. the needle jet is going to take some playing around with. trial and error.

Bikes does not run well right now. Idles OK but not super smooth. Initial acceleration is the main issue. Really bogs at first but once I get it to higher RPM it settles in, until I need to back off the throttle again to change gears. Bike had been sitting for about a year so I'm sure the carbs need a good cleaning. I might find that the jets in it right now are the right size but I have no idea until I tear them apart, clean it up, and try with carbs I know are clean.

As provided in the FSM, here's an illustration of the pilot circuit in the Mikuni 38mm cv carb.





When cleaning the carb, would assure that orifices at top of carb bore are perfectly clean and clear so that the pilot circuit mixture can pass into the carb bore.

May spray carb cleaner through the various passageways to watch it exit through the orifices and into the bore.

The #8 pilot jet and #1 pilot air jet must be perfectly clean and clear.
And pointed tip of the #3 pilot screw must be undamaged and in serviceable condition.

An "as-new" pilot circuit should help enable a steady idle and strong pull-away from idle.

Memo -- This post is a revision, with thanks to 80B4 for reminding that BS38 Mikuni carbs are different from other Mikuni carbs.

Good Fortune!

The float bowl gasket is very important, it seals the main jet and pilot jet passages.

Ok, carbs had stock jets so even if the carbs were clean, the bike would be running lean. Where can I get the right jets for this carb, aren't they a little different than standard Mikunis?

Steve AZ wrote: Ok, carbs had stock jets so even if the carbs were clean, the bike would be running lean. Where can I get the right jets for this carb, aren't they a little different than standard Mikunis?

I believe the pilot jets should be BS30-96 types which are widely available.

The mains are less available but one place is:

fourth item down:
www.allensperformance.co.uk/mikjets.html

Maybe somebody knows another source, that's the only one I have.

Check out "jets r us"
www.jetsrus.com/