Stock jet sizes for BS38 on a 76 KZ750 Twin

My guess would be 135 as a starting point, but I never tried running open pipes so it's just a guess. As for needle position. not sure on that. Start at the middle and then shift one slot lower (richer) and see if it runs better or worse.

I Have the 79 kz750 BS38's carbs/bike and doing same jets now also...50/135

so just to be sure there are only 2 jets..main/pilot in the carbs correct?

im doing the 50 pilot now and its great! but the 135 i got from Z1 is way to large for the main that goes in the bottom under the screw...the one in there is very small in size...its a 120 so i drilled it out just a tad...but now its to large..
i need Z1 to make things right with a reship or something..

just having an issue with how do u adjust the clip? where is it located?

i do agree the 50 pilot is great..
the 135 i cant speak on yet

Good luck bud...

dont want to jack this thread but...

i just spoke with Z1 due to the wrong main jet they sent me...
and they informed me that my 79 kz750 has keihn carbs...and thats why the main didnt fit??

but the pics above is the float bowl and pilot jet just like mine..arent the above mikuni?


this is my main jet...keihn...and i was told there is primary and secondary in there...but i only see the main and pilot in the bowl

The stock '79 750 definitely comes with Mikuni BS-38. And they use a very tiny size main jet that almost nobody stocks.



The main jets are this size:

N100606-SIZE



and I think you can get them here:

www.allensperformance.co.uk/mikjets.html

If you have Kehnin carbs, I am not sure what jets are in it.

Gotta go with Bountyhunter on that one. Your carbs should be Mikunis. You have the wrong type jet. I decided to try the 130 so I don't have to drill mine out. I'm hoping to adjust the needle clip to compensate for not going up any bigger on the main jet. As for the location of the clip on the needle... pull the top lids off your carbs, remove the diaphram carefully. Turn it upside down and the plastic disc and the needle will fall out. You'll see the circlip on the needle (most likely in the middle slot).
By the way, I ordered my jets from Niche Cycle Supply. Search for N100.606. It will show as a "pilot" jet but it's the right one. They have all different sizes including the 140 that look exactly like the picture Bountyhunter posted below.

bgmrc wrote: dont want to jack this thread but...

i just spoke with Z1 due to the wrong main jet they sent me...
and they informed me that my 79 kz750 has keihn carbs...and thats why the main didnt fit??

but the pics above is the float bowl and pilot jet just like mine..arent the above mikuni?


this is my main jet...keihn...and i was told there is primary and secondary in there...but i only see the main and pilot in the bowl

Attachment Z1E_0796s_small.jpg not found

Maybe you could post a picture of the carbs so we could see if they are Mikunis or not?

btkz650 wrote: Gotta go with Bountyhunter on that one. Your carbs should be Mikunis. You have the wrong type jet. I decided to try the 130 so I don't have to drill mine out. I'm hoping to adjust the needle clip to compensate for not going up any bigger on the main jet.

Needle clip does not compensate for main jet size. The main jet defines running at 3/4 to full throtttle where the float is fully up and the needle is out of the way. Needle position does affect throttle response in the "mid range" of throttle opening, but it won't fix a main jet problem. The tune sites I read say you always set the main jet FIRST and then work back to needles and pilot jets.

ill take a pic...
im sure it say what they are right on em also...


that looks exactly like the jet i need!!!

thank big time everyone!!

**yes they say mikuni right in the top..
and thats the jets that fit under the bowl..
i need a 135 of that...now to get it??!!

thanx again!

thanx for the help with the clip position...i had the top apart last weekend to see whats up and did not put it together in my mind...so i just left it alone..but the right carb seemed to be set different then the other..lil higher when compaied to the other...

now ill make sure..

thanx

Z1 made things right for me! just FYI if anyone needs the Main jet in the future...
sent me replacemnt for free..
Nice work Z1!!!

Got my new jets in today. 50 pilot and 130 main. Fired her up and she smoked like a chimney (black smoke). Did a compression test and it read 90. I don't know if that's good or bad. I haven't checked the valve clearances yet. I'm hoping that's it.

btkz650 wrote: Got my new jets in today. 50 pilot and 130 main. Fired her up and she smoked like a chimney (black smoke). Did a compression test and it read 90. I don't know if that's good or bad. I haven't checked the valve clearances yet. I'm hoping that's it.

90 compression is terrible. Stock is 155 and service limit is about 115 with not more than about 15 variance side to side. Check valve clearances. Spec is .002" - .004" but up to .006" is serviceable.