Jetting Help Keihin CV34 Carburetors

Wanted to get some input on jetting.

Bike is a 1982 kz750N1 Spectre, stock airbox with K&N filter, vance and hines 4 into 1 pipe. Here's whats in the carbs (Keihin CV34) when I got the bike:

Secondary Main - 90
Main - 65
Jet Needle - N10A
Pilot - 35

I was thinking 122 or 125 secondary main, 65 or 68 main, stock needles and pilots.

Any help would be appreciated.

Hi there almarconi

I have a 1980 kz750E1 4 cylinder with Keihin CV34 carbs. I have to admit I dont know anything about Spectres. Stock jets in my E1 were:
Secondary main 125
Primary main 62.
Pilot 35 ... I think

Keihin jets only cost about $2 each from Z1 Enterprises so experimintation is cheap if you feel the need to try larger jets.
Which brings me to the question - why do you think you need larger jets ?

Which brings me to the question - why do you think you need larger jets ?

I took the bike in on trade so I have very little history on it. I know the exhaust is not stock. The PO stated that the bike was very cold natured. When I tried starting the bike, it ran like crap. Choke seemed to not make any difference. I took the carbs apart and the pilot jets were clogged. No surprise there. The choke mechanism was also not working properly. Made a note of the jets in the carbs. The PO told me "his mechanic" rejetted the carbs to compensate for the 4 into 1 exhaust. According to my research, the jets that are in there are stock. The airbox is stock but I am going to install a K&N filter in the box. Since these bikes were jetted pretty lean from the factory, I wanted to rejet for the increased exhaust and intake flow.

Sounds like a plan. Have fun playing with larger jets.

When I got my 750 some years back I had to clean the carbs 3 times and that included poking every hole with a wire or a nylon bristle, spraying liberally with carb cleaner and using compressed air at the local gas station to blow them out. The stuff in a can did'nt have enough power. It took all that before I got them right. I also gave up on so called "mechanics".

Good luck

I received jets today from Z1 enterprises. Excellent service and pricing from them. I'm going to try 110 for the secondary main and 68 for the primary main. Stock needles and pilots. I also ordered 105's and 115's so I'll see how the bike runs.

Great
Let us all know how it works out. I know next to nothing about Spectres and there is very little information here.

Good Luck

Wanted to give a quick update. Installed the 110 sec main, 68 main, stock needle position, #35 pilots, initial mixture screw setting 2 turns out.

Engine starts very easily with full choke, comes off choke within a couple minutes. Base idle is around 1k rpm, valve are noisy (clearance set to loose side of tolerance). Try to rev engine, will not rev above 5k rpm, engine getting hot.

Opened mixture screws to 3 turns out, adjusted manual cam chain tensioner a little looser, engine revs to 8k now but rpms hang returning to idle.

Open mixture screws to 4 turns out, seems to idle better, revs up, revs drop but still seems to hang a a little. I still think I am lean on the pilot circuit.

I am going to go up one size on the pilot to a #38 and will try again. Once I can get it to idle reliably, I will sync the carbs and go for a ride.

Will not be able to evaluate the mains until I can ride the bike. Well at least I have been able to get the bike started, so I am making some progress.

Sounds like you're making progress.
I had a look at the parts diagrams at kawasaki.com and see that there are some similarities between your carbs and mine but also some diffferences - mostly the sizes of the 2secondary main and the needle on the end of the slide. Which means treat anything I say with a grain of salt

Anybody else out there with a 750 Spectre ?

The mixture screw you turned out should only effect the idle mix and turning out lets more air in. Spark plug colour should be a good indicator of whether lean or rich and should give you good informatio on whats happening and next steps

If rpms are slow to come down it usually means either a sticking throttle cable or an air leak around the carbs ( boots cracked or vacuum caps cracked or missing)

You sound like there is a manifold vacuum leak, air screws are not meant to be open that far. If pilot's are to small you might be at 2 1/2 turn's. I'd be checking throughly for vacuum leaks as you have been into the carb's. Of course don't over look the mechanical, even compression is very important.