Jet kit needed for KZ750T... but which one?

Well, today I started the 750 for the first time this year. It took FOR-BLOODY-EVER. Battery was flat, and I kicked myself breathless, but I DID get it started!

It's never run right while in my care. In my defense, even on the first day I got it home it ran poorly, thanks to some previous issues. Primary among those is the fact that the PO whacked the mufflers AND crossover off and welded on THREE FEET of 2" exhaust pipe, Looks bad, runs bad, but for right now, I don't have the money to get a new exhaust (I want a MAC 2-1, but can't afford it). Also, the airbox boots are cracked, but I think I've found a remedy for that. As of right now, they're leaking like sieves. So until further notice, the intake and exhaust have to stay how they are.

So I can get the bike to start and run, and after some time tooling up and down the road to warm it up, I was even able to get it to run at idle, but only just. A lot of burbling and stumbling, falling down just off-idle, and a LOT of cracking and backfiring. The mix screws are FOUR turns out, which points to primary jets being too small. Also, when I can get it up around 5k, it 'hunts', not holding a steady RPM, and additional throttle causes it to stumble unless I creep up on it, which indicates too-small mains.

MikesXS.net has a BS34 dyno jet kit which comes with two pilots, FOUR mains, two adjustable-height needles, and a drill bit, for $30.50. It's anyone's guess what the jet sizes are; they're not listed, although I could probably write and ask.

Contrastingly, a company called 6Sigma Racing sells CUSTOM jet kits on the 'bay for $49.50, and it comes with one set each of pilots and mains, plus adjustable needles and a bunch of info about mods and specs. The big thing, though, is that they custom-select the jet sizes for your application (intake, exhaust, filters, engine mods, etc) and will work with you after the sale to customize the set until it's running to your satisfaction.

My question is, which one to go with? The skinflint in me says to go with Mike's and muddle through jet selection myself; the part of me that knows my limitations says to go with the 6sig and 'set it n forget it'. What's YOUR recommendation?

You will be wasting your time and money trying to rejet if you have leaky carb holders. They should be checked and if necessary replaced first.

Here's how to test them for leaks:

Make sure the vacuum caps are tight on the carb holder nipples.

Warm the engine up to normal operating temperature.

Temporarily set the idle as low as possible without stalling the engine. It should be down below 1000 rpm. The lower the better because when it is set low the carb slides are closed (or nearly closed) and this raises the vacuum level in the carb holders. The combination of the increased carb holder vacuum level and the very low idle amplifies the effect of the leak test.

Once the idle is set low, spray carb cleaner around each of the carb holders where they bolt to the cylinder head and where the carbs attach to them. If there are leaks, the vacuum in the carb holders will suck the carb cleaner in and this will affect the idle. It may cause the engine to stall. If the leaks are at the carb holder / cylinder head mating surface you need to replace the holders. If the leak is where the carbs attach to the holders you may be able to tighten the clamps enough to seal the leak. Some folks use starter fluid or other substances for the test, but carb cleaner works best as it doesn’t evaporate too quickly like ether and leaves no residue on the engine like WD40.

If you do need new holders just bite the bullet and buy them. Trying to seal things up with some kind of sealant or goop will only lead to frustration as it will at best only last a short time. Ed

Two issues with that, and the rest I can pretty well pass up:
1) My carb boots have no vac ports, nipples, or caps. B model twins had them, the M and K did not.
2) I noted the AIRBOX boots had cracks, not the carb boots.

So yeah, no carb-to-engine leaks, that business is tight.

Also, as I said "I was even able to get it to run at idle, but only just," not sure how I'll get it to idle below 1000. It was a trial of comedy just getting it to 'idle' at about 1500. I felt like a Hardley rider, constantly blipping the throttle to keep the poor thing from dying.

n9viw wrote: MikesXS.net has a BS34 dyno jet kit which comes with two pilots, FOUR mains, two adjustable-height needles, and a drill bit, for $30.50. It's anyone's guess what the jet sizes are; they're not listed, although I could probably write and ask.

Contrastingly, a company called 6Sigma Racing sells CUSTOM jet kits on the 'bay for $49.50, and it comes with one set each of pilots and mains, plus adjustable needles and a bunch of info about mods and specs. The big thing, though, is that they custom-select the jet sizes for your application (intake, exhaust, filters, engine mods, etc) and will work with you after the sale to customize the set until it's running to your satisfaction.

My question is, which one to go with? The skinflint in me says to go with Mike's and muddle through jet selection myself; the part of me that knows my limitations says to go with the 6sig and 'set it n forget it'. What's YOUR recommendation?

Does this year have the BS-38 carbs? That's what the 79 750 twins ran.

Anyway, with straight pipes the thing is so far off that a kit which comes with "one set each of pilots and mains" surely won't have the right jets. The pilots for the BS-38 carbs are the BS30-96 type and are readily available. I would try to get some mufflers on it, even if they are cheapos it will help it run less lean.

Got this from www.wgcarbs.com/index.php/using-joomla/e...gories/93-kz750-carb :
"For some reason, Kawasaki didn't sell a KZ750 twin model in the US in 1981. In 1982, they marketted the KZ750M1 CSR model and switched the carburetors from the BS38 assmebly that had been used on the KZ750B model family to the BS34 assembly shown above. The BS34 assembly weighs about 4 pounds while the BS38 weighs in at over 6 pounds. The BS34 assembly shares many of the internal and external parts used across the KZ line from the KZ750, GPz750, KZ1000P and all other KZ1000 models plus the KZ1100. I suspect that the move was made to standardize parts."

I am planning to buy a pair of slip-on mufflers, but need to sell some parts first. I also have to have the airbox boots off to repair them, came across some info online about using gauze and 'liquid electrical tape' (found at many auto parts stores) to repair the cracks. Don't know how long it'll last, but as these boots are unobtainable, it's worth a shot. Once that's done, if I'm still having trouble, I'll get into the jets.

Thanks, all!

Also, just noting the number-of-jets discrepancy- the 6sigma kit is supposedly tailored (by software?) to match the engine's flow characteristics. The MikesXS kit has two pilots and four mains in the KIT- that means one pilot per carb, and two mains per carb. A better chance to try a different main, but if the trouble is the pilot and you only get the one size they send (whatever it is), and it doesn't work, you're back to searching.

Why, oh why do people monkey with a system that WORKED? I understand a fellow wanting to get a certain look or sound, but when it comes at the cost of the proper operation of the machine, and creates endless future fiddling to fix the problem THEY caused, well... as the LOLcats say, "Yuor doin it rong." LOL!

Can't help much with BS-34 mine have BS-38s. I don't know what the stock jets are or if the stock needles have adjustment slots (mine do).

Just got done doing some reading over at ChopCult about this. The BS38s had adjustable needles; the Canadian BS34s did as well, but the US ones did not. Also, the taper on the US single-slot needle is different from the Canadian, so if one is to get a set of Canadian needles for a set of US BS34s, you'd have to get the needle jets (emulsifiers) to go with them.

Still trying to sell those parts, can't buy new stuff until I do... I thought Fearless Leader said the economy was improving! If so, where's all the people looking to buy my old parts? LOL.