TOPIC:

Hello! So, I'm still very new at bikes. I've been learning off my 1982 KZ750 CSR. I wanted to replace the airbox (because it was damaged), and because of how scarce my model bike is, could not find a replacement. So, my option was to add pod filters instead. The problem with that, is the stock carbs are Mikuni bs34 CV, which are designed to use a very steady, low turbulent air flow. I have a pair of new Mikuni VM28 Roundslide carbs; would those be an adaquite substitute? I'd probably need to swap the jets out for larger ones, but I'm okay with that. If thesr are suitable, is there anything i should take into consideration, or information I shoukd know?

It might be easier to fix the airbox.

Are the 28s properly spaced for your engine? Will you be able to find intake manifolds to fit? Are they set up for the same number of throttle cables? Some bikes use one, others use two (one open, one close). Is the fuel inlet on the carbs close to the same size as the fuel outlet on the tank?

Agree on fixing the airbox. If you insist on pods a Dynojet kit and some quality pods, not some dimestore Emgo junkers, would make for a good path forward.

I'm with the others - stick with a stock air box if at all possible, and avoid cheap-o pod filters always!

I can't say for sure, as I generally play with KZ1000/1100J, LTD, CSR, and GPz1100's, but I think an air box from an 82 and up 750 LTD or 750 Spectre will fit your bike...can't be that hard to find one of those for cheap on evil-bay? Any bike parts salvage yards near where you live?

Otherwise, and last resort, you could try the slide carbs, or the BS34's with a Dynojet stage 3 kit and the K&N filters Dynojet recommends...

If you go with smooth bore (slide) carbs, you'll need a push / pull throttle assembly also! Otherwise operating slide carbs with a single cable set-up is extremely dangerous! The slides could stick open (stuck throttle) very easily due to engine intake vacuum or even intake air velocity...

The 750 CSR is a Twin. Is just the housing damaged or do you need a complete airbox?
According to the cross-reference at Partzilla the 82 750-M1 csr & 83-84 750-K1/K2 Ltd models have the same airbox.

Here's a 750K airbox. It's kinda dirty. the seller says there are no cracks or damage, but the ducts are torn. I don't know if the ducts are available new. I'm not sure if it's complete or not, but I think it is. I also saw a housing without the cap that appeared to be in good shape (#161246987492}.

1983 KAWASAKI 750 LTD KZ750K BELT AIRBOX AIR INTAKE FILTER BOX

Oh, so it is a twin! See what happens when you don't get out of the shop enough!

Well, I don't expect there is a Dynojet Stage III kit for that, then!!!

I thought they only made a twin LTD750...I remember now that I was supposed to fix one of those a few years ago, but the guy changed his mind when he found out I was going in for shoulder surgery and wouldn't get to his bike right away, so he never brought it to me. I wonder if he ever got it running again.......I still have his number somewhere.

Okay so, for starters, I apologize for my delayed response. I had actually replied to the first few posts, but i guess it never submitted (having issues with the moble "friendliness" of this site). Second, responses!

TexasKZ wrote: It might be easier to fix the airbox.

Are the 28s properly spaced for your engine? Will you be able to find intake manifolds to fit? Are they set up for the same number of throttle cables? Some bikes use one, others use two (one open, one close). Is the fuel inlet on the carbs close to the same size as the fuel outlet on the tank?

I'm not actually sure what "spacing" is in relation to carbs and bikes. I do indeed have manifolds that fit. I'll have to check again on the fuel inlet and outlet sizes. The stock CV carbs are part of an assembly where a single cable opens both butterfly valves. They can be worked individually by 1 cable outside of its assembly. The VM28 carbs also work with a single cable.

Nessism wrote: Agree on fixing the airbox. If you insist on pods a Dynojet kit and some quality pods, not some dimestore Emgo junkers, would make for a good path forward.

There isn't really much hope for the airbox

Yeah, I don't plan on using cheapo junk pods. I've tried ed doing my own research via google, and those who aren't completely biased against pod filters have recommended K&N or Dyna.

Kray-Z wrote: I'm with the others - stick with a stock air box if at all possible, and avoid cheap-o pod filters always!

I can't say for sure, as I generally play with KZ1000/1100J, LTD, CSR, and GPz1100's, but I think an air box from an 82 and up 750 LTD or 750 Spectre will fit your bike...can't be that hard to find one of those for cheap on evil-bay? Any bike parts salvage yards near where you live?

Otherwise, and last resort, you could try the slide carbs, or the BS34's with a Dynojet stage 3 kit and the K&N filters Dynojet recommends...

If you go with smooth bore (slide) carbs, you'll need a push / pull throttle assembly also! Otherwise operating slide carbs with a single cable set-up is extremely dangerous! The slides could stick open (stuck throttle) very easily due to engine intake vacuum or even intake air velocity...

I actually went to a salvage yard! They did not have any CSR's or parts for it at all. I did check on ebay (although this was last month) for an airbox, but they were all for different models and years.

The VM28 carbs i have new are roundslides. What is the difference between round and smooth slide carbs? I'd prefer not to wreck my bike (and neck) by a mechanical error...

martin_csr wrote: The 750 CSR is a Twin. Is just the housing damaged or do you need a complete airbox?
According to the cross-reference at Partzilla the 82 750-M1 csr & 83-84 750-K1/K2 Ltd models have the same airbox.

Here's a 750K airbox. It's kinda dirty. the seller says there are no cracks or damage, but the ducts are torn. I don't know if the ducts are available new. I'm not sure if it's complete or not, but I think it is. I also saw a housing without the cap that appeared to be in good shape (#161246987492}.

1983 KAWASAKI 750 LTD KZ750K BELT AIRBOX AIR INTAKE FILTER BOX

The airbox isn't in any repairable state due to corrosion caused by conventional batteries.

That's strange; it looks different than the stock one i had to chuck. The ducts on mine also need replaced as they were also damaged.

Kray-Z wrote: Oh, so it is a twin! See what happens when you don't get out of the shop enough!

Well, I don't expect there is a Dynojet Stage III kit for that, then!!!

I thought they only made a twin LTD750...I remember now that I was supposed to fix one of those a few years ago, but the guy changed his mind when he found out I was going in for shoulder surgery and wouldn't get to his bike right away, so he never brought it to me. I wonder if he ever got it running again.......I still have his number somewhere.

Yeah it's a twin. When i first went to a bike repair/parts store, they asked me my bike model and year. It took him like 10 minutes to find it because it wasn't in his system, and questioned me multiple times on the information lol. And all i wanted was spark plugs and an oil filter...

Atlamillias -

Now that I know it is a twin, and what carbs you have stock (a linked / paired set of Mikuni BS-34 CV's - CV means "Constant Velocity"), and what carbs you have new (individual, single pull cable Mikuni VM28's, which are a round slide "smooth bore" carburetor), I can more accurately answer some of your questions!

First - carb spacing is typically referring to the distance, measured center to center, between multiple carburetors when they are solidly mounted together in a set or "brace", as with most 4 - cylinder engine's stock carb sets and like your stock BS34's. The term "carb spacing" does not apply to your individually mounted VM28's.

Second - "smooth bore" carburetors refers to carbs that do not use a butterfly type valve to control how much air enters the engine intake port. If you look at the engine side of the BS34's, you will see a round disk (this is the butterfly valve) mounted to a horizontal throttle shaft with two screws that almost completely blocks the airflow through the carb when the throttle is closed. When you pull the throttle cable to wide open, the butterfly valve rotates, opening, thus allowing more air to flow into the engine intake port. Even at wide open throttle, however, the butterfly valve restricts airflow - some of the carb throat area is still blocked because the butterfly valve and throttle shaft can not get out of the way of the incoming air and this impedes airflow. If you pull the throttle cable of a smooth bore carburetor , like your VM28's, wide open, the needle slide (which acts as the "throttle valve" on this type of carburetor) gets pulled upward into the top of the carburetor and completely out of he way of the incoming airflow, leaving only the relatively small area of the needle itself to impede the incoming airflow. You can look pretty clearly straight through a smooth bore carb when it is at wide open throttle! This is the reason why a smooth bore carb allows an engine to make more torque and power than a butterfly valve carb.

A CV carb uses a butterfly valve and relies on a vacuum chamber above the needle slide to open the slide and raise the needle. The vacuum is created (and increased) at the inlet (air box) end of the carb when the velocity of incoming air increases as the throttle is opened and engine speed is increasing. A spring is used to push the needle slide back down when the throttle is closed, and there is no mechanical connection between the slide's movement and the throttle cable. The "CV" type carb can't be a smooth bore, as without the butterfly valve, the rider would not be able to control the amount of air entering the intake port. At a constant inlet air velocity (constant throttle opening and engine rpm's) , the position of the slide stabilizes (hovers), hence the name...

Third - there are two shapes of needle slides common to both CV and smooth bore carbs - round and flat slides. Both your CV BS34's and the smooth bore VM28's are round slide carbs. Round slides have been around longer and are better in most street bike applications than flat slides. Racers prefer flat slides because they can give quicker and more precise throttle control and performance. One of the big disadvantages of flat slides is that they are prone to "sticking" to the carb bodies when engine vacuum or even high intake air velocity presses them hard against the pathway they move up and down in. Unlike round slides, where there is usually a large spring that pushes directly down on the slide, flat slides rely on a mechanical linkage with an external spring to return the slides to the closed position, making the problem worse. That is why using flat slide smooth bores like Mikuni RS34's or TM33's requires the use of a push / pull throttle and cable assembly (or a very stiff slide return spring that would make holding the throttle open for long periods very tiring and painful). One cable opens the throttles (slides) like usual, while the other cable closes them. That way if the slide sticks, the rider can still force ably close the slides with the twist grip - much safer than having a run-away bike! A push pull throttle is likewise commonly used (and highly recommended) with multi cylinder (3, 4, or 6 cylinder bikes) round slide smooth bore carbs that are bolted together with a common throttle linkage between the carbs, as a set and used on a street motorcycle - for safety reasons.

Because your VM28's are individually mounted to the engine (and are cable pulled round slide smooth bores), you can only use a single throttle cable (split into two near the carbs), so the point of a push / pull throttle cable assembly doesn't apply . I would only advise that for street use on a bike with no more than two cylinders, however...and be sure the cables move freely and the slides snap back closed firmly when the throttle is released before attempting to ride the bike...

There were quite a few of the Twin 750 LTD's around my area back in the late 80's, but I didn't even know there was a CSR version! I would often see adds in the local printed classifieds that read "198X KZ750 for sale" and see an asking price far below what a GPz750 or four cylinder KZ750-Whatever was worth at the time. I would call, sometimes even go to look at the bike, only to find out it was a twin, never having thought I would / should have asked first....