TOPIC:

Hi Guys, I wrote a few months ago concerning my rebuild of an 82Kz750 twin. I've got it just about done and am in the process of hooking everything back together. I'm a little stumped right now about the 3 lines comming into the carb assembly. I've figured out that the short black tube going into a t-connector to both carbs is the fuel line and the small diameter black hose comming off the vacume switch goes to the small feed on the petcock but I also have a long clear lg diameter hose comming off of another t-connector, going to both carbs. Where does this long clear tube connect to, or does it connect to anything? There was one rather cryptic phrase in my Clymers book that seems to indicate that this line just gets fed to the back of the bike, and is not connected to anything. Is this right? Also can I replace the rather short fuel and vacume lines w/longer tubes, so it's not as much of a pain, adjusting the carbs w/the tank attached.
Thanks
Ron Jones
When bike is finished I'll post a pic. I replaced the spoke wheels w/Mags, longer handlebars and installed 2to1 Mac pipes. Otherwise it's pretty stock.

See the Mikuni BS carb connections link on my web page.

Thanks George,
Is this the paragraph that obtains to my question?

"Another type of venting is via pivoting plastic tee fittings located between carburetors #1 and #2 and #3 and #4.(in my case just #1 and #2?) These fittings should have hoses connected and routed over the swingarm. On originally equipped motorcycles, these hoses may be routed to the original airbox but this varies by model. In any case, the vent hoses should be routed away from the engine as gasoline could spill on a hot engine in the event the bike overturns. The picture to the right shows the location of the tee vent fittings on assemblies so equipped."

And am I correct that the clear plastic tube "gets routed over the swingarm...In any case, the vent hoses should be routed away from the engine..." and is not plugged? And how about my question about using longer fuel and vacume lines?
Thanks again very much for the help
Ron
BTW, the other day I sprayed some quick start(ether) into the air box and got a backfire, but no starting. (fuel tank not connected) Is this a good sign, that I'm getting spark?

There are minor variations in the Mikuni carbs used on the 750s so I am going from recent memory. First, no clear lines were installed at the factory. That line was added later. The fuel tee is in the center and is clearly a fuel tee as it is aluminum I believe and should be quite tight if the orings are in passable shape. Above it on the assembly and towards the center will be a floppy plastic tee. This is the vent. It doesn't matter if it flops too much but it is a good idea to put some sort of hose on the vent. A BS series carb has no overflow and if you turn the bike over, gas will pour out the vent which is essentially just a plain old passageway to the float chamber to keep the floats from getting vacuum locked and not being able to move. The hose should be routed to where gas spilling out of it (if bike is laid over) doesn't hit the hot engine. I like the swingarm and on the right side of the bike. As far as longer hoses, sure, why not. It is better to have looping curves in the fuel line rather than short and possibly kinked hoses. I use fuel lines that are about 18" longer than they would be stock on my carb test bikes. When I tune a bike (VM series carbs), I prop the tank up to get to the sync screws while the bike is running. With a bike with BS series carbs, I generally take the tank off as the screws (in your case screw) is a bit less accessible and I have a special tool to tighten the sync nut which also holds the screw in place while tightening that won't work UNDER a tank due to its length. I use an external gas tank supply when tuning CV carbs for this reason. If you can work on your carbs with the tank on, then longer hoses will certainly work.

Great:cheer: Thanks alot George, I think I have it now.
Ron

Didn't the 1982-M1 (CSR) KZ750 twin have a closed vent system for the carbs, connected to the air valve assy, together with the crankcase breather hose? It looks that way on the parts diagram for the air cleaner.
And what year did the 750 twin get 2 34mm carbs? They had 2 38mm Mikuni CV's between 1977 and 1980.

I can't really answer your question about the mikuni 38 carbs but there does seem to be quite a few things, about this 82 CSR, that are unique to that year and model. I had a heck of a time getting the correct mag front wheel, to replace the spoke wheel, and it never came w/a center stand. Also now that I'm thinking about it, I think there is a nipple on the bottom of the air box that is just the right size for the vacume tube I was asking about. I'll have to check it out, when I get home.

ibsen22000 wrote:

Didn't the 1982-M1 (CSR) KZ750 twin have a closed vent system for the carbs, connected to the air valve assy, together with the crankcase breather hose? It looks that way on the parts diagram for the air cleaner.
And what year did the 750 twin get 2 34mm carbs? They had 2 38mm Mikuni CV's between 1977 and 1980.

82 and 83 750 twins have the emission stuff (including the covers on the cam cover), and AFAIK they also used the 38mm carbs. The obvious difference compared to the 76-80 models is the choke pull knob on the left side that keeps the 82-83 carbs from working on the 76-80 models.

Post edited by: steell, at: 2006/06/20 15:07

At some point, I would like to do a carb ID guide on my web site. I sure don't know all the fine points about the twin carb set ups, be they Mikuni or Keihin and will be asking for help/pictures and such when I get around to it.

the long vent ube connects to nothing. I have mine routed along with the carb drain tubes to behind the kickstarter. the nipple on the bottom of the airbox is a drain tube for water and oil in case either get in the airbox.

Thanks for that little bit of info, Lifeliberty. The airbox nipple was too hard to get to anyway, w/o removing it again. I seem to have other issues w/starting it now. Will have to wait until I get back from San Antonio.