smoothe bores

[Gosling1]

Cool - good photos always help.

What you have there is a stock set of 28mm Mikunis. They are probably off a Z1000 from 1977 through 1980. (although they could be off a Suzuki from the same era, they also used VM Mikuni slide carbs).

The 1976 900 used 26mm carbs - earlier zeds used 28mm carbs but had a different design top cap. When I get the slide carbs off Shadowfax I will post up a picture to show the difference. Externally - there is SFA difference really - smoothbore carbs generally have a large 17mm nut on the base of the float bowl so you can change the main-jet quickly without having to drop the carbs off the motor. The main difference is internal - your carbs have the large cut-out on either side of the bore, to locate the slide as it moves up and down. Smoothbores only have 2 thin slots to locate the slide, which is a different type to a normal slide...although it is still a 'round' slide.

You can just twist the floats to get them sitting straight, and yes in these carbs the larger part of the float does sit up high. The carb diameter is measured directly in front of the slide - not at the mouth.

What sort of jetting are you running at the moment ? It would be interesting to know, as these carbs were designed for a slow-revving 2-valve 1000cc motor, not a high-revving 4-valve 750. Normally you would jet carbies down a bit when using them on a smaller capacity motor, but in this case you may need bigger jets to suit the faster revving 7fiddy ??

[z900/zx9]

Yep i was right, std carbs thought they looked like the ones that used to be on my old z900 which is a late model 75/76.I used to set the float level the hard way bend the tabs while the floats were in the carbs and line them up by eye.Then go for a run or just run the bike then carefully remove the bowls and check the petrol level and adjust from there.Also make sure that your needle/seat is not to pointy and sharp ,if it is then its pretty worn this will also cause fuel to piss out of the overflows. I always wondered why the drain plug on my carbs was bigger than standard,yeah i knew they were smoothbores buy never knew why the plug was different

[mick12]

when i put the needles back in i blew down the fuel line or at least tried to they were definatly sealing as for jet size its whatever is in them with these glasses i cant see too well might have to find a magnifying glass and take another squiz and post it up .I did find that the main jet [ tube carrier or whatever its called ] measures aprx 22mm above the bowl gasket so i set the floats to that with an engineers rule as in the photo. Whateve these carbs came off the only mod to fit them seems to be the adjuster knob on the idle screw has been cut off to fit them over the alternator

[mick12]

i have another question as i am setting the slides on the bench with the idle screw set right back no contact with the throttle linkage at all should the slides be closed compleatly or open just a touch i want to get them near the same on the bench and use the gauges when i put them back in i put a torch behind them and adjusted the screw and locknut until i was just able to see light underneath my theory is that when i adjust the idle they should be pretty dam close to right for a starting point Also there are 3 vacum hoses 1 is blocked off the others are open should i seal the other 2

[Gosling1]

The slides will close completely if the idle screw is backed right off with nil contact. When the idle is set, all the slides should be cracked open a tad - which is a bit less than a poofteenth but a bit more than a bees dick...

Your theory is good, setting all the slides on the bench to the same spot will be a good starting point once they are fitted to the bike and you do the balance. Those hoses are breather hoses for the float bowls, don't block them off. These old carbs did not use vacumn lines.

[mick12]

thanks for your help gos mabe carbs should have a special place on this site i will post in this thread later and let you know things do

[mick12]

heres one for gos the three hoses on the carbs are mounted on carb 2-3 &4 carb 1 has factory seal they mount on a brass dick at the base of of the slide towers above the venturi body 2& 4 have no air or vac flow but 3 sucks when the plug is removed the bike revs up evenly across all 4 cylinders

[Gosling1]

..... the three hoses on the carbs are mounted on carb 2-3 &4 carb 1 has factory seal they mount on a brass dick at the base of of the slide towers above the venturi body 2& 4 have no air or vac flow but 3 sucks when the plug is removed the bike revs up evenly across all 4 cylinders .......

aaah OK, what you probably have then is a set of Mikuni's from a GS1000 or other big 4T suzuki from back in that era. Some of these models used vacum fuel-taps which need a vacum signal from the inlet manifold.....If you have a look inside the #3 throat in front of the slide, there should be a small hole which leads up to that small brass dick. This is where the fuel tap gets its vacumn signal from.

If the fuel tap on that Gixxer 7fiddy needs a vacumn signal - take it from this #3 spigot. If the fuel tap is just On / Res / Off (like the Kawasaki taps of the era for many models) - then just keep the plug on the #3 fitting. The reason the revs go up when the cap is removed is due to the air-leak this creates and the subsequent leaning-out condition.

Mikuni made several types of slide carbs back in the 70's and 80's for Kawsaki, Suzuki and some Yamahas. They all look externally similiar but often have little internal differences like you have with these carbs.