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vm28's on a 750?

  • Thread starter Thread starter Tarbash 27
  • Start date Start date
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Tarbash 27

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Im considering putting vm28's on my 79 gs750. Will there be any increase in performance? Keihin sells cr specials that are 29mm for the 2 valve gs750 and says 10% increase in power. But they want $700, I figure I can get vm28's fairly cheap since vm29's are a rare bread.

But im wondering, the intake port on the motor is only about 26.5 mm. So would a bigger carb even do anything? I also plan on a 4-1, already have pods, electronic ignition and maybe some other things.

I might just buy them anyways and if they dont do anything, resell them. Just want to hear others opinions.
 
If you decide to run the 28's you need to buy some intake boots for the 1979 GS1000L or S motors. These will fit your head but the inlet tracks may need opening to match the boot inlet ID.
IMO, your best bet is to find a good 4-1 and re-tune your VM26SS carbs.
Your VM26's were fitted to the '79 850's as well, so they can deliver all the air/fuel you'll need with a basically standard motor.
I have recently bored my 850 to 900cc and I'm still running the VM26's with airbox and 4-1 pipe with exellent results.
 
750 vs 1000 boots

750 vs 1000 boots

Are you sure about the differences in boot sizes? I just bought a set of boots for my 1978 750 from Robinjo, and he tells me the 1978-1979 750 and 1000 boots have the same part number,
 
The intake boots should be the same. Anyways, I think Ill get a 4-1 first, keep my 26's for now than maybe consider carbs later on in the summer.
 
Hmm, these old motorcycles often benefit from (slightly) larger carbs, though set-up becomes a little more 'touchy'. On my old GT550, for example, a set of 32s makes a noticeable difference.

Whether it makes a difference on this particular model, I don't know, but these carbs are very easy to find. Pick a set up and do some experimenting :-D
 
jknappsax said:
Are you sure about the differences in boot sizes? I just bought a set of boots for my 1978 750 from Robinjo, and he tells me the 1978-1979 750 and 1000 boots have the same part number,
Click to expand...

I've just checked out Bike Bandits site. They do list the same part# for all the "79 VM inlets, on the 750,850 & 1000's. If the VM28SS carbs came out on the '79 1000's as the specs on the following site suggests, they must be forced into the same boot as for the 26's. I guess a 2mm larger bore doesn't take much stretching of the rubbers and would only produce a sight misalignment with the inlet track. I have heard from other sources that the 78-79 1000's were fitted with VM26SS carbs!!!
http://www.motorcyclespecs.co.za/model/suzu/suzuki_gs1000s 79.htm
 
'78/'79 GS1000 uses 26mm carbs. I believe some models sold in Britain used 28mm.
Most of the 28's were on Kawasaki's.
Technically, the 28's would provide a performance boost if you get the jetting right. A stock bike could improve a little at top end but used with pods/pipe...would be better.
Generally, anyone who really wants to change the carbs for performance goes to the 29 smoothbores, if the motor can use them. 810 kit, pods/pipe/street cam, goes well with 29's.
 
26,28,29 mm carbs all have the same outside dia to fit into the intake boot the inside dia is what is different
 
But the intake port on the head is only 26mm. The carbs would be bigger than the intake port. So this is where Im getting confused.
 
I haven't personally installed 28's on a 750, or smoothbores.
I wouldn't even bother running 28's if the bike is stock or running pods/pipe. I think the 26's can handle that set up just fine. If you go beyond those mods, then the 28's will provide more fuel to the cylinders to make use of those mods if you want to go for it.
The 29's are superior VM's. They simply allow better flow than standard VM's. How the engine flows matters too, not just how large the flow.
 
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