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RS34 carbs on 79 GS750 with 850 jugs and Wiseco pistons. Good idea?

  • Thread starter Thread starter SocialAnomaly99
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SocialAnomaly99

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Hey there everyone,
I'm currently working on a 1979 GS750L Brat that will soon have a set of GS850 jugs (already bought them because my 77 jugs and pistons were shot)and Wiseco high comp pistons.

It's my understanding that after I put the new jugs on, I can run the stock VM26 carbs with proper jetting. However, I don't want to use these carbs. I would like to use the bigger Mikuni RS34 Flatslide Smoothbore carbs, as I would like to also run a very free flowing custom built exhaust.

My questions are; has anyone ever done a mod like this to their own bike. What kind problems did you run into with these carbs? What kind of perks did you experience from using these carbs?
Thanks!
 
the RS34's will be to large unless you run it near wide open all the time.
it will be "not so fun" down low in the RPM's.
now if you could pick up a set of BS32's/BS34's with a st.3 jet kit...i think you'd be pretty happy from idle to redline.
 
You think even with a wide open/unbaffled exhaust I would have problems in the low end? I'll look into the BS32's for sure.
 
yes...
RS34's are actually 34mm and can even be to large on a stock GS1000.
the vacuum carbs will give you good performance at any RPM.
there are other choices but with vacuum carb's and no air box a st.3 jet kit is needed to perform properly without the jerking and bucking in the mid range.
you could try 86-88 GSXR1100 carbs.
1988-1993 katana 1100 carbs.
these are both 34mm vacuum flat slides and take the same jet kit.
in a perfect performance situation you would use a set of 29mm miks but those are like gold now a days.
 
blowerbike said:
yes...
RS34's are actually 34mm and can even be to large on a stock GS1000.
the vacuum carbs will give you good performance at any RPM.
there are other choices but with vacuum carb's and no air box a st.3 jet kit is needed to perform properly without the jerking and bucking in the mid range.
you could try 86-88 GSXR1100 carbs.
1988-1993 katana 1100 carbs.
these are both 34mm vacuum flat slides and take the same jet kit.
in a perfect performance situation you would use a set of 29mm miks but those are like gold now a days.
Click to expand...

Aren't the GSXR750 slides also an option?
 
blowerbike said:
86/87 GSXR750...yes they would be.
i haven't worked on a 86-87 GSXR750.
can i guess they are 34mm vacuum flat slides also?
i'm talking in the states of course.
Click to expand...

Not sure, never worked on one. Just remember reading it somewhere.
 
Yes, BST34's on those two years gsxr750's, good choice. He'd need a cv carb head though, right? Or some serious port work to go from the vm26 boots to a bst34 boot opening size.

Look into the maxi bore guy. He bores out vm26's to 28 or 30mm and does all kinds of flow bench reshaping of the carbs. 49er can drop some knowledge here on maxibore work vs the stock high-performance aftermarket vm28 or vm29 that was a bolt on for our bikes.
 
So the Wiseco piston kit with the 850 jugs will work no problem, yeah?

Do you guys know of any flat slide, smoothbore carbs that I can pick up NEW? I'm not at all a fan of buying used parts, as I don't like risking that they will be too messed up to use. I would rather spend the extra money and just have new components shipped with a warranty. I'd also prefer to stay away from vacuum carbs, as there is just something about the feel that I don't like.
 
SocialAnomaly99 said:
So the Wiseco piston kit with the 850 jugs will work no problem, yeah?

Do you guys know of any flat slide, smoothbore carbs that I can pick up NEW? I'm not at all a fan of buying used parts, as I don't like risking that they will be too messed up to use. I would rather spend the extra money and just have new components shipped with a warranty. I'd also prefer to stay away from vacuum carbs, as there is just something about the feel that I don't like.
Click to expand...

the smallest mechanical flat slides sold new to my knowledge is the RS 34's.
in the USA anyways..
i see set's of BS34 from GS1100 's for sale with jet kits installed from time to time.
i would go that route if buying from a trusting seller for a fair price.
as far as the "big boots".
you can mount the boots and mark the head...remove boots and funnel to match the big boots with a dremel ect.....all good and can do it on the bike.
close off the port of course with a rag or how ever.


NOTE
if you have to have mechanical carbs then pay up for a set of 29's or have your 26's bored out.
you really have very few choices..and when buying new racing carbs...there really is no warranty on racing parts.
 
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Maaaannn, :rolleyes: I plan on riding this bike like a bat out of hell anyway. Why not just put those RS34's on and make this thing scream? It's not going to be my daily driver or anything. Plus if I can't get them to work, or if I don't like how the bike runs, I can always just buy a GS1100 to accommodate the RS34s (Which is the eventual plan anyway).
 
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There was a flat slide model of the VM29's that were used on the first year GSXR750 ('85 from memory). They are hard to find though, and you're probably up for serious coin to buy them or either of the other 2 options, VM29 Smoothbores or Maxi bore VM26-28.

If you think you're going to be full throttle all the time then yes the RS34's will keep you smiling. But hey, I'm sure you're gonna be paying a lot of hefty fines, and some lengthly spells walking.

It's not much fun trying to cruise with an over-carbed engine!

The Maxi-bore option is probably the cheapest and will deliver a great range of torque.
 
how about this...
why not pop a 1000 engine in your frame and then the RS34's would be some what livable.
what are you going to spend on the CC upgrade?
just food for thought.
 
I see. I wanted to believe RS34's would work for the GS850. Thanks for talking me out of it guys. How much am I going to spend on a GS1000 engine and then all of the inevitable surprise odds-n-ends repairs that need to get done on THAT engine...? I already have the 850 jugs (purchased for $50). and the Wiseco piston kit is around $600 if I remember correctly.
I would probably end up spending closer to a $1000 in order to find and put a DECENT GS1000 engine in the bike. Don't you think? Then I would spend another $700 on the new carbs I want. Either way, I'm spending money. I just want to spend it on stuff that I already have.
For curiosity sake, what other engines (year and cc) fit in my 79 GS750?
 
i have seen 1000 engines for 100 and up.
it would need a HD clutch basket done if it is to be abused.
the RS carbs cost what they cost when buying new and you was going to spend that 800ish dollars either way.
for the 600 you was going to spend on pistons you could buy an 1100 16 valve engine and with a set of RS carbs added it will rock your world.
 
Well, the 750 they would be going on actually has 850 jugs and wiseco pistons. Should be fine with a little tuning work, right?
 
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