Mikuni RS34 carbs on GS1000

[DaveD]

Good evening all,

small introduction; the name is Dave andI live in the far and exotic Belgium.

I'm rather new to the aircooled Suzuki's - more familiar with the oil cooled bikes - and I am looking into replacing the tired old carbs of my recente aquired GS1000 with a set of new Mikuni RS flatslides. What I would like to ask is:

- what would be the best carb size; the engine is completely stock so I am thinking 34mm.

- can I reuse the original carb rubbers (seems not likely since the OD of the Mikuni's is 40mm versus the OD of the original carbs being 34mm) -  Topham states that the originals can be reused but I find that hard to believe, hence the question.

- If not, what intake rubbers do I need and who sells them ?

Many thanks.

[Rijko]

Hi Dave, that's a big carb for a stock GS1000.

You may not like how that works out.
The early GS1000 used 26 or 28 mm slide carbs, the later ones used larger CV carbs.
For driveability you may want to stick to original, maybe use a Dynojet kit if you want some extra oomph.

[DaveD]

Thanks Rijko,

the reason for the whole exercise wasn't really for wanting some extra oomph but more because of the existing carbs being worn out - no surprise since they are almost 40 years old.

I suppose this means that the options are limited to finding a better set of original carbs. 

[Dezza]

Apparently, the rubbers from oil cooled machines with BST carbs as stock go on a GS1000 head to enable the mounting of bigger carbs. These rubbers vary in size depending on which model they came from. According to the RS manual supplied with RS carbs, RS 34.36 and 38s all have an external stub diameter of 42mm, not 40mm, presumably because they all use the same castings. As far as I know, the only oIl cooled rubbers with an internal diameter of 42mm  are those from the GSXR750 l or m (1990, 1991). Good luck trying to source a set for a reasonable price though. An alternative is the rubbers from a bike with BST 36s as stock, e.g. Blandit 12, GSXR 750 j,k. GSXR rubbers bring the carbs 5mm closer to the head than Blandit rubbers so keep this in mind for clearances. These rubbers have an id of ~40mm, but they can be enlarged by sanding.

What about Blandit 12 rubbers with a later set of BSTs or some 29/33 mm smoothbores?

Edited August 3, 2020 by Dezza

[BigT]

DaveD, what do you mean, the carbs are worn out?

What symptoms do they have that makes you believe this?

My VMs are 42 years old with 84,000 miles and still work perfectly

The only thing that wears out is the O rings deteriorate over time

 

[Reinhoud]

On 8/4/2020 at 1:48 AM, DaveD said:

Thanks Rijko,

the reason for the whole exercise wasn't really for wanting some extra oomph but more because of the existing carbs being worn out - no surprise since they are almost 40 years old.

I suppose this means that the options are limited to finding a better set of original carbs. 

I had them on my GS1000, I had to make adaptors on the head to make the carbies fit.

I hardly noticed a gain in power, the throttle response was a hell of a lot better!!

 

Edited August 6, 2020 by Reinhoud

[Reinhoud]

The GS1000 with the CV carburetors, these are 34mm, these rubbers will fit, but they're not cheap!! I paid over 200AUD for a set. The RS will fit these heads.

So if you have the model with slide carbies, the easiest way is to install the head of a later model with CV carbs.

[80GS1000]

I have a set of RS34s on my tuned (1100 cc pistons, hotter cams etc) 1980 GS1000 which came stock with the 34 mm CV carbs.  The RS34s bolted straight up in the carb boots on this setup.

[Reinhoud]

15 hours ago, 80GS1000 said:

I have a set of RS34s on my tuned (1100 cc pistons, hotter cams etc) 1980 GS1000 which came stock with the 34 mm CV carbs.  The RS34s bolted straight up in the carb boots on this setup.

 

That's the head I meant.

Looove the throttle response of the RS'es

[DaveD]

Thanks all for the input / ideas - appologies for the (very) late reply.

Off to the shop to find a CV equipped model head :-).

[RGSX]

I have rs36's on my 1150, phenomenal improvement, effortless reliable startup fantastic response.

[Reinhoud]

18 hours ago, DaveD said:

Thanks all for the input / ideas - appologies for the (very) late reply.

Off to the shop to find a CV equipped model head :-).

 

i had to buy another set of needles for my RS'es.

Not sure if anyone else had to do that.

[RGSX]

On 8/18/2020 at 2:04 AM, Reinhoud said:

 

i had to buy another set of needles for my RS'es.

Not sure if anyone else had to do that.

How long have you had them, I only installed mine in april 2020.

[Reinhoud]

10 hours ago, RGSX said:

How long have you had them, I only installed mine in april 2020.

I didn't had them for long, a circlip for the piston pin came out, and after that I had a change of plan.

I sold them with the carburetors.

 

[Reinhoud]

On 8/18/2020 at 9:13 AM, RGSX said:

I have rs36's on my 1150, phenomenal improvement, effortless reliable startup fantastic response.

Did you notice more power?

I didn't realy, but that instant throttle response... oh mai..

Ran nicer too

[Reinhoud]

On 8/18/2020 at 12:00 AM, DaveD said:

Thanks all for the input / ideas - appologies for the (very) late reply.

Off to the shop to find a CV equipped model head :-).

You know that this sort of stuff is usually best availably from the US of A?

[Reinhoud]

On 8/18/2020 at 12:00 AM, DaveD said:

Thanks all for the input / ideas - appologies for the (very) late reply.

Off to the shop to find a CV equipped model head :-).

By the way, are you aware of the unwritten rule, that as the head comes off, you also need a high compression big bore kit?

[fab]

15 hours ago, Reinhoud said:

By the way, are you aware of the unwritten rule, that as the head comes off, you also need a high compression big bore kit?

yes that is a must ,why bother unless you upgrade. 

[gs7_11]

I had RS36s on my tuned 1000.

Worked really well, only a main jet tweak out of the box.

That was with 1085 kit, Kent cams, large port gas flowed head.

Was good for 115bhp at the back wheel.

[RGSX]

On 8/21/2020 at 12:03 AM, Reinhoud said:

By the way, are you aware of the unwritten rule, that as the head comes off, you also need a high compression big bore kit?

Yeah I'm a rule breaker, I should've done that when the head was rebuilt. Maybe in 2 or 3 years when I'm done everything else and to strip it down to paint the frame. That'll be the time for a 1230 big bore kit.