69mm bore with a 60mm stroke  will yield 448.7cc  at a loss of 500rpm....
with a bulletproof bottom end.....you can still wring it to 10.5-11k

that 84-86 GS400S..... read the specs.....56.6mm stroke.... and TSCC   now who got that bike.... other than NZ?

Actually, if the stroke is 56.6mm, it's the same as the GS500. So, might be interesting. I think that swap might complicate the project a little more than I'd like right now, though.

Measured out the flat-slides... Looks like they are 34mm, so 2mm larger than stock, and also smooth-bore, pumpers. Perfect.

I have to figure out a mounting bracket, throttle linkage, choke lever, clean them up, and tune. Kind of excited to try them out.

For future reference, would you mind posting all the dimensions? Input side, output side, spacing, etc?

have you tried racking them on the GS rails yet?

all the kanatunas have 34or 36mm carbs if ya just want the CV's
and the have the same outside dimensions as the GS carbs

Quote from: Big Rich on October 25, 2011, 03:12:03 PM
For future reference, would you mind posting all the dimensions? Input side, output side, spacing, etc?

Sure. Measurements are a little rough, but should be relatively accurate.

Engine side:

Engine side ID = 34mm (33.89mm ) <-- These are 34mm carbs
Engine side OD = 40mm (39.96mm)
Engine side racket screw spacing (L shaped bracket) = 30mm (29.95)

Center to center spacing, middle carbs = 90mm (30.15 - 39.96 = 90.19)

Airbox side:
Airbox side Intake OD = 50mm (50.14mm)
Airbox side bracket screw spacing (flat bracket) = 51mm (51.24mm)*

* Not entirely confident in this measurement. I suspect the actual spacing may be 50mm.

I will update this post with the measurements from the GS500 carbs.

Quote from: werase643 on October 25, 2011, 03:20:38 PM
have you tried racking them on the GS rails yet?

all the kanatunas have 34or 36mm carbs if ya just want the CV's
and the have the same outside dimensions as the GS carbs

I was thinking the same thing. The rails look very similar, and if the hole spacing isn't an exact match, I could probably drill and machine as necessary to make things fit. Throttle linkage and choke lever are an entirely different matter though. Choke is easy, since it's more or less a straight, lightly machined rod that I could just cut down. Not at all sure about the throttle; it's completely different than the GS linkage, and certain parts must be retained for the accelerator pump to function. I'll understand the problem when I start disassembling the carbs to clean them up.

I'm interested in these particular carbs because they are smoothbore flatslide pumpers. Should be good for some extra power on the GS compared to pretty much any CV carb on the market; less restrictive, and much more responsive. A rack of 4 usually costs $600+, but since they were stock on early GSX-R750 and GSX-R1100 models in the UK, they can be imported for ~$250 or less.

The only bolt on carbs I've seen advertised for the GS are ~$600 for a set of Keihin roundslide pumpers. Not quite as good, and much more expensive.

might trade ya if you don't tear them up..... i got a set of roundslides for a  gs...sitting in a box for 7-8 yrs after my last little superman impersonation.....  guess, i can't fly   35's if i member...

i think i have a rack-o-four...34-36 flatslides...off of a 92 GSXR1100  had a crack on one body up high where it didn't matter   same place...in a box   I HAVE WAY TOO MUCH S*IT

Stock GS500 carb measurements, taken from an older (~1993) era carb.

Center to center spacing: 108mm (150mm-41.95mm)
Carb throat diameter (inside, engine side): 32.5mm
Engine side outside diameter: 41.95mm
Airbox side outside diamater: 58.26 w x 63 h

Bracket spacing:
Engine side, L shaped bracket:  40mm (48.7-8.7mm)
Airbox side, flat bracket = 51.09mm (59.72-8.63)

So, the easy to reproduce flat bracket will work, but the harder to produce L bracket won't. Because of the way the L bracket is cut, it can't be easily modified to fit the FCR carbs.

More good news on the Flatslides; the throttle shaft is actually just a straight tube with some holes drilled in it; so worst case, I should be able to build something comparable. I'll also need to find a way to cap off and clean up a number of the hoses and tubes coming out of the carbs, and will need to confirm that the accelerator pumps still work as setup.

Can probably produce 2 complete sets for the GS from the rack I have, but each set will be a little different - each of the 4 carbs in the rack have subtle distinctions...

- Outer carbs have plugged fuel and vacuum tubes on outside, rather than caps. Will need to cap the lines, or somehow plug the carbs when I split the set.
- 2 carbs have acclerator pumps, 2 do not.
- Linkage is between the first and 2nd carb. Looks like the carbs are already drilled to accept another linkage, and springs though... So can probably buy some from sudco.

Quote from: burning1 on October 06, 2011, 12:21:19 PM
Would love to. They bolt on, but the exhaust ports are pointed directly at the GS500 engine cradle; can't be made to work without extensive modifications. If I'm going to go to the trouble, I'd rather use a GSX-R head.

that was done here by a former gs'er here. took a gsxr head, shaved off the outer two cyls. buddha or some of hte longer timers here, can fill you in. for life of me, i cannot remember hte guys name. but it IS within hte realm of doability

Was it Cedric?

Yeah... You can't race a GS in the AFM without hearing about that guy.

Now that I pulled apart my old engine and seen the carnage, I'm looking at ways to beef up the bottom end. One thing I noticed is that Suzuki has updated every major component down there. I'm curious what the changes are, and if I can get my hands on some of the updated parts I'd like to do a side by side comparison, looking at strength and oiling design.

Digging through the Fiche and making notes. It looks like the 1998+ GS500s get the latest crank shaft, part 12220-01D02. Previous models list 2 other cranks; (12220-01D00, & 12220-01D01) both of which are superseded by 12220-01D02. Negative here; the latest part costs $500 new, vs $250 for the older parts.

The latest connecting rod is part # 12160-44101, and is fitted from the factory on 07+ model year bikes. It's ~$79 each. Previous models get older rods (Part 12160-44100, $50.)

No updates to rings or pins in entire run of bikes. Nor do there appear to be updates to the crank bearing shells.

The latest piston is part # 12111-01D01-0F0  and is fitted to 98+ model year bikes. It replaces (12111-01D00-0F0.)

.5mm overbore pistons are available, part # 12100-01D00-050 $90. 1mm overbore kits appear to be discontinued.

The only direct parts number match between the Suzuki GS500 rods is with the GS450... Which is expected, to be honest. Might make it difficult to source an after-market rod.

After blowing up my stock motor, I'm thinking about adding after-market connecting rods to the build. Took some rough measurements of the stockers today...

Big end diameter is 37mm.
Little end is 18mm (wrist pin)
Length is 114mm

All numbers are very approximate; taken with a vernier caliper, not a set of mics.

There is some flexibility here... Combine adjustable sprockets and some milling, and it *may* be possible to run slightly shorter than stock rods. Conversely, the aftermarket KZ1000 pistons I've been eyeing are going to have a shorter compression height than the stock pistons (by 1-2mm, or greater depending on the year), allowing for slightly longer rods.

I finally had a chance to start test fitting parts together. First observation:

My ring compressor sucks. Not sure if I want to shell out $75 for a better tool, but it may be worth the price.

As expected, the GS450 head and pistons will drop right onto the GS500 bottom end. GS500 heads line up and bolt on. All the oil passages are correct (GS500 is really simple in this regard; 4 outside studs are used to carry oil from the crank journals up into the heads.

Bad news is that the GS500 heads are shaped for the slightly smaller dome of the GS500 piston. There's a slight clearance issue with the wider GS450 dome. It looks like the problem should be pretty easy to fix using my handy dremmel, though.

Have not had a chance to see how the GS500 valves line up with the GS450 valve reliefs. Expecting no issues there, but the alignment will affect how much I can trim the cylinders before the valves start hitting the edges of the pockets.

Boy! A guy doesn't log in for awhile and all sorts of neat stuff comes along!

This is one of the coolest projects I've seen in awhile. Good on you! I'd never paid attention to the 450 class rules. Nice!

Any updates?

Glad you like it. I'm going to post a bunch more pictures as I dig deeper.

I believe I mentioned that I'm planning to install KZ1000 pistons. I have one on order to compare, to get a general idea if it's worth pursuing. Major build work is on hold for the time being - just started a new job, funds and time is limited. Planning to bring my last spare engine home to see what the damage looks like.