78 GS750 Yoshimura Resto-mod

[SpecialK]

Hey Matt! I'm tuning into this project a bit late, but it looks GREAT!
What you really need for the engine is a set of at least VM29 or Keihin "CR Special" CR29 or CR31 Smoothbores. Mikuni RS34 flatslide smoothbore pumpers would be the absolute best. VM33 or CR33 smoothbores are too big, but the flatslide design of the RS's will allow the 34mm venturi carb to live happily on the street on the big bore 750 without killing the low-mid rpm street responsiveness as a set of CR33's etc would. The RS34's will also be way cheaper new vs Keihin CR Specials.

also, man I'd strongly advise you to stick with a twin shock setup and not attempt to engineer your own monoshock conversion... the bike will be worth substantially more as a twin shock, and any monoshock swingarm you get is going to be substantially longer due to bandit, gixxer, etc engines being more compact to allow a short wheelbase with long swingarm by moving the swingarm pivot substantially forward in the frame. The transmission is stacked in newer engines vs back to back on ours, takes up much less space front to rear to make swing arm pivot further forward for better suspension geometry due to the longer swingarm, BUT allowing the bike to still have a very short wheelbase for precision handling responsiveness

a GS1100E arm or calfab etc aftermarket is a fantastic upgrade and readily available...

Also, the 43mm conventional cartridge Bandit 1200 forks are GREAT, but the triples are completely wrong offset and will screw up your rake and trail due to wheel size AND the rake of the head tube of the frame. The bike will not reach any fantastic cornering/steering response level unlessential you are comparing it to a Harley Tankership.

look at VMAX 1200 (1993+?) 43mm fork triples with a spacer under the lower bearing if you are running 18" or 19" front wheel (50mm+ offset). Look at the V-Strom 1000 (DL1000?) 43mm fork tube triples (42mm or 45mm (?) offset and very nice aluminum stem perfect for GS frame height) if you are running a 17" wheelset or low profile 18" front tire with taller rear shocks - preferred stup to accommodate our GS engines' limited cornering clearance)

Running those tuples will restore your trail geometry to where it should be, the bike will not steer like a slow pig cruiser, and the bike will feel substantially lighter and easier to maneuver. The Bandit triples are made for a frame with a very steep aggressive frame rake (24.5 or 25.5 degrees) with a 120/70-17 front tire on a 3.50x17 front rim. Not at all compatible even if you can get stem conversion bearings for your GS frame or swap a GS1100E steering stem. The offset is wrong and screws up the rake and trail geometry which is what dictates steering feel (as well as front tire diameter or radius).

The first few years of gsxr750/1100 front wheels will be 2.50x18 and match up very well to the GS1150 3.50" wide rear wheel or the matched GSXR 6 spoke.
my other favorite mag wheels to fit onto a vintage bike without making it look like a hodge-podge junkyard special, would be Honda CBR600F2 or F3. The earliest ones run a bigger rotor bolt pattern, CBR600 "F1" I think? It's the second generation you want - uses the same rotor bolt pattern as the GS's so you can run CBR900RR 98-99 310mm rotors.

Of course wire spoke wheels are my top choice as always - 2.50/2.75/3.00 x 18 front, 3.50/4.25 / 4.50 x 18 rear. 18 for cornering clearance. BT016 Battlax tires, or Avon race tires come in the sizes. Or 3"/4.50 rims run Continental Road Attack 3 sport touring tires...



Can't wait til I can browse those picture links you posted later. On break now at work.

keep up the good work and keep updating the thread!

Afternoon Chuck! Couldn't have done any of this without you're help.

Lots of stuff you touched on so I'll try to respond to each as best as I can.

Regarding carbs: Yes you are entirely correct, the engine is choked out at the moment with the stock vm26's. Adding pods helped dramatically and the pull above 6000rpm has increased significantly as a result but I know it needs more air. I did not know that the rs 34's would work, so thank you for bringing that up. I will definitely put those on the shopping list.

Regarding suspension updates: I was never planning on going the monoshock route, from an aesthetic standpoint I feel it completely degrades the appeal of these old UJM's that originally cam with a dual shock setup. I have laser cute shock mounting tabs that will get welded to the bandit swingarm provided I go that route. Thanks for providing me with alternatives for the triple tree, I am currently mocking up the front end and rear end from the B12 on a spare 750 frame I have so I will analyze suspension geometry as that progresses.

Current updates: Over winter break from University I have been painting a spare set of body panels that I have and purchased a set of reproduction yoshimura decals to go onto them, got the base coat on, still have to clear coat it and add decals.

https://photos.app.goo.gl/wp55HaQ3z51TjQ9i1

[Chuck78]

Hey Matt! I'm tuning into this project a bit late, but it looks GREAT!
What you really need for the engine is a set of at least VM29 or Keihin "CR Special" CR29 or CR31 Smoothbores. Mikuni RS34 flatslide smoothbore pumpers would be the absolute best. VM33 or CR33 smoothbores are too big, but the flatslide design of the RS's will allow the 34mm venturi carb to live happily on the street on the big bore 750 without killing the low-mid rpm street responsiveness as a set of CR33's etc would. The RS34's will also be way cheaper new vs Keihin CR Specials.

also, man I'd strongly advise you to stick with a twin shock setup and not attempt to engineer your own monoshock conversion... the bike will be worth substantially more as a twin shock, and any monoshock swingarm you get is going to be substantially longer due to bandit, gixxer, etc engines being more compact to allow a short wheelbase with long swingarm by moving the swingarm pivot substantially forward in the frame. The transmission is stacked in newer engines vs back to back on ours, takes up much less space front to rear to make swing arm pivot further forward for better suspension geometry due to the longer swingarm, BUT allowing the bike to still have a very short wheelbase for precision handling responsiveness

a GS1100E arm or calfab etc aftermarket is a fantastic upgrade and readily available...

Also, the 43mm conventional cartridge Bandit 1200 forks are GREAT, but the triples are completely wrong offset and will screw up your rake and trail due to wheel size AND the rake of the head tube of the frame. The bike will not reach any fantastic cornering/steering response level unlessential you are comparing it to a Harley Tankership.

look at VMAX 1200 (1993+?) 43mm fork triples with a spacer under the lower bearing if you are running 18" or 19" front wheel (50mm+ offset). Look at the V-Strom 1000 (DL1000?) 43mm fork tube triples (42mm or 45mm (?) offset and very nice aluminum stem perfect for GS frame height) if you are running a 17" wheelset or low profile 18" front tire with taller rear shocks - preferred stup to accommodate our GS engines' limited cornering clearance)

Running those tripes will restore your trail geometry to where it should be, the bike will not steer like a slow pig cruiser, and the bike will feel substantially lighter and easier to maneuver. The Bandit triples are made for a frame with a very steep aggressive frame rake (24.5 or 25.5 degrees) with a 120/70-17 front tire on a 3.50x17 front rim. Not at all compatible even if you can get stem conversion bearings for your GS frame or swap a GS1100E steering stem. The offset is wrong and screws up the rake and trail geometry which is what dictates steering feel (as well as front tire diameter or radius).

The first few years of gsxr750/1100 front wheels will be 2.50x18 and match up very well to the GS1150 3.50" wide rear wheel or the matched GSXR 6 spoke.
my other favorite mag wheels to fit onto a vintage bike without making it look like a hodge-podge junkyard special, would be Honda CBR600F2 or F3. The earliest ones run a bigger rotor bolt pattern, CBR600 "F1" I think? It's the second generation you want - uses the same rotor bolt pattern as the GS's so you can run CBR900RR 98-99 310mm rotors.

Of course wire spoke wheels are my top choice as always - 2.50/2.75/3.00 x 18 front, 3.50/4.25 / 4.50 x 18 rear. 18 for cornering clearance. BT016 Battlax tires, or Avon race tires come in the sizes. Or 3"/4.50 rims run Continental Road Attack 3 sport touring tires...



Can't wait til I can browse those picture links you posted later. On break now at work.

keep up the good work and keep updating the thread!

[SpecialK]

Is that the $20.00 run-what-you-brung Friday night at Cayuga?
I remember doing that years ago and some times you could get 10 runs in.
Excellent, safe and fun.

Yup that's the spot! It's a fantastic time and pretty well organized

[steve murdoch]

Is that the $20.00 run-what-you-brung Friday night at Cayuga?
I remember doing that years ago and some times you could get 10 runs in.
Excellent, safe and fun.

[dweller]

Cool video!

[SpecialK]

Hey guys, went to the drag strip last night with some friends. The gs750 performed great, best time was 12.7 @ 107mph. Need some advice here, I feel in the upper gears (4 & 5) that it should be pulling harder near redline. I'm running stock vm26 carbs jetting:
112.5 main
needle clip lowered 1 notch
15 pilots
1 turn out on fuel screw
1.5 air screw

from 6000rpm to 7500 it absolutely hauls but the power tapers off instead of building further like you'd expect with this engine build. My cams might not be degreed in correctly also so that is a possibility. A friend of mine is letting me borrow some VM28's to see if there is an improvement up top.

check out the video

https://www.youtube.com/watch?v=vWvL9_aOdVA&feature=youtu.be&ab_channel=MattKnebel

OK - the front end is not so much a bearing swap as finding the right bearing to use. All Balls Racing has a conversion calculator, but the GS has a 48mm OD bottom bearing whilst the Bandit bottom bearing is 55mm. So, you need a 30 x 48 bearing to use the Bandit stem in the GS neck for the bottom. With the top you can use the GS bearing as it has the same ID as the Bandit (25mm).

I found my bearings on eBay for way cheaper and the same sizes that I needed. 30x55x17 bottom and 25x47x12 top.

[hillsy]

Front end is not a bearing swap, that is if the 750 stem is the same as the 1000 stem. The Bandit stem will not work on the 1000 that I can tell you.

I had to press out the Bandit stem, build up the 1000 stem with weld then machine it down and press into the Bandit lower.

However, it is way worth it with the modern wheels, brakes and suspension.

For the rear you need the GS1100 swingarm, modify the rear sprocket mount, narrow it some. Do a 530 chain conversion with an offset front sprocket. You will need to have some of the spacers modified or new ones manufactured.

good luck

OK - the front end is not so much a bearing swap as finding the right bearing to use. All Balls Racing has a conversion calculator, but the GS has a 48mm OD bottom bearing whilst the Bandit bottom bearing is 55mm. So, you need a 30 x 48 bearing to use the Bandit stem in the GS neck for the bottom. With the top you can use the GS bearing as it has the same ID as the Bandit (25mm).

[SpecialK]

Thanks everyone for the input! I probably won't be tackling this swap for a while, but I have a spare frame I can mock up both the front and rear end too which will be convenient. The machine work shouldn't be a problem,I have access to all the necessary tools. I'll post pictures when I pick the pieces up

[Fjbj40]

Front end is not a bearing swap, that is if the 750 stem is the same as the 1000 stem. The Bandit stem will not work on the 1000 that I can tell you.

I had to press out the Bandit stem, build up the 1000 stem with weld then machine it down and press into the Bandit lower.

However, it is way worth it with the modern wheels, brakes and suspension.

For the rear you need the GS1100 swingarm, modify the rear sprocket mount, narrow it some. Do a 530 chain conversion with an offset front sprocket. You will need to have some of the spacers modified or new ones manufactured.

good luck

[hillsy]

A friend of mine has an entire bandit 1200 front end and rear end for sale including rims, brakes, everything. I've heard alot of these parts can be made to work on the 750 is this true?

The front end is relatively easy as it is more or less just a bearing swap. The rear is more involved as the Bandit rear rim will be too wide for the GS swingarm. If you got the Bandit swingarm, you could use that but you'd need to weld on shock mounts and machine / spacer the pivot. Then adjust the chain line.

All do-able but depends on what you can do / how much you want to modify / spend.

[SpecialK]

A friend of mine has an entire bandit 1200 front end and rear end for sale including rims, brakes, everything. I've heard alot of these parts can be made to work on the 750 is this true?

Send me a pm

[SpecialK]

I'll have to keep an eye out for them then! Machine work isn't an issue, I can do that all at work.

What was your setup?

your gonna wanna also upgrade your stock ignition to a dyna electronic and coils