78 GS750 Yoshimura Resto-mod

[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]

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]

If you EVER want to sell that Yoshimura GS750 pipe, or if you EVER see another one for sale, GS550 also, PLEASE get in touch with me IMMEDIATELY!!!

On the picture of those SW Stroker shocks, it looks like one has a big rusty spot on the shaft. Do you know if parts are available for those? I know of a few sources to get shafts custom made. Are those things rebuildable?

[Chuck78]

Oh yeah, also, how big are the intake ports opened up to on the head? I was under the assumption that may have had bigger boots and RS34's on it already, but perhaps you meant that it just had Mikuni VM 29 smoothbores on it previously?

More porting work would need to be done to open it up to benefit from RS34 carbs. VM29, CR 29, or CR 31 smoothbores are the ticket otherwise.

[SpecialK]

Oh yeah, also, how big are the intake ports opened up to on the head? I was under the assumption that may have had bigger boots and RS34's on it already, but perhaps you meant that it just had Mikuni VM 29 smoothbores on it previously?

More porting work would need to be done to open it up to benefit from RS34 carbs. VM29, CR 29, or CR 31 smoothbores ate the ticket otherwise.

If I ever part with the yosh exhaust you'll definitely have first choice! The S&W shocks did have some rust on the shafts, most of it was surface and came off with some minor wetsanding. I painted the bodies of them and have some NOS springs coming in the mail.

Never got around to measuring the port sizes but they were noticeably larger than stock. The guy a bought it from is now a good friend of mine and did confirm that the race bike that this engine was in when he bought it was running RS 34's, which was way he had bought it in the first place not knowing it had internal engine work.

[Chuck78]

I've heard mentions of SW shocks on dirt bikes from vintage bike forums in recent times, but I have not seen or heard much of them for street bikes.

EDIT - I dont believe any SW shocks were ever rebuildable

Running a shock with a rust pitted shaft means it will soon chew up the wiper seal and o-ring in the seal head, and then start spewing out all of its oil. So you will soon lose all damping if that is the case, and also lose all lubrication for the piston, which will then in turn destroy the internals of the shock... So a rust pitted shaft or leaking oil means rebuilding or throwing them in the scrap heap is the next step.

If you have a way to remove the spring, such as a DIY ratchet strap bench vise method to compress the spring to remove the lower perch, you can check and see if it has all of its damping still. You might be able to just compress it on the ground with it sitting on a floor mat or a 2 x 4 and feel the damping, but the spring maybe stiff enough that you don't have enough force.

YSS makes a pretty impressive budget line of shocks in the E-302 emulsion shock ($280?) and the C-302 piggyback ($460?)
A rebuilt vintage set of Koni Dial-A-Ride shocks or Fox Street Shox would be a good period correct shock that would do real good if the time comes to replace those SW's.


Gotta get off here, lunchbreak on my day off, finally get to do some work to straighten up my shop and make some shop space improvements!

[SpecialK]

Got the clear coat on the panels, going to let it cure for quite a while then I'll sand and buff it and add the decals.

Chuck with regards to shocks, these SW shocks are just temporary to replace the stock ones until I find something better.

https://photos.app.goo.gl/jWqwUM59O6zutcFl1

[Chuck78]

Looks GREAT!

[thebrandonbeezy]

i love this bike!

[SpecialK]

Appreciate the kind words guys! And thanks for adding the photos Chuck, I need to apologize for the lack of depth on my posts. In my 3rd year of Mech. Engg and time is not on my side at the moment. Would just like to say that without the help of this board, building the bike of my dreams at this age would not have been possible, so thank you all for your expertise and encouragement. Plenty of tasteful mods (specifically suspension related) to come.

[SpecialK]

20180218_160416.jpg
Finished polishing the clear coat today and applied the Yoshi Decals, overall pretty happy with the results!

[SpecialK]

20180218_160424.jpg
Another view

[steve murdoch]

Very nice.
Did you do the paintwork yourself?

[SpecialK]

Yup! Two part automotive paint, Dodge Viper Red. More economical than spray cans and the finish is more durable

[Chuck78]

Do you have any pictures with the red bodywork back on the bike????
Current shots, please...I'm getting really amped up for riding season about now... and a GS1100E that I've never seen just passed me on the highway...