1977 GS750B - my long awaited first bike!

[Chuck78]

Fox Factory Shox spring rates?????

I checked out the MX manual for the Fox Factory Shox, and here is what I have gotten from it. Installed with the preload in the middle somewhere, my springs measure 6-1/2" (long red progressive spring with yellow paint dot) and 2-3/16" long (short blue spring with orange paint dot).

According to the manual, if it's spring codes are still applicable for the 13.25" long road version of the shock, I probably have the 7-1/2" and 2-3/4" springs that this manual says fit the 13.75" long shocks (haven't found my calipers yet to check diameters):

red 7-1/2" spring w/yellow dot
.295" wire diameter
p/n 96-2570
rate - medium-soft
(the other .295" wire w/pink paint dot spring lists 146 lbs/in, so I assume the chart reflects the med-soft as a progressive rate that is softer than that at first and stiffer when the tight spaced coils bottom out)

red 7-1/2" spring w/yellow dot
.306" wire diameter
p/n 96-1515
rate 166 lbs/in

2-3/4" long blue spring w/orange dot:
.263 wire diameter
rate - medium
96-2180

So it seems as if these springs will not be too harsh for me, and I probably lucked out with the spring rates and that the long red is a progressive and not a straight rate. I was going to go with around 110 lbs/in "averaged rate" progressive rear springs in a new shock. Adding the unlisted lbs/in of the short blue spring will decrease the rate, but the tight spaced coils bottoming out will increase the rate a lot upon hard cornering compression. I have no clue how to add the two rates/wire diameters together even using a spring rate calculator, but I think they will be just about right for my weight and lightened bike. Whaddya think? I'm very thankful that the springs are right in the neighborhood of where I wanted, so that I can keep the trademark originals on it!

Now I just have to decide what kind of valving I need after I tear it apart to see how it's set up as-is.

[Chuck78]

Well, today I dropped $50 on two of those s.s. teflon lined spherical eye bearings on ebay, and I also figured out spring rates. Salty Monk on here is 10lbs heavier than me and has a slightly heavier bike, and he runs a 43 lb/in fork spring and progressive rear springs in the 95/140 lbs-in intial/final spring rate. He says thats a sporty ride but still not harsh.

My bike is a bit lighter, and will be shedding more weight down to 480 lbs this coming season, and I am 10+ lbs lighter.
I just spent a long time figuring out how to calculate the rates of a progressive spring, AND the rates of two different springs stacked in one shock, talk about confusion in the late night hours!


Fox Factory Shox orange/yellow-progressive code springs:
93 lbs/in initial spring rate
117 lbs/in after 2.7" suspension travel
131 lbs/in after 3" suspension travel.
Fork springs (modded stockers):
46 lbs/in (removed the short tight wound spring in favor of an aluminum tube spacer).

Not too bad! I was planning on a 110 lbs/in straight rate rear, so this fits the bill pretty well but a bit on the soft side (maybe I can make up for that a bit with more preload to get it to arrive at the 117 lbs/in a bit sooner?) Awesome! Also discovered that the Hagon Nitro doesn't come in eye to clevis, so the 2810 is the best option for Hagons on a GS... the Nitro AND the YSS Z series are still emulsion shocks, and the YSS G series are $699 for the piggyback model that seperates the oil from the gas. So it seems as if I got the best bang for the buck even if I spend around $450-500 rebuilding the Fox and messing with the jet and the shim stack to change the dampening. No wonder people referred to them as the best vintage shock ever made. They were probably the first piggyback DeCarbon style shock available for these bikes

[Chuck78]

springtime is here!

I finally got the bike mostly back together with the cosmetic upgrades that the deer collision made me do sooner rather than later. Carbs need some work and swapping of needle jets, jet needles, and maybe pilots, but I went out for my first ride of the year today on the bike.

EMGO headlight brackets (required lots of re-bending and some drilling) fitted to the GS1000L chrome headlight bucket, GS400 gauges, CB400 dual filament turn signals, etc... I just have to wire in LED's for my indicator lights now! Got a used Vance and Hines pipe also, not installed yet. I forgot how much of a bark that homemade baffle I built for the MAC muffler has, love those GS750 cams and an unrestricted unpacked baffle!



Tore apart the Fox Shox today also in order to measure for a replacement shaft, since one has rust pitting on the chrome. Can't wait to ride it with these things after a rebuild and ditching the TOTAL CRAP BikeMaster fork seals that leaked ever since installation 11 months ago...

[Chuck78]

I am REALLY happy with the way the front end looks now with the GS400 gauges especially. I like the look of the new turn signals and narrower stems much better as well, and the EMGO headlight brackets... I always had hoped it'd look like this. I also now have 1157 dual filament bulb sockets up front thanks to the Honda turn signals, so I have running lights for more visibility. I had to drill out the EMGO brackets and ditch the mounting screws and use the turn signal stem attachment stud as the new headlight clamp bracket bolt in order to keep things looking clean and give the turn signals a place to mount. This in turn put the turn signals a bit lower than stock, which along with the narrowest stems I could find at the junkyard, give it a nicer cleaner look.

[Chuck78]

I've got parts in the mail for the Fox Factory Shox, got the springs curing for 7 days after painting satin black with VHT Epoxy paint, got the aluminum parts buffed to a mirror polish, & surprisingly the zinc(?) plated bodies polished like chrome, and I sanded the rubbed-bare rusted steel parts of the main cylinder & they buffed out almost like chrome as well! The plating looked too good to paint vht black or bake-on brake caliper silver, so I got some Brownell's gun finish clear epoxy paint to seal the steel main cylinders and preserve the polished look on the plating and polished bare steel. I was going to do black main body cylinders & clevises, but this polish surprised me so I thought I'd run them like that.

[Chuck78]

Still waiting on shock shafts for the Fox Shox from Thor/Evolution Suspension, who hasn't responded to my email for almost a month!!! Really dying to get these things on the bike...

In the meantime, my battery totally died, as in not even enough voltage stored to assist my Dyna-S in working at all... Electric start hasn't had enough battery this whole season to crank, but the ignition worked at least. This led me to research the kickstart battery delete option that I have been wanting.

Apparently it takes at least a 40,000uF capacitor that is rated for at least 30 volts (upwards of 75 or 100 is better bet in my opinion) to smooth out the low spots in the pulsed DC output of the regulator-rectifier enough to start a points ignition bike easily (as well as lessen the seriously flickering lights you have if you get rid of the battery). The Dyna-S on the other hand requires much more electricity to produce a spark, and so may or may not work well with a large capacitor. I am thinking the later 1980+ suzuki stators and rotors with more poles (11 vs 7 I think??) may work better for this application, less large split second drops in the voltage, but the Dyna is definitely going to require more power, and therefore I researched the tiny battery option...

I looked into Shorai, Ballistic (Alien Motion is the same thing basically, rebranded), and Antigravity. Antigravity was the most highly spoken of amongst the caferacer/dotheton forums, Ballistic was #2. They use Lithium-Iron-Phosphate battery technology, which gives you a battery that is double the cost but 1/6th the weight and 1/3 the size... But these batteries will get fried by old regulator-rectifiers that often let out voltage spikes above 14.6 (an upgrade to a Compufire or SH-775 is a great idea regardless), and also will be damaged if their charge gets drained below 9.5 volts...

Anyhow, to have a headlight if the bike dies or I am camping with it and need some quick light, and to make the Dyna-S happier than a cap, I shelled out $107 for the smallest Antigravity (4 cell) battery, and I am very pleased! 16oz vs 6lbs3oz in the smaller lead acid battery I had!



I don't want to push it with this battery trying to crank the new 920cc high compression engine that I am building, so I am just yanking the starter, idler gear, and starter clutch gear to save weight.

I looked into Lou's aka LoudGPZ/LoudHVX GM Cavalier HEI module based ignition using some 80-81 electronic pickups, and it uses about 1/5th the voltage of the Dyna, and auto parts stores and radio shacks are everywhere across the US in case of an ignition failure, so I am really thinking I may swap the Dyna out eventually in favor of the DIY HEI circuit, which also would start much easier with a battery delete capacitor than the Dyna... Points are still the best option for a battery delete kickstart bike, require way less voltage to fire, but more maintenance.

As I mentioned above, I have also ordered all new gaskets, o-rings, and seals for my bike, and I will be tearing down a spare parts engine to swap the 850 cylinders and a fresh 750 head with a high performance radius (inner) cut valve job. Finally I get to use those MTC 72mm pistons I picked up a few years ago!

Also desperately needing to trash the BikeMaster fork seals and swap some AllBalls seals in place, and upgrade to a needle bearing setup for the steering while it's apart. Been putting those off for some time. Stay tuned for engine rebuild details!

[Chuck78]

Look what I picked up yesterday! Performance valve job with radius cut transitions into the 45 degree valve seat, valves lapped and back cut 30 degrees to improve low lift flow quite a bit, head decked slightly to true up surface and bump compression slightly, GS850 cylinders bored out 3mm over, which is 7mm overbore compared to a stock GS750! GS650 cylinders in the background were inspected and given a clean bill of health for a hone-n-go ring job on the GS550 engine upgrade project as well. Woohoo!

Now I'm waiting on 2 orders of Suzuki engine parts and still waiting on the Fox Factory Shox rebuild parts, with no correspondence from the sole proprietor of Evolution Suspension for one month... Still waiting on the repro shafts from the forge or chrome platers probably, but some correspondence would be nice.




If I'm real lucky, I may get this together to test ride to the Vintage Grand Prix at Mid Ohio Sports Car Course (NICE road race course) last weekend of June. If not, I will be breaking in this engine going to AMA Vintage Motorcycle Days at the same race track. HUGE swap meet and weekend of vintage racing and hundreds of awesome spectator's bikes to appease the eyes!

[Chuck78]

STILL waiting to get some correspondence from Thor about the Fox Factory Shox rebuild parts... I believe he was waiting on the shafts to get back from the forge and then to the chrome platers... No replies at all from him.

I got the polished steel zinc plated cylinders polished very well and then degreased 10 times with acetone, then clearcoated with Brownell's firearm epoxy paint. WOW do these things look good, I am VERY HAPPY with that at least! Now if I could only ever get the darn parts to rebuild them with! If it weren't for the shafts and shaft seals, I'd be good to go, the o rings are all pretty soft and supple still.



That's obviously just a mockup with the shorter spring absent, as I just wanted to see how the colors looked together. Very pleased.

[jbird7262]

yes they are designed for VM26 carbs as found on the GS750/850/1000 and KZ900/1000, possibly KZ750, all of the late 70's before cv's were the norm. the carbs on all those bikes are interchangeable basically or at least have the same spacing just not the same jetting etc

So will those air filters also fit 1980 GS750E, running a uni set up with V/H 4 to1

[Chuck78]

No, they only fit the vm26/28/29 carbs. Check the k&n filters for a 1990 katana 600, they may work. RU-2422 or something. There is a long list of k&n universal filters, look it up & check dimensions and you should be able to match something up.

[blackhammer]

Hey Chuck, i don't know if it's just me, but i can't load up your pics...

[Chuck78]

Hmmm didn't look like they were there until I signed in, and then I saw them. I wonder what was going on? Limited access to non-registered or non-logged in users?

I've since started using photobucket again to make sharing easier.


That's the latest incarnation since right before AMA Vintage Motorcycle Days weekend in early July. The rebuilt front end with straight triples and fork legs, more compression dampening on the emulators, and a slight bit more preload made a world of difference in the handling, coupled with those amazing Fox Factory Shox that I finally got rebuilt and installed a year later...


Bike is riding better than ever. The mud & dust from the camping area at the racetrack helped me discover that my bike was running slightly lean in some areas, and with a little restriction in those massive air filters, my bike all the sudden was pulling unintended acceleration wheelies without even hitting full throttle from about 10 or 15 mph throttle roll ons! even with the massively wide 280 degrees duration gs750 camshafts that bleed off a lot of compression at low rpms, a cold engine kickstart-only compression test was yielding almost 180 psi on all cylinders, those MTC 10:1 pistons are doing awesome!

[Chuck78]

meanwhile, a lot of my old parts and spares are now turning into this, a 78 gs750 for my good buddy Andy who has had nothing but headaches with DOHC cb750's charging system and electricals.


GS1000 37 mm forks, GS1100 aluminum lower triple, dual discs from GS750E parts bike he got for $80. My old MAC exhaust, maybe a set of 2.50&3.50 DID rims next spring. Custom seat coming also. Maybe a 798cc 10.5:1 or 894cc 11:1 engine build next year for it.

The bike was a base model that had Z1 carbs on it that were flooding and overflowing, valves out of adjustment and engine backfiring, which led to the uni pod filters catching on fire and melting all of the wiring on the bike while the bike was still running! Tank got a little messed up, so he still doesn't have a good tank out of the three that we have collectively. we were looking for a titled frame and a wiring harness, but picked up this burnt up bike for $250 and another rusted up stripped down parts bike for $80 to donate the wiring harness, front brakes, and carbs to the burnt bike. and eventually the gas tank that was on the $80 bike also. And then he dumped the rolling hulk of a gs750 engine holder into my backyard, so I now have 3 spare gs750 engines!

Once I get my house rehab done on the new 115 yr old brick fortress, I am hoping to come across a Rickman CR or Predator frame & repro aluminum stretched rsce tank to build up with all of my parts, and maybe upgrade to some late model Honda cartridge forks off a Superhawk that work with the same awesome 296mm CBR900RR floating rotors that I currently run, which are a direct bolt on to GS hubs after drilling the holes out larger. Dreaming... But it would ride light years better than even my current setup that rides awesome, and the Reynolds 531 tubing Rick frames are lighter and stiffer than even GS frames!

[blackhammer]

Thanks for posting updates, you've done a great job on the bike, very well thought out mods.

I found some VTR-1000 (02 superhawk) forks and calipers I can get pretty cheap, no discs though..im thinking about picking them up now after reading your enthusiasm for them instead of using the GK 41s I've currently got..

[Chuck78]

the 97~06 VTR1000 Superhawk forks are great. A Dunstall-fared GS1000 vintage racer that a local guy modified and restored here in town used those forks by the time he got done with it, which turned me on to them, & I met another guy at AMA vintage motorcycle days from New Jersey that had the same forks on his bike I believe. The springs are typically a little bit soft and the rebound damping leaves a little bit to be desired according to some modern sport bike gurus, but those are easily fixed with Racetech add on parts. for something that runs the CBR rotor that practically bolts to our hubs with the addition of a spacer, having the correct steering stem height, & I believe the same axle diameter, not certain on that, these are a great modern forks for our bikes for a fully adjustable cartridge fork and rotors that will be able to be used fairly easily with the original GS spoked wheels.

also, with the popular Tokico twin pot mod for our bike using the Honda cbr/vfr/etc rotors, the pads only cover about 85% of the rotor surface, by using the Superhawk fork and its intended caliper, you get a pad that has full coverage of the rotor, increasing braking surface area even more. Bonus.