1977 GS750B - my long awaited first bike!

[Chuck78]

I've been playing around with jetting and needles trying to find the right set up lately, and have been putting a ton of miles on the bike blazing through the hills and twistys of Southeast Ohio as well as further east. the bike corners so well but those cheap bikeMaster fork seals are leaking already!!! I guess oem are only slightly better and all balls makes the best ones. the Bike Master inner tubes don't hold air for very long either I have to check them every week or two! due to the phenomenally low cost of $83 shipped, and my hard riding in the hills with a very soft tire, my second Shinko SR 741 rear tire just arrived in the mail. it will probably be mandatory by August if not sooner if I ride a lot.

my head gasket is leaking a good bit of oil now and I am afraid it might be sucking and blowing from the cylinders as well as I developed a few other oil leaks possibly from blow by. my buddies at the local VJMC junk yard said they would make me a deal on a spare engine if I wanted, so it sounds like I could either swap one of those in and/or get these 850 cylinders bored out to 72 mm for the big big bore upgrade to 920cc's ASAP! I will be retorquing the head gasket before the weekend riding in the hills of Mohican State Forest and beyond as well as going to AMA vintage motorcycle days swap meet & road races this weeekend at the racetrack

[Hone101]

Am interested in seeing the RC-2222s on the bike. You got any pics?

[T8erbug]

Sounds like you're having fun man! Glad at least somebody got out on their bike this riding season.. ha Mine is ALMOST there.. I've gotta throw some shocks on (when they get here from NJ) and do some welding and finish the body work/fiberglass seat and I'll be riding too! Let us know what you end up doing with the engine.

[Chuck78]

I will definitely be tearing down the engine to do a valve job and install the 920cc pistons bored into 3mm oversized gs850 sleeves, but not sure when in the next 6-7 months that will happen. I thought about just buying a second engine to mod, but with several oil leaks in this one, it needs torn down anyways.

I swapped in some Mikuni 115 main jets yesterday, & it definitely continues to improve accelleration at WOT. now it's feeling close to it's full potential. I think 112.5's will be needed, vut no plug chops ywt to read the 115's.

I think it's time to upgrade to some Dynamite coils (Dyna Green 3 ohm knockoffs made locally) and a Dyna ignition. I have had trouble getting it to idle smooth even with a colortune to adjust the pilot mixture. Every cylinder seems to have a misfire every 5-10 seconds no matter where the air screw is at within the acceptable color range on the colortune (clear top spark plug used to tune pilot circuit by flame color)
I can't tune it out, and it runs perfect in between misfires. Funny thing is, I can see a spark, but there is no combustion going on - like the spark is at the wrong timing or something. Ive never messed with the points on it, so I suspected maybe something was not quite right with the condensers or something. I recall the same non-firing cylinder murmur/stutter sound at lower throttle openings on the road as well.

I can't explain how it could fire perfectly and then just not fire at all - maybe coil relay mod is needed also, could be in the coils as well (weak?, originals).

actually runs pretty good on the road on the pilots accelerating at less than a quarter throttle, and running it is if I were drag racing, the bike is incredibly fast. Putzing around town at constant low throttle openings it is a little choppy though. I also noticed that starting in 3rd gear it becomes very pronounced that anything off of the pilot circuit does not accelerate worth a darn at wider throttle openings at lower RPM's until you hit 4500. About 5,000 wider throttle openings really really make it go fast.

I suspect it's probably way too lean there and I need to raise the needle from clip slot #4 to the highest position #5 (lowest clip notch/highest needle height), although the needle seems to be good above 5000 rpm's - it's really powerful at any vehicle speed/gear/load at 1/2-3/4 throttle in the upper rpm ranges. I havent dedicated any decent amount of time to tweaking the carbs since I rebuilt them, but hope to next week. Dropping from 122.5 down to 115 and raising the needles is all Ive been able to do so far, with three WOT plug chops to guide me on the mains.

[Chuck78]

Hone, I'll have to get a photo for you this weekend. I'm working out of town all week for the next several weeks (brought my gs to tinker with and ride), so I am away from the computer until the weekends, android-only.

The RC2222's flow SSSOOOOOO mych air, I cant believe no one here is running them but me...

Also I'd like to say again how INCREDIBLY PLEASED I am with how my bike handles now with 50 lbs of weight loss, chopped springs, cartridge emulators, tarozzi fork brace, gs1100e alloy swing arm, wider alloy rims, & super sticky Shinko 18" tires in 140/70 & 110/90 sizes. I can corner so well that I am scraping my muffler frequently when I ride the twisties around the Hocking Hills region in SE Ohio (sport buke heaven & amazing scenery/forests/cliffs).

I really am needing to get some stiffer rear springs & good adjustable dampening shocks by next spring also. Ikon rebuildables ($380), Hagon 2810's ($309), or rebuildable YSS's (seem pretty great, & rebuildable, decent $'s).

Seat reshaping, rear fender swap, & custom face gs400 pod gauges by next year also. Just enjoying riding this corner burner while I tinker with the carbs for the rest if this season it looks like! & swapping my rear tire after 4000 miles asap, shredded it!

[Tsunami]

1977 GS 750 same exact symptoms with low rpm misfire. Tsunami has pods and 4:1 jets are 115 and 15. Needles are 1 click below center. Runs decent. But misfire is jetting? Or ignition? A peek under the tank recently revealed a lot of ghost shorts on ignition wires. Even the base of plugs in contact with the head have a vapor of electrical ghosting at low rpm. Rev it up and they fade away. Since that discovery I have been adding ground wires to everything. I should mention this is all based on a dynex with 3 ohm greenies.

[Chuck78]

mine doesn't seem to be the mixture I don't believe because it misfires regardless of whether it is too rich too lean or anywhere in between. I am monitoring the flame color with a Gunson ColorTune spark plug which has a clear top to use to tune the mixture to a perfect blue flame. it was perplexing however that I could clearly see its parking when I would see the misfire, I would see no flame whatsoever but a spark. The only way I could explain it is that maybe the coils are discharging too early or too late, maybe the caps have too much resistance, maybe I need to do a coil relay mod or clean all of my switches and wiring connections, or maybe a coiled are just weak or I have a bad wire.

[Chuck78]

I got a set of Dynamite coils that The Rice Paddy (local vjmc parts place/junkyard)has manufactured to their spec (they are basically an exact copy of the dyna green coils), some ngk 5k ohm caps, some nngk solid core 7mm wire, and some new b8es plugs. I am highly considering switching over to the Denso plugs, as I believe even the standard Denso plugs have a U-shaped ground strap to increase the area for the spark to jump to.

I was also toying with the idea of iridium plugs, but the NGK only comes in the BR8EIX style - with the 5k ohm resistor built into the plug (B8ES has no internal resistor) I didn't want to have to mess around taking the resistors out of my plug caps and installing a solid piece of metal. The Denso IW24 is their version of the Iridium plug, has a U-shaped ground strap, and has a finer point electrode than the NGK has.

if your bike is running strong and perfectly well tuned, the only benefit you get from iridium is that they last significantly longer due to the much harder metal. If you ride in a wide variety of temperatures and altitudes, or if your bike is not tuned perfectly, the Iridium plugs and their finer points electrode and the U shaped ground strap resist fouling substantially more due to their sharper edges. they will also start the bike better with much lower voltage available ( A BIG PLUS FOR ME IF I WANT TO DO A KICKSTART-ONLY BATTERY DELETE!). A set of aftermarket coils and these IW24 plugs will surely give you the strongest spark possible.

it's more than just a gimmick, but they do last much longer. $33 for a set of 4 vs $11 for the standard NGK B8ES is a bit of change, but you should be able to run them for many years longer. Worth trying for that alone.

[Chuck78]

Aha... Too much gap on a custom HEI ignition setup causes improper dwell angle, which causes a misfire. That must be what's happening with my points... My buddy is going to sell me a honda CB Dyna setup missing the rotor for $20, so I can transfer the pickups to the Suzuki Dyna plate I have with a bad 1-4 pickup and use the Dyna Suzuki rotor I have. Score!
I'd still really like to do the Lou D. "LoudGPZ" custom GM HEI ignition module setup to get thecelectronics out of the very hot engine case, but this combining these two incomplete Dyna-S setups for $20 seems to be the logical solution for now.

[Chuck78]

Well, I got the unknown $20 dyna (missing the rotor) from my buddy, and found that it also had a bad cylinders1&4 pickup module, same as the one from my wife's bike! I have two theories after reading about Dyna-S failures on the net. First is that they maybe dont hold up well if supplied with low voltage, second theory is that they dont hold up well if you let an air cooled bike idle for a long time on a hot hot day, or if the bikd just runs hot. They are sealed off inside a 230-280 degree engine, & the 1-4 module is at the rear, cool air cools off the front (2-3 module on right) first. I read of more 1-4's failing.

Anyhow, I chopped & swapped the other 2-3 module in upside down in the 1-4 spot & extended the wires from the top around to the bottom where the old 1-4 hooked up. Runs better now for sure!
Edit- adding photos finally, notice the junk 1-4 modules laying loose, and the left side of the complete unit has the wires coming out of the top, wrong side! Had to flip the spare working 2-3 module and extend/solder/heatshrink tubing the wiring. works perfect for unknown used parts!




My oem resistor caps read 7,000ohms, 8,000ohms, 9,800ohms, & 3,300,000ohms! Can't believe the bike ran so well like that! Swapped new coils/wires/caps on & couldn’t figure out why the bike would barely run!the points were timed for the 10,000 ohm & 3,300,000 ohm cap resistance, so 2 cylinders were waaayyyy off after getting the coil resistance back to 25,000 ohms total cap-to-cap! Re-timed both points and it ran better, but I realized it was time for a points tuneup, so I just spent some time splicing & soldering to make 1 dyna from 2.

Dyna says I can send a complete broken dyna (modules & plate) for their exchange program & get the brand new design dyna for $76, since Reda's failed 1 month out of warranty. I may build the GM HEI module ignitor setup still & test that with some 80-81 pickups & advancer, & upgrade my dyna for the heck of it. Most people never have trouble with Dyna-S ignitions, but after hers failing, I did find some info online on failures, makes me like the autozone/radioshack widespread parts availability of the GM module ignitor.

One guy summed up Dyna-S reliability as " I've been running them for 20 years with ZERO problems, but I have picked several spare Dyna units with 1 failed module."

[Chuck78]

Dropped down to a 112.5 main jet now, WOT is even better now, 110 may even be a possibility. I still had that high load (hills/higher speed) sub-4500rpm bog at anything over 1/4 throttle, thought it sounded too rich. Dropped the 5F21 needles to the middle clip position (at at the same time lowered the floats to 27mm from 26mm, shoulda done things one at a time), and the bike acted like it was running out of gas! I took the carbs apart again the other day and raised the needles up to the highest spot (clip notch #5 from top), the richest setting, and FINALLY the bike runs pretty awesome!

I determined that my poor idle, long warm up time, and even an occasional idle stumble once warmed up was due to me needing a 17.5 pilot over the 15. I could dial in the flame color to be pretty good but my settings were off, and the idle still wasn't good. 1-5/8 or 1-3/4 out on the fuel screw, 1-3/8 to 1-1/2 on the air screw. I later realized that at 1-3/4 or 2 turns on the air screw (baseline setting), I simply cannot back the fuel screw out far enough to make the mixture too rich! Carbs were cleaned extensively, but i may spray and blow them out again, but looks like I need 17.5 pilots.

The 76-79 GS750, 79 GS850, and 79 GS1000 all have VM26 carbs. the 750 mains went from 97.5 to 105, 850 was 102.5, 1000 was 95. Bigger displacement = more air velocity through a fixed (VM26) venturi = more fuel siphoned. I am wanting to swap to the 5DL35 or 5DL36 needles as I am maxed out on the 5F21's - and those are a dual taper, and the taper starts 3.7mm sooner, so they won't need raised as much to achieve the same onset of the taper in the throttle range. For a good transition, it is imperative to match the needle jet to the needle. Not sure if I have an O-6 or a P-1 needle in my 750 carbs, but for now O-6 would be good to run the 5DL35 skinny aggressive dual taper needles, but with the 920cc upgrade (next year?), I think the O-4 will be a must. P-1 is the richest by far, O-6 leaner, O-4 one step leaner again. 183 series needle jets that these carbs use don't have the size marked in them unfortunately, so I can only try and measure a few thousandths of an inch difference to determine sizing, or else cough up $16.99x4 to jets r us and buy the O-4's.

[Chuck78]

Sorry for lack of photos, since upgrading my Android phone to a newer custom ROM (operating system), I am unable to get my open source Linux computer operating system to connect to my phone to transfer photos, so I have to email them to myself (pita).

FINALLY... Here is a picture of the K&N RC-2222 dual oval air filters that are made for VM26's. They screwed up and packed two left filters in the package, so the right side is a left upside down. It works out better this way, as the they are offset down and out for clearance, and an upside down left on the right keeps the filter's rubber base from rubbing the kickstarter lever. It would be fine and maybe could be adjusted in the splines on the kicker, but I never bothered complaining as this works. These filters REALLY flow!




Well since rebuilding the carbs and adding these very large surface area K&N RC-2222 dual oval air filters, I have been struggling with tuning it both due to this being somewhat uncharted territory (filters no one here has used before on a bike with GS850 pistons), and lacking any great amount of spare time to spend days doing plug chops and pulling the carbs on and off and tearing them down etc...

Last night after raising the stock needles to the max height I would definitely say is the BEST the bike has ran to date! Still looking to swap to the 5DL35 and O-6 or O-4's, and definitely a 17.5 pilot, but this is running very strong!

The bike is running so good (compared to previously) that I went out for a 45 minute cruise before sunset and ended up riding to Hocking Hills State Forest (best twisties and cliffs/waterfalls/hills in Ohio) that turned into a 3 hour 111 mile round trip through the northern boundaries of the Hocking Hills region! What a blast! Got there at dusk, and spotted approximately 9 deer on or just beyond the sides of the road over almost 2 hours in the hills, but luckily my obnoxiously loud exhaust and the radical GS750 cams under acceleration or higher rpm's usually scares them away. locked up the back brake on a long downhill turn for one deer that was at the gaurdrail at the edge of a long steep hill drop. I swear two of the deer looked up and walked towards me as I slowed down while passing them! Gotta be so so careful riding into the late evening within hour before dusk & beyond when out in the hills...

[Chuck78]

I failed to mention a few months back that I chopped up and rewelded a standard brake stay for these bikes to fit the later model GS1150 caliper. I didn't snap any photos of the caliper other than showing half of it in this photo below, but it was a slightly lighter and newer design, and the pads are smaller, and it has slightly larger pistons - so I have more grab and modulation in the rear brake. My stock rear brake had no modulation and loved to just lock up - you would press and not much braking, same with pressing a little harder, slightly harder again and it would just lock up. I dropped the large and thick 295mm rotor for a newer lighter GSX front floating 275mm rotor that just needed the holes re-drilled to fit, and swapped I think it was a GS1100E brake hanger to match the diameter. With some new EBC pads fitted, this stops perfectly for mostly OEM parts from 1980-1991 with only one modded part! The caliper was designed for it's custom cast aluminum fancy looking lightened brake stay that mounted outboard I think, on a big allen head shoulder bolt, and took a special mount n the 1150 swingarm to use the brake stay intended for it. I shortened the standard big steel GS brake stay an inch or so and chopped and narrowed the caliper mount end to wrap around the GS1150 caliper. The caliper was gold in color, but I used carb cleaner and a toothbrush to strip it for repainting and just decided to leave it bare aluminium for now.



Gold GS1100/1150 caliper at top, stock GS750/1100/etc brake stay in the middle, in the process of modifying one of those in the bottom photo. The other end is flush, so that is how much I had to shorten it to fit the gold caliper whose mount is that same distance further to the front. I also chopped and narrowed the "C" piece on the end as you can see.

[Chuck78]

I also did the smoothed out treatment on the welds to shave some weight and look fancy, using a sanding flap disc on my grinder. those things are awesome for metal shaping. I'll have to get an installed picture sometime. The rear setup looks sharp, and is all the brake you need, only locks up when you really stand on it, perfect modulation with the standard EBC pads installed.





I also got an AllBallsRacing needle bearing conversion set for the steering bearings. I have yet to install them, but plan to soon. I noticed when doing very stupid high speeds that I could look at the front axle and see the forks wobbling front to rear ever so slightly, as in either my fork legs are flexing (even with the 35mm tubes, they are 5mm thick walls and stiff as can be) or else the old out of date ball bearings were allowing a little bit of bounce back and forth. There must have been a good reason that shortly after 1977, ball bearings for the steering bearings were phased out!

Also, I replaced the original OEM fork seals with some BikeMaster brand seals when I did the dual disc fork swap and emulator install, and those d#$##*@!!!!! things started leaking two weeks later, and are really leaking now! I did immediately ride nearly 100 miles of a 1200 mile road trip on gravel roads, sometimes in the rain, and have done 500 miles in the rain so far this year, but sheesh! My d*&&*^!!!! BikeMaster brand inner tubes don't hold air worth a d!@#U@*(!!!! either, even after tightening the valve cores down. So I got some AllBalls fork seals instead, the Rice Paddy (local VJMC junkyard and parts store) told me the AllBalls seals were better than OEM.

Re-making my ejected and severed muffler baffle and doing the steering bearings and fork seals are next on the list. My muffler baffle bolt vibrated loose and launched my very prized DIY baffle out at my buddy at 80mph, he ran over it, and so did a car, so I only got the rear half back, and it's just too darn loud to tolerate. Quieter than no baffle, but man it was perfect before - very throaty and aggressive, still pretty darn loud, but tolerable - made it sound like a musclecar with glasspacks!

[Chuck78]

I am also working on chopping up and reshaping my original seat foam and slightly modifying the seat pan and recover it in the near future, as the flat 550 seat (shares same pan, no hump in padding though) has a big rip in it and tape only covers it temporarily... I pulled off the cover last night and started measuring and marking with a straightedge on the foam like a plastic surgeon doing a facelift! shaving the back flat, welding a back onto the seat pan and wrapping some foam around that so that the new vinyl cover will wrap down to the fender. Going to slightly slim up the sides so that it doesn't bump out much wider at the rear. Looking for a chrome L model fender (from a bike with no trunk/tail) to swap onto it for a more old school look, and then going to mod the sheetmetal at the rear to wrap down to the fender so that I can delete the trunk without a void under the seat.

Also planning on doing that GS400X gauge swap soon, as I found a 10mm LED at RadioShack that will be perfect for the oil pressure warning light since that is the only indicator that was absent from the GS400X tach face. Two slightly smaller chrome pods and no console will really clean the bike up and make it look more old school, ditch the big plastic spaceship console dash. I am debating UV resistant vinyl decals vs painting the faces flat black or the stock dark antique brown color and screen printing on them, possibly with epoxy ink. Might as well cut out some more 3-1/8" or whatever they are aluminium circles and make another few sets just in case I ever want them on another bike or anyone else really wants some.

I've also been looking into a possible battery delete. See my responses on the thread titled something like "Deleting the E-Starter." Without the battery, you have DC pulses from the AC generated from the stator. you will get full voltage and then a few millisecond lag where the voltage drops off before the next pulse. A large enough capacitor will store the full charge and then discharge it rapidly between DC pulses, to smooth out the unevenness of not having a charged/charging battery. 4800uf is the standard bobber/chopper battery eliminator capacitor size, but you will have hard starts and flickering lights at idle, as well as not the best idle. Higher rpm's aren't a problem as the stator's pulses are so rapid. With a 14000 or 22000uF (microFarad) capacitor rated for at least twice the voltage of the bike, your 12V system will never drop below 12V between pulses, with a 22000 it will probably never get below 13. This is not something you could monitor well with equipment we can afford, because it is only for maybe 2 milliseconds, but it definitely makes noticeable changes in the headlight and engine idle. a 22000uf cap will be fully charged with about 1/2 engine revolution on a good firm kickstart, so a large cap like this will make kickstarting almost as fast as an electric start. Losing the weight of the battery, starter, and starter gears and clutch will be one more step to drop the weight of the bike down to an even snappier handling road machine to run in the twisties! I figured maybe 14-18 lbs total with all of that and the wiring removed.