1983 GS750E Rebuild

[Guest]

Hello all! Posting from the beautiful (and cold) Pacific North West. I recently picked up a '83 GS750E and have begun the slow process of rebuilding. This will be a new challenge, as I've only half rebuilt one bike before, a 1981 Yamaha XS400.

Here it is just after I picked it up. Definitely not the stock set up. The guy that originally owned it did a lot of custom work on it. Unfortunately, it has been sitting since 1990 or so, when the guy died. His son sold it in a lot of bikes to an exporter, who sold it to me for $350. Definitely gonna need some work. Here's the kicker though. Those carbs on it? Definitely not original. Definitely Mikuni VM29s, which are apparently worth some money. So I have rebuilt those and plan to sell them, hopefully help fund the rebuild.

Here's the carbs after a full rebuild. Soon to be posted on eBay, had to wait till I got back from visiting the folks over Christmas.

Bike as it sits now. Going to start tearing down the rest of it very soon. It's pretty cold for me outside (California native) but I'll have to suck it up, hah.

Will be rebuilding some original stock carbs when they come in. Ordered a set off Canadian eBay that should be here soon.

Cheers,
Patrick

 

[Sandy]

I wonder if any internal performance mods were done to the motor. Smoothbores, braced or aftermarket swingarm, aftermarket exhaust as well home brew rearsets and lower clipons I would think there must be some fancy stuff hiding inside the engine. Welcome to the nut house and good luck with the project. Any history on it?

 

[Guest]

Hey, thanks Sandy. I appreciate the welcome.

Not much history I could glean from the exporter I bought it from. He basically just wanted to get rid of it since it wasn't a classic enough bike for him to export to Europe, apparently. As I said, the guy who originally owned it and did all the work on it died this past year, and it was sold by his son to the exporter. Really wish I could know, all the work on it really seems like it was done by someone who knew their stuff. He made custom sleeves out of aluminum to put the VM29s on there. I'm sure I'll be finding surprises through out the build.

I actually got the new (well, to me) carbs in today. I just tore them down to soak in chem dip, and boy, I'm amazed at how good condition they are yet how bad condition they are. What I get for $35 on eBay. First carb came apart fine, although there was powder (rust and other corrosion from leftover gas I assume) everywhere in it. Same with the others. Second carb the pilot jet decided to not budge and the brass came apart like butter. Did my best to extract it, but to no avail. It's stuck and it wont be worth getting out at this point. Third and fourth were fine except for the fact that the float posts were broken. Third not so bad, fourth absolutely gone off, though someone tried to repair them (not the best work it seems).

First one coming apart. That pile of rust/powder came out of the bowl. Nothing seems to damaged or in bad condition however.

Third one's broken post. Still usable actually.

Fourth one. I'm afraid the previous owners repair did not hold up.

Good news is I've managed to track down some extra carb bodies on eBay and will hopefully be able to get them altogether next week. Time will tell.

Cheers,
Patrick

 

[steve murdoch]

Welcome to the site, Patrick.
The classified section on this site is very active, just another place to check before hitting e-Bay.
Hopefully you recorded the size of the jets in the 29s.
Once you find out what is in the engine it might be helpful for someone else to know the numbers.

 

[Guest]

Carbs smaller than stock, i'd bet big money, that engine is stock inside. Those 29's would work great on a stock engine.

 

[Nessism]

Those VM29's hold some value for sure. Check "sold auction" prices on ebay to judge. Pretty sure they flow a more air than the stock BS32 CV carbs that came on the bike stock. In terms of those other carbs, what a disappointment. Even if they were cheap I'd go back on the seller for the carnage. Some people sell pure junk on ebay hoping not get caught.

 

[thebrandonbeezy]

Why not just restor it to how it was modified way back when? It'd be a period correct "restomod"

 

[Charlie G]

I have one of these 750s and am a bit stalled in getting going again. I rotated the engine with the cam chain tensioner off the bike and jumped a couple of teeth on the timing chain. Mean while I've acquired a couple of more bikes that run and need room. Welcome from another Cali Native!

 

[GSXR7ED]

Nice bike. I thought those were the wrong carbs on that bike. I definitely like the look of the bike.


Ed

 

[Chuck78]

I may be interested in the carbs depending on the price, though I would have much preferred to rebuild them myself, and would still probably tear them completely back down unless you have experience rebuilding smoothbores. Those jet blocks are fragile, and jet blocks gaskets as well. VM29 smoothbore jet block gaskets are also pretty rare at times, and don't fare well when ultrasonic cleaning or chem dipping the carbs with the jet blocks still installed, removing them is a must for full submersion cleaning, at which point they may get ruined just from removal and regardless you are best off replacing with new (or NOS) anyway.

Before you throw them up on ebay, let me know what you would like to get without having to pay ebay listing fees and commissions and paypal fees

Thanks,

Chuck

 

[Nessism]

I may be interested in the carbs depending on the price, though I would have much preferred to rebuild them myself, and would still probably tear them completely back down unless you have experience rebuilding smoothbores. Those jet blocks are fragile, and jet blocks gaskets as well. VM29 smoothbore jet block gaskets are also pretty rare at times, and don't fare well when ultrasonic cleaning or chem dipping the carbs with the jet blocks still installed, removing them is a must for full submersion cleaning, at which point they may get ruined just from removal and regardless you are best off replacing with new (or NOS) anyway.

Before you throw them up on ebay, let me know what you would like to get without having to pay ebay listing fees and commissions and paypal fees

Thanks,

Chuck

Jet Block gaskets are $2.64 each at Z1.

 

[Chuck78]

Jet Block gaskets are $2.64 each at Z1.

The last time I tried to get some, I had to wait SIX WEEKS to get 3 jet block gaskets!
Z1 sometimes has reproduction jet blocks as well, but they are custom-made just for them I believe. Redline Cycle Service is the other place that sells hard to get vm29 smoothbore parts.

 

[Guest]

Hey, thanks guys. I can tell it's gonna be a great being a part of the community; looking forwards to getting insight from you guys.

In regards to the VM29s, and the current configuration of the bike, my plan is to restore it to stock as it is a design that really appeals to me. Of course, some parts are missing and will not be able to be be completely stock, but hey, I'm not a purist. The main two things I don't have and don't seem worth getting originals are the airbox and the gauge cluster. So I'll be using pods and probably some kind of a modern gauge. Not a huge deal. I'm definitely going to part with the VM29s as I'm not interested in any extra performance and I think someone else could make better usage of them. Chuck, I will send you a PM regarding them.

Good news on the carbs is they're cleaning up nicely. It's too bad 3 out of 4 are basically useless. Hopefully the replacements pan out. Will definitely send the eBay seller a message about them.

About all I've gotten to in the past couple days. Hoping to get back to tearing it down tomorrow.

 

[Guest]

Well, I have had a bit of a busy couple months with my last couple months at work before leaving to start back at school. Have been slowly working on the bike and getting the parts and tools needed, so should be pretty quick from here. Only thing that's gonna slow me down is getting things painted, as its still pretty cold and humid up here, but spring is definitely on its way.

Waiting on a new set of carbs to replace a couple of the broken ones and then I'll be done with those. If anyone has recommendations on jetting for a 1983 GS750 with pods, I would be appreciative, atleast a good starting point.

Got everything separated out and managed to gracefully (okay, not really) get the engine out of the frame. Going to start taking the frame down to metal this week to get it ready for powder coating, along with the triple tree.

Planning on soda blasting most of the engine exterior as well as the cylinder head (lots of carbon built up), have cleaned up as much as I can until I start that process.

Bores look good and are within spec, as well as the pistons, so will hone bores and replace piston rings.

Finally found a new gasket kit on eBay after looking everywhere for one. Well, I had found on before, but when ordered and not shipped for 2 weeks, I inquired and it turned out they didn't have it at all. Hmm, maybe it shouldn't be listed in stock then. Ah well.

Have the calipers taken apart and removed as much paint as I could. I took this picture before I actually took the allen bolts out (had to use a breaker bar and vice to knock them loose, they did not want to budge). Not sure if I need to really soda blast these, I think I can rough them up with sand paper before painting just fine.

That's about where I'm at right now. If anyone has any input or advice I am all ears. Definitely looking forwards to getting this moving forward at a quicker pace. Maybe even get it rolling before spring is over.

Cheers.

 

[Guest]

Slowly but surely making progress. Spring keeps teasing with warm weather here and there, so I haven't gotten to painting parts yet. Once I do, I can get the engine back together and into the frame and then start focusing on the rest of the bike. Doing as much research as I can right now, shouldn't have too much left I need to figure out. The Service Manual is a god send, everything is pretty well explained.

Getting almost all the parts ready for paint. Still have a few more to mask off and a little bit of sanding. I'll wipe everything down with Duplicolor grease and wax remover before painting.

Took the frame down to bare metal almost all over. Have a bit more left that I'll probably have to hit with sand paper as it's hard to get the angle grinder in there. I'm not sure if I should maybe hit the frame with some kind of a rust stopper or something before priming. Anyone know if that's a good idea?

Got the forks taken apart, waiting on new straight rate springs from Sonic and anti-dive bypass plates from FastFromThePast. I considered RaceTech emulators but that's a bit out of the budget, maybe an upgrade for next year. I'm just going to clean up the fork outer tubes instead of painting, the original finish is still in very good shape.

Latest issue I'm facing is the rear master cylinder. I took it apart in an effort to rebuild it, but it seems water got into the boot and rusted it pretty good. The piston is stuck pretty far in, tried tapping it in with some heat applied to get it to loosen and it just went further and wont come unstuck. Tried compressed air and still nothing.

The bore that I can see looks pretty ugly, though maybe it can clean up, but at this point I'm thinking of just getting a new one. I can of course get a new OEM one for 160 or so, but that's a little steep. I see a lot of 14mm cheap ones on eBay, but the mounting hole clearance is 45mm, I need 40mm. Could probably make it work. Does anyone know of a direct bolt on 14mm master cylinder I can use, maybe from another bike?

 

[Guest]

Welp. It's definitely been a bit since I posted. Nice weather is finally here in the PNW and I'm making good progress. I have been sidetracked by school (Mechanical Engineering) and work, as well as the wet weather, but getting back to work on this.
Got the frame and triple tree (and some other parts) back from powder coating and have the engine painted and rebuilt. Going to get it back in the frame once I have the valves adjusted and fins polished. I'll post pictures tomorrow. Have taken the time to do research and make some informed decisions regarding this build while I wasn't working on the bike. Decided to build a new electrical harness, and use a Motogadget M.Unit Blue to make the system simpler and more advanced. Hoping the old igniter unit is still good, but if it turns out not to be will replace with a system from Boyer Brandsen. Hardest part right now is just balancing time to work on it and waiting of parts/being able to order parts.

Cheers

 

[MaurieG]

Your rear master cyl. Remove the nozzle off a std. grease gun, and pump the piston out. Messy ... but never fails!

 

[Guest]

Man, I've done a bad job at keeping this thread going. Luckily, I've been better about the bike. Made great progress, just waiting for school and work to die down to really get through the final stretch.

MaurieG, thanks for the advice. I gave that a shot and unfortunately it didn't work. I'm afraid the bore is simply too pitted to really save, as well. That's okay though. I'm going to try using an after market 14mm Master for the rear, just need to measure and CAD up a bracket to mount it, and have a machinist friend make it for me. Actually have a few brackets to make. Rear master, gauge cluster, speed sensor/hall sensor, and a tray to hold electronics.

Here's pictures leading up to the most recent.
https://photos.app.goo.gl/DTdXrrQ4k5cm5eFA9

I unfortunately am posting this from work (Shhhh, no one needs to know), so I can't post the pictures directly, but can later if need be.

I ended up getting a late 90s/ early 2000s Ducati M900 shock and using that plus the original spring for my rear suspension. Old shock was unfortunately in bad shape when I got it apart to check everything. Maybe I'll upgrade to a Hagon in a year or two, hah.

Waiting on the tins and tank to get back from paint. Actually decided to "convert" the bike to an ES model, a I can no longer find the original E fairing/cowling. I do like the ES look immensely, so it's fine by me. Going to go with the original white with red decals.

At the moment the latest thing I've done, which has made me question my work so far, is test the started motor (works great, have a new brush kit just in case) and checked compression. I understand compression will be low after a top end rebuild, especially with a new hone and rings, but I'm getting 35 PSI across the board (with or without oil squirted in cylinders). I feel like that's too low, so I'm going to double check my valve clearances. I did my best to follow the factory manual, but it isn't the best written, and the main photo for it seems to be labeled incorrectly. Once I re-adjust valves, I'll re-check compression and see if that makes a difference. I did notice a little tiny bit of oil seepage on the gasket between head and jugs, at the very front (there's a projection on the front in the middle that has a single bolt connecting jugs to head) so keeping my eye on that. Also getting leakage from the clutch/shift rod seal, so will replace that. In my experience and by looking at the seal, it can be simply pulled out and pressed in, atleast I hope.

Hopefully will keep making progress!

 

[Guest]

Actually wondering if I should try a different compression gauge...