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1977 GS 750 mutt..Carb problem/identification.

  • Thread starter Thread starter banshee
  • Start date Start date
banshee said:
Do you know for sure what was done to it? I checked the compression and I got between 165-175 PSI on all 4...Seems high to me, maybe the head was milled? . My compression gauge is accurate, I cross checked it with my 4mil banshee after to ensure it was still on point. To me it looks like someone loved it, then someone started jacking around. As far as I can tell the swing arm was done right. The gauges and signals are all modern, but they are all functional and correct. Someone fabbed some nice looking exhaust brackets to worth with the aluminum
swinger, and some nice brackets for the modern gauges.
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No idea. I just saw pictures. Things you'll want to check are things like assuring the wheel is in line with the front wheel, chain alignment is correct, pivot bearings are smooth and there's no slop in the pivot, steering mast bearings are kosher, etc etc.

There are LOTS of threads on upgrading these bikes using modern suspension and running gear, and some AMAZING bikes have been put together (isleomans, posplayr, and all of Katmans bikes are stunning examples just to name a few) but there are a lot of things that you can seriously screw up and make the bike handle like crap, or worse, be a death trap. If you can, just for our own curiosity, take some better pics of whats going on with that thing and we might be able to point out any issues, if there are any.

I don't know for sure, but the carbs may be slingshot carbs or the like. Either way they look like they need to be cleaned up. Im not trying to stomp on Chucks sale by any means, but I'd see what you can find out about what those are, and what's been done to the motor before making any changes.

As for your compression numbers, a cold test means little. The bike needs to be warm, and then tested by turning the motor over with the throttle wide open (but not running) to get an accurate reading....

Fill us in on what you figure out, it is an interesting little monster that could end up being an awesome runner when you get it sorted.
 
Im not really trying to sell anything as much as help the guy out. If he wants to keep those then thats cool too. I just figured since i got stockers laying around collecting dust then why not offer a set up.
 
chuck hahn said:
Im not really trying to sell anything as much as help the guy out. If he wants to keep those then thats cool too. I just figured since i got stockers laying around collecting dust then why not offer a set up.
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Oh no it a totally cool and generous offer from you Chuck, like I said I wasn't trying to undercut you or anything of the sort. But if it turns out that motor has a bunch of head work and big pistons and such, and those carbs are better for his set up than stockers, he wouldn't want to mess that up. I'm just saying he should dig in and see what's going on before making any decision about anything. That's what I'd do anyway. Who knows? It could be a stock motor and those carbs aren't doing him any good, if not bad. But without documentation, someone could say they had done this that and the other thing to it and you'd not be able to tell in most cases without cracking a cover or two open...
 
How would he verify short of pulling the head and measuring the bore and stroke??? Im sure he isnt into that much tech work.
 
I can always jet bigger with the stockers, if the guy really did do some work. This is my first four stroke so I am not really wanting to split the cases if I can avoid it.
 
You would not have to split the cases, but you would have to pull the head. It can done with the engine in the frame, but it is not for the faint of heart. Procedures can probably be found in the factory manual, which you can get from BassCliff's web site. This is the only way to verify displacement because you need to measure both the diameter of the bore and also the stroke.
 
Tell tale signs of head work would be slotted cam sprockets, polished or cleaned up intake runners...which can be seen without pulling the head...

Sure you could jet 26s for whatever is in it, but A) if it does have work done, it's a waste as the carbs choke it off and B) you'll have to guess at where to start jetting....

Pulling the head isnt hard, or daunting, if you have any mechanical skill whatsoever. It's certainly no harder than re-jetting carbs for an engine of unknown displacement...

But, again, it's your bike, do what you're comfortable with.
 
rustybronco said:
Is that a 4 into 2 exhaust on that bike?
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Looks to be but doesn't look stock either... Maybe a Mac?

Looking at the slide he has in his hand in the pic it looks like (what you can see of it) a flat or radial slide maybe?
And looking at it closer im seeing what appears to be the Keihin logo on the bottom of the carb/bowl there.
Man, what a Frankenstein! But it's got potential. More pics! Is that a stock rear rim with a bandit or Katana front. Radial and bias tires on the same bike is a no no...
I though maybe they were bandit forks but the calipers don't look right. Tiny pic though..
 
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They are all torn down and ready for action...he sent me a PM saying he ordered the orings...so last call. Am i pulling the trigger or not?
 
more pictures as requested, looks like someone has cleaned up the intake at least. Also its a 4 to 2 exhaust. The plates are good until 11-2012 so someone had it on the road. I also noticed the back tire is bald, so either then put on a used one or someone has been laying down some rubber.



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banshee said:
Will do thanks for all the help. I am unsure if the bike is actually 1000ccs or 750cc what would you guys do tune for 750 or 1000cc
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Well, you can't bore a 750 to 1000. I think 840cc is the biggest piston kit available

What does it say on the motor serial number?

BTW, the aluminum swing arm (off a 1100) and the 90s katana front end are popular upgrades
 
Looks like someone has cleaned up that intake port. dunno about those carbs, 80~90's Yamaha's possibly. ginsu headlight, turn signals and carb boots, stock style rear shocks, 4 into 2 exhaust. my gut thinks the bikes nothing but a bodge...
 
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Got the brass bits and bowls already in the dip..I will clean him up a sweet set and send him all the info on the jetting. I gotts get me one of those loops Dale..cant see those little stampings even with the bifocals..LOL As for what the carbs are..doesnt matter really. Jap Bike Randy will know instantly what they are. He may even want them for a project??
 
Big T said:
Well, you can't bore a 750 to 1000. I think 840cc is the biggest piston kit available

What does it say on the motor serial number?

BTW, the aluminum swing arm (off a 1100) and the 90s katana front end are popular upgrades
Click to expand...

No but you can bore (apparently) a set of 850 jugs to 920...
 
Chuck its a done deal. Your carbs and $75 went out in the mail today. I also ordered the o-ring kit and intake o rings. I had them shipped to your addy.

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Im rebuilding and cleaning theses carbs too...75 for the carbs and 4 intake boots. Carbs i considered a swap for labor and return shipping..heck I dont even know what those carbs are. Someone said Yamaha carbs?? Dont know myself. If they bring me 50 or 60 buck resell them thats what i made for labor. I wont ever use them thats for sure. If they turn out to be something really extravagant and worth some seriuos dough then I will throw him a bone. And as always, he has my no fuss guarentee..if he doesnt like the carbs i send then he returns them and i return his..hes got nothing to loose.
 
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