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'78 GS550 carbs- what fits?

  • Thread starter Thread starter scum
  • Start date Start date
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scum

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Hi folks. I just picked up a pretty nice ( but non-running) 3,000 mile '78 GS550. I took off the carbs to clean them and found that someone had turned in the air screws to the point of destroying them, and probably the orfices they seat in as well. I was thinking of maybe picking up a new set of carbs but it seems like all the ones out there are the CV type for the '79 and later. Will these fit right up to a '78 or are more parts needed to make them fit.?
I suppose I could send the old ones somewhere to have them checked for repairability, but those needles were Soooo bent/twisted/squashed that the holes are almost certainly wrecked and would need some kind of machining work.And when you figure in the cost of four rebiuld kits on top of that it gets a little spendy. I'd like to know what my options are. Thanks, Brother Scum
 
scum said:
Hi folks. I just picked up a pretty nice ( but non-running) 3,000 mile '78 GS550. I took off the carbs to clean them and found that someone had turned in the air screws to the point of destroying them, and probably the orfices they seat in as well. I was thinking of maybe picking up a new set of carbs but it seems like all the ones out there are the CV type for the '79 and later. Will these fit right up to a '78 or are more parts needed to make them fit.?
I suppose I could send the old ones somewhere to have them checked for repairability, but those needles were Soooo bent/twisted/squashed that the holes are almost certainly wrecked and would need some kind of machining work.And when you figure in the cost of four rebiuld kits on top of that it gets a little spendy. I'd like to know what my options are. Thanks, Brother Scum
Click to expand...

1980 is when the CV carbs started, you need a different cylinder head to use them. 1979 and earlier are about the same. The holes are probably not ruined, were you able to get the screws out? If so try them, the air screws may end up adjusted slightly differently to get the same idle, but that doesn't really matter. Rebuild kits are a waste of time, see the carb cleaning tutorial on Cliff's site.
 
It's the fuel screws that usually get damaged, not the air screws. I suggest checking the carb bodies for the broken off fuel screw tips, and removing any you find (an awl to push the tip backwards out of the carb body works). Once you have the tips out you can take an inventory of how damaged the bodies are. VM22 carbs are not very common so your best bet is to fix what you have or look for a replacement set. ebay is usually a good source, and of course the Parts forums here.

VM carb rebuild tutorial here... http://www.thegsresources.com/files/vm_carb_rebuild.pdf

VM fuel screws are hard to come by. The only place I know where you can get them is in the K&L brand GS750 rebuild kits that Z1 Enterprises sells. One member here reported good results with resharpening his old fuel screws. Worth a try. Also, get an O-ring kit from cycleorings.com

Good luck.
 
Last edited:
Thanks for the help.
From the photo in that tutorial, I can see that it's the pilot fuel screws. Three of them are pretty wasted.
 
Happens to the best of us, make sure you get the tips out of the carbs! theyre probably stuck.
 
Nessism said:
VM fuel screws are hard to come by. The only place I know where you can get them is in the K&L brand GS750 rebuild kits that Z1 Enterprises sells. One member here reported good results with resharpening his old fuel screws. Worth a try. Also, get an O-ring kit from cycleorings.com
Good luck.
Click to expand...

Thank you for the info Nessism. My daughter passed her motorcycle safety course the weekend before last and wanted an old school bike. She found a '78 GS550 that hadn't been run in couple of years but it did start when I put a spare battery in it. Got it home yesterday and found that it was missing on at least two cylinders. Carb drain screws didn't so I figured it was best to pull the rack and go through them. Found exactly what was described here; two broken tips (easily pushed out with a map tack and needle-nosed pliers) and two damaged tips. Also found two badly damaged o-rings on the air screws. Just finished ordering the o-ring kit and rebuild kits you mentioned to replace the o-rings and screws.

Rest of the bike is in pretty good shape for its age, new tires, new brake pads, lights all work, etc. Should have her on two wheels before the end of the week.

Airengineer
 
Airengineer said:
Thank you for the info Nessism. My daughter passed her motorcycle safety course the weekend before last and wanted an old school bike. She found a '78 GS550 that hadn't been run in couple of years but it did start when I put a spare battery in it. Got it home yesterday and found that it was missing on at least two cylinders. Carb drain screws didn't so I figured it was best to pull the rack and go through them. Found exactly what was described here; two broken tips (easily pushed out with a map tack and needle-nosed pliers) and two damaged tips. Also found two badly damaged o-rings on the air screws. Just finished ordering the o-ring kit and rebuild kits you mentioned to replace the o-rings and screws.

Rest of the bike is in pretty good shape for its age, new tires, new brake pads, lights all work, etc. Should have her on two wheels before the end of the week.

Airengineer
Click to expand...

Sounds good.:) One other thing that's 100% mandatory is to replace the intake pipe boot O-rings, but unfortunately cycleorings.com doesn't sell that size so you may have to go to the dealer and order some. A dash number size is a good fit so if you want to chase them down that way let me know and I'll dig around and try to come up with the exact size you will need.

Good luck.
 
Nessism said:
A dash number size is a good fit so if you want to chase them down that way let me know and I'll dig around and try to come up with the exact size you will need.
Good luck.
Click to expand...

If you have the dash size that would be great as I have access to a lot of Viton o-rings at a couple of hydraulics reps.

Air
 
I also need the 4 viton o-rings for my intake boots.(1979 550) I think they are 28mm.
Do you think can I just go to a hydraulic hose/fitting outlet and get them there?
Also, when re-installing the slides into the vm carbs, the jet needle seems to point off angle a bit which doesn't allow the needle to go into the seat at the bottom. Any suggestions? Sorry to jump in on your post scum, but thought my question about the o-rings was sort of related.
thanks,
Bill
 
Any O ring and SEAL place will have them, just bring in the boots to get the correct size.

I was going to buy a big bag to send to 550 folks but there was no interest.
 
tkent02 said:
Any O ring and SEAL place will have them, just bring in the boots to get the correct size.

I was going to buy a big bag to send to 550 folks but there was no interest.
Click to expand...

Just remember to tell 'em you need Viton, anything else wont withstand the heat and die pretty quick.
 
william550 said:
Also, when re-installing the slides into the vm carbs, the jet needle seems to point off angle a bit which doesn't allow the needle to go into the seat at the bottom. Any suggestions? Sorry to jump in on your post scum, but thought my question about the o-rings was sort of related.
thanks,
Bill
Click to expand...

Hi Bill. Just use a screw driver inserted from the rear or front mouth of the carbs and line up the needle before pushing slide fully home.
 
Don,
I feel dumb. It took 2 seconds to install the slides, gently using a screwdriver to straighten the needle while lowering it in.
I was only looking down from the top when trying the first time.

btw. we're making the long trip to sydney next march.
thanks
Bill
 
Well, we got the carb kits in today and swapped out the pilot air and fuel screws. The pic shows the four fuel screws next to a new one on the right. Suffice to say tuning was going to be a real b(*& with those, especially with the two broken tips jammed into the bodies.

Carb boot O-rings are shot too with two of them split and opened up. I have socket head screws coming to replace the useless Phillips head screws.

Hope to have it buttoned up this weekend so she can ride it. Thanks again for the info guys. The carb kits were here in one day.

Air
f:%5CGS550%5CCarbs%20&%20Tuning%5CDSC02380-crop.jpg
 
william550 said:
Don,
I feel dumb. It took 2 seconds to install the slides, gently using a screwdriver to straighten the needle while lowering it in.
I was only looking down from the top when trying the first time.

btw. we're making the long trip to sydney next march.
thanks
Bill
Click to expand...

That is a BIG trip from the snow drenched country to the sun burnt country (Dorothy McKellar)
 
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