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Honest opinions needed on restoration or scrap of 81 GS750.

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Hi Guys,

I recently acquired a yellow 1981 GS 750 with 70,000 miles on it. A friend gave me the bike, I have nothing much invested.

I fixed the minor electrical issues, etc and the bike was running fine save an occasional problem where visible white/gray smoke would be emitted from the exhaust...but only sometimes. When the bike smoked, it would have trouble idling.

Well, the bike now smokes all the time, and won't idle reliably. Even after warmed up, you can set the idle at any speed you like and slowly the rpms will drop and the engine will eventually stall. If you blip the throttle, the process repeats. Once in a blue moon, it'll stop smoking and will run like a dream, holding a steady idle at or below 900rpm.

The bike has visible oil leaks on/around the head gasket area.

The exhaust does not smell like oil; more like fuel.

The plugs are clean, all 4, light brown/tan.

I'd like to get some honest opinions from those that know.

- Should I proceed with troubleshooting this problem or given the high mileage on the bike; plan for a complete rebuild.

- Is a complete rebuild a good idea? Is the bike worth it? Or, should I part it or sell it off cheap / scrap it?

- Is there a specialty house somewhere that rebuilds GS750 engines affordably or is this something that would be strictly DIY? Associated costs? I know automotive engines and have built several; this would be my first bike engine rebuild.

Thank you, your opinions are appreciated.

Byron
 
A compression test and a leak down test to check for worn valves and guides will tell you a lot about the condition of the top end and help you decide whether to keep the bike or sell. Sounds like the guides may be OK if the bike will run right intermittently. I would change the oil and filter again right away, maybe twice more within the next 50-100 miles to clean it out some. Then the typical "get it roadworthy" process would be to set the valves, service the camchain tensioner, clean and balance the carbs and service the airbox/filter/intake boots, clean the harness and resolve any charging/ignition issues. Oh and the tires, brakes, and suspension before any serious riding is done. There are stories of GS's running for very high mileages. Check www.umgweb.com (just block pop-ups). Those Brits use their bikes! More of a tool than a toy for many riders. Any used bike you acquire no matter how cheaply is going to need money put into it. How much are you willing to invest and what will the bike be worth when it is roadworthy? IF that matters! :wink: I paid $600 for my bike which seemed like a bargain (and was with only 8k miles). The first surprise was $381 in back fees to get registered. Then followed tires, stator, RR, fork springs, brake pads, etc. etc. 7 months later the total is over $1500 but I've had 5000 miles of riding! What's that, $0.30/mile? Still sounds like a bargain to me. I still drool over the SV650 and DL650's at the dealer, though. Lots of guys will say "Save it! Don't part it out!" but a bike that old has to really float yer boat before it becomes a worthy endeavor.
 
Before I did anything I'd do a compression test and a look at the carbs. I'm still learning all this stuff myself but I wonder if maybe you have one or more carb "slides" sticking open giving you a very rich mix at low revs.

Will it pick right up when its smoking or does it seem to bog down?

I hate to see a good bike parted out when it doesn't need to be. If you like the bike maybe its worth putting a little money or time into since it was free and if it isn't really what you want maybe you can sell it as a whole bike to someone who does like it for around the same cash as parting it.

Remember that parting means pulling it all apart and selling each piece, how much is your time worth for $ and not a labour of love?

Chances are there is someone on this board who'd want to buy it and I know you can get some good info on fixing it.

Good luck!
/\/\ac
 
Sounds like your diaphram in your fuel petcock is bad. My 81 1100 has the same petcock and did the exact same thing as yours. I replaced with OEM at www.bikebandit.com . You should be able to suck a vacuum on the little hose that runs from carb number 2 to the petcock. Careful, if it won't create a vacuum gas is going to come out of that hose and into your mouth. If you can creat a vacuum the petcock should open and close as vacuum is added or taken away.
Your bike is well worth fixing and a factory replacement petcock is under $70.00. Check and replace if needed before anything else.
 
Thank you for the posts.

Thank you for the posts.

I'll study the function of what a petcock is and what it is for, then go see if it's defective per your instructions. I think the petcock is that fuel valve thingy on the side; which I can't turn. I havn't used pliers yet, for fear of breaking it.

If this does have anything to do with the petcock, would it tend to cause fuel starvation as the fuel level drops lower and lower? If so, we may have a winner. I never let the tank level get below about half full in the past. When it first started having trouble, it was below 1/2 tank and I did not fill it since. I'll try that as well and see if the problem magically vanishes with a full tank.

It sounds as though, with the resources available here, this might be an interesting project bike to play with after all.

Byron
 
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