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Fuel switch and dead tach needle on GS750...

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

Anonymous

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Alright guys, I just got an amazing 1977 GS750, but have some questions.

1. The fuel switch on the left side of the bike, which reads:

West/Left side: "RES"-Obviously reserve.

South/Bottom side: "ON"-Normal tank, of course.

East/Right side: "PRI"-Causes the carbs to "urinate" fuel, a fuel drain switch, right?

Just checking here. My main issue is that the bike only starts when I spray starting fluid in the airbox. Will this "cure" itself with time, because the bike has sat from about a decade before I bought it.

I know my step-father's Triumph had the same starting problem, but after continued use after prolonged sitting, she fires right up, no problem.

Alright, on to issue number two.

2. I am a gearhead at heart, but I cannot figure out for the life of me why my tach needle is dead, I mean, it does not even twitch under hard acceleration.

I have replaced the tach cable with a new unit, and the instrument cluster works with precision othewise.

My questions are these: Why is the tach dead, and what can I do, as a poor college student and USAF veteran to get it back to life?

Any comments are welcome, so let the gearheads unite!
 
My 1983 GS750ES has the same fuel switch or petcock valve. If you look at it carefully you will find a second hose barb. It goes to the engine side of a carb for a vacuum source. It is really a vacuum actuated petcock. In the "ON" or "RES" positions gas will not flow unless the engine is running and the vacuum line is connected. The "PRI" (Prime) position is there to allow the carbs to fill with the engine off. If you let it sit for a while the carb resovoirs will dry out and it will take extended cranking to refill the carbs.

I would say you need to check to see that the vacuum barb doe haver a hose on it and that it is connected to the intake. You don't need to have it connected. If it isn't there make sure any ports on the intake for it are capped. If they aren't then you have an intake leak that will cause poor performance.

As for the pissing carb that is normally a stuck float valve. The flow to the carb doesn't stop when the resovoir is full. I guess it could also be fuel leaking down the vacuum line and draining off the carb.
 
I have pretty much the same bike and I am also a broke college student. what a coincidence!! if course yours isnt in pieces right now.

I have the same problem with the tach, I have been told the unit needs replacing. PRI stands for prime. I have found the best way to start that bike is to set the petcock to prime then turn the engine over once or twice via the kickstart then switch on and give it a good start. Also if the carbs are "pissing" make sure the drain screws are tight enough, they are located at the bottom of the bowls.

Good luck with the bike it is a hell of a ride. Plus it has a WIDE power band, somthing I definately mis on my ultra peaky 600.
 
fgh said:
My 1983 GS750ES has the same fuel switch or petcock valve. If you look at it carefully you will find a second hose barb. It goes to the engine side of a carb for a vacuum source. It is really a vacuum actuated petcock. In the "ON" or "RES" positions gas will not flow unless the engine is running and the vacuum line is connected. The "PRI" (Prime) position is there to allow the carbs to fill with the engine off. If you let it sit for a while the carb resovoirs will dry out and it will take extended cranking to refill the carbs.

I would say you need to check to see that the vacuum barb doe haver a hose on it and that it is connected to the intake. You don't need to have it connected. If it isn't there make sure any ports on the intake for it are capped. If they aren't then you have an intake leak that will cause poor performance.

As for the pissing carb that is normally a stuck float valve. The flow to the carb doesn't stop when the resovoir is full. I guess it could also be fuel leaking down the vacuum line and draining off the carb.
Click to expand...

It is not a stuck float valve, the fuel was leaking out from the base of the carb where the vacuum line should have been!

Thanks.
 
where the vacumm line should be??? If fuel is comming out You are probably looking at the overflow / vent for the carbs their is one between the 1&2 carb & the 3&4 carb The vacumm attachment for the oetcock is on the left side of the #3 carb towards the top
 
I would still suspect a problem with the float mechanism if there's gas pissing out of anythwere on the carb when in prime. A little leakage after an extended period in prime could be something like a worn needle or a speck of something in the seat, but immediate profuse urination is most likely a stuck float, which could easily affect the way the bike runs whether it's in Prime or not.

Did you verify that the tach cable is turning at the tach end? Just to be sure, you might want to disconnect it at the tach and turn the engine over, watching for movement. You can also make sure it doesn't move when the engine's off to verify a solid connection. Then you can start worrying about the tach, which may or may not be repairable. Several of us have sucessfully operated on these tachs, so there is some hope.
 
By the way, the GS750 is an awesome bike, enjoy it! I got mine last year with 9,000 on it. I was lucky, the thing practically came out of a time warp, nothing wrong with it, rubber parts almost like new.
 
Hotblack said:
By the way, the GS750 is an awesome bike, enjoy it! I got mine last year with 9,000 on it. I was lucky, the thing practically came out of a time warp, nothing wrong with it, rubber parts almost like new.
Click to expand...

Let's hope mine proves just as reliable. I am too poor to do anything major.
 
Oh we will pull you through brother, one way or the other!
 
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