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gs750 carbs on an GS850?

  • Thread starter Thread starter queenmonkey
  • Start date Start date
Q

queenmonkey

Guest
Hi guys i'm struggling to resolve a carb problem and i'm fast coming to the conclusion that i've the wrong carbs on the bike? The bike should have CV carbs (it's a GN with electronic ignition) but it's got slide carbs. The running problem is that it misses badly at standstill (have yet to ride on road). I've been thinking that the petrol tap might be the problem? It has what looks like a vaccum hose fitment on carbs 2, 3 and 4. when all connected to the back of the petrol tap it wont run. If i connect the hose from carb 3 to the tap and blank off the others it'll run but no'1 pot misses?

I've looked at both the Factory and Haynes manuals - it doesn't show my carbs? Mine has a choke lever on the left. Just had a look at a Haynes manual for the GS750 - it has a choke lever on the left. Am i running GS750 carbs (i've jetted up to 110 for bellends)?

Also can someone please explain which fuel and vacuum pipes should go where (between carbs and fuel tap) please? If they are GS750 carbs - the manual doesn't seem to list their existence but they are clearly visible on the diagram.


I'm hoping to get it running soon for a ride so any help would be appreciated as the suns not likely to last long
Thanks
QM
 
Nope, the GN is the one year, 1979 model 850G. VM carbs, kickstarter, different brakes, etc.
 
Hi,

Please feel free to visit my little website. You'll find lots of GS850G lovin' there. :dancing:

The stock GS850GN, "N" denoting the 1979 model year, has VM carbs, kick starter, chrome front fender, points ignition, solid disc brake rotors, etc. Have a look at my website and then look at the picture gallery off the main GSR page, or just post up a few pictures of your bike, so we can figure out what you have and you can ask better questions about what you need.

Thank you for your indulgence,

BassCliff
 
Last edited:
queenmonkey said:
Hi guys i'm struggling to resolve a carb problem and i'm fast coming to the conclusion that i've the wrong carbs on the bike? The bike should have CV carbs (it's a GN with electronic ignition) but it's got slide carbs. The running problem is that it misses badly at standstill (have yet to ride on road). I've been thinking that the petrol tap might be the problem? It has what looks like a vaccum hose fitment on carbs 2, 3 and 4. when all connected to the back of the petrol tap it wont run. If i connect the hose from carb 3 to the tap and blank off the others it'll run but no'1 pot misses?

I've looked at both the Factory and Haynes manuals - it doesn't show my carbs? Mine has a choke lever on the left. Just had a look at a Haynes manual for the GS750 - it has a choke lever on the left. Am i running GS750 carbs (i've jetted up to 110 for bellends)?

Also can someone please explain which fuel and vacuum pipes should go where (between carbs and fuel tap) please? If they are GS750 carbs - the manual doesn't seem to list their existence but they are clearly visible on the diagram.


I'm hoping to get it running soon for a ride so any help would be appreciated as the suns not likely to last long
Thanks
QM
Click to expand...

Pictures of your carbs would make it easier to answer your question. It is 34 years old and we have no idea what mods may have been done to it

It sounds like you have the VM carbs as noted above. The vacuum line from the petcock goes on #3, the other 2 are vents and should be left open

Check out Basscliffs site and review that info. We need a lot more specific info to get you an answer

The 750 carbs should be identical to the 850 carbs
 
The only difference in the '78-79 VM 750 and 870 carburetors was float height 23.0 +/- 1.0 mm and 24.0 +/- 1.0 mm and main jet 100 and 102.5 respectively. The Dyna-S electronic ignition was a common upgrade back then (and today). I have a '79 parts bike that had a Martek electronic ignition on it and my Son's '79 850GN had a Dyna-S. The 850G had such a good reputation for smoothness and reliability, why would you want to get rid of the stock air box and go to bellends? The 100 cc increase over the 750 was probably necessary to compensate for the shaft drive but they are not noted for being hot rods, They were noted for being nearly bullet proof, smooth mile eaters.
 
Last edited:
Hi,

Further, the GS750 and GS850 use basically the same carbs, just different jetting. However, most '79 and earlier models use VM carbs, and the '80 and later models use CV carbs. CV and VM carbs are not normally interchangeable without intake modifications.

Give us more information and a few pictures so that we can help you make good decisions. There is lots of information and pictures on my website that may be useful to you.


Thank you for your indulgence,

BassCliff
 
Last edited:
Hi guys and thanks for your advice. I can't post a picture at the moment but the bike is not standard - cafe racer style, hence the bellends.

Connected carb 3 vacuum pipe left the others free. Took it up the road and it ran well!

Only now problem is the flashers. They only seem to flash when engine is revved. Flashers were working and i've charged the battery? The flashers are after market - cant make the markings out either 21 0r 23? Earths seem ok?

QM
 
The '79 850GN had the same self canceling turn signal module as the GS1000E. They all fail eventually.
 
Hi,

The stock flasher thermal relay wants to see a certain load (resistance) in the system before it can start flashing. If you have installed aftermarket blinkers they probably have less resistance than the stock bulbs. You can install an off-the-shelf electronic flasher that doesn't care about the total load.

However, if yours will only blink when the bike is revved up then you may have a charging system issue too. Perhaps you should go through the Stator Paper tests and the other supporting documentation in the electrical section of my little website.


Thank you for your indulgence,

BassCliff
 
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Thanks Baycliff i'll have a look on your site. I suppose i'm a liitle confused because whilst the bike was in when i fitted them - they falshed (although the motor wasn't running). Now some months later i've got the motor working (and a new battery on board) and they dont flash?
 
queenmonkey said:
Thanks Baycliff i'll have a look on your site. I suppose i'm a liitle confused because whilst the bike was in when i fitted them - they falshed (although the motor wasn't running). Now some months later i've got the motor working (and a new battery on board) and they don't flash?
Click to expand...

Apologies BassCliff i've just realized my spelling error
 
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