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1000 /850 carbs

  • Thread starter Thread starter intruder1800
  • Start date Start date
I

intruder1800

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Hi, newbie here, I have embarked on a new project by turning a 1980 gs850 into a caf? racer, however I have now got hold of a 1000g engine as the 850 now needs work, I have been told that the 1000 will go straight in the frame but I need to ask if the carbs will go on with jet changes and also anything else I need to know for the change, thanks.
 
intruder1800 said:
Hi, newbie here, I have embarked on a new project by turning a 1980 gs850 into a caf? racer, however I have now got hold of a 1000g engine as the 850 now needs work, I have been told that the 1000 will go straight in the frame but I need to ask if the carbs will go on with jet changes and also anything else I need to know for the change, thanks.
Click to expand...

Before you start cutting and what not, put up a pic of the bike first.
 
IIRC, you will need to use the front upper engine mounts from the 1000 and the rear top mount may need a spacer modification. If you use the 850 head, as I did, it will bump the compression ratio up almost one point and increase torque/HP throughout the entire range. I also remember having 1mm larger intake valves made for it but I don't think that is necessary for your build. As for jetting, if the intake and exhaust remain the same as it currently is, will only need a main jet change (120 or 122.5). Either set of cams will work fine. (I would use the 1000 cams) Good luck and post plenty of pictures.

Edit: Use the 1000 head gasket.
 
Last edited:
The GS100G's used BS34SS carbs. Your GS850G uses BS32SS (34 Vs 32mm)
 
Thanks for the replies chaps,
Putting the 850 head on sounds like a good idea to gain more power out of these old bikes but the 1000 has a power gain over the 850 of about14 bhp, considering the brakes and handling of these 70s machines I conclude that this is more than enough plus a blown gasket is a pain to change so I will leave the compression alone. I didn't realise about the engine mounts so I will have to get 1000s for them. All in all I will put in the motor with minimal changes and see what happens with bigger main jets in, if that's crap then I will have to get some 34mm carbs.
I put a lot of time and effort into trying to jet a project tracker (1980 xs750 triple) in the end I paid a dyno guy and he had it licked in an hour , well worth the ?70 as I was in and out of the carbs many times with frustration, turns out they ended up hugely over where I was, pod filters and power exhausts look great but can be a pain, bike turned out nice tho and sold very quickly.
 
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