GS650G carbs on GS850G ?

[Danie.e]

I bought a GS850G and after opening up found some damage in two of the float chambers (Float attachments broken and tied with wire). I noticed on carbs specs that the carbs on 650 and 850 are same except for the number. With the correct jets and needles installed, will the 650 carbs work on the 850? - reason is that I have a good set of 650 carbs.

[tom203]

Yes, they will work. Just swap out the jets/ needles and use the mounting bars off the 850 rack

[Steve]

You will also need to lengthen the throttle shaft on #2 carb, install a longer fuel T and install a longer "choke" activation rod.

The spacing between carbs 2 and 3 is a bit longer on the 850.

EDIT: Yes, you could also change individual carbs, if one of your damaged carbs is not #2.

The difference in the carb numbers is because of the different holes for the transition ports in the pilot circuit. The 850 carbs have holes that are ever-so-slightly larger, but you might never notice the difference in a real-world situation.

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[Danie.e]

Thanks for the positive replies. The mods suggested are very easy and I am going to go ahead with the 650 carb conversion to fit the 850.

[Danie.e]

I made the swap from the 85o to the 650 carbs and it works. The return to idle takes slightly longer than with the original carbs and would a slightly larger pilot jet maybe do the trick? - the GS pilot jets are 40'swhile the 650's are 42.5 - I used the 40's from the 850 carb so as thinking the the 42.5 jets from the 650 carbs may be the way too go?

[Danie.e]

Took the bike out for test drive after balancing the carbs. The bike runs smooth, power transition from pull away to WOT is smooth and the bike is a pleasure to ride once more. Thanks for the advice that the 650 carbs will work. This is a do-able and worthwhile mod if you run out of options

[steve murdoch]

Glad to hear the carbs worked out.
Also, thank you for following up on swap.

[sbmisajw]

While we are on the subject, I just started a new thread but will ask here anyway. Will a set of 1981 gs650g carbs bolt up to my 1980 gs 550e. I know about the jetting differences but I'm more interested in the physical bolt on. The 650 and 550 cabs sure look alike!
Thanks

[Steve]

Yep, same size, different jets.

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[sbmisajw]

GS Whisperer---- Thanks for your reply to my inquiry about the GS 650 carbs bolting up to my GS 550! You the man!

Yep, same size, different jets.

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[sbmisajw]

So Steve, it seems like you are saying that basically all the individual carbs for the 550, 650 750 and 850 are the same with the exception of the #2 carb because of the throttle shaft length which seems to be the key difference (excluding the mounting brackets/bars) between the 550-650-750- and 850? I know the throttle plates have different numbers stamped on them and I believe that the number represents the degree angle/bevel of the plates--right?
Thanks again

You will also need to lengthen the throttle shaft on #2 carb, install a longer fuel T and install a longer "choke" activation rod.

The spacing between carbs 2 and 3 is a bit longer on the 850.

EDIT: Yes, you could also change individual carbs, if one of your damaged carbs is not #2.

The difference in the carb numbers is because of the different holes for the transition ports in the pilot circuit. The 850 carbs have holes that are ever-so-slightly larger, but you might never notice the difference in a real-world situation.

.

[Steve]

I know the throttle plates have different numbers stamped on them and I believe that the number represents the degree angle/bevel of the plates--right?

I never have figured out what those numbers are for.

If it is an angle, it should be possible to measure that for verification. I will have to check it out some time.

.

[tom203]

I never have figured out what those numbers are for.

If it is an angle, it should be possible to measure that for verification. I will have to check it out some time.

.

My spare 650 rack has 135 stamped on throttle plates
my rescued 850 rack has 130 stamped on plates. And no , I'm not taking them apart to measure bevel/angle differences

[sbmisajw]

So is the #2 carb body (the length of the throttle shaft) the key difference in the 550, 650, 750, and 850 carb rack? Of course the choke rod length and the connecting brackets are different.

thanks

[sbmisajw]

I found this interesting information regarding the numbers stamped on the throttle plates. This is from the XS650 forum. The XS650 use Mikuni BS carbs also. This guy did a bunch of research and experimenting. Here's what he says;
In summary, it appears that:

Mikuni #120 throttle plates have a 12.0° bevel angle.

Mikuni #125 throttle plates have a 12.5° bevel angle.

Mikuni #135 throttle plates have a 13.5° bevel angle.

My spare 650 rack has 135 stamped on throttle plates
my rescued 850 rack has 130 stamped on plates. And no , I'm not taking them apart to measure bevel/angle differences