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Those carb numbers

  • Thread starter Thread starter rickt
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rickt

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The '78 GS750 that was given to me was put to rest in 1981 by the PO with 2098 original miles. The PO drained the fuel and removed the carbs. Only one of the four was partially diassembled. Each carb was placed in a coffee can and remained there until I received the bike about a month ago. Of course the carbs were not numbered. I'm wondering if it makes a difference which carb is 1,2,3, and 4 when I get them rebuild and ready to mount on the bike. Is there any way that I can tell by looking at them which is which?

Thanks,
rickt
 
I'm pretty sure it does matter. I think they will only go together one way, but it's kind of hard to describe. I think a picture would help. You need the fuel inlets and other things to mate up properly.

I don't have a GIF resizer handy or I would post an illustration.
 
Last edited:
Yes, it DOES matter.

Look for the fuel and vent openings on the sides, and the throttle adjustment plates.

Carb 1 will have fuel and vent openings on the right side only.
Carb 2 will have fuel openings on both sides and a vent openings on left side only.
Carb 3 will have fuel openings on both sides and a vent opening on the right side only.
Carb 4 will have fuel and vent openings on the left side only.

The fuel fittings between 1&2 and 3&4 are straight pipes. The fitting between 2&3 is a T fitting that brings the gas from the tank.

The vent fittings are both T fittings, and they are betwen 1&2 and 3&4.

Carb 1 throttle rod has an adjuster mechanism on the right side.
Carb 2 has the tab for carb 1 on the left and an adjuster on the right.
Carb 3 is the master carb, to which the throttle cable attaches, usually on the left side. It also has a tab on the right side.
Carb 4 has an adjuster mechanism on the left side.

Disclaimer: This is the way it is on my 650 and 850. I can only presume that it is the same on your 750.


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rickt said:
The '78 GS750 that was given to me was put to rest in 1981 by the PO with 2098 original miles. The PO drained the fuel and removed the carbs. Only one of the four was partially diassembled. Each carb was placed in a coffee can and remained there until I received the bike about a month ago. Of course the carbs were not numbered. I'm wondering if it makes a difference which carb is 1,2,3, and 4 when I get them rebuild and ready to mount on the bike. Is there any way that I can tell by looking at them which is which?

Thanks,
rickt
Click to expand...
Yes it matters. The stock carbs are Mikuni VM 26mm. No throttle plates. Round slides are used.
Easiest way to remember...sitting on the bike, left to right = 1 to 4.
#1 and #2 brass side air screw will face left/outward with #2 also having a brass float bowl vent nipple pointing back/upward at its left side. #2 supplies venting for both 1 and 2.
#3 and #4 will have the brass side air screw facing to the right/outward with #4 also having a brass floatbowl vent nipple pointing back/upward at its left side. #4 supplies venting for both 3 and 4.
#3 also has a brass nipple in the same location but it's for vacuum, not venting. Easy to see which is which.
#3 will also have the fuel passage open on both sides. #4 will be open left side only.
 
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