Rebuilt Mikuni VM26's now GS750 won't start

[mdelosrey]

Recently acquired a 78 GS750, Ran but needed a high idle (choke?) to stay running. Owner gave me an extra set of VM26's. Found a rebuild kit, cleaned em up, and installed all the new brass. I wanted to install these until I could rebuild the VM29's.

Installed them onto the bike but now it does not want to start at all. Checked spark and it has spark. I checked for fuel at the bowl, I cracked open the drain bolt and fuel came out. As far as setting wise, I set the slide at .030" gap. Air screw was seated and backed out 1.25 turns, Pilot jet is seated all the way in (unsure if this is correct), and needle is at lowest c-clip.

I noticed these VM26's have an extra brass port opposite of the choke plunger on carb 2,3, and 4. The VM29's only have these ports on carb 2 and 4 and the lines just led to ground (guess they're drains/overflow?). I'm not sure what I should do to the VM26 ports?

I'd appreciate it if anyone can help point me in the right direction...

VM26's rebuilt with Keyster KS-0231:

VM29's:

 

[Macbethpoe]

By pilot jet, do you mean the fuel screw on the bottom on the engine side of the carbs?

 

[Hoosier Daddy]

You could spray a SMALL shot of either (starting fluid) in there and see if she even barks... That'll at least tell you if is a fuel issue and not something else you disturbed.
I believe the adjustment screw for the pilot jet needs to be open to let fuel past. At least it is on my VM's

The term Pilot Air Screw may be incorrect. He states that on these carbs use a Fuel Flow Screw instead. This means that you are controlling fuel running through the passages with this adjustment, not air. So when turning the screw counterclockwise you are increasing fuel flow and when you turn it clockwise you decrease fuel flow.

 

[mechdesign2k4]

Plug the brass port on the #3 carb, this port on #3 is a vacuum port for the vac operated petcock. Third carb from left if your sitting on the bike. On 2 &3 they are just vents. Air screw should be 1.5 turns out from lightly seated. Fuel screw ( under carb) should be no more than 5/8 turned out from lightly seated.

Cleaning carbs requires at least 24 hrs in carb dip and a blowout of compressed air. Also, did you replace orings in the carbs? Good luck!



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