Lost carburetor linkage screw (2 Viewers)

[40cruiserdad]

My son came home from work today complaining that my cruiser would not go over 50 and the gas peddle felt sloppy and when I went out to look at it I found a screw had fallen out on one of the linkages. I'm hoping someone can tell me what size screw I need to get to replace it.
I've attached a picture of the missing screw location. The carb is off a 1971 I'm pretty sure.

 

[mattressking]

It's a hex shoulder bolt, not a off-the-shelf item unfortunately...but potentially with some sleuthing. Just needs to be M6 into carb body and shoulder is low tolerance fit to linkage arm....

Your best option is a used spare otherwise you could take an M6 bolt with the correct length and put a nylon bushing to fill the gap.

That said, the throttle positioner isn't required, especially if your VSV isn't connected and/or the diaphragm is disconnected.

 

[40cruiserdad]

Thank @mattressfor the quick reply. I'll try to make a quick fix tonight from the hardware store until I can get the proper shoulder bolt replacement. Kids got to get to school tomorrow. I assume the thread pitch is 1.0?

 

[40cruiserdad]

Any idea on the shoulder length for that bolt? Or maybe a picture of one?

 

[charliemeyer007]

M6 is half the picture thread pitch is the other. Length can be cut to fit if you start long enough.
Home Despot has M6 x 1.0 and M6 x 1.25 bolts 20mm long for $2.75 for 2 - so for $6 you can get 2 of each. Nylon tubing could work as a shoulder. Thin brass shim stock (0.002) cut in say 3/16 wide strips can be wrapped around the bolt to build up a precise shoulder - a touch of solder will hold the coil tight.

Everbilt M6-1.0x20mm Zinc Hex Head External Hex Drive Hex Bolt 2-Pieces (D8-D) 861258 - The Home Depot

Hex bolts are hexagonal head fasteners with machine threads. They are commonly used for machinery and construction projects, both residential and commercial. Fully threaded sizes provide excellent grip

www.homedepot.com

 

[mattressking]

It’s the depth of the linkage, I’m 2000miles away from any of my carb spares else I’d tell you. A quick measurement will yield the answer. You won’t get what you’re looking for at the store, it’s going to need the correct bolt used or bolt with a nylon spacer that is ID of 6mm bolt and OD of linkage opening. Might require putting on a drill to get the right size.
Otherwise just run it disconnected, not a problem to disconnect.

 

[40cruiserdad]

Just tried some m6x1.0 bolts and they won't start...must be the m6x1.25 fine thread that I need. Unfortunately stores are closed now it'll have to wait till tomorrow. Thanks for all your help!

 

[65swb45]

In the first year or so of production of that carburetor (started in 10/69) the throttle positioner pivot did use a smaller screw on a smaller pivot. I don’t remember the size, but you can pull one of the 5mm screws from the air horn to see if that’s it.

As far as shoulder length, form follows function. Measure the length of the collar in the pivot and add 1/32 to 1/16” so that the bolt will have a positive stop against the fuel bowl without pinching the pivot so that it doesn’t move.

 

[MDH33]

I dug through my spare carb parts box and came up with this. Looks correct based on an early 70's carb I have on the parts shelf, maybe Mark can verify? PM me your address and I'll send to you.

 

[40cruiserdad]

Thanks @65swb it was an M5x.80 screw size after all. Temporary fix is in place and it's back on the road.

 

[MDH33]

Thanks @65swb it was an M5x.80 screw size after all. Temporary fix is in place and it's back on the road.

Hmm, the one I posted above must be from a slightly later F, pretty sure it's M6.

 

[B y r o n]

If you can't find a factory replacement you may be able to find a non-OEM at McMaster-Carr.

 

[45Dougal]

If you happen to have a Japanese motorcycle rusting in your shed, then this also makes an excellent source of metric fasteners

 

[40cruiserdad]

If you happen to have a Japanese motorcycle rusting in your shed, then this also makes an excellent source of metric fasteners

Lol! I used to have a 1986 Honda Magna. I should have thought about that before I sold it.

 

[45Dougal]

Lol! I used to have a 1986 Honda Magna. I should have thought about that before I sold it.

I actually have an 87 super magna. Small world.

 

[charliemeyer007]

Even a cheap set of metric tap and dies can be a life saver. I have recut many a bolt down to the next size smaller thread - that will leave room for a shoulder area. Drill motor and a file plus a dial caliper can be an awesome milling machine. I have a Unimat that does really well with carbide bits and the compound low pulley.
As a kid I made dozens of firing pins for my dad's gun trading hobby using an eggbeater drill and a file. I still that drill around here someplace.