Idle Mix Screw

[Tim Meaders]

I have 2 sets of BS34's that have different size idle mixture screws. I have tried to determine which size is correct for the 81 carb but I have not been able to find the info anywhere. If anyone knows which size is correct I would appreciate the help. The image shows both screws with the diameter at the tip of each screw.

 

[5twins]

Well, this is a new one, lol. My best guess is that the "skinny" tipped screw is an aftermarket replacement. I say that because the BS34s were highly E.P.A. mandated so I would assume they'd have that leaner "fat" tipped screw. But, I'm only guessing here. I'm sure either will work just fine but the best setting for each may differ slightly.

 

[gggGary]

I vote for the used one
but here's some dimensioned pics from 81 carbs on the bench, screws are factory ( I removed the plugs) The two are slightly different.

 

[Tim Meaders]

Thanks 5T.

If anyone has one out of the carb and can measure what size you have, it could get interesting.

 

[Tim Meaders]

I vote for the used one
but here's some dimensioned pics from 81 carbs on the bench, screws are factory ( I removed the plugs) The two are slightly different.

View attachment 129744

View attachment 129743

Thanks Gary:
It appears there was more than one size used in these? Seems strange they don't reference this anywhere.

 

[gggGary]

note in the second pic the 3 holes in the back ground, the screw only controls 1/4 of the idle flow once the butterflies are opened the slightest bit, why synch is so important. If you get just one carb pulling off the three holes...