[markpj23]

Originally Posted by Tom Vaught

Good Post, NeighborsComplaint, 8.5" Power Valves are rarely used on any street cars but are used on delivery trucks and power boats where you need a lot of fuel quickly when a higher load is imposed on the engine.

If the OP could post up the stamped numbers on the air horn we could identify the exact application he has.

Tom V.

Only numbers I see on the air horn, front of carb, read: 80555-1, and below that is 0327 (date code I assume).

[markpj23]

So I got out ye olde trusty timing light - an older model Craftsman with a dial advance knob - to see what the timing looks like.

YIKES. I'm not sure how this this is running - timing is waaaayyy retarded. Else the balancer is on wrong but I don't think it's possible to do that...? It has to be 25 degrees after TDC or more.

Yes I tweaked the advance knob and it moves the mark as it should.

So what should my idle advance be - 8 degrees BTDC?

[NeighborsComplaint]

Originally Posted by markpj23

So I got out ye olde trusty timing light - an older model Craftsman with a dial advance knob - to see what the timing looks like.

YIKES. I'm not sure how this this is running - timing is waaaayyy retarded. Else the balancer is on wrong but I don't think it's possible to do that...? It has to be 25 degrees after TDC or more.

Yes I tweaked the advance knob and it moves the mark as it should.

So what should my idle advance be - 8 degrees BTDC?

Did you disconnect the vacuum advance before checking (#1 front driver side)?

[Tom Vaught]

Originally Posted by markpj23

Only numbers I see on the air horn, front of carb, read: 80555-1, and below that is 0327 (date code I assume).

Spreadbore Carb 8055-1 is typically marked only with 5 numbers:
The "List Number" in this case 8055 and the revision number -1 for your carb.
The Carb # is for a 1971-1972 Chevy engine.

There is also a carb with the number 8051-1 that is also for a Chevy.

Look at your numbers again. You have one too many numbers. 8051 or 8055?

Tom V.

[NeighborsComplaint]

Vacuum secondary spread-bores used a 6.5 Power Valve so yours has the 6.5 and does not need changing unless leaking due to backfire damage. Again, it would run so poorly it would be obvious.

The double pumper used an 8.5 Primary power valve and 6.5 secondary which is where I got that 8.5 number from.