How do I disable the fuel pump to do a compression test?
 

1969 F100 360

How do I disable the fuel pump to do a compression test?

I know some of my valve seats are trash because I can see exhaust coming from my valve covers. When I do a compression test to see which ones need recut fuel sprays out of the unplugged cylinders. :\

Thanks in advance.
Smellii

I don't disable the pump, haven't had any problems.:)

Prop the throttle open all the way. At cranking speed with the carb open all the way there will not be enough vacuum created to draw fuel out of the carb. If you still get fuel spray out of the spark plug holes, then you also have a carb problem. Good luck.

fuel spraying out spark plug holes ? all the engines i have tested none have done this . something don't sound right .

electric or mechanical pump ?

Exhaust from the breather is not a valve issue. That is worn compression rings, blowing air down into the block and out any open hole.

If you have gas blowing out a cylinder, then you have carb issues. I've never had to disable the pump to do a compression test. Leaving the carb alone, it should not draw that much fuel to get wet.

Same here, done hundreds of compression tests and never had gas spray out. Also, If you tear it down, ALL the valves/seats/guides/springs need brought back to factory spec, not just the worst ones.

Ok. Thanks fellas.

I'd say at this age they are all wore out.