Over the last couple months I've straightened out a couple of problems with my carbs I thought I'd share (I have '97 454 Mag 365's):

1) Long crank time after sitting-Replacing the fuel pumps cured both motors of this. Now the motors start in about 3 seconds after sitting a week.

2) Fouled #3 plug (fuel soaked)-Float adjustment was the culprit here. The odd cylinder side float was allowing fuel to dump into the intake which gave it a direct route into #3 cylinder. I adjusted the floats in both carbs to within .001" of merc spec and now have the crispest throttle response I've ever had and the motors sound fantastic. If you have webers I strongly suggest adjusting the floats very carefully, as they seem to affect the mixture (they shouldn't I know, but my 2 motors say otherwise), get it right and you will be amazed at the difference!

3) Loss of WOT RPM's- At WOT ONLY, 80% was just fine, my port motor would starve for fuel. I chased this one for a while and finally discovered the rubber fuel line was collapsing internally right at the fuel inlet barb. I'll post the pic but I don't know how much you can see.

Good for you. I'm always glad to hear when someone solves a hard to find problem. Now, we need to know a couple more things.

What fuel pumps did you replace the the stockers with?

What is your float setting?

The hose collapsing internally is weird. Maybe looking for that problem can help someone else, too.


I had a Weber on my 502 Mag and it had the same hard starting problem. This year I replaced it with a Holley 800. That cured the starting problem for me. Now it starts right up after a week and I gained 2 MPH, too. It seems that the Webers must be much more sensitive to the level of fuel in the float bowl than a Holley.

Hope your luck continues

Thanks Macdad260!

I installed stock merc fuel pumps (mechanical)

The float drop is 2" and the float level is 1.281"

I'm running a poker run Saturday, that will put everything to the test, I forsee no problems though.

Which model Holley did you use? Do you think this would work well on a 7.4L?

The off-road spring-loaded needle and seat sold by Eldebrock will fit the Weber carbs and cures the problem of fuel dumping over the bowl vents while under way. It could be part of the problem. I used a Weber on my 454 and thought it was a great carb for tweeking.