1994 7.4L - rebuilt carb, won't start / idle

TBarCYa

Senior Chief Petty Officer
Joined
Apr 13, 2005
Messages
781
Last week I rebuilt the carburetor due to it leaking fuel from the bowl vents and now the engine won't run. I have the mechanical fuel pump connected to an auxilliary fuel tank with fresh gas and the rebuilt seems to have gone well except that the documentation called for 2 turns out on the idle mix screws and they were set 4 turns out when I started working on it.

If I give it throttle while cranking, it sprays fuel and will continue to run as long as I keep the throttle open and I can see the fuel spraying from the primary jets but as soon as I close the throttle it dies. I tried adjusting the idle screw to open the primary throttle plate but not as much as I had it open when it would run. I tried messing with the timing which I believe is CLOSE but I know it not set exactly. I set the idle mix screws everywhere from 2-turns out (per the spec sheet) to 4-turns out (as it was when I started) and there is no change.

There are 4 jets in the float bowls (2 per side) and I believe that I put them back in the same holes they came out of, but would the symptom indicate that I have them backwards? That's the only place where I believe I may have gone wrong during the rebuild.

Any other ideas for getting it to idle? Go wild and crank the idle speed screw until it runs then set the timing? Pull the carb back apart and make sure the idle orifices (below the blades) are extra clean? I was able to spray carb cleaner thru them after leaving the carb in a bucket of dip for a couple days.Swap the jets in the bowls around?

Thanks.
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,363
If I give it throttle while cranking, it sprays fuel and will continue to run as long as I keep the throttle open

No carb that I know of sprays fuel while cranking the motor and this type of carb you have worked on is.???????????????
 

TBarCYa

Senior Chief Petty Officer
Joined
Apr 13, 2005
Messages
781
No carb that I know of sprays fuel while cranking the motor and this type of carb you have worked on is.???????????????

Sorry, I open the throttle which causes the accelerator pump to pump fuel. I misspoke when I said that it sprays fuel while cranking, it's once it fires that I can see the fuel coming from the primaries but I assume that's because I have the throttle plate open.

I believe it's a 4bbl Weber. The stock carb for the 94 7.4L.
 

SimeC

Cadet
Joined
Jul 11, 2017
Messages
13
So that says 1-9/32 to the top of the float and the doc that came with the kit says 5/32 to the bottom (when inverted). I'll have to take it apart and check it but the float body is level with the gasket. It can't hurt to go back through the whole carb again... The hard part is done.

Hello
I rebuilt my carb on 7,4 Merc, 2 moths ago. Weber AFB 4 bbl.
I think those above are wrong measures.
When inverted, there should be 5/16. CAUTION DO NOT PRESS NEEDLE INTO SEAT WHEN ADJUSTING FLOAT LEVER.
In upright position is 15/16 between outer end of float and gasket.

I did it as I wrote above, on third crank motor started. That was it.
Later when I put a boat into the water, adjust the idle mixture screws
 

TBarCYa

Senior Chief Petty Officer
Joined
Apr 13, 2005
Messages
781
I haven't had a chance to take the carb apart again to make more adjustments... Hopefully I get to it, and get the boat started, this week.
 

TBarCYa

Senior Chief Petty Officer
Joined
Apr 13, 2005
Messages
781
I bit the bullet and bought a carburetor yesterday and within 30 minutes had the engine running and idling on it's own. So after being under water, I now have a running engine which means now I get to rewire the whole boat, replace the control cables and steering cables and... Who knows what else. But at least the engine runs!! WOOHOO!!
 
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