1979 Johnson 4hp carb won't stop overflowing

[Dabbler_E]

Hi all,

This one has me pulling my hair out and I'm hoping somebody sees something I've missed. Picked up a 1979 4hp off CL, good compression, very good spark, had to fix the recoil starter (minor battle there), got it started. Yay.

Problem is that no matter what I do, fuel comes running up the high speed jet and out the front of the carb. This is an internal tank motor (gravity feed, no fuel pump), so it's not like the fuel is coming in at high pressure. I've replaced the float valve and seat, adjusted the float level about 8 gadzillion times, checked the float buoyancy (it's a newer one, so it's not really going to get fuel-logged, but I checked anyway), re-cleaned float valve and seat and blew everything out with compressed air (again, about 8 gadzillion times). Nothing. When I do the blow test, it works fine, but when I hook it up to the fuel line it is either shut off because the float level is so high that just closing up the float bowl shuts the valve, or it has a little stream of fuel running out. At one point, I thought I had it licked, but it turned out the tank was just out of fuel.

Anyway, I am pleading to the OMC gurus to help me out before I lose what little hair I have left.

--Eric

 

[oldboat1]

float installed upside down?

 

[Dabbler_E]

Nope, double checked that as well. With the carb all together, I can blow air into the inlet with the carb right side up but not with it upside down. So, the mechanism works with gravity providing the pressure. Just not when buoyancy is supposed to provide the pressure.

 

[Dabbler_E]

OK, I may be on to something here: if I just hold the float bowl on with my finger & thumb, the carb can hold its fuel. If I screw the bowl on with any more than the tiniest amount of torque, it comes streaming out again. And, by "tiniest amount of torque" I mean stopping as soon as I feel the screw contact the bowl (no longer turns freely). Actually, that's true for 3 of the 4 screws -- the other screw seems to cause the problem if it is on at all. I happen to have another comparable float bowl from a different carb ('76 9.9), and it does the same thing (overflow when screwed on to this carb).

Curiouser and curiouser.

 

[pro-crastinator]

pics?

 

[Dabbler_E]

I'll post some pics this evening.

 

[AlTn]

if you still have the original float install it and see what happens....I messed with a 6 hp. for a friend of mine and the carb would not fill with a new float < the carb passed the "blow test" as well>...thought it might be hitting the side of the float bowl and hanging up so I sanded the float in the close clearance area, no change...reinstalled the old cork float, problem solved....this may be just coincidental to your problem, but it doesn't take much time to try

 

[Silvertip]

If installing the float bowl causes the needle to unseat, then the problem is 1) a combination of incorrect adjustment of float height and float drop 2) wrong float, 3) incorrect inlet needle and seat, 4) bowl gasket too thin. I'm guessing you simply are misadjusting the float or that you have an incorrect needle and seat or a mismatched needle and seat.

 

[Fed]

There was a thread a few years ago here where the problem was caused by the float bowl not being open to the atmosphere at the top because of a blocked breather hole.
Imagine a bubble of air trapped in the top of the bowl not allowing the bowl level and float to rise but still pushing fuel up out of the main jet once the bottom of the jet was covered by fuel.
That lines up with the problem occurring only when the gasket seals.

Sorry I can't remember any more, I think the poster's name/handle was 'Tall Canadian', or not.

 

[Dabbler_E]

Fed -- ooooooh, you might be onto something there.

I tried the cork float -- same problem.
Double checked all float adjustments -- same problem.
Switched back to original float valve & seat -- same problem
Sanded the edges of the float in case it's sticking -- same problem.
Cut out a duplicate gasket out of card stock and added its thickness to the original gasket -- same problem.





Couldn't get the pic with the ruler, but that's 3/4"

 

[Dabbler_E]

Fed -- WHOO HOOO! Took me a while to find the bowl vent but it was indeed plugged up. Cleared it out, problem solved!

THANKS IBOAT OMC FORUM BRAINS!

 

[AlTn]

Great!!...learn something everyday here