TOPIC: 60's 40hp carb high speed nozzle

Does the boss gasket on the bottom of the nozzle seat against the boss on the bottom of the float chamber? If it does, how does fuel get in the nozzle for delivery to the carb throat? I've been working on the carb all week and I do not see any route for fuel into the boss for the nozzle to pick it up. I know carbs are supposed to be mysterious, but I like to understand how things actually work. If the gasket does not seat, what is it there for? Let me know, thanks!

What make, model, & serial number is your motor?
doc

The main jet is in the bottom of the float bowl, where you'll find a brass hex-head (maybe slotted) plug on the outside of the float bowl, screwed into the bowl and sealed by a fiber washer.

There's an opening cast into the bottom of the float bowl that gravity-feeds fuel to the "intake" side of the main jet; fuel flows thru the jet to the center of the chamber that seals against the carburetor via the "boss" gasket, and thru which fuel is drawn up the emulsion tube and into the carburetor.

Note that there are holes drilled in the sides of the emulsion tube and when you do a carb rebuild you need to unscrew the tube and make sure the tube is clean and clear.

See the attached pics of a generic 379965 float "chamber" aka "bowl. You'll see in one pic the main jet cover hole. Also the passage that goes to the main jet, so you can get your screwdriver on it for removal.

Note the other passage that's at 90 degrees to the front of the carb, that's where the idle fuel is pulled up the side of the carb, thru the punched hole in the float bowl gasket, and up into the idle circuit.

I've seen this hole all squeezed-off from age/deterioration, such that it blocked any fuel from going up into the idle circuit. So it wouldn't idle. A new gasket fixed it right up! So check that gasket if it's used.

On the pic showing the inside of the bowl, see the small idle passage in the one side of the chamber wall. Also note the opening in the floor of the bowl, the fuel feed to the main jet.

This all has to be clean and clear or you'll have fuel supply issues. It may run above idle, but not get fuel to the idle circuit.

Since you've screwed the idle mixture needle in-and-out with little effect, that would suggest that something is still plugging up your idle circuit.

So I'd recommend pulling the carb and checking all that out. Blow air/carb cleaner thru every passage to make sure they are clear. Hopefully you'll find your issue and go on having fun with your 40hp!

HTH..........ed

Great explanation! I see the passage way and now I understand. Thank you!

You Betcha!!

Mystery solved! The end of last season I replaced the float bowl gasket. The gasket matched the original except for sealing the low speed passage. The gasket fit around the outside of the passage but was open to the inside. This left suction for the low speed circuit to draw from the top of the fuel level (air) instead of drawing fuel from the bottom of the bowl. Put in the correct gasket, she's running as smooth as silk!

Glad you've got 'er whipped finally!

I've had way more than one of those gaskets cause problems in the past. So if it's got low-speed fueling problems I always look there first. At times I've needed to get one out fast and didn't have a new gasket handy, so I took a small gasket punch and punched out the squeezed-off rubber hole, after that the motor would run perfectly! Funny how those things don't change!! They do have some better-built float gaskets that last longer, but that's about it.

Nice to be back on the Site, eh!!