Merc 485 3.7L float bowl leak?

[billywhizz]

Rochester 2bbl carb, where does all the petrol go? accepted it cant syphon back out, so does it really all evapourate? starts fine if left for a few days but after 2 weeks have to crank for ages to get the fuel back up, tested the pump at 7psi ok? also hard to start when hot, so if the leak is from within the float bowl where do i look?

Lets go back to the explantion.


4. The only possible reason for the carb to not have fuel in it after 2 weeks, is because of a leak from the bowl of the carb.


OK Don, Quite happy to take your word for it and just about grasped the theory, my engine does exactly the same, so where should i be looking for the leak from within the bowl?

 

[Don S]

Re: Merc 485 3.7L float bowl leak?

On a Rochester 2bbl carb, there are 2 well plugs similar to the QuadraJet well plugs. They are located between the bottom and center section of the carb.
Here is a picture of the QJet carb (couldn't find a 2bbl picture), the circled plugs are what you will find in the 2bbl carb, and they will leak.
JB weld has worked for me after a thorough cleaning to remove all gas and oil from around the plugs.

 

[Bondo]

Re: Merc 485 3.7L float bowl leak?

Ayuh,... Tear it apart,+ rebuild it... If you do it Right, you'll find your answer...

There are various drillings,+ passages that are below fuel level in carbs,...
Some are capped with welchplugs, some are Not...
It could be ANY of 'em...

 

[billywhizz]

Re: Merc 485 3.7L float bowl leak?

On a Rochester 2bbl carb, there are 2 well plugs similar to the QuadraJet well plugs. They are located between the bottom and center section of the carb.
Here is a picture of the QJet carb (couldn't find a 2bbl picture), the circled plugs are what you will find in the 2bbl carb, and they will leak.
JB weld has worked for me after a thorough cleaning to remove all gas and oil from around the plugs.

OK Don, Gotcha, thank you for your superb informative and indeed timely response, will keep you posted.

 

[zbnutcase]

Re: Merc 485 3.7L float bowl leak?

Yes a bowl of fuel WILL evaporate in 2 weeks easily, prob nothing wrong with carb. 'nutcase

 

[billywhizz]

Re: Merc 485 3.7L float bowl leak?

Don, cant find the plugs you mentioned, also noticed slight movement in the throttle plate shaft bushes, is this normal or should there be no movement at all, stumped now as where should i be looking for float bowl leak?

 

[Don S]

Re: Merc 485 3.7L float bowl leak?

That's the wrong section of the carb, if you have a float bowl leak, look in the section that has the float bowl in it.

 

[billywhizz]

Re: Merc 485 3.7L float bowl leak?

Ok in the float bowl section we have the 2 main jets that supply the venturi and another little brass plunger type thing, dont know what that does it looks like it is pressed by a rod with a spring wraped around it attached to the top section (air horn)
and also the plunger for the accl pump, i filled the bowl with cleaner but cannot see any drips or leaks anywhere?
i notice that there is a hole about 6mm dia going through the air horn (top section) straight into the top of the float chamber which i guess is to direct fumes/fuel etc back down through the carb into the manifold, what stops the fuel slopping down there when the sea is lumpy?