Fuel Leak At Carb(top)

[egclassic]

I finally got the 73' Merc 850 running this weekend. I have already replaced all the wiring and the water and fuel pumps. I let her run for about 15 mins or so, checking to make sure my water pump install was good. Then I noticed that the black plastic linkage between the upper and lower carb(on the bottom side) looked "wet". Thinking it was just from when I sprayed carb cleaner at the carbs, I wiped it off. Ran it somemore and it was wet again. I am guessing that this linkage is the "Throttle Stop" mechanism, not the choke linkage. My manual shows the break down of a single carb(type A, BTW) but I can't seem to figure out where the fuel is coming from. I also replaced all the fuel hoses and barb fitting and checked them for leaks already. Am I going to have to rebuild the carbs?

 

[emckelvy]

Re: Fuel Leak At Carb(top)

Sounds like the carb is flooding and fuel is leaking down the throttle shaft. There's no seal between the throttle shaft and carb body (just a snug fit), so any gas pooled in the carb throat could readily seep thru.

Very common issue and best thing to do is replace both carb floats and also replace carb needle/seats and check/adjust the float level.

Note that older motors had a steel needle and rubber insert; later-style replacement needle/seat assy's have a rubber-tipped needle with solid body to seat against. You have to be sure not to mix these up, rubber-against-rubber or steel-against-brass will not work.

The floats are relatively inexpensive as are the needle/seat assy's. You'll also want to pick up (2) "carb packing kits" which will contain the gaskets you'll need to service the carbs.

Note that you should be able to pull the float chamber covers off the carbs without removing the carb bodies. You'll have to pull the starter to gain access. The carb packing kit also contains a carb-to-intake gasket if you wind up having to pull the carbs.

Here's a good place to look up Mercury part numbers, with diagrams:

http://www.mercruiserparts.com/SelectModelType3.asp?class_id=2

Here's a few aftermarket part #'s from my Sierra catalog:

Carb needle/seat assy: 18-7061

Float assy: 18-7208

Packing Kit: 18-7003

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

 

[egclassic]

Re: Fuel Leak At Carb(top)

Thank you for the info. I suspected a rebuild was in order.