Carb needle and seat; choose metal or rubber-tipped needle?

[ajgraz]

Need to replace needles and seats in the carburetors in my Mercury 70hp 3cyl 1979.

Given the choice, should I go with the OEM needle and seat set with the old-fashioned all-metal needle:

(representative photo)

Or the Sierra set with the rubber-tipped needle:

(representative photo)

 

[hotrod53]

Re: Carb needle and seat; choose metal or rubber-tipped needle?

I would do further research, but here is my thought.... the ethanol in todays fuel can swell the rubber tip and make it stick in the seat. It has happened to me 3 times, once I started running my motor out of fuel each time, I have been OK. I need to change mine and I am told that they have a "ethanol compliant" needle, I think that just means, no rubber tip.

 

[ajgraz]

Re: Carb needle and seat; choose metal or rubber-tipped needle?

Any other opinions on this?

Unless someone can give me a compelling reason to go with the rubber-tip, I am leaning toward the all-metal needle at this point.

 

[Chris1956]

Re: Carb needle and seat; choose metal or rubber-tipped needle?

Are you sure the needle and seat are all metal? Normally there is a rubber component to provide the seal. The merc inlet needles I have seen were satinless with a neopreme tip and all-bass seat, or stainless needle and bass seat with rubber center.

 

[Chris1956]

Re: Carb needle and seat; choose metal or rubber-tipped needle?

BTW - newer inlet needles and seats will be compatable with ethanol fuel. I would not worry about it.

 

[ajgraz]

Re: Carb needle and seat; choose metal or rubber-tipped needle?

Hmm, you make a good point Chris. There's going to be a rubber sealing surface in there one way or the other, and I suppose it stands to reason that a NOS OEM part--that could be many years old--is less likely to have ethanol-compliant rubber than a new Sierra part.

Any other opinions?

 

[Texasmark]

Re: Carb needle and seat; choose metal or rubber-tipped needle?

The thing I like to have happen is to relieve the pressure on the needle seating area which means let the fuel in the bowl drop causing the float to drop and relieve the pressure. My current setup siphons the fuel out of the carb while the boat is at home and not in use which automatically supports my desire for what I said.

I know this because every time I take the boat out the bulb is soft and I have to pump up the fuel line. Were It not for that, i would remove the fuel line from the engine while still running (on the trailer,LU in the water and let the engine idle for a minute or two and then shut it off. I use Sea Foam so I don't worry about varnished up carbs.

HTH,

Mark

 

[ajgraz]

Re: Carb needle and seat; choose metal or rubber-tipped needle?

I know people run the fuel out of the carbs after they get home. I actually stopped doing that myself a couple weeks ago after reading some stuff on this forum about potential for gumming up and (more importantly IMO) the run-the-motor-lean potential. Maybe stopping draining is what ruined my current rubber-tipped needles? Maybe I should just run them out "partway"?

In fact, when I installed all-new fuel lines and a separator filter a few weeks ago, I consciously eliminated the bayonet connectors between the primer bulb and the engine (so my fuel hose goes "unbroken" between the primer and the pump on the powerhead) because they were old and no longer sealing together--best I can tell the seals in the female bayonet were worn out--and I wanted to eliminate potential failure points. So unless I replace the bayonet connectors, I can't easily run the carbs dry anyway as it sits. Great, more rubber to put back into the system

...My current setup siphons the fuel out of the carb while the boat is at home and not in use...

Is that something you engineered yourself? Tell me more. I know I could pull the main jet plugs and drain the carbs, but I have to remove eight screws and a faceplate to get to them and IMO that's not an "everytime I come home" easy solution.

Dangit, why'd they have to screw around with our gas? All I want is a bullet-proof fuel system!

 

[Chris1956]

Re: Carb needle and seat; choose metal or rubber-tipped needle?

Mark, Normally the gasoline in the carbs evaporates. That is why you have to prime the motor before each day's usage. Did you install some kind of "carb draining" equipment in your motor?

It is not wise to run fuel out of larger multicylinder Outboard motors. When you do this, some carbs run out of fuel first. When this happens, the cylinders w/o fuel and lubrication are still moving due to the action of the cylinders still running. That cannot be good for them.