Mercarb 2BBl

[ChrisCraftJohnny]

Hello all,

In process of rebuilding my 2BBL Mercarb. It's going well. This Carb is quite simple and I have had no trouble so far.

One question:

My Carb had the solid plunger for the needle valve in the bowl. The kit came with both the solid and the smaller spring loaded plunger.

Merc says if the Carb was flooding at idle and running rough, (mine was, hence the rebuild) to switch out to the other plunger during rebuild.

In other words, If the solid plunger was there, switch to the spring loaded and visa-versa.

I am planning on switching to the spring loaded unit since mine was flooding at idle and running rough.

Here is a picture of what exactly I am talking about.

Does anyone have any experience with the solid vs. the spring loaded plunger? Thanks.

 

[Gary H NC]

Re: Mercarb 2BBl

The kits i have done on the Merc carbs had the same needle and seat but 2 different plungers for the accelerator pump.One with a straight shaft and one with the 90* shaft.
I never run across one with 2 different needle and seat designs.
Maybe one of the Merc pros will chime in.

I would say use the needle and seat with the small spring or clip that hooks to the float arm.

 

[zbnutcase]

Re: Mercarb 2BBl

Yes a lot of rebuild kits for these come with the two style needle valves (plunger!?). Generally the spring loaded one is used on 4cyl engines which tend to run rougher at idle than a V6/V8. But if its a 4cyl I would use the sprung one. 'nutcase

 

[ChrisCraftJohnny]

Re: Mercarb 2BBl

The Merc instructions say to switch to the other design if you are having troubles with the current one you are using. Nothing about 4cly or V6, V8.

And yes, plunger. The needle valve is the part with the 30 Deg. point on the end. The plunger is the small pin that goes inside to activate the movement of the needle valve. This is mechanical engineering 101. Part's in a assembly have their own names. A needle valve is a needle valve and a plunger is a plunger. Or you could say the needle valve assembly.

But my question has not been answered yet. Has anyone ever changed over from the solid to the spring loaded before? And what were the results?

 

[ENSIGN]

Re: Mercarb 2BBl

On a mercarb i normaly always use the spring loaded needle and set the float level to 9/16 of a inch and never had a problem. Good luck,Ted

 

[guyaverage]

Re: Mercarb 2BBl

But my question has not been answered yet. Has anyone ever changed over from the solid to the spring loaded before? And what were the results?

I did. I was getting a rough idle and hard-start when warm, noticed fuel dripping into the venturis while idling and just after a hot shutdown. Switched to the spring loaded needle and reset the float measurements per the instructions. Dripping stopped and had no problem restarting.

My instructions had a footnote on the bottom that switching to the spring loaded needle can cause hesitation or stalling on very sharp left turns, and I do get this now, but it isnt much of a problem because I dont make too many very sharp turns, maybe a few if we are doing some wild tubing, but it hasnt caused a problem.

Anyway I have a 470, I have plenty of worse problems to worry about.....

 

[cr2k]

Re: Mercarb 2BBl

Well when you said "plunger" in relation to carburetor I (and I'm sure most others) thought accelerator pump. That is the only real "plunger" in the carb. The spring on the needle is more like a shock absorber.

But anyway you got it fixed and it works!

I would consider the spring needle for rough water to eliminate hammering of the needle in to the seat.

 

[John_S]

Re: Mercarb 2BBl

But my question has not been answered yet. Has anyone ever changed over from the solid to the spring loaded before? And what were the results?

Yes, on a '96 1/2 5.7L, because of dribling of gas during idling. Switching to the spring fixed it to make it to the ramp for end of season. Ran fine for that last run. I switched to a 4brl that winter and sold carb, and never heard of any complaints.

Turned out latter, that the fuel pump was putting out too much pressure, and the spring type was able to control it better than the solid. As someone already mentioned, check your instructions, I believe the float setting was different for the two, but it has been a few years since I did it.