Two barrel carb issue

[Spiderhole]

Good morning,

I just finished a resealing on my motor thanks to a lot of your advice on from a previous post. I have a 4.3L Alpha 1 Gen 1, and I just swapped in vortec heads (the motor originally was pre-vortec), intake, and all marine seals to fix several issues. The boat itself is a 1986 4 Winns. Everything went together nicely and it appears to be sealed up very well. I am using the original two barrel carb that came with the original motor which was not a vortec motor, but I was informed that it has enough CFM to supply these heads with good fuel and air. In order to use this carb that I had to use the OEM mercury marine base gasket and genuine spacer that raises the height of the carb to the linkage doesn't contact the intake. Once I set the motor to TDC and set the timing, the motor fires right up, and goes to idle very easy and smooth.

I am however having an issue getting my carb dialed in. It is a two barrel carb with an electric choke and is set two degrees out. I rebuilt the carb to the prior to reinstalling. The air screw on the bottom of the carb was turned out two complete turns from it's seat. When you punch it quickly the motor stumbles and pops and takes a second to accelerate, which it does. If I ease the throttle up to it seems to accelerate better and get up to speed, but the it still starts popping. I can't tell what with the mixture is off... if it's getting too much, or two little fuel or air.

The only other thing which may be important is that the electric fuel pump is not OEM, which I don't really like the idea of, but it is what was in the boat from the previous owner and it worked. It says it is 4-7 PSI 35GPH.

 

[GA_Boater]

Don't know about the popping, but the bog from idle and better acceleration easing the throttle sounds like the accelerator pump isn't squirting.

Take off the flame arrestor and manually advance the carb linkage quickly and see if gas is squirting down the throat.

Probably some other checks after that.

 

[Bondo]

When you punch it quickly the motor stumbles and pops and takes a second to accelerate, which it does. If I ease the throttle up to it seems to accelerate better and get up to speed, but the it still starts popping.

Ayuh,..... Poppin' through the carb is sayin' it's lean,......

You might be able to richen the acc. pump circuit, 'n the hi-speed circuit,.....

 

[Lou C]

Is this a 2 bbl Mercarb? I think this might be Merc's adaptation of the old Rochester 2bbl carb that both Merc and OMC used. the first thing is if you are using a spacer, make sure there are no vacuum leaks, that will for sure cause lean running problems. In addition to checking if the accelerator pump is working, did you set the idle fuel mixture? Take a look at your spark plugs, if the center insulator is white, you are lean, if medium grey or brown you are good, if very dark brown or black too rich. If the electric fuel pump is putting out 4-7 psi that should be fine. Are you sure all the passages in the carb were blown out?

 

[Spiderhole]

Yes this is a two barrel merc carb. The only two adjustment screws that I am aware of are at the bottom of the carb, and the idle screw.

I pulled three of the plugs. They center insulators are black. I guess that means I'm actually running rich?? I too believe it seems more like a lean running condition so I'm kind of stumped?

Also, I disconnected the linkage. The accelerator pump appears to be functioning normal. When I open the throttle the fuel squirts out of both sides down into the carb and intake.

I am positive the carb was clean as a whistle when it was put back together.

 

[Lou C]

Did you replace the needle valve and check the float adjustment? Black plugs mean its running way too rich.

 

[Spiderhole]

Did you replace the needle valve and check the float adjustment? Black plugs mean its running way too rich.

I did replace the needle, seat, and checked the float... thought I did it correctly??

Other thing I think I found a mistake. When I set the base timing, I think I needed to do it to 8 degrees over TDC... I know I was at TDC, but I set it at 0. That was a mistake on my part I believe. Not sure if that would cause this problem, but I know I need to fix that.

 

[Tycer]

If you’ve got two idle air screws it is not a Mercarb. It’s a Rochester.

 

[Lou C]

I have never seen a mercarb up close but in pix it looks like what they did, was change the casting so that it covers were the idle mixture screws were on the Rochester design (EPA nonsense no doubt) I bet that these can be drilled out carefully so you can adjust the damn idle the way it should be. We had this same BS in the '70s with the stupid plastic limiter caps on the mixture screws. In fact we have a '12 Suzuki outboard that would never run right with the factory setting. A tin cover over the idle mix screw. Took it in under warrantee, the Suzuki rep removed the tin cover, re-adjusted it and then put some kind of epoxy over the screw. Well it was better but not 100%. So after the warrantee was over, something happened to that epoxy, ahh....and now....its all better....all it took was 1/2 more turn of the idle mixture screw. Set way way too lean from the factory.

 

[Tycer]

I have never seen a mercarb up close but in pix it looks like what they did, was change the casting so that it covers were the idle mixture screws were on the Rochester design (EPA nonsense no doubt) I bet that these can be drilled out carefully so you can adjust the damn idle the way it should be. We had this same BS in the '70s with the stupid plastic limiter caps on the mixture screws. In fact we have a '12 Suzuki outboard that would never run right with the factory setting. A tin cover over the idle mix screw. Took it in under warrantee, the Suzuki rep removed the tin cover, re-adjusted it and then put some kind of epoxy over the screw. Well it was better but not 100%. So after the warrantee was over, something happened to that epoxy, ahh....and now....its all better....all it took was 1/2 more turn of the idle mixture screw. Set way way too lean from the factory.

They did cover the single idle air screw just as you describe.

 

[Spiderhole]

I'm somewhat ready to rip my hair out. I took the carb out of the boat to inspect everything again and see where the problem may be. I still had the original brass valve seat and needle which really didn't look that bad. When I did the rebuild I had checked the float height and I thought it seemed close. I swapped the original valve and need back in and set the float height to what I believe are the factory setting. When I went restart the boat it would no longer start at all, and the carb was completely flooded. I am not sure what exactly I should do if I flooded the motor - I just thought it was hard starting. Everything else is the same, so with that much fuel I am at a loss why it wouldn't at least fire off. This is by the way, no doubt an original Mercarb, it's tagged as such. I've built many other carbs, but this little thing for as simple as it is, is a pain to adjust. Other question I suppose... it has an area beneath the pump where it appears a checkball is supposed to go under a screen. For the life of me I can't remember if it had one before I did the rebuild, but I used the one that was in the rebuild kit as it clearly has a seat for it. Is that checkball essential?

 

[Chris51280]

There is a ball bearing that is held down with a stacked piece and a spring under the venturi piece. This check ball gets pushed with the plunger from the accelerator.
Mine flooded too. I had it ata mechanic and he told me i have a cracked carb which was BS. I cleaned everything and made sure my needle and seat are clean and actually closing correctly with the adjusted float height. and what ya know, It fired right up without flooding.
So take the top off and make sure your float is closing. I tipped it upside down so the weight of the float closed the valve and i blew in with my mouth to see if it will let air through. Float height is absolutely critical and I would rather make it so it closes a bit sooner than later. Also check the other low setting

 

[Spiderhole]

I bring forward good news. I believe I have completely resolved all the issues. My boat now rips when I punch it - 0 hesitation, no popping, smooth acceleration all the way through. It was a combination of getting the float height exactly correct, and I also adjusted the choke just a tad more open. It starts easy and goes right to idle. Thanks for all your help. Too bad I am finally finishing this up so close to the end of the season here in Dallas!