1994 Merc 5.0 2brl Carb issue when off

[MorbidMedicz]

Hello everyone. New to the forum, appreciate any input. I’m pulling my hair out.
94 bayliner 2452 5.0 with thunderbolt ignition. Purchased boat and took it to a shop. They said it ran fine but needed a new fuel pump due to throwing fuel in carb. I agreed.
Took the boat home and got it running. After hours of running, I shut it off and heard gurgling. Looked in the carb and I see it’s full of fuel and dribbling in. Tapping didn’t help, venting the fuel cap, or disconnecting throttle cable.
Had same shop rebuild carb. Took home and ran fine. Took on the water and boat ran horrible. Fast forward, carb full of fuel. Wtf.
Had them re-rebuild the carb. He put in new needs and seat and verified float. I also verified float by flipping upside down and verifying it is closing. I also verified fuel pump is putting out 7psi. No fuel in the fail tube displaying a bad (new) pump.
I’ve had some spark issues and cleaned the thunderbolt ignition plug and such. I’m out of ideas and money lol.
Does anyone know if the thunderbolt ignition has a control to shut off fuel I’m missing? I’ve heard carbs sometimes can be bad requiring replacement but I paid $400 to get it rebuilt.
Any help is much appreciated. I want to get this boat on the water and take disabled vets to the fish. Can’t do much on a dang trailer. Thx again.
Lucas

 

[MorbidMedicz]

I want to clarify what I cleaned on the thunderbolt. It was the piece held behind the distributor, ignition control modul . Put new heat transfer compound on as to help the hopeful intermittent spark issue. Not sure if it affects the fuel flow or not.

 

[Scott Danforth]

your engine should be mechanical fuel pump yet. did someone convert it to electric?

7 psi seams a bit high

 

[alldodge]

Agree 7 psi is on the upper limit. Depending on what needle valve is installed (spring loaded or fixed) its most likely just a bit to much pressure. Install a fuel pressure regulator and get it down to at least 6, and 5 would work

https://www.holley.com/products/fue...regulators/carbureted_regulators/parts/12-803

 

[havoc_squad]

I'm curious, did they install a Mercury/Quicksliver 27-34213 gasket or some 3rd party gasket?

If that gasket is not thick enough to get the correct spacing from the block, the fuel pump will deliver too much fuel pressure.

It's more likely the pump because its only about 1 to 2 PSI over max but worth maybe buying the genuine quicksilver gasket and replacing whatever gasket they put on it if the new one is thicker and see if the issue goes away.

 

[Lou C]

If it dribbles like that with the engine OFF I doubt it’s too much fuel pump pressure. I’d remove the carb dump out the gas turn it upside down and rig up a hose so you can blow thru the inlet. With the carb upside down you should not be able to blow air into it. If you can the needle & seat are not sealing. Either that or the float absorbed gas and it’s heavy or the float is hanging up on something. This looks like a Rochester 2 bbl or a Mercarb (Merc version of old Rochester 2 bbl). On the Quadrajet 4bbl I know if the retainer for the float isn’t installed right it can cause flooding. I have not been inside one of those old 2bbl carbs in many years.

 

[MorbidMedicz]

Thanks for the suggestions everyone. Took the carb off again and purchased a holly in line regulator as suggested. Re-checked the float and needle. They put the 3 piece in with spring. The only thing we noticed was the power valve was sticking? Bottom of the bowl. Re-installed and tested. Ran great at idle. Turned it off multiple times with no sign of fuel leakage. Put it in a Troff and tester in gear. Idled up and as soon as I went pass 3k she started bogging.
Looked in the carb and sure enough it’s filling fast and looks to be coming out of the Ventury. Disconnected the fuel line to see if it would help, did not. Still continues to dump what’s in the bowl.
Shop said they would refund my money so I can get a new one. I’m at a loss. Appreciate all the help. She idled great for 30 minutes til I gave it acceleration.

 

[MorbidMedicz]

As I look to replace the carb, looks like Rochester / Sierra have a new designed carb with a rear port. Not sure what or how this would work on mine. Is it a vacuum type line?
Picking up money from the marine shop Monday and I’ll order a new carb.

 

[MorbidMedicz]

your engine should be mechanical fuel pump yet. did someone convert it to electric?

7 psi seams a bit high

Yes sir just mechanical. We followed everything and noted just an in-line fuel/water separator. Disconnected power to Gauge just in case with no luck.

 

[alldodge]

As I look to replace the carb, looks like Rochester / Sierra have a new designed carb with a rear port. Not sure what or how this would work on mine. Is it a vacuum type line?

Might be a stock photo, could ask the vendor. You don't need the vacuum line and it could be capped