Please help with possible carb problem??

[jason0316]

Hey .. Here's what I have. It's a 96 marada with a 350 mercruiser. I have been having this issue all summer ever since the first time I took it out this year. After you run the boat a little and shut it off and let it sit awhile it doesn't like to start back up. You have to give the warm up lever full throttle for it to start and then quickly let off the throttle and bring it back down to idle. It seems to me like te carb is flooding itself. I rebuilt the carb beginning of summer and it didn't seem to help my issue. I have also let the blower motor run the entire time I had the boat shut off and then try to restart and that doesn't seem to help either. Not too sure which direction to go? Also sometimes after I finally get it started again and take off it seems to like want to hesitate when I give it gas and u have to bring it back down to idle and then take off again and it's fine. This is part of my reasoning that my problem has to be with carb??

 

[Another retired guy]

Re: Please help with possible carb problem??

Sure sounds like the fuel mix is too rich for a warm restart. What's it like starting from cold - quick start? Have you checked the choke plate to make sure it's opening fully?
What carb do you have?

 

[jason0316]

Re: Please help with possible carb problem??

Sure sounds like the fuel mix is too rich for a warm restart. What's it like starting from cold - quick start? Have you checked the choke plate to make sure it's opening fully?
What carb do you have?

Starts quickly when it's cold. And yes the choke opens up all the way. And it's the merc carb 2 barrel carb. The fuel mixture may be off but it was doing this even before I rebuilt the carb and hadnt messed with any adjustments.

 

[Another retired guy]

Re: Please help with possible carb problem??

Still sounds like a rich mixture, have you noticed black exhaust smoke?- pull a couple of spark plugs - if they're black it's too rich.
If so, the cause may be an incorrect float level ( too high ).
Did you set float level to specs during the rebuild?

 

[Bt Doctur]

Re: Please help with possible carb problem??

you cant rebuild a carb without removing the mixture screws ,so you always need to adjust after a rebuild.
Run the engine to normal temps, remove flame arrestor, shut engine off and look into the carb for any fuel dripping/leaking

 

[NHGuy]

Re: Please help with possible carb problem??

I have checked the manual. Here's the readers digest version on the setup.
For preliminary adjustment you set the idle speed screw by backing it out til it's off the idle cam. Turn it in til it contacts the cam, then turn it 2 revolutions. For the mixture screw you turn it til LIGHTLY seated, then back it out 1 & 1/4 revolutions.
For final adjustment you run it til warm at 1500 rpms, then remove the throttle linkage and adjust it to 600 rpm. Now adjust the mix screw in til it stumbles from lack of fuel, that's too lean. Then back the mix screw out til it stumbles from extra fuel, that's too rich...then put the mix screw centered between rich and lean. Reset your idle speed to 750 or 800. Reconnect your throttle link. Run it, it should turn around 650 rpm in gear with no throttle applied. If not adjust to 650 in gear.
If that fixes it good.
But Mercruiser is also specific about accelerator pump rod height which I could not find for the 5.7 Mercarb. I can tell you that they want you to put the pump arm in the middle hole. Since you get a bad takeoff try the closer hole which will give you a better accelerator pump burst of fuel.
The float height should be 9/16",and he float drop 1 & 3/32". If you didn't measure & reset those values your rebuild was not complete. Hopefully the Mercarb rebuild kit will give the pump arm measurement. I can't find it and the manual seems to make it an important step.
Additionally if your boat is running at a different altitude than it was at previously there are over a dozen jet sizes to work from. The manual did not say how to make a choice but it did list the part #s and their orifice sizes. This could be your richness issue! To identify them you remove them and find the part #, then compare to the chart. If you feel that the carb is otherwise right, try some smaller jets.
Go here Boatinfo - Mercruiser Service Manual nr. 17 - 1993-1997 - Engines GM V8 305 & 350 CID (5.0L 1993-1995) (page 438 of Manual 17) and you will get the Mercarb information I was looking at.
You can't download from there, but at least you can see the manual.
Hopefully that is what you need!

 

[cr2k]

Re: Please help with possible carb problem??

That in till it stumbles and out and center it is for a Holly, but might get you in the ball park or at least the parking lot. It takes a good experienced ear to properly adjust the idle mix screws. Merccarb usually around 1 3/4 to 2 1/2 turns depending on altitude and climate.

 

[jason0316]

Re: Please help with possible carb problem??

you cant rebuild a carb without removing the mixture screws ,so you always need to adjust after a rebuild.
Run the engine to normal temps, remove flame arrestor, shut engine off and look into the carb for any fuel dripping/leaking

I understand this but what I'm getting at is i don't think it has to do with the mixture sxrews only because before I rebuilt the carb it was doing the same thing. Meaning it just started acting up beginning of season and I had never messed with idle or mixture screws since it was running fine