5.7 Merc won’t start warm/Stalling slowly at idle

kyles609

Cadet
Joined
Aug 31, 2016
Messages
18
Hi, I’m not sure if I have one issue or two but the title says it all. I had a surging issue years ago and posted here and got great and accurate help (it was the carb). After much delay I just had the carb rebuilt and it’s now starting like a dream and runs perfect in the water.. until I shut it off (it’s always had this issue but always started, I swam my family to the ramp yesterday). It’s also slowly stalling at idle unless I catch it and bring up the rpms, and then I can’t get it started.

My first idea was check the idle and air mixture screw but then realized with the T5 I need to ground the Purp/wt wire to do this. Do I just disconnect it and ground the wire coming off the T5 box? I’m wondering if my old school shop rebuilt it great but didn’t set the idle properly with the T5? Obviously not since they never put it in the water.

The only manual I can find describing the procedure only mentions the 4.3 Merc. I have a 96 5.7 Serial number 0F605391 W/ 2 Barrel MerCarb part number 807312 Date stamp is 5402.

http://download.brunswick-marine.co...n/mercruiser/gasoline/861328-1/8613281_4b.pdf

If I head on on the water what should I be doing and checking first? I know timing should be checked but carb adjustments could be easier and may solve this I hope. I’ll check to see if it will start WOT and watch for gas entering the carb in case this is a flooded situation on shutdown.

Thanks

Also, I’ve done a lot of research on the hot start issue and read a lot about vapor lock and other hot fuel issues but I’m still narrowing it down.
 

Rick Stephens

Admiral
Joined
Aug 13, 2013
Messages
6,118
Most likely the needle valve in the carburetor has crud in it and is overfilling, flooding your motor. Dump the fuel water separator into a clear container ad see if it has anything but clear clean gas in it. Then get a kit for the carburetor.
 

kyles609

Cadet
Joined
Aug 31, 2016
Messages
18
Thanks for the reply, Carb was just rebuilt last week from a boat shop and this was my first trip on the water.

It’s definitely flooding after shut down after looking into this. As soon as I shut down the butterfly valves are getting soaked with gas dripping. See the video

https://youtu.be/b5hKbgPzI6c

My mechanic recommended tearing it down, cleaning and putting back together. Is this just a bad carb or something that can be fixed?
 

St8-E

Cadet
Joined
Sep 27, 2012
Messages
12
I am having the exact same issues with mine. Gas isn’t dumping as much after shut off on mine as it is on yours. It’s still does steadily drip gas after shut off, though. I have had my Mercarb rebuilt twice by two different people...replaced the nitophil float with a brass one, replaced the needle/seat, power valve, etc., etc...this boat has historically cold started faster than any carb’d engine I have ever owned, but cranks and cranks and needs throttle manipulation to start when the engine is warm. It will never miss a beat when cruising/powering up to get onto plane. When coming down into a no-wake, it recently wants to stumble and die unless I quickly Jack it into neutral and keep the RPM’s up for a little bit. The boat smells like it’s running rich. I NEVER did anything with the ign. Timing/T-bolt 5 system when re-installing the carb after these rebuilds (was unaware this needed to be done and don’t know the process).

I would be VERY INTERESTED if you do figure this issue out. I am one step shy of buying a reman carb and replacing my fuel pump just to “see if it works”. I really don’t feel like throwing parts at it.

at any rate here is a video of what my carb does when shutting it down...

https://youtu.be/4zf0xca8Cjg
 
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