1988 Marlin, 4.3 Mercruiser, 2 bbl carb'd cold start issue

[JBC118]

I've got a cold start issue that started recently. After a bit of research it seems it's fairly common. After a week or so sitting idle in my garage the motor takes a while to start. I'm not seeing a good stream of gas while priming the carb. The boat will eventually start but it takes of bit of coaxing.
If I park it and go right back out the next day it starts and runs like brand new.
Regardless the boat runs very well once started, idling, top end, etc.

I saw something where the carb bowl is emptying or draining leaving a dry carb bowl for the next start up.

Will a carb rebuild fix this? Any idea where the fuel is draining?

Thanks for any help..

 

[poconojoe]

How are your spark plugs?
I had a similar problem, however, I could smell gas was getting to the carb. After sitting for a week or so, it would be hard to start. Cranking fine, but a struggle to fire up. Afterwards it ran pretty good and restarted fine.
I changed the spark plugs, the fuel/water separator and the inline screen at the carb fuel line fitting and it now fires right up like new. I believe it was the spark plugs. The two season spark plugs looked good and so did the fuel screen and water separator. Instead of the AC Delco plugs, I used NGK.
Unless your sure about a fuel issue, changing the spark plugs would be an easy thing to try.

Originally I discounted the plugs going bad so soon since plugs run fine for years in most cars and trucks.

 

[Scott Danforth]

my first guess is that the welsh plugs are leaking in your carb, dumping the contents of the fuel bowl down your intake when sitting.

and yes a carb rebuild would cure that. (it will also cure any accelerator pump issues you may have)

 

[poconojoe]

Another thought I had when troubleshooting was to check the choke, but the butterfly was in fact closing on cold starts. So that was ruled out.

 

[JBC118]

ok, the choke (electric) is set right and opens properly. am I wrong in assuming that if the accelerator pump was going bad that it would affect performance throughout? such as a lot of throttle when starting

 

[Scott Danforth]

yes,

however only for throttle response related changes (such as throttling up under load)

 

[JBC118]

ok, thank you for the help with this...acceleration under load is fine..

the welsh plug thought is a bit of mystery, I'm not a true mechanic but have tinkered around a bit..

this may be a dumb question but....the welsh plug is essentially a cap that covers something? I don't see any fuel leaking on the outside of the carb body, so not exactly sure where the gas is draining to, other than out of the bowl..

 

[Bondo]

ok, thank you for the help with this...acceleration under load is fine..

the welsh plug thought is a bit of mystery, I'm not a true mechanic but have tinkered around a bit..

this may be a dumb question but....the welsh plug is essentially a cap that covers something? I don't see any fuel leaking on the outside of the carb body, so not exactly sure where the gas is draining to, other than out of the bowl..

Ayuh,..... They leak into the manifold,......

 

[JBC118]

Ok, I guess I’m not sure what’s causing the leak from the bowl into the manifold...
thanks for the input