Somewhat Odd 4.3 Mercruiser Issue

[Yachtsman1304]

Greetings,
I am running a 1997 4.3, 2bbl Mercarb, T5 ignition set-up. The boat starts great, idles great, great power, no misfires, no backfires. The issue is if I run at WOT for anytime at all and I come back to idle it will stall (sometimes). From what I can tell it is only when I am WOT that the issue presents itself. The boat starts right back up and I can power THROUGH the stall if I elect to do that.

I have new plugs, fresh gas, fresh fuel/water separator, oil pressure is good, temp is good.

My "thought" is maybe it is a vapor lock type issue. The engine vents are at the rear of the boat, not on the sides. I THINK when I run the blower that seems to help the issue.

Any thoughts?

Thanks and have a great holiday weekend everybody!!

 

[Kainon]

Re: Somewhat Odd 4.3 Mercruiser Issue

Welcome, HAH ! you think you have an odd issue eh ?..

Though the engine may seem to idle great, your carb may need the idle mixture adjusted, if it was adjusted last on a cooler day and your in the 80's plus, it may need a slight adjustment, but I think it may be a little lean. I would pull a couple spark plugs and have a look at the color of the ceramic, that's the best way to tell whats going on.

I would do a test run first without the blower on to get it to die then do a few runs with the blower on constantly and see if you can get it to die.

 

[JustJason]

Re: Somewhat Odd 4.3 Mercruiser Issue

Is it hard to restart or does it fire right back up? When it does fire back up, does it cough and heave for a second and is there any black smoke?

 

[Yachtsman1304]

Re: Somewhat Odd 4.3 Mercruiser Issue

Thanks for the input gents.

The engine fires right back up after it stalls...no smoke, no hard start. I want to say it ACTS like it is a fuel starvation issue. New fuel pump last year too. Also, a complete tune-up was done by the dealer in the middle of summer last year.

 

[Chris1956]

Re: Somewhat Odd 4.3 Mercruiser Issue

I would inspect the Antisiphon valve in the fuel tank pickup. They can get partially clogged, allowing enough fuel for mid-range RPM, but not enough for WOT.

 

[Yachtsman1304]

Re: Somewhat Odd 4.3 Mercruiser Issue - solved

Re: Somewhat Odd 4.3 Mercruiser Issue - solved

Just an update: the idle speed was set a bit too low and that was causing the stalling.