Engine gets sluggish/stalls @3/4 WOT

[thephoneman]

1994 Merc 5.0 on a hurricane deck boat. Took it out today to test the new prop and it was running really good. Had a hard time starting but after that no issues. Getting 4200+/- WOT and 33+/- mph. Stopped for a while and then when we got back going it would start to have issues @ 3200 rpm. It would either, lose power, start surging, stall, cough/backfire a little, or all of the above. Here's what I've done so far this spring: new fuel water seperater, 25 or so gallons of fresh gas. We checked the engine and it was emiting some smoke/steam out of the hoses that connect to the air filter. First thought is maybe some bad gas is still in there or maybe a clog in the pickup. I'm open to suggestions, I'll hang up and listen. Thank you!

 

[tank1949]

1994 Merc 5.0 on a hurricane deck boat. Took it out today to test the new prop and it was running really good. Had a hard time starting but after that no issues. Getting 4200+/- WOT and 33+/- mph. Stopped for a while and then when we got back going it would start to have issues @ 3200 rpm. It would either, lose power, start surging, stall, cough/backfire a little, or all of the above. Here's what I've done so far this spring: new fuel water seperater, 25 or so gallons of fresh gas. We checked the engine and it was emiting some smoke/steam out of the hoses that connect to the air filter. First thought is maybe some bad gas is still in there or maybe a clog in the pickup. I'm open to suggestions, I'll hang up and listen. Thank you!

How long did it sit? May have crap in carb? Hard to start is a hint.

 

[alldodge]

was emiting some smoke/steam out of the hoses that connect to the air filter.

Lower power, backfire, steam/smoke, I'm thinking a blown head gasket
Do a compression test

 

[thephoneman]

How long did it sit? May have crap in carb? Hard to start is a hint.

Last time I took it out was a week or so ago. I was sitting in the water yesterday for maybe an hour. I'll check the oil to see if there is any water, but like I said it only started acting up once I tried to open it up.

 

[Bondo]

Ayuh,...... Check the Contents of the fuel filter, for anything but clean fresh gasoline,.....

 

[QBhoy]

You usually don’t get away entirely with just adding fresh fuel into contaminated or bad fuel. Just a thought.

 

[thephoneman]

Ayuh,...... Check the Contents of the fuel filter, for anything but clean fresh gasoline,.....

Is there another filter besides the fuel water seperater?

 

[alldodge]

Is there another filter besides the fuel water seperater?

No, just the one but a motor serial number would verify

 

[thephoneman]

So after a little more digging, it has the 2 bbl mercarb on it. I'm going to check the filter going into the carb. Unfortunately we're dealing with a monsoon here in Michigan so I have to wait for the rain to stop. I'll keep you updated.

 

[Bondo]

Is there another filter besides the fuel water seperater?

Here's what I've done so far this spring: new fuel water seperater, 25 or so gallons of fresh gas.

Ayuh,...... My point is, a brand new fuel filter is still junk, if ya pump a slug of bad gas/ water through it, even the same day you install it,......

 

[thephoneman]

Ayuh,...... My point is, a brand new fuel filter is still junk, if ya pump a slug of bad gas/ water through it, even the same day you install it,......

That makes sense. Since the only stupid question is one that's not asked, is there a way to tell if the seperater is bad other than replacing it and three problem going away?

 

[alldodge]

That makes sense. Since the only stupid question is one that's not asked, is there a way to tell if the seperater is bad other than replacing it and three problem going away?

As Bondo always says: Dump the contents of the filter into a clear container and see what there other then clean gas

 

[thephoneman]

So I took the seperater off and dumped it into a jar... Didn't think gas was supposed to seperate into 3 sections lol. Needless to say the tank is drained and will get a can of seafoam and fresh gas. Any other suggestions on how to clean it real good? It's under the floor and no way to take it out and clean it.

 

[Scott06]

So I took the seperater off and dumped it into a jar... Didn't think gas was supposed to seperate into 3 sections lol. Needless to say the tank is drained and will get a can of seafoam and fresh gas. Any other suggestions on how to clean it real good? It's under the floor and no way to take it out and clean it.

Put some gas in drive it around on the trailer , pump that out. Repeat until clean ...

replace or blow out or push gas through the fuel lines until clean, then When you are certain the tank the lines etc are clean ...rebuild the carb.

 

[nola mike]

No need for a carb rebuild yet, the water is enough for those symptoms

 

[alldodge]

Could remove the fuel sender and use a power washer and blast the tank. Can use a shop vac to suck the water out and repeat until clean.

Don't forget to clean or replace the antisiphon valve

 

[nola mike]

Blasting the tank with a power washer seems like it would unleash a Pandora's box of crud...

 

[thephoneman]

Update! Drained the tank and put a new filter and seperater on it. Fresh gas and runs like it should. Thanks for the help.