Mercruiser 140hp acceleration

[mikeapi]

I just purchased a boat with a Mercruiser 140hp 3.0l engine. Replaced points, plugs, wires, condenser and distributor cap. I took it out to the lake today for the first time. It started right up idled well and ran good at half throttle. When I opened the throttle all the way the engine would bog down most of the time. Every couple of minutes it would have some power, then it would go back to several different degrees of being bogged down. It would back fire every once in a while. It sounded like it wasn?t getting enough fuel. I guess that I?m a little confused, because it was running good for about 5 minutes of every hour. Can someone give me some suggestions?

 

[Bondo]

Re: Mercruiser 140hp acceleration

It sounded like it wasn?t getting enough fuel.

Ayuh,... That's the Problem,.... Change the Fuel Filters for starters...

 

[mikeapi]

Re: Mercruiser 140hp acceleration

I did replace both fuel filters when I replaced the ignition parts.
Thanks for the suggestion.

 

[Bondo]

Re: Mercruiser 140hp acceleration

Ayuh,... You made No mention of that,...
So,.. Check the Tank,.... Is there a restriction there,..??
Are the fuel Lines rotten,+ collapsing,..??
Is the fuel pump up to snuff,..??
Is the carb full of Crap,..??

You have a fuel delivery issue,... You have to find Where it is...

 

[ziggy]

Re: Mercruiser 140hp acceleration

assume you set dwell then timing after the point R&R, right?
does sound like fuel though. have ya gone to the adults only sticky and read the one on fuel system diagnosis? or the oem sevice manual also has trouble shooting guides in them too.

 

[ken_23434]

Re: Mercruiser 140hp acceleration

You said you just bought the boat.

Do you know how long it had been sitting before you bought it?

Old gas or dirty fuel tank might be contributing to your issue.

Did you change ALL the fuel filters? The 140 will have at least 2. One INSIDE the fuel pump, one inside the inlet to the carb. Those two are in addition to an inline fuel/water separating type. If you do not have that third one, that is a highly recommended upgrade to do.

My guess is there is junk in the tank that is collecting at the suction tube in the tank or clogging up your filter.

 

[Commissionpoint]

Re: Mercruiser 140hp acceleration

Yeah the list could go on and on for this problem. Condensation, ancient gasoline, internal carb problems,, crappy spark advance at higher revs, etc, etc.....

Fuel system is probably the best place to start as everyone here has already suggested. Clean tank, fresh gas, good lines and filters for starters. Then go through ignition and timing to make sure you are still in spec. After you know that you have fuel and ignition sorted out properly, let us know if you are still experiencing the problem.

 

[mikeapi]

Re: Mercruiser 140hp acceleration

Thank you for the suggestions, they give me a good place to start.

 

[mikeapi]

Re: Mercruiser 140hp acceleration

I took the boat out for a second test drive last weekend. It ran good at first, but after the first 15 minutes it went back to the same problems as before. Also at the end of our ride I couldn't get it to go into a forward gear.
I ended up taking it to a shop. They rebuilt the carburetor, and replaced the throttle cable. It cost $618 before tax for both items. Can anybody give me an opinion on the cost. I'm not going to go back and complain, but I thought the price was high. I would like to just get some others opinions before I use them again.

 

[slasmith1]

Re: Mercruiser 140hp acceleration

most shops here are above $100 /hr so it sounds reasonable. did their work fix the problem?

 

[mikeapi]

Re: Mercruiser 140hp acceleration

It's going in forward gear now, but I'm not sure about the WOT problem till I get it in the water.

 

[mikeapi]

Re: Mercruiser 140hp acceleration

I took the boat out a couple of times and I?m still having troubles at WOT. I called the mechanic that did the carburetor rebuild and he said that I had bad gas. So I siphoned out every last drop of gas into my truck. The truck had no problems with the gas.
I put a Sea Foam into the tank with the new gas. I also poured some Sea Foam into the carburetor. The boat ran great for about 15 minutes, then it ran sluggish again at WOT. Every time it ran sluggish I would pour more Sea Foam into the carburetor, and it would run good for about another 15 minutes. I tried the same thing with gasoline, but I did not get the same result.
So far I got a full tune up, I replaced all of the fuel filters, replaced the fuel line going from the gas tank to the fuel pump including the siphoning valve, I replaced the metal fuel line that goes from the fuel pump to the carburetor, I had the carburetor rebuilt, and I replaced all of the gas.
I think its some kind of fuel problem. Like I said it runs great for a while when I pour Sea Foam into the carb. The one thing left is replacing the fuel pump.
Does anyone have advise on what else could be the problem.

 

[Schmoe]

Re: Mercruiser 140hp acceleration

I was going to say just the opposite, maybe your getting too much fuel in the carb. It could be a choke problem, mine was. On the 3.0LX, it has an electric choke. You can adjust that to a leaner setting, it made all the difference in the world on mine. But yeah, check the fuel pump. You've just about eliminated everything else.

 

[marlboro180]

Re: Mercruiser 140hp acceleration

I was going to say just the opposite, maybe your getting too much fuel in the carb. It could be a choke problem, mine was. On the 3.0LX, it has an electric choke. You can adjust that to a leaner setting, it made all the difference in the world on mine. But yeah, check the fuel pump. You've just about eliminated everything else.

I'd have to agree on the electric choke assuming it is the Rochester carb. Mine was doing the same thing this spring just after I put it in. Good work eliminating most everything else.

 

[P 0 P E Y E]

Re: Mercruiser 140hp acceleration

Have you checked the vent line to the fuel tank?

How do your plugs look?

Have you checked to see if all 4 Cylinders are firing?

You might even have a bad condenser. The tune up parts may have nbeen sitting on the shelf for a long time.

Hope you are able to locate the gremlin.