82 Mercruiser 140 bogs in forward but has high rpms in reverse

[apoc330]

I have been dealing with a bogging issue on my 82 wellcraft that has a mercuiser 140 engine. The boat has a new fuel pump and lines as well as a revbuilt carb, and full tune-up.

The boat ran great for about half an hour and then started bogging in the middle of a run and has been bogging down every since when in drive.

I recently readjusted the timing on the water because of some pinging that was happening and that went away but it still bogs at WOT.

I took it out again last night to rule out the fuel because the boat sat for 5 yrs although I have put tank cleaner and fresh fuel in. I ran on a temp tank with new 89 octane gas and had the same "BOG" issue, the difference this time out is that i accidentally slammed the drive in reverse and the RPMs climbed and the boat ran faster backwards without bogging down. Does this seem like a prop or some type of gearing issue. Just wondering now if I have been checking the wrong things.

The boat always starts and idles perferct and never dies out on the water, just this bogging issue when in drive and can never get above 200-2500 rpms.

Looking for some help.

 

[havasuboatman]

Re: 82 Mercruiser 140 bogs in forward but has high rpms in reverse

It sounds like you have some blockage in the carb. Even possibly a loose fuel line on the vacuum side of the fuel pump, though my first guess is this is a carb issue since it happened mid-trip, so to speak. Some crud got loose and fouled the metering passage.
I am curious, have you recently replaced your water seperater? When they start to fill up with water, they start to starve the engine of fuel.
And, the reason the boat rev'ed higher in reverse is simple, a prop is designed to push a boat forward. In reverse their efficiency is radically reduced, meaning less load is placed on the prop so it is easier to spin using less fuel.
Check your carb.

 

[apoc330]

Re: 82 Mercruiser 140 bogs in forward but has high rpms in reverse

I will check the carb, but i rebuilt it since this happened and have the same issue, but maybe my adjustments are off. I have not installed a fuel/water separator yet but plan to do that this weekend. I also checked the fuel filter in the pump but it seems to be clean as well but I am going to replace it and see if that helps. "Even possibly a loose fuel line on the vacuum side of the fuel pump", is that the side between the tank and the pump?

Thanks for the prop explanation, that makes perfect sense.

 

[ErieRon]

Re: 82 Mercruiser 140 bogs in forward but has high rpms in reverse

I followed your other post, and I agree with the previous poster...carb. I have had the same issues a couple of times over the years. Each time it was a clogged fuel filter or carb rebuild issue. Like you, I assumed since it was all new and I had taken all of the right steps, it couldn't be fuel...but I was wrong each time.

Double check, or just replace your fuel filters. The one on the side of the carb and the one in the fuel pump bell. If you are by chance reusing the old cermaic bowl style filter, throw it out and get the new paper style. Also, make sure they are installed properly...facing the right direction relative to the hole in the one end. Proper orientation is in the manual.

Despite your thoroughness, it only takes one little piece of foreign material to clog up a passage in your carb. I would have look in there again.

 

[havasuboatman]

Re: 82 Mercruiser 140 bogs in forward but has high rpms in reverse

Yes, the vacuum side is between the tank and the pump. A loose or damaged hose can cause air to leak into the fuel system.
Erieron has a point with that bowl filter, I'd go one further and tell you to throw it away so long as you first put in the water seperating fuel filter.

 

[apoc330]

Re: 82 Mercruiser 140 bogs in forward but has high rpms in reverse

Will do, I will replace both filters and check the carb. Should I check the metering valve and the venturi cluster or would this usually be an issue with one or the other and not both?

My fuel pump has the bell on top and uses a paper filter, when i replace it I am putting the filter in hole side down which I believe is correct.

Thanks havasuboatman, and ErieRon for your help.

 

[apoc330]

Re: 82 Mercruiser 140 bogs in forward but has high rpms in reverse

Yes, the vacuum side is between the tank and the pump. A loose or damaged hose can cause air to leak into the fuel system.

I will check this with a vacuum gauge, I think the range is in the manual of what this should be.

 

[havasuboatman]

Re: 82 Mercruiser 140 bogs in forward but has high rpms in reverse

Yes check both

 

[apoc330]

Re: 82 Mercruiser 140 bogs in forward but has high rpms in reverse

I'd go one further and tell you to throw it away so long as you first put in the water seperating fuel filter.

So with the fuel water separator attached are you saying the filter in the pump is no longer needed?

 

[havasuboatman]

Re: 82 Mercruiser 140 bogs in forward but has high rpms in reverse

as long as the water seperating fuel filter is between the fuel tank and fuel pump, yes, you can remove the paper filter, but I doubt that is your issue.
The fuel filter I was referring to is the one on the side of the carb., behind the fuel inlet nipple. That is the one I would remove, and the one that if placed incorrectly, will starve the carb for fuel.

 

[apoc330]

Re: 82 Mercruiser 140 bogs in forward but has high rpms in reverse

Ok, I will definately check that one and make sure it is correct, although it did run correctly for a while so i am more inclined to agree with the fact that it is an internal carb issue. I will keep you guys posted on the outcome, and thanks again.