Mercruiser bogs down and stalls

[marco_0521]

I have a Mercruiser 4.3L carb. Alpha. It has been working great, it has about 40 hours of use on it (about 1 year). Shift cable was replaced when the engine was replaced. I stopped using it for about two months and wanted to take it out today.

It started well, and then when shifting the engine would stall. I let it warm up a bit, and it seemed good, so I took the boat to my first fishing spot. Spend about an hour and then, it would start really hard, and when shifting it would bog down. We took it back to the pier by disconnecting the carb fuel lever (so to disconnect from the shifting mechanism) and then I would pump the carb manually so that gas would go into the carb. It worked and of course it was like an start and stop sort of thing.

Checked the motor oil, it is clean, no water. Oil pressure was good. I checked for spark, it was good on all 6 spark plugs. I checked the fuel before it got to the carb, good pressure, the filter was clean, the gasoline did not seem to have water on it.

Checked the drive oil, clean, no water or milky, no metal particles. Turns by hand easily when in neutral. Engages both forward and in reverse.

Adjusted the shift cable, and it shifts well. The kill switch remains centered both when in full position forward and in reverse. The drive engages as it should both in forward and in reverse.

Right now, I have it out of the water. I start the engine and sometimes it stalls without even shfiting. I checked the drive and it is not engaged. Some other times, it engages in forward or reverse, continues working, accelerates well for 20 seconds and then it bogs down.

Any ideas? I will try to check the compression and spark plugs. Maybe I need to rebuilt the carb? Any other suggestion?

Thanks,

 

[Don S]

Re: Mercruiser bogs down and stalls

What year and/or Merc SN?

accelerates well for 20 seconds and then it bogs down

When you say bogs, does that mean it slows down or engine dies completely?

 

[Bondo]

Re: Mercruiser bogs down and stalls

Maybe I need to rebuilt the carb?

Ayuh,...

From your rather thorough description,....It Does sound like a Fuel Delivery Issue.....
(Excellent post)

 

[gcboat]

Re: Mercruiser bogs down and stalls

I would do a search here for ethanol related fuel issues. Ethanol is a wonderful cleaning agent so any crud that has developed in your fuel system
just might be clogging and choking up your carb.
Agree with Bond-o on the carb thought but a rebuild might be a little harsh at the moment. Run some Sea Foam through it first - then go from there.

 

[marco_0521]

Re: Mercruiser bogs down and stalls

Don,

The engine is supposedly a 2007 model. S/N is 1A062191. The engine doesn't just suddenly stops working. It starts dropping revs, almost stop, then it revs up, then it drops revs again almost stopping again. It does this like 3 or 4 times before totally stopping.

Gcboat,

I will try the Sea Foam before the rebuilt. How do you apply it?

Thanks guys,

 

[meesh]

Re: Mercruiser bogs down and stalls

Dump it in the fuel tank

 

[Don S]

Re: Mercruiser bogs down and stalls

I can't see a 2007 engine needing a carb rebuild, unless you put gas in it from an old 55 gal drum sitting outback for the past 10 years.
From some of your statements, it sounds like a new engine put in an older boat. If that is the case then a lot of other things can happen. Water, rust, crap and corrosion in the OLD gas tank, plugged screens in the pickup in the tank, air leaks from the tank to the engine, really hard to say at this point. The good news, is there is a thread that covers checking it out.
Read the thread at the link below, do the tests so you find the problam. Don't just start throwing parts at it.

HOW TO: Testing your boats fuel system.

 

[marco_0521]

Re: Mercruiser bogs down and stalls

Thanks for the link. Very straightforward and clear.

I spent the whole day today going to Sears, NAPA, Boaters World, Advance Autoparts, Autozone, Lowes, ACE Hardware, Wal-Mart, and Home Depot. But finally, I got the vacuum / fuel pressure tester and the rig for the boat.

Tomorrow, I'll take the boat to the river and will do the boat fuel test. I'll post results.

 

[marco_0521]

Re: Mercruiser bogs down and stalls

Went to the river and performed the three tests that were suggested in the prior link. Everything seems to be OK.

1. Airbound / leaky testing: A small bubble here and there, nothing consistent or significant.
2. Vacuum testing. Passed, stayed very close to 0.
3. Fuel pump ability to create vacuum. Passed.

Still, believing that maybe I made a mistake during the testing, I decided to buy fresh gasoline that I put in a new portable gasoline tank. Plugged in a new fuel pump (my spare which I hadn't used before) to the carb and from the new fuel pump to the fresh gasoline tank.

Started the engine for about 5 minutes, and it continued giving me the same issues. This time with enough light and without the pressure of being in the middle of the river, I saw a couple of additional things:

1. I positioned myself facing towards the rear of the boat, but facing the front of the engine. I took out the flame arrestor and was able to see the inside of the carburator. It has two round holes (that I think are the barrels?) On top of the two barrels is the venturi. The venturi has two small holes in the middle (the accelerator pump discharge holes) that pumps a stream of gasoline everytime I move the shift lever forward, but such a stream stops once I stop moving the shift lever. Next to each of the accelerator pump discharge holes, there are two pipes that supply a constant stream of gasoline. The stream of gasoline looks more like drops rather than a spray (which I would have expected).

2. My idle works, rough but works. Also If I pump the accelerator enough to get to 2300 rpms (meaning, I supply fuel moving the shift lever up and down so that gasoline goes to the carb in streams through the accelerator pump discharge holes), then I would be OK (the engine runs smoother and without hesitations). The problem is between shifting and about 2000 rpms when it seems that there is not enough gasoline and the engine stalls.

3. So, I was able to see that when the engine is idle, only the left of the two pipes out of the venturi drops gasoline, so it seems that only the left barrel is getting gas. If I accelerate more, the pipe from the venturi on the right starts working and supplies enough gasoline to get the engine to about 2000 rpms.

4. I added sea foam to the fresh gasoline and let the engine work at about 2500 rpms. Over time the engine improved (ran smoother), but still stalls If I don't accelerate fast enough to get to at least 2000 rpms.

So, I had the following questions

1. Is it normal that at idle only one of the two pipes out of the venturi provides gasoline? Shouldn't both work at the same time? Should the stream be like a spray rather than drops?

2. Could it be that the right pipe is somehow restricted? If so, should I continue runing Sea Foam or other cleaning agents? Or should I open the carb?

Any additional ideas will be welcomed. Thanks,

 

[chiefalen]

Re: Mercruiser bogs down and stalls

My 2 cents carb cleaned and rebuilt, and every filter cleaned.

Than run it on the external tank of gas. Filter in the fitting by the carb, filter in fuel pump if it has one, and fuel, water separator filter changed.

Good luck !

 

[Don S]

Re: Mercruiser bogs down and stalls

Do you have the TKS (Turn Key Start) system on your carb?
The big problem right now with troubleshooting, is that no one has any info on the real new stuff.
It does sound like you may have carb problem, perhaps water in the carb from the ethenol fuel, who knows. May be the filter in the carb is plugged for some strange reason. Might pull it out and look.
Have you removed and emptied out the water seperating fuel filter and actually checked for water in the fuel?

IS this a new engine in an old boat ???????????????

 

[marco_0521]

Re: Mercruiser bogs down and stalls

Don,

Yes to both questions. It is a new engine in an old boat (2000) and it has the TKS system.

The engine was purchased in December 2007 and installed in March 2008. It has about 40 hours on it from the break in and ocassional use this year.

I hadn't emptied the water separator filter as you suggested, but I just did and all I get is clean gasoline (a bit on the dark yellow side but doesn't smell sour), no water at all.

Also, if I need to check the carb, is there a new manual? I have the Mercruiser #25 for the old engine, but it does not talk about the TKS system at all. Any link or instructions on what to look for in the carb, would be appreciated.

Thanks,

 

[marco_0521]

Re: Mercruiser bogs down and stalls

Just to close the thread.

For the last two days, I have taken the boat to the river, replaced the water separator filter, applied sealant to all the fittings on the fuel line and ran about 10 galons of clean fresh gasoline with a high concentration of Sea Foam from a portable tank.

Now it is working by far better. It still loses some power but it does not stall anymore.

I will keep an eye on how it works, and I might need to rebuild the carb in the future, but I think this time it was avoided. Thanks to all for your comments. They helped isolate the problem and focus on the specific tests needed.

Again, thanks a lot.

 

[Don S]

Re: Mercruiser bogs down and stalls

There is a service manual suppliment for the TKS carbs. Might check with your local Merc dealer to purchace one. There isn't one online that I am aware of.
If you are still having problems, get it fixed. If it's leaning things down, you WILL burn a hole in a piston, or worse.

 

[marco_0521]

Re: Mercruiser bogs down and stalls

Thanks for the advice Don. I just ordered Mercruiser Service Manual #41, Turn Key Start (TKS) Carburetors, P/N 90-866202.