Poor engine performance, out of ideas, Help!

[br0]

Back around July I had the intake manifold crack on my Merc 4.3L when we were loading up at the dock. It was the first time I had the boat out since winterizing it in 2011 and we were still in the wake area when I noticed the bilge was filled with milkshake.

I've done nearly everything I have thought of to do, listed below:

1) New manifold + both gaskets
2) Drained old gas from tank, refilled with non-ethanol fuel - my truck didn't complain in the least about the old gas, probably because I mixed it with Seafoam in 2011.
3) New fuel filter
4) New spark plugs gapped to 0.045 IIRC
5) Tested exhaust manifolds with acetone
6) Verified compression 3 times during various steps of this repair process, all 6 cylinders remained within 10psi of each other
7) Verified timing a couple of times during the repair process (in base timing mode)
8) Rebuilt carburetor
9) Changed oil/ filter three times, water in engine appears to be completely gone. The oil level on dipstick hasn't changed in the last 3 or 4 times I've had the boat out (twice to go fishing and a few more times on land).

As it sits, the motor will not go above ~1500 rpm without stuttering harshly, and flat out will not go above ~1800 rpm at all. Top speed is 10 mph with the trim all the way down. This makes for a bit of difficulty moving to good fishing spots

The only thing I know of that could be left is the fuel pump, but I have no idea how to check it. I'm really not that hyped about verifying yet another thing after 3 months of on/off work on this boat and chasing ghosts each time.

Am I overlooking something here? I don't see how the head could be warped/cracked or the head gaskets be busted since the water in the oil appears to completely gone and the engine has been run many times since I replaced the manifold.

I generally enjoy working on engines, but this is getting absurd.

 

[Bondo]

Re: Poor engine performance, out of ideas, Help!

Back around July I had the intake manifold crack on my Merc 4.3L when we were loading up at the dock. It was the first time I had the boat out since winterizing it in 2011 and we were still in the wake area when I noticed the bilge was filled with milkshake.

I've done nearly everything I have thought of to do, listed below:

1) New manifold + both gaskets
2) Drained old gas from tank, refilled with non-ethanol fuel - my truck didn't complain in the least about the old gas, probably because I mixed it with Seafoam in 2011.
3) New fuel filter
4) New spark plugs gapped to 0.045 IIRC
5) Tested exhaust manifolds with acetone
6) Verified compression 3 times during various steps of this repair process, all 6 cylinders remained within 10psi of each other
7) Verified timing a couple of times during the repair process (in base timing mode)
8) Rebuilt carburetor
9) Changed oil/ filter three times, water in engine appears to be completely gone. The oil level on dipstick hasn't changed in the last 3 or 4 times I've had the boat out (twice to go fishing and a few more times on land).

As it sits, the motor will not go above ~1500 rpm without stuttering harshly, and flat out will not go above ~1800 rpm at all. Top speed is 10 mph with the trim all the way down. This makes for a bit of difficulty moving to good fishing spots

The only thing I know of that could be left is the fuel pump, but I have no idea how to check it. I'm really not that hyped about verifying yet another thing after 3 months of on/off work on this boat and chasing ghosts each time.

Am I overlooking something here? I don't see how the head could be warped/cracked or the head gaskets be busted since the water in the oil appears to completely gone and the engine has been run many times since I replaced the manifold.

I generally enjoy working on engines, but this is getting absurd.

Ayuh,... Sounds like a lack of fuel, or water in the gas....

Have ya checked the contents of the fuel filter,..??

 

[tpenfield]

Re: Poor engine performance, out of ideas, Help!

My only thought, based on what you have described, is that there is additional internal engine damage that has not been found.

I know you said that the compression was within 10 psi across the cylinders, but what was the actual value range?

My thoughts are:

1) engine block crack somewhere down low - pressure test of the cooling system could help out here.

2) bent connecting rods from water ingestion - The actual value on a compression test would give some evidence, but visual inspection is going to be best.

 

[br0]

Re: Poor engine performance, out of ideas, Help!

Ayuh,... Sounds like a lack of fuel, or water in the gas....

Have ya checked the contents of the fuel filter,..??

When I emptied the old gas, the first thing I did was dump the fuel filter contents into a clean white bucket. There wasn't any gunk that came out, just gas.

 

[br0]

Re: Poor engine performance, out of ideas, Help!

My only thought, based on what you have described, is that there is additional internal engine damage that has not been found.

I know you said that the compression was within 10 psi across the cylinders, but what was the actual value range?

My thoughts are:

1) engine block crack somewhere down low - pressure test of the cooling system could help out here.

2) bent connecting rods from water ingestion - The actual value on a compression test would give some evidence, but visual inspection is going to be best.

Compression was 155 - 165 psi in each.

The cooling is raw water. What kind of tools would I need to test it, and how do you do it?

 

[Another retired guy]

Re: Poor engine performance, out of ideas, Help!

I would have another look at that " rebuilt" carb. Symptoms indicate a carb/choke problem.

 

[FreeBeeTony]

Re: Poor engine performance, out of ideas, Help!

Plug wire connected properly?

 

[br0]

Re: Poor engine performance, out of ideas, Help!

I would have another look at that " rebuilt" carb. Symptoms indicate a carb/choke problem.

What specifically should I be looking for? I rebuilt it w/ the proper rebuild kit. New parts were needle/seat, inlet filter, accelerator pump, internal gaskets, check balls, float, and idle screw. The only reused parts were the jets, and some long screw in cylinder thing (emulsion tube?) that I think assists in the idle function. It's turn-key start btw, no choke mechanism on the carb. When I cleaned the parts I let them sit in cleaner overnight and used lots of compressed air on every opening I could find.

 

[81 Checkmate]

Re: Poor engine performance, out of ideas, Help!

When checking for water in gas - undo water seperator filter and dump into a glass jar and look for seperation...

Do you have a mechanical or elect fuel pump?

 

[Another retired guy]

Re: Poor engine performance, out of ideas, Help!

What specifically should I be looking for? I rebuilt it w/ the proper rebuild kit. New parts were needle/seat, inlet filter, accelerator pump, internal gaskets, check balls, float, and idle screw. The only reused parts were the jets, and some long screw in cylinder thing that I think assists in the idle function. It's turn-key start btw, no choke mechanism on the carb. When I cleaned the parts I let them sit in cleaner overnight and used lots of compressed air on every opening I could find.

Ok, this is a new one to me - I've never seen a carb that didn't have a choke mechanism

 

[br0]

Re: Poor engine performance, out of ideas, Help!

When checking for water in gas - undo water seperator filter and dump into a glass jar and look for seperation...

Do you have a mechanical or elect fuel pump?

I have this:

http://www.mercruiserparts.com/Show...11812&bnbr=60&bdesc=Fuel+Filter+and+Fuel+Pump

It looks like it's electrical. I do seem to recall hooking the wiring harness back up to that general area (I'm not at home to look at it right now).

 

[br0]

Re: Poor engine performance, out of ideas, Help!

Ok, this is a new one to me - I've never seen a carb that didn't have a choke mechanism

Well I'm no carb expert, so maybe I'm wrong? Here's the diagram for it:

http://www.mercruiserparts.com/Show...11540.png&inbr=11812&bnbr=80&bdesc=Carburetor

 

[Tail_Gunner]

Re: Poor engine performance, out of ideas, Help!

Item 28 did you open the circut and clean it? Power valve...What manual did you use to set the float level...Did you soak the carb and clean it mechically or under pressure?..You have to have the right guide there a lot of differnt 2bl merc carbs...

 

[Another retired guy]

Re: Poor engine performance, out of ideas, Help!

Well I'm no carb expert, so maybe I'm wrong? Here's the diagram for it:

http://www.mercruiserparts.com/Show...11540.png&inbr=11812&bnbr=80&bdesc=Carburetor

I'm not familiar with this particular carb, but I'm assuming #6 and surrounding parts are the throttle connections. In that case # 1 must be the choke ( maybe other way around?). Your symptoms indicate the choke is not opening properly. Pull a plug and check color - if it's black then fuel mix is too rich.

 

[br0]

Re: Poor engine performance, out of ideas, Help!

I'm not familiar with this particular carb, but I'm assuming #6 and surrounding parts are the throttle connections. In that case # 1 must be the choke ( maybe other way around?). Your symptoms indicate the choke is not opening properly. Pull a plug and check color - if it's black then fuel mix is too rich.

Yep, #6 is the throttle connection.
After reading your earlier post, I realized that #1 probably was the choke. Which of course is a $170 part :-/ I'm also guessing it's not servicable.

I'll check the plugs this weekend.

 

[br0]

Re: Poor engine performance, out of ideas, Help!

Item 28 did you open the circut and clean it? Power valve...What manual did you use to set the float level...Did you soak the carb and clean it mechically or under pressure?..You have to have the right guide there a lot of differnt 2bl merc carbs...

#28 was replaced. To set the float level and float drop I used the directions and paper ruler that were included in the Merc rebuild kit.

 

[Another retired guy]

Re: Poor engine performance, out of ideas, Help!

Yep, #6 is the throttle connection.
After reading your earlier post, I realized that #1 probably was the choke. Which of course is a $170 part :-/ I'm also guessing it's not servicable.

I'll check the plugs this weekend.

I assume this is an electric choke?? If so, turn the ignition on, but don't start the engine. The choke plate should start to open after a minute or two. If it doesn't, check wiring to make sure it has voltage before spending $170

 

[br0]

Re: Poor engine performance, out of ideas, Help!

I assume this is an electric choke?? If so, turn the ignition on, but don't start the engine. The choke plate should start to open after a minute or two. If it doesn't, check wiring to make sure it has voltage before spending $170

Ok so since we're on the subject of the choke/carb, I'll mention this since I forgot to earlier: The carb rebuild was the most recent thing I've done, and that was last weekend. After installing it and cranking the engine in the driveway, I noticed a higher level of emissions until the engine warmed up or I took it out of idle. This was a higher level than what I recall from last year working on it on land. The smoke was dark but still transparent, with a slight blue tint.

 

[QC]

Re: Poor engine performance, out of ideas, Help!

a slight blue tint.

That's usually associated with oil.

 

[Another retired guy]

Re: Poor engine performance, out of ideas, Help!

Ok so since we're on the subject of the choke/carb, I'll mention this since I forgot to earlier: The carb rebuild was the most recent thing I've done, and that was last weekend. After installing it and cranking the engine in the driveway, I noticed a higher level of emissions until the engine warmed up or I took it out of idle. This was a higher level than what I recall from last year working on it on land. The smoke was dark but still transparent, with a slight blue tint.

If the smoke/emissions cleared after a minute of two then it was probably just cleaning fluid residue burning off. If it continued when engine was warm then that would be an indication of a rich mixture.