MerCruiser 3.0L 140 No Acceleration

[Jacalore]

Problem: 1985 MerCruiser 3.0L 140 No Acceleration - dies above 1500 rpm

Background: Bought boat with "carb" problem, prev owner said he rebuilt carb but didn't replace float, resulting in no acceleration. I attempted to rebuild carb, but threads on carb at fuel inlet stripped, so I replaced with a carb from a 1986 engine with identical part numbers. On muffs, ran smooth, idled ok.

Today: On the water for first trial run - no acceleration above 1500 rpm. Runs all day below that in forward/reverse. Easing the throttle up, or not, stalls above 1500 rpm.

I assume this is the original problem, and not the carb. Where do I look for likely problem?

Thanks

 

[Don S]

Re: MerCruiser 3.0L 140 No Acceleration

On a 3.0L, I would suspect the fuel filter in the fuel pump as the first place to look. Since it's out of sight, people don't replace it.
Put in a new one, and install a water separating fuel filter between the tank and fuel pump.

Further testing here http://forums.iboats.com/showthread.php?t=283269

 

[Jacalore]

Re: MerCruiser 3.0L 140 No Acceleration

Don, this may help...
I siphoned all the old fuel out of the tank, (from the primary fuel filter - tank side) and it took quite a while to fill each 5 gal bucket. A couple times while pumping to start the flow, the hose collapsed - like a straw when the end's clogged. I'm thinking this symptom could be connected, no?

 

[Bondo]

Re: MerCruiser 3.0L 140 No Acceleration

Don, this may help...
I siphoned all the old fuel out of the tank, (from the primary fuel filter - tank side) and it took quite a while to fill each 5 gal bucket. A couple times while pumping to start the flow, the hose collapsed - like a straw when the end's clogged. I'm thinking this symptom could be connected, no?

Ayuh,.... It shouldn't siphon, at All,....

That's why there's the anti-siphon valve at the tank's outlet, looks like a hose barb,...

Ya supposed the have to Pump it out,...

 

[Jacalore]

Re: MerCruiser 3.0L 140 No Acceleration

Oh... so I thought I had the problem surrounded, evidently not.
But wait, isn't that how the fuel pump on the engine gets fuel from the tank?

Ok, so where to from here?

And again, thanks for your help. I'm all ears, this is all new to me...

 

[Don S]

Re: MerCruiser 3.0L 140 No Acceleration

Don, this may help...
I siphoned all the old fuel out of the tank, (from the primary fuel filter - tank side) and it took quite a while to fill each 5 gal bucket. A couple times while pumping to start the flow, the hose collapsed - like a straw when the end's clogged. I'm thinking this symptom could be connected, no?

Pull the pickup tube out of the tank and see if the screen on the end of it's all plugged up, or partially plugged. It sure sounds like that'a your problem.

 

[Jacalore]

Re: MerCruiser 3.0L 140 No Acceleration

Will do... thanks

 

[Jacalore]

Re: MerCruiser 3.0L 140 No Acceleration

Finally got all the fittings off... no tube, no anti-siphon valve, just a fitting on top of the tank. 90? fitting then thru a shutoff valve to fuel line. Shutoff valve was corroded at lever, but clean inside. Obviously not used for quite a while. Replaced fittings and installed new fuel line. Don't know if the problems solved or not. Old fuel hose was kinda ratty at one end, maybe partially collapsed. And shutoff possibly leaking air into the line from corroded lever. They are guesses on my part. It's all new parts now from fuel tank to engine fuel pump. Guess I'll taker her out for a test... unless there is something else I can check first?
Not feeling real confident I fixed the problem...

 

[Bondo]

Re: MerCruiser 3.0L 140 No Acceleration

Finally got all the fittings off... no tube, no anti-siphon valve, just a fitting on top of the tank. 90? fitting then thru a shutoff valve to fuel line. Shutoff valve was corroded at lever, but clean inside. Obviously not used for quite a while. Replaced fittings and installed new fuel line. Don't know if the problems solved or not. Old fuel hose was kinda ratty at one end, maybe partially collapsed. And shutoff possibly leaking air into the line from corroded lever. They are guesses on my part. It's all new parts now from fuel tank to engine fuel pump. Guess I'll taker her out for a test... unless there is something else I can check first?
Not feeling real confident I fixed the problem...

Ayuh,.... did you replace the dip-tube, 'n anti-siphon valve,..??

 

[Jacalore]

Re: MerCruiser 3.0L 140 No Acceleration

Ayuh,.... did you replace the dip-tube, 'n anti-siphon valve,..??

No dip tube, no anti-siphon valve that I could find.
Fuel line attaches directly to fuel tank (internal pipe).

 

[Jacalore]

Re: MerCruiser 3.0L 140 No Acceleration

Gonna follow up on an earlier suggestion to check fuel pump filter tomorrow. I assume that's where the input line is connected. Never seen one, is it a screen?

 

[Bondo]

Re: MerCruiser 3.0L 140 No Acceleration

Gonna follow up on an earlier suggestion to check fuel pump filter tomorrow. I assume that's where the input line is connected. Never seen one, is it a screen?

Ayuh,... Usually a paper or ceramic element,...

 

[Jacalore]

Re: MerCruiser 3.0L 140 No Acceleration

Thanks. Can they be cleaned or only replaced?

 

[bonzoscott]

Re: MerCruiser 3.0L 140 No Acceleration

Replacement filter at the auto store are usually the paper type. I wouldn't try and clean it. It's maybe $2. Make sure you put it in the correct direction. I can't quite remember, but I think the open end of the filter goes toward the fuel line / fitting. It would be best to rebuild the carb so you know where you stand.

 

[Jacalore]

Re: MerCruiser 3.0L 140 No Acceleration

I'm talking about the fuel pump... I was told there's a filter there also. Carb has been eliminated as cause of problem. Thanks.

 

[Jacalore]

Re: MerCruiser 3.0L 140 No Acceleration

Ok, replaced all fuel lines and fittings from fuel tank to fuel pump to carb. Installed new inline fuel filter and replaced fuel filter in fuel pump. Time for another water test. Guess the only thing left is the fuel pump itself... anything else it could be?
Thanks.

 

[fixxupp]

Re: MerCruiser 3.0L 140 No Acceleration

Timing. If it's retarded, you won't have decent power. Use a timing light, paint the flywheel mark white, look up the degrees advance BTDC at low rpms. While you are at it, remove the distributor cap and the base plate, and check that the centrifugal mechanism moves easily. Two flat plates inside the distributor (mostly hidden when stopped) that slide outward on higher rpms, and are spring-loaded to pull back inward at lower rpms. Don't pull the distributor shaft out, that makes more work on re-assembly.

 

[Jacalore]

Re: MerCruiser 3.0L 140 No Acceleration

This is really an area I have no experience... Does it matter that the engine was converted to electronic ignition?

 

[fixxupp]

Re: MerCruiser 3.0L 140 No Acceleration

Oops, yes it does matter. Depends if your electronic version does or does not look after timing advance. If it does not, you still are using the centrifugal thingies for spark advance. If the entire distributor was replaced as part of the package, chances are your spark advance is looked after electronically. If your electronic ignition stuff was inserted into your existing distributor, chances are you are using the centrifugal thingies, so they must move easily. Look at what your electronic version says about timing. Paper is so easy to lose, so maybe they have something on a tech support webpage.

 

[Jacalore]

Re: MerCruiser 3.0L 140 No Acceleration

I have no paperwork on conversion... I'll contact PO see what I can find out.
Last I talked to him, he said engine ran fine after conversion, timing checked ok (TDC).