Engine bogs down under load

[AndrewsArk]

I have a 5.0 MerCruiser AlphaOne. Last weekend we to ok it out and it ran great for a while, but then it wouldn't go past 3000 rpms under load. I could throw it in neutral and hold it near redline without any problems. It goes to 3000 and then just cuts out like it loses fuel.

So yesterday I took the carburetor off and cleaned it all up, cleaned the jets and checked it out to make sure it wasn't the problem. There was some crud in one of the jets so I thought I had it. Take it out on the lake for a test run and it does the same thing. Hit 3000 rpms under load and it just bogs down like its not getting fuel. If I stay on it it'll backfire. However, if I throttle down, it'll rev down and idle fine.

I can push water all day as long as I don't go over 3,000 rpms. Any ideas?

 

[Bondo]

Re: Engine bogs down under load

I have a 5.0 MerCruiser AlphaOne. Last weekend we to ok it out and it ran great for a while, but then it wouldn't go past 3000 rpms under load. I could throw it in neutral and hold it near redline without any problems. It goes to 3000 and then just cuts out like it loses fuel.

So yesterday I took the carburetor off and cleaned it all up, cleaned the jets and checked it out to make sure it wasn't the problem. There was some crud in one of the jets so I thought I had it. Take it out on the lake for a test run and it does the same thing. Hit 3000 rpms under load and it just bogs down like its not getting fuel. If I stay on it it'll backfire. However, if I throttle down, it'll rev down and idle fine.

I can push water all day as long as I don't go over 3,000 rpms. Any ideas?

Ayuh,.... Did ya check the contents of, 'n change the fuel Filters,..??

It no doubt IS runnin' outa fuel,... You've gotta figure out WHY....

Btw,... runnin' it to redline, in neutral is of No use, 'n can lead to a 500lb Anchor, where yer motor used to be....

 

[AndrewsArk]

Re: Engine bogs down under load

Ayuh,.... Did ya check the contents of, 'n change the fuel Filters,..??

It no doubt IS runnin' outa fuel,... You've gotta figure out WHY....

Btw,... runnin' it to redline, in neutral is of No use, 'n can lead to a 500lb Anchor, where yer motor used to be....

Thanks for the confirmation. I'll have to look at the fuel pump and lines next then. The filters were new in the fall for winterization but I'll check anyway.

 

[Bondo]

Re: Engine bogs down under load

Thanks for the confirmation. I'll have to look at the fuel pump and lines next then. The filters were new in the fall for winterization but I'll check anyway.

Ayuh,... Filters don't have a Time limit on they're usefulness... They Do have a Water, 'n Crud limit though...

 

[AndrewsArk]

Re: Engine bogs down under load

Thanks for the tip of looking at the filters. The fuel filter was full of water. How do these separating filters work if there's no drain valve? I'm assuming it hold the water and once it's so full it won't flow as well.

 

[Bondo]

Re: Engine bogs down under load

Thanks for the tip of looking at the filters. The fuel filter was full of water. How do these separating filters work if there's no drain valve? I'm assuming it hold the water and once it's so full it won't flow as well.

Ayuh,.... By Gravity....

As the fuel passes through, the water falls out of suspension, 'n collects in the canister...

When it gets Full of water,...
The water passes through to the carb, or efi, or whatever...

 

[AndrewsArk]

Re: Engine bogs down under load

Filter replaced. Engine compression is 205psi on all 8. Replaced distributor cap and wires. Spark plugs are still fantastic. No water in the gas tank and the fuel pick up looks good.

Vacuum or fuel pump most likely...?

 

[AndrewsArk]

Re: Engine bogs down under load

Figured it out... Fuel pump is giving up on me.

 

[Bondo]

Re: Engine bogs down under load

Figured it out... Fuel pump is giving up on me.

Ayuh,... Cool,...