Engine Surges Under Load

[taalpert71]

I put a new engine in my 1991 Mercruiser 4.3L. Engine was running great for a couple hours, then moored for about 20 minutes. Decided to go one more time and all of a sudden the engine was hard starting. Made some adjustments just to get it running and then it started surging under load.

Got it home and same problem in driveway. Hard starting and seemed to be a fuel delivery problem. It would start with stater fluid and then stall. I bypassed the water strainer filter to eliminate that as a problem. Got it started and warmed up and tried putting under load again. Engine surges. I was able to lean the mixture to normal agin and it idles fine.

Any ideas why it would surge under load?

 

[Scott Danforth]

Any ideas why it would surge under load?

A few of the common reasons

Bad fuel

Bad fuel pump

Plugged fuel vent

Carb really out of adjustment

Dirt in carb (bypassing the filter probably didn't help)

Plugged AS valve

Fuel pickup tube has hole in it

 

[taalpert71]

A few of the common reasons

Bad fuel

Bad fuel pump

Plugged fuel vent

Carb really out of adjustment

Dirt in carb (bypassing the filter probably didn't help)

Plugged AS valve

Fuel pickup tube has hole in it

Still have a secondary fuel filter.

Put a full tank of fresh gas in.

Fuel pump is working well and was recently replaced.

Carb had air fuel mix set at about one full turn out both screws. Was set there when it was running good.

Not familiar with the AS valve?
Fuel vent is a good place to check. I’ll check the fuel pickup as well. Thanks!

 

[taalpert71]

Still have a secondary fuel filter.

Put a full tank of fresh gas in.

Fuel pump is working well and was recently replaced.

Carb had air fuel mix set at about one full turn out both screws. Was set there when it was running good.

Not familiar with the AS valve?
Fuel vent is a good place to check. I’ll check the fuel pickup as well. Thanks!

Yep, my fuel line vent was routed bad and had fuel in it. Timing was a little off as well. Thanks!

Still a little surge when I bring up the RPMs in my driveway, but now thinking it may be because no load on the out drive?