Low WOT RPM after repower

[drpboston]

hey there,

99 Mercruiser 5.7 w/ Alpha 1 26' Larson - blew starboard head gasket at end of last season, so did both sides and had heads rebuilt. Mechanic also found pitting inside carb, so we bought a rebuilt rochester 2bbl. New plugs, dist cap and rotor, coil, and . Threw it all back together and have adjusted lash and checked timing couple of times. Compression good across cylinders.

She starts right up, but under load won't go over 2800 RPM, really struggles to hit 12 mph per GPS. I checked the tach with an external and its accurate. Ran through a tank and a half of gas, changed filters 3 times, cleaned out anti syphon valve and checked fuel vent and fuel pump. On a few occasions she surges to 3200 RPM And I've hit 24mph, but that doesn't last long. There is also a vibrations from 2000 - 3000 RPM, worse at lower range. Today, no go, back to sluggish behavior, running at around 140-150 degrees

I'm scratching my head here. Any ideas? She was running just fine up until last year when she suddenly lost power at the end of the season, and I pulled it out of water.

Thanks all

 

[Bondo]

Re: Low WOT RPM after repower

On a few occasions she surges to 3200 RPM And I've hit 24mph, but that doesn't last long.

Ayuh,... Sounds like Fuel Delivery,... Maybe it was a Bad carb... Bad fuelpump,..??

There is also a vibrations from 2000 - 3000 RPM, worse at lower range.

Recheck the plug wire firing order...

 

[Icefire55]

Re: Low WOT RPM after repower

was the carb a 4 barrel before?
My 5.7L with 4 barrel wouldn't go over 3000 because the secondairy were frozen.

Maybe your throttle cable/ carb bracket prevent it to go higher?

 

[drpboston]

Re: Low WOT RPM after repower

Thanks for responses so far.

I went from a 2 bbl to a 2bbl, so I didn't change that aspect.

As far as firing order, I've checked that as well.

Is there an efficient way to check an electric fuel pump? It spits fuel at start-up (into a collection container of course). Also, what is the likelihood that a rebuilt 2bbl carb would need internal or external adjustements at install?

It did seem to get power spurts as the fuel went down and the boat got lighter. I filled her up and now she doesn't go over 11 mph at 2800 rpm.