5.7L idles smooth will not get on plane
 

My buddy took his boat out for the first time this season and it ran perfect until he shut it off! When he restarted it, the boat would not get on plane. We drained the fuel, rebuilt the carb, inspected the pickup, tank vent, replaced the fuel pump (which seemed to have questionable internals) and spun on a new fuel filter. Off to the launch and no improvement. We did a full ignition tune up and although the engine now idles beautifully it still lacks power to plane off. There is some noise coming from the carb when the engine is under a load and the transom has a small accumulation of soot after a water test. At this point we are unsure where to go! Leakdown test? Verify timing advance? Any suggestions would be greatly appreciated this has gone on for weeks now!

Check the lifters. Had this happen to me years ago. Chased everything (fuel, carb, ignition system, etc.). Turned out to be a broken lifter.

A bad lifter would usually make a ticking noise. Has anyone inspected the prop to see if it has spun the hub?

Rpm
 

Thanks for the tips, i should have mentioned that we cant get the engine to rev above 2500-3000 rpm. It is just not making any power. On the garden hose it revs fine, as soon as a load is applied it wont tach out.

Mine was a head gasket. Same conditions. Good luck

Timing check
 

Today we got out the timing light and it appears that the ignition is advancing. From the 1 o'clock position the mark advances to approximatley 12 o'clock at about 3k rpm. Does this sound like enough? By my calculations that is about 30 degrees. I think this engine may have real problems.

Sounds like the choke is sticking closed
Wire it open and see if that helps

small blocks are notorious for sunken valves and will start backfiring through the carb as load increases.do a simple compression check or a leak down if needed

Fixx
 

Carb or efi? if a carb which model?? Webber?

Snap on timing light
 

I got my hands on a snap on timing light which supposidly will tell me how far the ignition is advancing. Will test with this tomorrow and see what the results are.
It is a weber carb and I verified today that the choke plate is open. Thanks again for all of the suggestions. We'll see what tomorrow brings.

We started out the day by verifying that the timing advance was working properly. We then began a compression test and quickly found two cylinders on the fuel pump side of the engine had no compression. All other cylinders had between 150 and 160 psi. I guess the question now is pull the head or pull the motor? There is ample room to get the head off. If by chance the pistons/ cylinders look ok would it make sense to just have the head rebuilt?

Head gasket it is. Unfortunatley the head and block are missing material where the gasket came apart between cylinders. We will be looking for a replacement engine. Thanks for all the tips.

Have you checked your fuel pump? Do you have and electric pump or manual diaphram pump? Also check your anti shypon valve at the tank these will stick and cause a very lean condition your engine will literly starve for fuel. Take out your anti syphon valve and put in a straight barbed fitting and try it again. Also tee in a pressure gauge on the inlet side to your carb start it up it shoulld run about 5 to 7 psi then take it out on the water there should be no drop in fuel pressure. There is also a fuel volumn test that you can run during crannk but I dont remember how much fuel should go into a pre mesured container in a minute but if you need to know I can look it up for you.