hi guys, i am reacing out to you because i am at a stand still and noone on the boating forums are any more helpful than what i already know so i am giving this forum a try. I hope you can help because this one is kicking my *** and has me going nuts.
heresthe jist of it::
rebuilt engine installed, built by a local machine shop , 5.7, with thunderbolt 5 ignition system with knock sensor. 4 barrel weber. proffesionally rebuilt carb, new knock sensor, new mechanical fuel pump, new cap, rotor, ignition sensor and coil, new plugs, wires, installed remote fuel tank to insure good clean gas. timing checked several times , base and advance system ok. the boat will idle smooth and rev nicely in neutral all day long but put a load on it and as you pick up speed and rpms, you'll hear it pinging, if i do not pull back on the throttle, it will backfire and stall out but start right back up. and act the same way.

 

ive played with the timing, retarted it and advanced with no positive results, i know that pinging is the result of running lean but al ltests indicate the fuel system is working as designed.
someone has suggested doing a cylinder leakdown test to see if there is blowby. others have suggested pulling the timing cover cnad checking to see if the timing gears lign up, this is my last resort because i will have to pull the motor from the boat to get the timing and oil pan covers back on.

 

predetonation/ping can also be to far advanced timing. fuel octane rating correct?

can you confirm the base timing( crank/cam) is correct? distributor indexed correct?

 

Was this the original motor and carb on the boat before rebuild?
What boat is it in and what's motor's HP rating - same as before rebuild or was it built up?

 

Personally, I'd suggest checking the fuel pump. Unhook the output line, crank it into a container, see if it is able to produce the fuel needed.

 

, the engine was not built by me, it was a machine shop in town, i got involved after the person who was supposed to install it got hurt and the engine sat for a year waiting for insta;ll.
the fuel has been changed 2x, the base timing has been chacked and rechecked. distributor is right were it should be based on the #s on the cap.

 

this was the original motor and carb to this boat, the motor is a 260hp rating and it was built back to original specs
itis in a 22' falcon, just a litttle cuddy cabin boat.

 

I agree with Kevin; make sure you have proper fuel pressure; lots of threads over at Malibu Crew about similar symptoms - revs good until put under load, then bogs down; suggests starving for fuel

 

the fuel pump was checked and even though the pressiure was fine, i installed a new carter pump as well as a new anti siphon valve, then i ran it on an external tank with fresh gas,

 

A couple of things,
If the dist is one tooth off , could produce performance problems.
Usually when starving for fuel, engine just doesn't have the guts to deliver. Possible fuel volume problem.
Your best bet is to start from the beginning and confirm dist is installed correctly then set timing to spec.It has to be removed and done correctly from the start.
We agree low fuel will starve engine , run lean and misfire .
The problem sounds like spark is not getting to where it is supposed to be at the right time.