351 idling rough, help me OB1
 

351 in a ski boat.

idles rough, dies, will not run on its own without throttle.

takes off fair, but runs ok once moving, but will occasionally hiccup (backfire).

has a new carb, and all tuned up.

what do you think? bad cam lobe or burnt valves?:confused:

If it got hot ....could be water in cylinders ..pull a plug and check for water ....

ill do that. i was thinking more towards cam and burnt valves though?? the boat is my brothers, and at this point he will check anything.

Tune up = new plugs + wires + cap + rotor + checked timing and advance?
Fuel supply & quality OK? New fuel/water separator? No water in gas tank? Good fuel pressure?
Have you done a compression check?
Gary

just got off the phone with him. tune up stuff, all done, fuel is good and ok, new fuel/water, has NOT checked fuel pressure.

but if it had low fuel pressure then how would it run top end ok?

Poor idle and the symptoms you described are usually due to too rich condition. Are you sure the carb doesnt have a blown power valve or stuck float (Holley?). Is the choke opening?
What do the plugs look like, black? Again, this could indicate rich condition, or bad fuel, or bad spark (coil OK?)
Compression check should indicate if it's avalvetrain problem.
Gary

i posted on the problem before and the consensus was a bad carb, so he bought a new one.

he needs a compression test next.

he didnt do a compression test, but instead took it into a shop. they did one, and heres what they found.

on one side, 2 dead cylinders, pulled the heads and ones a gt-40 head and ones regular. they said it was sucking the valves down and ruined them :confused:

getting a matched set of heads and putting it back together.

Hey...I'm working on that boat!

Bob

thats it :D