360 lack of power

Port counter rotation engine starts and runs perfect to about 2800 rpm. Although I give it more throttle it doesn't respond.Used to run at 4000. No misses or backfires. Carb swithched from starboard which ran 4000 , no change. Dist. rebuilt no change. Comp.. test well with in spec. Both filters changed no change.timing checkedat 5 degrees before tdc. new plugs and wires no change. Can set at 2800 and run for hrs on plane but something isn't right. Any ideas. I'm stumped and so is my mechanic.

Did you check the spark advance with an indicating timing light? I'll bet it's not getting full advance.

Jeff

No but thats a good thought. What do you think about the rear barrels not opening?

Thats a possibility

Easy enough to check if the rear barrels are opening. Motor off, warmed up (important!) open the throttle and see if the shaft rotates as the throttle is opened.

Jeff

just went thru the same thing myself, only kept getting worse til it wouldn't even turn over 1000 rpm under power. i even went as far as rebuilding the tranny fiquring that something internal was binding up under load....even that didn't cure the problem. even tho the engine had good compession, i pulled the heads anyway....turned out to be cracked heads. machine shop guy said that when idling or with no load the cracks were able to handle the pressures between the cylinders, but under load the cracks tend to have more stresses on them from the added torque, open up a little, and lose compression thru the other cylinders. i'd never heard of such a thing, but after spending $3500 and half the summer scratching my head, i replaced the heads with new ones and now the boat runs better than ever. not saying that this is your problem, but it sounds like you might want to have the heads magnafluxed just to be sure...........

I'll try the spark advance and the rear barrels first and if that doesn't do it, it's a long winter and the heads might come off. Thanks

If your carb is a weber AFB or an edelbrock performer 1409, the secondaries are opened by vacuum, not mechanically.

I think you meant to say they are NOT opened by vacuum (which is correct). There's a "flip over" valve that airflow rotates (providing an accelerator pump action) but the butterflies open with the throttle. You can see this happening on the right side of the carb.

Jeff

Checked the rear barrels and they are opening. Timimg may stilll be an issue. Timimg light didn't function properly. Will try again this week end.

You can borrow a timing light from Auto Zone or Advance auto parts stores.

Jeff

Boats out for the season.Pulled the dist. and am going to rebiuld over the winter. Seems you were right. The dist couldn't go to full advance. Thanks. John

Next season it will fly!

Jeff