57 Mercruiser RPMbs fall at wot

"I have been rebuilding a 1994

"I have been rebuilding a 1994 Maxum sr2 with a 5.7 Merc. Reworked the heads, replaced all gaskets, plugs rotor and cap. Boat did not come with a prop, it has 1.5 gear ratio on alpha one outdrive. 4 barrel carb.
I put a 23 pitch cleaver prop on her, I took her out today and got a max of 3600 rpm, then the engine would just lose power and slowly fall to about 2900.

On the way back in the engine started to skip and backfire. I could not get more than 2100 rpm a wot. I have not replaced the spark plug wire but plan on that tomorrow. I have a new fuel filter, but not sure about the quality of my gas. The tank was full when I got the boat, about 50 gallons in a 60 gallon tank. Not sure how long it has been sitting there so i put the new water removing fuel treatment in the tank and ran it. Any other thoughts on what I should be doing to make her run smooth and reach full rpm would be appreciated."

"You dont say how long or heav

"You dont say how long or heavy the boat is so,Try a smaller prop for starters"

Bad gas doesn't help. If

Bad gas doesn't help. If it has an odor like varnish then it is crap and needs to come out. Make sure the four barrell carb is opening up all the way. Check that the timing is advancing. You can connect a six gallon can of fresh gas to rule out the tank gas.

"The boat is 23' long and

"The boat is 23' long and weighs 4300 pounds.

If the gas is bad, does it all have to be trashed or is it possible to put the additives in it to bring it back?"

"I just reead an interesting a

"I just reead an interesting atricle on prop pitch. In a nutshell it said that too high a pitch will rob your engine of horsepower and cause the plugs to foul up. This sounds like my problem. Im gonna try running a 17 pitch prop today, probably still gonna replace the plug wires since Im going to pull the plugs to clean them and adjust the gap."

"[b]"If the gas is bad, do

""If the gas is bad, does it all have to be trashed or is it possible to put the additives in it to bring it back?"

Ayuh,... Do the Sniff Test,... If it Smells like Gas,.. It'll burn...
If it Don't,... It's Trash,+ Nothing will bring it back..."

"you did a compression test on

"you did a compression test on a warm motor with all the plugs out and the throttle fully engaged?

You should run it on a external tank of fresh fuel after you clean the filter in the fitting that enters the carb.

Fuel pump giving you 4-7 psi no less you checked it?

The bottom clean on the boat and no water in the hull?

The motor is timed correctly and tuned?

The valves not to tight?

You did a vacuum test?

Here is 2 sites to help:

http://www.secondchancegarage.com/public/186.cfm

http://www.users.bigpond.com/ergoff/vac1.htm

I gave you a good days work if you are serious about fixing it, post the results of the test and we will go from there.

I forgot to mention i don't know if you rebuilt the carb, if not thats the next step.

But you need to get to 4200-4600 rpm borrow/ steal
a shop tach to verify the dash tach.

May the force be with you, grasshopper."

"I pulled my plugs and cleaned

"I pulled my plugs and cleaned them....all fouled, set the gap and then put on new spark plug wires. I changed my prop, went down to an 18 pitch x 14. Replaced fuel filter, drained tank and put in new gas....high test. Took her out today and ran her for about an hour, engine rps were good at 4600 at the beginning of the day. had to idle through the no wake zone to go get some lunch, after eating the boat did not run good. WOT rpms were never higher than 4300, and the engine was bogging down again. Loss of rpms when turning. Opened engine compartment and noticed more blow back smoke than norm from the breather hoses on the valve covers. Would over tight valves cause this problem?"

yes and who set up the valves?

yes and who set up the valves? But have you checked the fuel filters again?

And the results of the tests i posted using 2 stickin fingers and took me almost a half hour to post my reply. And copy and paste the links.

Carb might need cleaning out. The new fuel has ethanol. It's acting as a scrubbing action on the inside of the tank and i bet the filter in the fitting that enters the carb is full of gunk and every other filter in the system.

"I set the valves......new hyd

"I set the valves......new hydraulic lifters too. I set the rods to zero lash then added half a turn. I upgraded my rockers to roller rockers when i rebuilt the heads. Always had good compression on the cylenders.

As far as fuel filters go, I only have the one, a water seperating fuel filter, looks like an oil filter, screw on in front of the engine. no other filters on the line. I cleaned out the carb, scrubbed all the gunk off the needles, all my seals were good."

"there is no filter in the fit

"there is no filter in the fitting that enters the carb? there is no screen on the bottom of the fuel pickup tube? Clean out the carb again.

Redo the valves. And please, please, please do a vacuum test."