totalrex

Just got the 5.7 mercruiser rebuilt with performance Xtreme Marine cam, bored .030 and just took it on the lake last night - it is only running 4000rpm on top end, prior to the rebuild I could get 4500-4600 no problem, any ideas? I am running it at 8deg before TDC on the base timing, if I bumped this would it help get more RPM? not sure what to do now..... any input would be greatly appreciated. Thanks in advance!

totalrex

how do I properly set the timing - it is a 1986 with the ingnition that has the big box on the riser..... do I have to dis-connect something? Could the cam I put in need more advance to get the RPM's???

1BIGJIM

iTrader: (1)

No there is nothing to dis-connect.
Was the cam installed using a degree wheel to make sure it was installed correctly?

Many years ago when I was a young pup and always in a hurry, I installed a comp cam in a 350 with the timing marks off. Boat idled good, sounded good but would not come on plane.

rdoactive

Do the simple stuff first.
1) Check to see your secondaries are fully opening.
2) Check to see your ignition is advancing with rpm.
3)Also check your ignition, wires, plugs, cap, etc are in good shape.
Do not try to advance your ignition base timing. This will result in advancing the total timing and could amage your engine.

pachanga

LOL! I did the same thing in a truck one time! I had always been a ford man and was my 1st chevy! Ford used the keyway on the crank gear and chevy's had a dot! Ran smooth as a kitten but no power. Difference was a couple a teeth!

Thunderstruck

After the basics do a leak down. I had a newly rebuilt motor that had an intake valve that was not lapped in. After a miserable dyno experience, did the leakdown, new valve job and gained 30 hp on a 502 NA engine after paying $300 more to the dyno operator for another dyno day.

Also valves adjusted too tight can hurt power but I don't think it would run smoothly.

Flattened lobe on cam.

SmallPP

Stay basic at first. Check fuel and air flow. Replace water seperator, check filter inside Q-Jet carb (if that is what you have), clean flame arrestor with carb cleaner, most daily boaters never do this.

If the engine is popping at high RPM, I'd suspect weak or wrong valve springs.

If all else, could be cam timing as mentioned above. I installed my Crane marine roller straight up (no degree wheel), used the springs they recommended, and it feels like it could pull a house off the foundation, can qucikly go over 5700RPM (need to change drive ratio next).

totalrex

don't know about cam the cam timing - it was built by a reputable local shop.... as for the water separator and fuel filters, both are new and no affect at all on WOT RPM. I checked plugs and ignition wires everything is new and looks good..... any other ideas??? motor is coming out this week and going back tot he shop because it has an oil leak on the rear main.......

SeaRay Jim

Make sure he knows how it's running and makes sure he got the cam right and generally, put together right.