Poor performing 351?

[Hagman]

Where is your trim tab set. If it’s down to fare the nose of the boat will plow slightly slowing you down. If you carry your weight to the back this could help raze the nose. Hence less drag more speed. Is your boat heavy -water ,people, beer. A heavy boat is a slower boat. Craggs has one of the finest boat on the forum , it’s been newly rebuilt its going to be as light as it was when it was new.

[csuggs]

Where is your trim tab set. If it’s down to fare the nose of the boat will plow slightly slowing you down. If you carry your weight to the back this could help raze the nose. Hence less drag more speed. Is your boat heavy -water ,people, beer. A heavy boat is a slower boat. Craggs has one of the finest boat on the forum , it’s been newly rebuilt its going to be as light as it was when it was new.

Hey thanks for the compliment Hagman! My motor is not all that "fresh", and by that I mean it has not been rebuilt. I have rebuilt the carb and the electronic ignition is nearly new as are the plugs and wires. My prop is the Acme 13x11.5 that has been re-pitched to the spec. (the prop was new last spring and after I ran over my tow rope and bent a blade, I had it repaired. The shop I use not only straightens and balances the prop, but they "pitch" the blades to spec!). After I got the prop back I noticed an improvement in top end of about 2mph. Also, I think there is something to the weight issue with regard to a newly rebuilt hull and floor. Without knowing Chris' situation, I'm sure my boat is light compared to his if he has not had his floor and stringers done. The other factor is the speedo. Both of mine are relatively new and have new tournament style pitot tubes with new lines run all the way back. Even the bronze tubes have been repaired. I'm pretty certain that my speedos are correct, although they have not been checked.

Chris - you don't have to spend a fortune, but I'd start with a tune-up. Carburetor and ignition.

Clint

[cadunkle]

110-120 psi and never rebuilt? I'd say you've got a genuinely worn out engine. Be happy your only 10 psi from high to low, they've worn evenly. Either be content with the performance you've got or rebuild it. Ignition and carb will not help much with such low cranking psi but may show some gains. Either rebuild next winter or just run it until it dies.

[chrisk]

CSuggs, I'm fairly certain the previous owner replaced the stringers but I'm not sure about which method he used. Also, I'm basing my speed off of GPS on my phone, not the speedos.

I'm content with the performance of the boat, only reason I'm looking for more top end is to be able to barefoot. I suppose if it can't go fast enough for me to barefoot it'll prevent me from getting injured again ; )

I'm going to continue with checking timing, replacing plugs, and cleaning the dist cap contacts. Just the easy stuff to see if anything comes of it. I'm not going to pursue a rebuild since it's running so dang well aside from this.

[cadunkle]

Yep give it a good tune up, timing, carb tune and call it a day. You'll probably get a few more seasons out of it before performance really drops off. When you eventually go through the engine it'll be like night and day and you'll be able to barefoot. Well cared for engines wear out evenyl as rings lose tension and cylinders taper... So no worries if it's otherwise running good.

[chrisk]

Just an update: Replaced the plugs with platinum Autolite's and didn't see any performance change. Currently have sea foam running through the engine but I haven't taken the time to test timing and clean distro cap contacts. Still starts, idles, and runs like a top so I'm not too worried.

[DAFF]

Given a choice of boats .... One with a fresh engine and a worn out non ajusted carb and the other engine worn but tuned correctly the old engine will will typicially out perform the new.

I would keep the factory old school plug style in the boats, those fancy ones will cause too much greif down the road. I have seen way too many bad running older vehicles where the owners put platnums in during a tune up to drop there vehicle off for rough running and hard starts. Spark systems are designed specifically for a certain plug, even changing name brands can cause grief once in a while.

I would start on the carb and fuel mixtures..... Perhaps the boat is running out of fuel at the higher RPM's.

[chrisk]

Resurrecting an older thread here but these thoughts are back in my mind.

During a long boat trip over the weekend I pulled out of a lock and dam and hammered down to WOT. I was able to get almost 4300 rpm's and it felt like we were really flying. I had 6 people and gear in the boat. Normally, the whole time I've owned the boat I can normally only get barely 3900 rpm's. Right now I have two thoughts:

1) The carb needs rebuilt. I don't know much about 4 barrels and whatnot so this may be a dumb question but could this be an issue where the 4 barrel isn't opening all the way at WOT? In your opinion, will a rebuild kit show an improvement?

2) My second theory is simpler. There was a chop on the water when I achieved 4300. I know speed boats and even skis and wakeboards are sometimes designed without continual surfaces to break up the water tension on the bottom of the hull. Is it possible that reduced water tension on the hull allowed the boat to spin higher RPM's?

Also, the ignition system is all good. I've since learned that all parts were replaced right before I purchased 3 years ago and the timing is good.

[chrisk]

Also, this thread really belongs in Service if a Mod wants to move it over, that's my bad.