MEANGREEN231

Have a long on going issue of low wot. Boat is a wellcraft nova 3, (basically a scarab 29's twin brother) and it has twin merc 350's and both will not rev higher then 4000rpm. I have been replacing parts here and there but no change in wot. Even swapped props from 23p to 21p. Boat normally moves around 2 adults and two kids, but when it had 4 adults and 5 kids still 4000rpms. I am starting to think carbs are the issue. My solution.....
Why waste money on rebuilding q-jets. I can just upgrade to edelbrock 1409's. But why stop there, so I am thinking of staying with stock cam, to avoid water reversion issues, but throwing on some twisted wedge heads with roller rockers, twisted wedge's version of the air gap intake. Twisted wedge has a 400 and something HP top end kit, so thats what I am thinking. I am a twisted wedge fan from prior dealings with there TFS heads on my mustang. They make better power compared to the edelbrocks and vortecs, and the price is fair.

Thoughts from any of the other gearheads???? I just find it odd that both motors are tapping out within 50 rpms of eachother, and that a prop swap yeilded virtually no change......starting to wonder if it was jetted for higher elevation as she was a lake powell area boat.

A.O. Razor

Have you checked the timing and will it rev past 4000 in neutral? Does the carb open all the way up when the controls are at wot?

For a power upgrade, I would look for the cheapest way to get those 260's running, then sell them and find a pair of 350MAG MPI or 377 MPI takeouts. Merc also has the 357MAG, 383MAG, 383MAG Stroker and 383MAG Stroker Scorpion re-power motors. I would stick with a stock Merc brand motor as not to hurt resale.

keith2500hd

agree with A.O.RAZOR and i would use handheld tach to verify dash tachs. i would change as little as possible, spending lots of money may not get desired results. i would go through engines, compression, spark/plugwires, timing, cap and rotor. what is condition of hull, drives and props.

MEANGREEN231

Boat will rev all the way up in neutral, and the secondaries only open under load, so I really cant tell by revving in neutral, but based on acceleration I would say they open, it just seems that at 4k it hits a wall.

I really am not worried about resale, the boat is a classic and i love the lines so she aint going anywhere. Plus all new upholstry and gelcoat, and sound system, basically all that is left untouched is the motors and drives, but she was well taken care of over the years by the OG owner. When I bought it I could dine off the motors and engine bay.

My thoughts are I can pull more power for less money using the motors I have just building the top end properly. Plus the aluminum heads will save alot of weight when replacing all 4 and the cast iron manifolds as well.

MEANGREEN231

Tachs are plus or minus 50rpms from the dash to timing gun. Full tune up, fuel filters, oil pressure 50-55psi under load and I even pulled the anti siphon valves to see if those were the culprit. She starts and runs great just does not rev out. Plus like I said it baffles me that both motors are behaving exactly the same, and the only thing they share in common is the fuel tank. I am thinking gummed up carbs, as the boat sat for almost 3 years. Last owner got to old and sat on it for 2 years before he sold it, and then it took me about 1 year to bring it current instead of looking like a miami vice special!

Props are brand new SS, and the drives are in great shape, end play within spec and good clean synthetic gear lube. Hull is spotless brand new gel coat, and the only time it is in the water is for play time, then back on the trailer.

Knot 4 Me

Hull straight? No hooks from sitting on trailer so long? Pull the caps and make sure the advance weights aren't sticking?

A.O. Razor

Hm, gummed up carbs or fuel lines can deffinetly happen over 3 years. Have you checked your fuel pressure under load wot? Even if the carbs were set up for high altitude, the motors should rev higher with lower pitch props and I can't imagine the difference being that much. If it's not a timing issue, I think you are on the right track with fuel starvation. Only thought about that is, then the carbs should be clogged up the exact same amount, unless it's in the fuel tank or lines. You could remove the flame arrestors and have someone look or drive while under way, and see if the secondaries are fully opening. I remember hearing about something similar where the cams were installed wrong after a rebuild.

MEANGREEN231

Hull looked good, when it was on a cradle getting the gel coat. The only damage was gel coat was worn off on the leading edge of the keel from beaching. Curiosity drove me to check it out with a straight edge, long before I noticed this problem. When I test drove it, I never really paid attention to the wot, but based on the fact that welly put 23p from the factory I should be overrevving the 21p.

Where in central IL? I am a nativo myself, just transplanted to AZ.

MEANGREEN231

El sucko if it is cam timing! But I could check it when I tear it down. I am sure that the motors were rebuilt at some time in the last 26 years!!

Never checked fuel psi, because I am not experiencing surging or falling off, but may be worth a shot. I replaced the lines from the tank to the filters when I pulled the anti siphons, and have tried sea foam and trans fluid in a few tanks of gas, also the tune up made no difference.

Plus your thoughts on the equal gumming up, is on par with me thinking that mechanically if the motors were tired or having mechanical issues what are the odds that they would be equally comprimised...what are the odds of that? Plus I have no other signs of tired or troubled motors .

GTOFFSHORE

Have you checked your ingniton. What type is it? Gummed up carbs wouldn't just stop you at 4k on both motors. Can you you the advance cOming on with a timing light? I had a motor do this and it was because it never really went into advance.