Boat Loses Power at 35mph
 

I have a 97 Sanger V-210 just got it tuned up. New rotor, cap, spark plugs and fuel filter. When I get it up to 35mph or around 4,000 rpm it sputters/back fires and looses power until I throttle down. Runs great at all speeds up to 35mph. Any ideas?

This is just a shot in the dark, but does it have a 4000 rpm rev limiter? When I re-propped my SAN for more ballast, I started hitting the rev limiter right before I got to max speed which is around 35mph.

No it does not have a rev limiter. It usually cruises really nice at 45mph.

Sounds fuel related maybe? The flow is a lot higher running that hard than below it. Clogged fuel filter? Bad fuel pump? Too much water in the fuel water separator such that some is getting sucked in the motor high flow rates?

What Michael said, fuel related

I had a similar problem on an old boat. After replacing filters, clean carb, etc it turned out there were plastic fragments stuck in the fuel lines restricting flow. Mechanic said they were from the original fuel tank build from drilling holes in the plastic.

My sanger was doing the same thing only at top speed wide open. I changed the cap and rotor and issue went away. Was it running fine before you had the tune up?

Yes the boat had the same problem and that inspired me to get a major tune up and it still is having the same problem.

Carb or EFI?

Check anti-siphon valve on fuel tank

Do those come with the gt40? Sounds like limp mode.

Check your oil pressure valve. Mine did that last year. Bad valve needed replacing.

I'm leaning more towards electical as well. I had a n issue in my 94 centurion, and it had a cut off at an exact MPH (load) on the ****ty pro-tec ignition on the GT40, replaced with a new coil and Mallory breakerless distributor.

What motor?

I have a 350 in my malibu. Mine would run fine WOT planing weight off. Unloaded at WOT it would send it into limp mode. I've only taken it up to WOT twice since changing the cap and rotor the first time it went in limp mode. Shut it off and turned the battery switch off and on and the second time no limp mode. I haven't been WOT without any weight in it since.

Is the motor a Merc 350 MPI Skier by any chance? I have that motor and it was doing what you described a few years ago. Found out there was a recall and it was fixed for free by my local dealer. I cant recall the issue but I think it was electrical and had something to do with the Fuel management system. ( Fuel Injection)

First thing, get a fuel pressure gauge on the fuel rail to determine if its a fuel or spark issue. If your fuel pressure is dropping off, you've eliminated half your problems. If it is fuel related, start at the tank and work your way to the injectors. I had a similar issue. I blew the line with compressed air, replaced the booster pump, checked all the wiring, before I determined it was a clogged fuel filter.

They hooked up the distributor wrong. Happened to a buddies LSV. He spent a bunch trying to figure it out and it was just the wiring to the wrong plug(s).

my guess also but was happening before the tune up too

I'm with Boarder85 on what you should do. Your description seems like it's a fuel problem.

who tuned it up?

take it back to them.

He probably "tuned it up" by getting new cap, rotor, plugs and wires. When in reality it could be the 90 degree fuel fitting on top the tank (had that happen once), his fuel filter, the entire ignition, or even a knock sensor malfunction. There is a easy way to diagnose each. Just have to see if it is fuel or spark that's the issue first.

Im with Paul...wires on dist cap are switched...2 are not right. it will run really well until you push it.

Bit late to the party but I had a very similar issue with my boat, every so often a bit lumpy too and the odd backfire and a rich smell. Turned out 6 & 8 were switched, it would top out at 3k ish RPM / 35mph, I found out inspected the plugs and 6 & 8 were wet whilst the others were spot on perfect. Swapped the leads and it topped out the speedo's and ran so sweet it was unreal!

Throw a timing light on it.