94 sport Nautique mid range loss of power

[Toolman22]

Just purchased 94 sport nautique, 5.8L HO 351 with 4061 holley. after about 30 minutes of operation (not consistent times) engine hesitates and losses power between 25 to 30 mph range. Don't remember RPM range. Lower speeds and higher speeds runs fine. Previous owner says never rebuilt carb in 15 years use and has been using ethanol gas, but religiously used sea foam. Thinking this is most likely a fuel or carburetor problem. Engine has (aftermarket?) electronic ignition. Any ideas would be appreciated. Love this boat and want to ensure I have power just in the sweet spot for slalom! Thanks Toolman22

[ScooterMcgavin]

I would definitely consider a new carberator after just because of the age or at least have it rebuilt. When was the last time the fuel filter has been changed?

[Jonny Quest]

I would check on a couple of things first. Does your engine have the Pro-Tech engine management system? You can determine fairly quickly. It is a Pro-Tech system if all the spark plug wires run to the rear of the engine (above the transmission). The wires run into 4 coil packs. If your system has Pro-Tech, then I suspect that could be the culprit. The Pro-Tech systems are ticking time-bombs and replacement parts are non-existent. Not to worry, though. If you have Pro-Tech, it is a fairly simple process to remove the Pro-Tech and retro-fit to a traditional distributor set-up. If this is the case, then I would recommend an HEI distributor from Davis Unified Ignition. Do a search for Davis Unified Ignition and look at their marine specific distributors. You will likely need the Ford 351W standard rotation in 7,000 RPM (not the 10,000 RPM model).

If your system does not have Pro-Tech, then I would look at the carburetor. (BTW, it's a Holley 4160, not a 4061). Sounds like it could be a Power Valve that has gone round the bend or your vacuum secondaries. Both are easy fixes. You don't have to buy a new carb, but you can rebuild your Holley 4160. If you aren't comfortable with rebuilding yourself, you can have a local shop do it for your. Skidim.com or NautiqueParts.com will have the proper rebuild kit. Look on the air horn of the carb (close to where the flame arrestor sits) and you will see some numbers. Those numbers will tell you the exact model carb you have so that you can order the proper rebuild kit.

If you choose to buy a new carb, I would strongly recommend the QuickFuel Marine M-600 carb. It is a little less expensive than the Holley 4160 but is a MUCH better carb. It should bolt right up. You may need to order a 90 degree fitting for the fuel inlet.

JQ

[Toolman22]

JQ, Thanks for the info! Yes the boat has the pro tech coil packs. I think I will rebuild the carb first. Thanks for the feedback. Sincerely TT