motor issues

[sportsman500efi7]

i recently bought a used boat. it's 72 tri-sonics with a 120/140 mercrusier i/o. the engine is a 4 cyl. my problem is it will only go 5-9 mph on the water and when i go to put it in reverse the engine wants to stall out. i'm new to boats and any thoughts or help would be greatly appreciated.

[marine_man]

Welcome to Fishing Minnesota!

Can you provide a little more info? When you say it will only go 5-9 mph, does that mean that you've got the throttle and full throttle, the motor sounds like it's running wide open, and you're only getting that speed?

marine_man

[sportsman500efi7]

First of all thank you for welcoming me to the site and helping me out.

the boat will only go 5-9 mph at full throttle. It doesn't sound like the motor is running wide open.

i put the muffs on it in the driveway and as i give it more throttle the engine and prop speed up like they should. if more info is required let me know.

[Surface Tension]

How long has the boat been stored?

Is the engine stumbling or is it smooth with a bog sound?

Change filter(s).

You'll have a filter behind the gas fitting on the carb. The fuel pump should have a filter there inside the bowl. You might also have an in-line filter between the carb and tank. Do you have more then one tank?

For now and to trouble shoot the tank and fuel you could use a portable tank. Any outboard tank will work, hook up one end to the fuel pump.

You should replace the filters at this point too.

If it were my boat I'd most likely remove and drain the fuel tank then a visual inspection for rust before using the tank with new filters. I'd also replace the pickup line and check valve inside the tank and replace all fuel lines.

If you still have the symptom, check the fuel pressure.

If that checks out I'd clean and rebuild the carb then onto a tuneup. New plugs, wires, points, condenser, dist cap, rotor, clean the flame arrest, choke adjustment, timing.

A few more things to do as far as maintenance. Check the exhaust, drive, and shift bellows for splits. Drain and replace lower unit oil. The drive will have areas to grease. You can go to your library and take out the manual for the your I/O.