Early 80's Force 125 not faster than 5 MP - I think it's the mix.

I just bought a GradyWhite 19' with a 125 Force. Not sure yet of year, early 80's I think. I tested the engine with earmuffs, not in the water - and trusted the previous owner's word that it works fine.

On my first sea trial the engine wasn't going faster than 5 MPH at max RPM, and it didn't sound right - some shaking and the engine sounded 'forced'. [I think] luckily for me I ran out of gas during that trial -as that may have given me "the key" to what's happening.

The last 2 seconds before the engine died (out of gas) it sped up to a normal speed, the engine sounded 'right', kept the momentum for 2 seconds then died. Once I put gas again it started up normal but again not giving me more than 5 MPH.

The "non-mechanic light-bulb" in my head says that during those last 2 seconds, because the last injection of gas was not a 'full-delivery' but 'partial-delivery' of gas, the proportion of gas and air was perfect thus the change in speed, performance, and sound. I think there is an issue with the amount of air being delivered to the mix.

Am I on the right track?
If so, where do I start checking parts to find the one creating the trouble?
If not, what could be the cause? maybe the opposite, too much gas being delivered?

I don't know if it helps to know, or if it's related since it's also an issue with the air in the mix, but to start the engine I open the cover and place my hands for 1/2 sec in the air intakes or else the engine won't start when cold.

Any advice is much appreciated.

Thank you in advance

Welcome.
The running faster as it ran out of gas: That's a normal thing, for some reason the motor speeds up when the last of the gas is getting used.

The hands over the intake: What your doing is choking the motor, it increases the amount of fuel to the motor.

The 5mph at max throttle: Does the engine rev up ? If it revs up and doesn't go anywhere, the prop hub is probably spun.=new prop.

Do you know that the motor has choke that helps start the motor? You push in the key as you turn it to start. Holding it in increases the amount gas to help start.

You mix oil and gas. 1 pint to 6 gal. Too little and your gonna do damage.
Too much oil isn't good either.

You should get a mechanic to check it over and do a compression and spark test.
Change the impeller and check the fuel system.
Maybe rebuild the fuel pump and install a filter between the carb and the pump.

Hi Jerry,

Thank you for all your advise, and than you for the 'welcome'

It does rev up. I'd to change the prop before getting in the water, and before I ran out of gas I was more inclined to think it was a prop issue. You put me back on that track - thanks for the advise.

I'll check the prop first.

Thank you!

Don't forget to post the results.