New motor doesnt seem to have the power i expected

[plio7]

i just got a new boat it runs well, very smooth, its a 1980 70hp merc. and its on a 14' 1980 vanguard. i'm topping out just bearly over 30 mph but my rpms are only running about 4000. when i put her in neutral, and rev it up it revs good, but when in gear it doesnt push past 4000. is this normal, could it be a wrong prop?

thanks very much for any help

 

[hkeiner]

Re: New motor doesnt seem to have the power i expected

Revving the motor in neutral does not indicate anything as there is no resistance on the motor. In fact, it is not a good idea to rev the motor in neutral at all. Regarding your lack of power problem, there are many possibilities, such as poor compression, failing ignition system, failing fuel delivery system, and improper link and sync settings. Another possibility, as you pointed out, is that the motor is overpropped.

Instead of throwing parts at the motor, you would likely be better off first doing some systematic troubleshooting to narrow down the cause. I suggest that you get an OEM shop manual for your motor, as it would provide troubleshootig guidance. Also, this forum contains a wealth of posts already describing such troubleshooting steps. Rather than my repeating them all here, I suggest that you do some searches on this forum. Good luck.

Of course, if you have access to a free/cheap/loaner lower pitch prop, then swapping props would be an quick way to eliminate incorrect prop pitch as the cause.

 

[achris]

Re: New motor doesnt seem to have the power i expected

Start off with a compression test, check that you have spark on all cylinders and a set of new plugs. Then check that the cable is opening the carbs up all the way and the spark is reaching maximum advance. You're going to need the manual for all this, so the very first thing is to buy the genuine Merc manual. Don't even think about the others, they are rubbish and shouldn't even be sold....

Chris............

 

[Chris1956]

Re: New motor doesnt seem to have the power i expected

I am not familar with that particular boat make, however, a 70HP motor on a 14 footer should give excellent (maybe scary) performance. After you execute the checks suggested and the power is restored, let us know if the boat cooks.....