Mercury 2.5HP - no high speed power

bdeis61159

Recruit
Joined
Oct 26, 2010
Messages
2
I am a newbee to the forum and my engine. I just bought it used. Its a 1993 Mercury 2.5HP. It starts right up and accelerates well out of the water. When in the water, it does fine at low speed but moving the throttle forward I get little increase in speed. Its like the engine stays in 1st gear. Could it be the lower unit? Carb seems fine, new plug. Thanks for any input. Barrie Deis
 
Last edited:

bassman284

Commander
Joined
Jun 24, 2006
Messages
2,840
Re: Mercury 2.5HP - no high speed power

How big is the boat? You might just be hitting the wall on what that motor can push.

Example: I have a 2003 9.9 Merc 4 stroke. It moves right out to a little over 1/3 throttle (about 6 mph) and thenn won't really open up much more. The faster you go, the harder the boat is to push.
 

bdeis61159

Recruit
Joined
Oct 26, 2010
Messages
2
Re: Mercury 2.5HP - no high speed power

Interesting theory. The boat is just a 10' jon boat with a motor rating of 3HP. I would think it could do a little better. Thank you for your reply.
 

starcraft1982

Petty Officer 1st Class
Joined
Feb 7, 2010
Messages
277
Re: Mercury 2.5HP - no high speed power

This is interesting.I honestly cannot see a 2.5hp pushing anything at more that trolling motor speed(and not a 101lb 36v TM either).Youre NEVER even gonna get close to planing speed so therefore youre just plowing water.As previous poster said,youre probably hitting "the wall".Think of moving your arm underwater in a pool.Move it slow and isnt all that much resistance.But,the harder you push/try to push your arm through the water,the more resistance you feel.Boats are the same way until you plane on top and lose the resistance.Never owning one(and I may be wrong),I would say you could almost row as fast as that motor will push you.I am NOT trying to be mean in any way.I just dont see it.ou could try marking the hub on the prop(if it even has one?)and see if it slips at all.Other than that and a compression and spark test on the motor I cant see how even to get any info on performance to help diagnose or even see if theres a problem.Good luck.
 
Joined
Oct 28, 2010
Messages
923
Re: Mercury 2.5HP - no high speed power

Prop may be spun. Inspect prop for a tar like substance around the hub indicates spun.
 
Top