mercury 4.5hp

[kulsh]

i just bought a mercury 4.5hp outboard and i had a question for you guys..
the guy i bought it off of said that it starts right up but when you go to full power it starts to lose power he said he thinks it has low compresion. i havnt had time to look at it yet but to me i would think that their is a fuel problem but has anyone ever ran into this problem? and if it is low compresion would it do this?
thanks for your help
keith

[Beave]

Low compression manifests itself at idle speeds, not on the top end. Especially if you've only got it in one cylinder. Typically you'll find it's missing or running really rough and doesn't like to start. I wouldn't immediately suspect compression based on what you're describing. 98% chance it's a fuel problem IMO.

I'd check in the following order:

1) Plugs (properly gapped? fouled?)
2) Fuel filter, fuel lines (clear, do they allow free flow, does the pump ball stay pressurize?)
3) Intake/air filter (clean and clear? I had a moth make a cocoon in the intake to my 9.9 merc last summer. Fun stuff.)
4) Carb, Carb adjustment (Try running some carb cleaner through the gas first. If the plugs foul you're probably too rich. If they don't foul you're likely too lean.)

If all that fails you might want to take the carb apart and really clean it out good. Sometimes there are rubber seals and membranes in carbs that can deteriorate.

[TONGA]

Besides checking out your fuel system,check to make sure she is not running hot those little mercs get hot real fast with a bad impeller or seals..so make sure you are getting a good solid stream of water out of the tell-tale...often on those little mercs the seal on the pick-up tube will go bad,,so at idle she will pull water fine,but as soon as you bring the rpm off idle they will break the seal and get hot within just a few seconds.then when you back the throttle down she will resume pulling water and cool down..
As for the compression you need to get a tester and have a look see...those little mercs wont show you a ton of compression.what you are looking for is a big difference from one cyl to the other...

[kulsh]

thanks guys for your help i will check out everything you guys sugested but i have to wait for warmmer weather i dont have a test tank i will have to use the muffs on it to start it up and i dont want to make my drive way a ice skating rink
thanks
again
keith

[TONGA]

keep us posted

[andy capp]

Keith I may have the litle engine stand I built...........And use a garbage can. Muffs just dont seem to get enough water to tell for me.