corosion on pistons???

[Part-time]

I have an early 70's 85hp that I picked up a few weeks ago.
It runs but is hard to start. I have to crank for a long time, WOT with the choke on to get it to fire up and it has no power whatsoever. It does get my boat to plane but then, a 20 would probably get that boat to go...
The PO had a new distributor cap on it, I reclamped it properly, and I put new spark plugs in. It didn't change anything.
When I took the plugs back out to check the compresion (135 to 145 psi on all 4 cyl) I noticed deposits on two of the 4 plugs and the top of those 2 pistons (1 & 2) look like coroded aluminum? I wish I could get a good pic.
#1 had the highest compresion at 145psi

this is the motor here, (sorry about my ugly mug, it's the only pic I can find).

 

[Jake.]

Re: corosion on pistons???

Have a look at the link below. Any of them look familiar? Aluminum throw off perhaps?

http://www.gnttype.org/techarea/engine/plugs.html

 

[Chris1956]

Re: corosion on pistons???

OK, Your compression is good. Check for spark on all 4 cylinders, and especially watch and listen for arcing from the plug wires to the block. I presume both choke shutters close when the choke is activated? Are the wires on the correct psark plugs? The distributor cap should have molded in cylinder numbers, so you can check it out. It is a merc cap, right?

What is your top speed and RPM. I disagree that a 20HP motor would plane that boat - BTW

 

[Part-time]

Re: corosion on pistons???

Here it is after it first starts, if I open it right up it just dies. If I try to bring the throttle back it dies.
I hold it about 1/2 to 3/4 throttle and eventualy it will go, a bit...
http://www.youtube.com/watch?v=sq9cBDPEY5Q
http://www.youtube.com/watch?v=lwt_ye5bglA
I don't have a tach.
I don't know how the videos sound because my sound card gave up on me as well but it might give you an idea on how it's running.
The second vid is what I'm getting for top speed right now.

I didn't find the problem with the motor but I did find a solution to my problem...
I'm trading boat and motor for a '64 Olds, THAT RUNS!!!