Losing Compression....Sometimes

[Nahart]

I hadn't run my engine for a bunch of months, but got her running with a carb rebuild, filters replaced, gas replaced and treated with Startron. Last Friday ran for an hour no problem. Sunday motored out of the Harbor, sailed then motored back in no problem. Thursday went to start engine and it sounded like my starter was spinning. No problem, got a crank. Went to crank the motor and after a couple of cranks, the engine spun like a fan, without resistance. pulled the plugs one at a time and 2 and 3 had no compression. But after a few spins, got compression on my thumb. poured a little Marvel in each cylinder, put everything back together and went back to cranking. after a couple of cranks, no compression again.

Got pissed, decided to go to the Dark Side and get a Beta. After calming down and realizing how much that would cost, I know I can figure this out (with a little help from my friends.)

My plan is to pull the valve cover plate and inspect, then pull the head and go from there.

Specs: 75 model A4, Indigo ignition, CDI 3 blade prop, new Racor and polishing filters, new exhaust hose, new fuel lines, new electric fuel pump, plugs looked decent, ethanol free gas.

I'll provide pics and details next time.

[lat 64]

That sure sounds like sticking valves.

Three ways to think about that(if that is what it is);

1- rust from sitting so long,
2- something is gooing up the valve stems in the guides.
3- overheated engine


What is "Starton"? could that be turning to glue on the valve stems?

This is a VERY fixable problem if I am correct.

Good luck,

Russ

[Antibes]

Star Tron is a fuel enzyme/ stabilizer

[Dave Neptune]

Dave, intermittent valve sticking is a sign of water in many cases. I suggest you get some TCW-3 2 stroke oil and add it to the fuel to get to a ratio of around 80~100:1. This will get oil onto the valve stems while running and help free them up. A little MMO or my preference a spray oil spritzed into the cylinders via the spark plug holes, WHILE CRANKING THE ENGINE.

A pic of the plugs may help too. Look for any signs of rust on the plug body EXPOSED to the cylinder.

As Russ stated this is usually an easy fix if attended to quickly so there's no more rust.

Dave Neptune

[Nahart]

Thanks guys, that makes me feel better that it's probably not a major catastrophe.

Sorry, it's Star Tron fuel additive.

I'm going back to the boat this weekend to diagnose.

The plugs were not rusty but I had water intrusion about 6 months ago....changed the oil until it was clean. However, I had not been to the boat for a few weeks before I noticed the water intrusion. So that may be the culprit that came back to bite me months later. I had a busted scupper hose that drained rain water directly into the bilge which overflowed until it was above the dip stick opening. The battery was dead so the bilge pump wasn't pumping. It had been raining in Louisiana for weeks and the river rose above the banks and we had to turn off the electricity to the boats, so no charger for the battery.