1979 70 HP bogging down

[Carl Billey]

Purchased this motor and, of course, was told it was running when pulled. Took a while to find controls for it but finally got it installed and it ran well until one day. After taking off, the motor bogged down and I could only run 5 -7 mph at 1/4 to WOT. Took it to the shop, the owner was known as the best mechanic around. He had it for 2 weeks then called and said it was done. Good compression but they changed sparkplugs, stator, impeller and rebuilt the carburetors. $600 later I put it on the water and same thing happened. Called the shop and they sent one of the guys up to the lake to see what was going on. Same thing happened to him so we hauled it back to the shop. They kept it another 2 weeks and then called and said they had no idea what was going on and were giving up. I was leaving in two days on vacation to a distant lake so I ended up pulling it and buying another motor. So now I'm over 1000 into it and it's sitting in a barn. I'd like to get it out of the way and get part of my money back on it but I don't feel right about selling something that's not %100. Anyone else had these issues with this motor?

 

[Chris1956]

It could be something as simple as the wrong prop, causing the issue. However, the compression must be verified as equal within 15% on all cylinders, and that you have spark on all cylinders. If compression and spark are all good, the motor is good, and should be able to be made to run well.

A lot of those older Mercs need to have the idle mixture set properly, or they just bog down or stall upon acceleration. An older Merc mechanic would know that, a younger guy, not so likely.

 

[racerone]

4 things make a 2 stroke run----Compression in the cylinder / spark at the right time / fuel / And that elusive crankcase compression.----So was the crankcase compression investigated ??-----And did they inspect exhaust housing for blockage.---Did you check reed valves ?

 

[jimmbo]

Maybe the problem isn't the engine. What condition are the fuel line and tank in?