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bob s

New member
Hello,

I am a first timer so please bear with me on this. I have been working on a 1998 25M Mariner 25 horsepower outboard engine. The engine had been sitting outside and not run for at least 2 years when I got it. Taking the cowel off I discovered the usual goo from the well baked linkage lubricant. I knew the carburetor would need rebuilding so I bought a kit and did so after soaking the parts in a carburetor cleaning solution available at NAPA in a gallon can. The engine started right up after a good tune up including spark plugs, wires, and new fuel lines with filter. I also installed a new water pump. After some minor adjustments I thought I had a pretty good running little outboard. But once it began warming up it started to miss and backfire. The backfiring became so intense it shut itself off. It started again immediately but again began to carry on missing and backfiring until it shut itself off again.
I am wondering how to test for a cracked block? All the signs seem to be there.
 
was it backfiring or was it sneezing back through the carb? did you check the flywheel key, make sure its not broken or loose.
 
Not only did I check that but I also cleaned throughly under the flywheel do to some corrosion from spending time in salt water and being stored at the beach. No the backfire is definately coming from the exhaust. When it backfires it also belches more smoke as well. I am running it on a stand with ear muffs on the water intake for cooling.
 
I have adjusted that screw in and out until the engine nearly quits in both directions. I am pretty much convinced the block is cracked and water is seeping into one of the cylinders. It gets worse the hotter it gets. The additional puff of smoke when it backfires is probably steam. I would like to test for a cracked block but don't know how.
 
do compression and leak down test on it and see what you get. you can google each test to see how to do them.
 
I already did a compression test and the results were pretty good I thought (125 psi) in both cylinders. I didn't think you could do a leak down test on a two stroke engine?
 
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