Screech, backfire and extra oil...

Hey guys,
I just recently purchased a 1988 2-stroke oil-injected 50HP Yamaha outboard off of e-bay. This is my first excursion into the world of outboards.

I have a question or two:
1.) I heard it run the day I picked it up. It smoked a little much when it started and backfired through the exhaust a couple of times making a "screech" sound each time. But the gentleman told me that he was running pre-mixed gas in the tank along with the oil injection. Does a backfire make a "screech" sound? (When I got it home and on an engine stand, I cranked it using fresh gas. It smoked a little much at first, as I would expect, backfired a couple of times and then straightened up and ran fine.) I ran it a few minutes, then had to put it away. I would have run it longer but had a previous engagement to attend.

2.) When I returned I noticed some oil on the lower unit of the motor, actually, it was the area where a hydra-foil would attach. After examining it closer, there are two small holes on the front of the motor, the oil seemed to have dripped/ran from. I am wondering if this could be from the engine being run oil-rich from earlier that day?

I bought a manual and am planning on doing a semi-tuneup soon. Change the water pump impeller, check the plugs, etc. I am somewhat proficient with mechanicals, I'm just not familiar with 2-strokes and outboards.

Does the extra smoke, screech, and extra oil seem normal given the circumstances I described?

I appreciate any input. And thanks in advance for taking it easy on a "newbie".

 

outboard

most outboards are cooled by water. You didn't mention using any. The screech could be the water pump self destructing. Normally the exhaust travels down the shaft and exits through the prop. Since you were told that it was run with mixed gas it is probably unburnt oil from the exhaust. Outboards do not screech, I would find a manual and give the engine a thorough check up before I trusted it on the water.

 

Oops, sorry. I had a water flusher (two suction cup apparatus) hooked up to the motor. So did the gentleman I purchased it from initially. The puffs of smoke accompanied by a screech came from the front of the motor, where the motor attaches to the hinge (I believe at what would be about the water level normally).

 

puffs

the timing might be slightly off causing the engine to backfire through the carb. They are usually located low on the front of the engine. Next time you start it, pull the engine cover off to get a better view of what is happening. Most 2 strokes have flapper type valves called reed valves. The screech may be compression air are forcing it's way past the reed. 2 cycles engines are fairly easy to work on, but you need to find a manual. I have no yamaha specific knowledge.

 

Thanks Ken, I had the cover off when I started it. Nothing unusual that I could tell. I don't think it is backfiring through the carbs. But I wondered also if it could be the reed valves creating the screech. I did purchase a Yamaha manual for it though and intend to look it over thoroughly.

 

I bought an old Johnson 40 that had not been run in 5-6 years. Once I got the carb off and cleaned all of the varnish and sludge out it cranked right up. It made what I am going to assume is the same screeching noise for a while. I asked around and was told it was more than likely the reed valves sticking. I ran the oil mix pretty steep like a new engine break in for about 20 gallons of gas. The noises eventually stopped and she would stary on the 1st or 2nd pull every time.

Good luck...

 

Well... I win the 'bonehead of the year' award

Man, am I embarrassed.

Thanks for all the suggestions guys, but it was all user error.

I have the motor on a stand. I would start it and then adjust the throttle by moving the linkage on the carbs. (Just like you would on a car.) I was not adjusting the throttle by moving the linkage that the throttle cables attach to. Doh! The throttle cable linkage is attached not only to the carbs, but what I am guessing is a mechanical timing advance. Right?

Anyhow, it ran fine after I figured that out.

Thanks again.