Motor stalls when idling

[Pappy]

50# compression will never support a strong idle in a two stroke.
Second clue was the smoking issue. Engine had prob. been overheated and stuck by the previous owner and passed on to you. Sounds like it overheated again.

What has happened to the engine in question is the pistons have stuck, scoring both the piston and the cylinder walls.
Chances are the rings are mechanically stuck (by metal not carbon).
The damaged piston skirt and cylinder is now well outside the recommended factory clearance. When this happens the engine loses the tight seal needed for crankcase vacuum on the up stroke and crankcase compression on the down stroke. NO....not the compression you measure with your gauge.
This seal, inside the crankcase, is what creates the pulses to suck in and "blow" the incoming charge up to the top of the piston for the following power stroke. Loop charged engines are much more sensitive to this than a cross flow.

Here is a tip.
When buying a used two stroke engine make sure the engine is capable of a good strong idle.....on the water, not on a hose. This will indicate good crankcase compression. The lower the engine idles the better condition the rotating assembly is in.
If the engine gradually slows and shuts off that is your first clue to lack of the above.
If a two stroke engine will support a good strong idle I will just about guarantee it will run well at WOT.
As always....check the other stuff out that has been covered here a million times already.

 

[CMOS]

Pappy,

There's a lot of folks on this site, including me, that have picked up used motors for dirt cheap that were not in running condition. In general, we check compression and spark-jump to get a baseline idea of the motor's health.

Are you suggesting that we not buy used motors that are not "running"?

CMOS

 

[Pappy]

Not at all ! Sorry if I wasn't clear on that.

The way I read this was that the OP may not have been as savvy or as much of a gear head as some of us are. Nothing wrong with that!
If someone falls into that category and has a chance at an engine the guidelines I outlined would work and work well for them.
For those of us who are more into the gearhead category by all means use the tools, your intuition, and methods you are used to for non-runners.
I pick up more non-runners than runners for the most part.

Now....for the gearheads out here, when you do get a chance at a runner follow those guidelines above if you don't have a compression gauge handy.

No two stroke will idle well if it is suffering from lack of crankcase compression. They can be "fooled" into running a little better.
Tell-tale signs that someone has dealt with this are:
1. The idle timing has been advanced to get it to run.
2. The idle circuit has been richened over production.
These are two common methods of helping out an internally damaged engine and getting it to idle better with the internal damage.

Thanks for picking up on that and letting me know I needed to clarify.

 

[CMOS]

Thank YOU Pappy. :mrgreen:

CMOS

 

[Charger25]

That's why I like this site , guys working together sharing knowledge helping other out . =D> =D>

 

[The10Man]

I contacted the owner of the motor and asked for the model# and serial number. He said that when he got the motor from the previous owner it didn't have the plat that has the model and S/N......(go figure!). He said that when he got it, the previous owner told him it was 15 HP but the "throat in the carb was too small to be 15 HP". He said he eventually scraped off some of the paint on the hood/cowling and saw a 9.9 decal. He thinks that it maybe an '87 but is basing his assertion just by the cowling.

My motor is a '91. CMOS, I did what you recommended and looked at each part number in the gear casing. However since I can't know for certain which year the motor is without the S/N I looked at a bunch of different years surrounding my motor. From '88-'93 the parts in the gear casing are the same. '87 models have different parts in the gear casing.

The guy sent me some additional photos and sure enough the S/N tag is missing in the spot where it should be (sketchy). I looked up where to find the S/N for Suzuki outboards and there is another location on the motor that has the S/N. Apparently a second serial number plate is stamped into a boss on the cylinder block. Can someone tell me what a "boss" is on the cylinder block and how to find it? I tried to locate it on my motor but did t exact know what to look for and where to look

If I can't get the owner to find the second location for the S/N then I might do some research on how to tell the different model/years apart and drive to the other side of town and try and find the second S/N myself or try to decipher what year the motor by some it's features and characteristics.

Any other additional tips would be greatly appreciated!

 

[JMichael]

Does Suzuki not put the serial number on the freeze plug like other mfgs?

 

[Pappy]

If you want to know more than you need to know about the engine and have some extra time, drive over to Dunellon and Dunellon Marine. Paul Adams is the owner. Those guys are great on Suzuki products and well worth your investment of time to drive there. You can look up the number and call if you prefer. Tell him Pappy from the antique outboard bunch recommended you to him.