Rob Gifford

[Alajoyn]

Got a '61 Merc 500 50HP. Took it to dealer with problem.
Ran first test this summer took off great, then lost power. Did it twice.
Pin connecting choke butterfly rods came out allowing top carb's butterfly to slam shut at full power. Limped back to shore. Did a quick fix but engine ran poorly. Pulled plug wires. Found #2 and #4 would not change the idle when the boot was removed meaning theyre not firing. Plug #2 was washed quite clean and with a greyish film on the base of the plug thread edge. Tested for spark and both have spark. Both have Fuel. Both have compression (don't know how much tho).
Took to dealer and explained.
After 2 weeks wait Mechanic said he didnt go into it very far but he didnt know what was wrong but since it had spark and compression it was probably a crank seal or something requiring it to be torn into. Hmmmm.
Any good thoughts out there. I am willing to rebuild if necessary over this winter, it would be my first outboard attempt. I hate to ever get rid of this classic motor. It is attached to a little 11' 2 seater I restored over the last 4 years. A perfect combo. Any help would be appreciated. I have been a fan of Kiekhaefer Merc engines for years. Thanks in advance.

[Raceman]

A crank seal wouldn't effect 2 AND 4. Pulling a plug wire isn't always a good test on an inline Merc. Although I don't have any experience with 4 cyl ones, an inline 150 will actually speed up at idle if you pull the #2 sparkplug off. Nobody's ever told me why.:confused:

There are certain things the cyl's share............ 1 & 2 and 3 & 4 have common reed blocks and carbs, but 2 & 4 having a common problem would seem unlikely to be related to the choke butterfly hangin' shut. The greyish film sometimes means water. Water will kill a cyl that has spark, compression and fuel. Crank seals are ONLY in top and bottom of powerhead.

Are you SURE you don't have water in fuel? Bad fuel? Could be ignition. Could be water from another source than fuel tank.

[Alajoyn]

Thanks Raceman,
Newly installed fuel cell, fresh fuel mix. 1st time out for season.
Eliminating those two, it leaves ignition and water.
Any idea how water can get into the cyl. Could I have at the same time blown something? Hmmmm.
I purchased a complete magneto 2 yrs ago just in case. So I have a backup but now the water thing's got me head scratch'in.

Maybe I'll be in the garage reading my manuals I need to purchase and figuring out how to tear one of these down?

Thanks for all the great info.

Robert