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Merc 40 hp year and problem no top end

rongnow

New member
"Sorry for the long story. Pi

"Sorry for the long story. Picked up a used boat and motor (16' Lund Chellenger and 40hp Merc s/n: 0C159693) last fall. Ran great last year (about 15 hours). My buddy the boat guy pulled it out of the Winnipeg river and winterised it for me. Ran it with muffs this spring and was running rough. Swapped out the plugs and ran like a dream. We put the boat back in the really cold water late may. Ran for an hour before losing top end. Was running at WOT and suddenly had no RPMs. I thought the trottle cable slipped. We checked all the linkages and such and it looked good. Took it in to a highly recommended, very reputable rapist, sorry, meant to say boat shop.
Their report: spark and compression - ok. removed and replaced water jacket gasket, inspected pistons, block had water in top end. Ran up ok.
$425 labour, $75 parts.

Put it back in the water and ran like new for an hour and then same problem. only 300 yards from where it happened the first time. Starts great, runs smooth, no RPMs.

Back in the shop. They say with all the work they've done the motor's running so good that the rev limiter is kicking in. Recommended changing prop to a courser pitch. Was running an 11 they suggested a 13.
$65 Labour.

Guy at the prop shop looked at me like I had three heads when I asked for a 13 pitch prop for my setup. Said a 12 was the most he'd put an it. Laughed at my prop. Was supposed to be an 11 but absolutly no cupping on the blades. Picked an 11 and a 12. Tried them both out with no improvement.

Question: Does the rev limiter need to be manually reset and if so, how? Any other theories to the root cause of my power loss? Should I expect any other problems with the motor? (Normally a good runner?)

Thanks

Ron"
 
"get a timing light, run the e

"get a timing light, run the engine till it messes up, put timing light on each plug wire and check for spark, sounds like its dropping a cyl or loosing high speed stator when hot"
 
Thanks. I've passed this

Thanks. I've passed this on to my buddy.
The shop was saying it was the rev limiter so we had a theory that to reset it maybe we could try disconecting the battery for a while. He tried this on Monday and it ran the same. No top end.
Once it loses top end it doesn't come back. I've waited a couple of weeks between attempts and it just doesn't produce the power. My buddy did however notice that the water behind the boat was completely undisturbed. IE. no exhaust coming out the prop. It's back in the shop.
Any thoughts?
 
"Based on what I've read,

"Based on what I've read, I'm thinking either there's cooties clogging up the exhaust plate or critters plugging something in the LU. The tell tale is strong and no hotter than normal.

Comments? Suggestions?"
 
heard back from the shop. the

heard back from the shop. they found water in the top cylendars again. now they say it's a cracked block.
 
"It's NOT a cracked block.

"It's NOT a cracked block. The exhaust cover plate has a hole in it (along with your mechanic's head!)

Water is spraying into the open exhaust ports. That's the reason is dies so consistently--it takes that long for water pressure to build up, then blows through the hole into the cylinder. At idle speed the water pressure is much lower, so it's less of a problem.

Jeff

PS: Got an '82 Merc 400 that does the exact same thing, though on the other cylinder."
 
Thanks guys. You've given

Thanks guys. You've given me hope. I'm gonna pick up a manual and have a backyard mechanic look at it this weekend. Might actually be able to get out to camp again this year after all.

Would you happen to know the part number for the exhaust plate and any gaskets I might need? Is a kit available? Any big gotcha's?


Thanks

Ron
 
"Do NOT try to remove any of t

"Do NOT try to remove any of those 3 zillion bolts holding the cover on without checking with me FIRST. Put a ratchet on them, and start grunting away, and you'll snap every one of them off, but there is a way.

Jeff"
 
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