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Mariner 40 wont idle with cowling in place

C

comoxvi

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"Just found this forum, what a

"Just found this forum, what a great resource, thanks to all. I've discovered here I have a 1984 40E mariner 40 hp. Problems have developed this year, after trolling a while the engine starts smoking/running rough, and then won't idle at all.

One mechanic looked at it, cleaned both carbs, changed thermostat, adjusted carbs. Runs great at high speeds. Now we've discovered it runs good with cowling off, he suggests the exhaust seals are gone, and its too big a job to be worth fixing. Seems the exhaust builds up under the cowling and then the carbs suck this in which makes it run worse, and it snowballs from there, fouling, more smoke, etc...

His suggestion was to run a second leaner 80:1 tank for trolling, and/or cut some holes in the front of the cowling/carb cover to let fresh air in. I've also read somewhere it could be leaking diagram from fuel pump.

Any ideas would be appreciated,

thanks"
 
"Rob, sounds like a lazy mecha

"Rob, sounds like a lazy mechanic. It's likely that an exhaust leak would cause the issue you mention.

However, the "seal" is nothing more than a powerhead to exhaust plate gasket (a few bucks) which is accessed by removing (6 bolts if I remember right) and pulling the powerhead.

Might sound like alot, but well under an hour to complete the change.

Now if the exhaust plate itself is rusted/shot, then yes - discontinued and would have to find one in "old stock" somewhere, but still only sold for about 75 bucks.

If it is in fact the seal, sooner or later you are also going to develop a water leak under the hood to go along with the exhast fumes since the same gasket also surrounds the water channels in the lower powerhead.

Not as big a deal (although could cause electrical issues) if it leaks after it's made it though the engine, but quite a big deal if it develops at the top of the water-tube and your engine overheats.

I would find another mechanic or get myself a manual and replace the 15 dollar seal...."
 
"thanks Graham, I would rather

"thanks Graham, I would rather see this fixed than drill a bunch of holes in the cowling as he suggested. The old manual I borrowed from the library talks about removing the starter, rewind starter assbly, carbs, CDI, & flywheel to remove the powerhead. Is all this necessary to change the exhaust plate gasket or is it all if you need to strip the powerhead for other reasons. Also, would you have the part # for the gasket? The little manual didnt have a blowup. 1984 40E, ser # 6E9 S103027 thanks again"
 
"Rob, there are two separate g

"Rob, there are two separate gaskets which could be the culprit, one above and below the exhaust plate.

Merc part number 27-11885 (driveshaft housing gasket) and 27-19175 (upper housing gasket) sandwich the exhaust plate.

Both are still available through a Merc dealer for 15 and 10 bucks respectively.

You don't have to disassemble the entire powerhead to remove it.

You only need unhook/disconnect anything that is otherwise secured to or through the lower cowl - so things such as the gas line, tell-tale hose and choke lever etc (as applicable). The rest of the powerhead can be left intact and lifted as an entire unit.

If you do pull the powerhead, also take the time to clean out the exhaust plate and exhaust tube - it may be severely carboned up which could be causing at least some of your issue..."
 
"I have a 40 hp Mariner that a

"I have a 40 hp Mariner that also does not idle smoothly. It has really never been able to troll. Runs great at faster speeds and always starts right up. We have had this motor for many years and always had the same problem. We have taken to several shops with no resolution. Any suggestions, I'm ready to try to fix myself. We now would like to use the boat regularly for Salmon fishing and need to troll."
 
"Bruce, most likely the idle c

"Bruce, most likely the idle circuit in the carb is messed up. But this is a guess, one would have to start from scratch here, compression spark, timing and then remove and clean carb with setting the float. Could just be a mixture setting also."
 
"I have a Mariner 40 about 199

"I have a Mariner 40 about 1992. Won't troll, runs very rough a low speeds (and dies often), runs great at higher speeds. Also, plugs are wet after warming up. Someone said check the idle circuit, what is that? Thanks for any help."
 
"Hi Bruce, sounds like you&#39

"Hi Bruce, sounds like you've got the same problem as mine. Have you tried running it with the cowling off, let it warm right up, and then put the cover on? Mine is fine, evens idles good, but dies within a minute when the cowling is put back on. Waiting for a shop manual to arrive in the mail, then I'm going to tackle the exhaust gaskets, as per graham's suggestions."
 
"my 40 hp mariner (2 stroc

"my 40 hp mariner (2 strockes) as the following probleme : wont stay at idle state such that it is almost impossible to get the reverse. If the engine is to high(pushing the accelerator), i can t get the reverse and if the engine is to low, when i get the reverse, it stoppes.Note that at high speed, in forward speed, it runs very good.
I need help, thank you.
218133.jpg
picture of the engine
 
comoxvi said:
"Just found this forum, what a

"Just found this forum, what a great resource, thanks to all. I've discovered here I have a 1984 40E mariner 40 hp. Problems have developed this year, after trolling a while the engine starts smoking/running rough, and then won't idle at all.

One mechanic looked at it, cleaned both carbs, changed thermostat, adjusted carbs. Runs great at high speeds. Now we've discovered it runs good with cowling off, he suggests the exhaust seals are gone, and its too big a job to be worth fixing. Seems the exhaust builds up under the cowling and then the carbs suck this in which makes it run worse, and it snowballs from there, fouling, more smoke, etc...

His suggestion was to run a second leaner 80:1 tank for trolling, and/or cut some holes in the front of the cowling/carb cover to let fresh air in. I've also read somewhere it could be leaking diagram from fuel pump.

Any ideas would be appreciated,

thanks"
Click to expand...
Two strokes are not good for trolling, the oil is not being burnt off at constant low speeds.
You need a 4 stroke for trolling.
 
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