# 1979 Mercury 40hp 2 Cylinder - Help



## huntingbronco (Jan 30, 2011)

Hey Motorheads - I am seeking wisdom. I have a project boat and it came with this motor. I was really hoping to make it work, but I am having doubts. The wiring in the boat is a mess. To get a sense of the motor, I jumped the starter directly to see if it would turn over. With the spark plugs removed, it turned over really well. With the plugs installed, it would turn over, but very slowly. This is with the battery from my truck, which turns its V10 over just fine. I was jumping post to post straight through the starter. 

I pulled the starter and took it apart. Cleaned everything up, brushes looked good. As part of the reinstall, I soldered in splices to repair the badly cracked wiring. A common problem on this vintage engine, I believe. Anyway, the motor still turns over very slowly. (Too slowly to start. BTW- I was never expecting it to fire. Just trying to roll it over.) 

Anyway, I am starting to have second thoughts. I really need tilt/trim and I would like a reliable motor. As you can see, the skeg is also broken. So, as I see it, I am going to spend $600 for tilt/trim and $100 skeg repair - and that is before I get it running. I know it ran 5 years ago, but it was left unattended since that time...no telling how she stands today. Gear selector seems functional, as it would turn the prop correctly with the starter turning everything over. 

Here's the motor, note the skeg:






Here's what the wiring looked like when I removed up the engine cover. 





So what do you guys think? Fix her up or what? Or am I better off picking up a newer used 40hp with factory trim/tilt? Does this motor have a


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## Lil' Blue Rude (Jan 31, 2011)

The cables that you where using to jump it might not be thick enough gauge to turn it over. My brother motor had the same problem good starter, good battery, and it wouldn't turn fast enough to start it. We grabbed a second set of cables to jump the starter with and it would cranck till the cows come home. We just ended up getting some bigger battery cables and he hasn't had any problems since then. As for fixing the motor or buying a new one is your call. Don't know alot about the mercs. I guess it depends on the time and money you are willing to invest in the motor You could always part out the powerhead and mid section on this motor and buy a newer one.Hope this helps some.


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## crazymanme2 (Jan 31, 2011)

I own a few Mercs.The electrical can be a challenge some times.I would take compression reading & see if it has spark & go from there.


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## huntingbronco (Jan 31, 2011)

BTW - where I come from, Motorhead is a compliment.


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## Lil' Blue Rude (Jan 31, 2011)

huntingbronco said:


> BTW - where I come from, Motorhead is a compliment.


Isn't it a copmliment every where :mrgreen:


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## wasilvers (Feb 1, 2011)

I'd go with you're just not getting enough juice to the starter. It does turn over, so it answered your question on that right? But unless you are powering everything else it will not start with the power only to the starter. Since it turns over, you might be in good shape. Tilt/trim is nice, but not a necessity. And craigslist might have tile/trim for a decent price - I know I've seen them for $200ish

Skegs... well, my dad ran one for a long time with it broken off like yours. All it does is protect the prop, and provide a tiny bit of rudder action.


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## huntingbronco (Feb 11, 2011)

Hey guys - the latch that holds the front cover on is broken - anyone know where something like that can be found or do I need to fabricate something?


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## Flat Bottom (Feb 11, 2011)

The latch on the back of my suzuki cover was broken... so far i put a stainless eye in it and use a rubber bungie to hold it down... As for the motor, if it were me i would fix it, because that just seems to be what i do, usually what can go wrong does too haha, but i learn and have fun.


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## huntingbronco (Mar 11, 2011)

Great news!

As I was about to give up on this motor - I decided to do a compression check. Mind you, this was after stripping her off the boat with controls and everything. Hooked up the wiring and the key worked! So did the choke button! (Neither worked when installed on the boat. When I keyed it over, she turned over like an engine is supposed to, not this struggling, barely turning over thing I had before. I was shocked. I thought my luck was turning. So, I had my son come out and hold the compression gauge while I turned the engine over. Much to my surprise - he exclaimed "there's spark"! This thing just might run!

Dry compression checked out at 125psi on the top cylinder. I could not check the bottom cylinder, but that is good enough for me to continue forward with the engine. Went ahead and changed the impeller and housing - screwed up the reverse lock out cam, so the lower unit is coming back off. 

Only thing left at this time is to wonder if the carb is going to need rebuilding - I am guessing yes, given the fuel in the tank looked like mud. We shall see. Tank is cleaned, new bulb and fuel lines to the motor. Probably should flush the fuel in the carb - but it has been in there for 5 years - maybe its dry, if I am lucky. I'll report on that next week.


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## wasilvers (Mar 11, 2011)

Congrats! Carb aren't all that bad


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## Bobg (Mar 12, 2011)

Always check connections when dealing with 12v, to the point of loosening them just to disturb the connection, then retighten.

Jumping the solenoid , battery positive to yellow wire with red strip should be all you need to do if all connections are tight and battery is hot, and solenoid is good. All I usually need is remote a starter button.

Mercury wiring is the pits from back in the 70's/80's. Going directly to the starter is sometimes all you can do.


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## huntingbronco (Mar 17, 2011)

Okay - had her running on the hose/muffs in the driveway last night. Little concerned about the lack of water flowing out the pee hole. Motor was getting hot. With a little vacuum, I could get water to flow out the pee hole with motor running on higher RPM - but it would not pick up itself. Hopefully this is normal, I'll see if she works in the lake later, unless you guys have a suggestion on what I might have done wrong. 

The fuel lines were a mess - I am thinking at a minimum the carb needs to come out and be cleaned. In your experience, is that all I need to do? Or should I try to find a "carb rebuild kit" and use whatever parts it includes? As always, your advice is appreciated..


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## wasilvers (Mar 17, 2011)

huntingbronco said:


> Okay - had her running on the hose/muffs in the driveway last night. Little concerned about the lack of water flowing out the pee hole. Motor was getting hot. With a little vacuum, I could get water to flow out the pee hole with motor running on higher RPM - but it would not pick up itself. Hopefully this is normal, I'll see if she works in the lake later, unless you guys have a suggestion on what I might have done wrong.
> 
> The fuel lines were a mess - I am thinking at a minimum the carb needs to come out and be cleaned. In your experience, is that all I need to do? Or should I try to find a "carb rebuild kit" and use whatever parts it includes? As always, your advice is appreciated..



The water pressure from the muffs themselves should push some water out the hole - at least it does on my 50hp. 
Two things to try, reposition the muffs over the entrance holes (and turn on water full blast) - or get a garbage can and put the motor in this. I usually use this method to test it, there's less mess while you're working on the motor or boat. Just one big mess when you are done.
Maybe the waterpump isn't working?

As to carbs, sometimes it just needs a rebuild kit done to insure the fix lasts. If you can wait for it to arrive and then another night to rebuild them, that is what I'd do.


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## huntingbronco (Mar 17, 2011)

Thanks WASILVER - I think I found a carb kit locally. We'll see if I can get it done tonight.

I just replaced the water pump housing and impleller. I am always concerned that I don't get a good seal on that tube that extends up from the waterpump to the engine. I suspect if that seal is not good, water pressure will not be good. Wish I was more confident in my installation - I just don't do it enough to have a feel for it.


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## huntingbronco (Mar 17, 2011)

Carb came out, cleaned up, gaskets replaced and slipped back in. We'll see if she runs better on Saturday - going to try her in the bucket, see if the water pump is in fact working correctly.


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## Skidz (Mar 18, 2011)

Not sure about Mercs, but Johnson/Evinrudes have holes in the lower unit to let the water drain out; it's best to tape them up if you're running muffs. I like a large trash can best myself for driveway testing.

Skidz


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## huntingbronco (Mar 19, 2011)

Thanks Skidz.


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## huntingbronco (Mar 19, 2011)

Got the engine in the tank tonight. Ran much better and I had a great stream from the water pump. 

Question - engine would not run real well without the choke partially on. Is there a chance the fuel pump needs rebuilding or is this something I did wrong in the carb rebuild?


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## crazymanme2 (Mar 19, 2011)

Could be both.Try squeezing primer bulb while running to see if it makes any difference.If not try turning out the idle adjustment.


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## huntingbronco (Mar 19, 2011)

Craig - thanks. I squeezed the bulb - it got firm and held pressure. (It did not get soft while running.) 

Operating the engine at everything but very fast required choke to maintain operation. This was in a tank, no prop. I'll look into symptoms regarding fuel pumps. Seems to me with all of the jets cleaned and float functioning, it would not likely be the carb. I did not dissasemble the need valve above the float, it was washed really well from above and blow and it seemed to move freely. Pretty simple single carb setup. Of course, I might have overlooked something in the reassembly. 

How does a fuel pump needing a rebuild evidence itself?


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## crazymanme2 (Mar 19, 2011)

It wouldn't hurt to rebuild the fuel pump but I don't think that's it because if you pump your primer ball you are like the fuel pump but you say it still needs choke.

I had it one time that a little piece of rubber,from the hose, got behind the needle & seat & would restrict the fuel flow, which would cause a lean condition.


When you take apart a carb take everything apart & blow everything out than make sure each passage is clear by blowing solvent through it.


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## huntingbronco (Mar 20, 2011)

Thanks Craig. On the carb, I just could not figure out how to release the two levers that the float contacts to close/open the needle - so I left it in place. I blasted it with carb cleaner from top and bottom and it seemed to work just fine. Could be the problem, I'll verify using your technique of squeezing the bulb while it is running.


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## huntingbronco (Mar 28, 2011)

Okay - approaching what I consider to be the final challenge for this motor and I definitely need some help/advice/ideas. The front cover has been left off, no doubt being the cause of some of the challenges I have faced in getting this thing running. Anyway, check out the photos and let me know how I can fasten this front cover on so I won't loose it on the road or water. 

Front Cover






I am missing the top fastener - don't know what to use - screws don't seem to fit real well. 





The lower latch is broken, spring works, but the hook is busted off, so it won't engage the bottom of the cover. 





What are your recommendations: replace, remove and reconstruct or just come up with a different mechanism for securely fastening this front cover? Ideas please....

Thanks - HB


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## crazymanme2 (Mar 28, 2011)

:idea: How about a little bungee cord.Bend the hook so the end locks into the hole in the cover,pull down tight & find a place to hook or put a little bolt through the hole to give you something to hook onto & pull down. :?: 

I might have an old Merc that might have the piece you need,I'll look tomorrow.


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## huntingbronco (Mar 28, 2011)

Thanks Craig - appreciate the idea. Let me know about the parts.


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## huntingbronco (Jun 19, 2011)

I finally got the boat on the water last night. All attention has been focused on getting the boat done.

Now I need some advice on the motor. I had water coming out the pee hole, but the engine got really hot and did not run right. Let describe my observations and maybe you guys have some ideas. 

After I rebuilt the carb, I flushed the gas tank and hooked it to the motor. Unfortunately, I think there was still some bad gas in the lines. Anyhow, she fired up, so I thought I would get it on the water and give it a go. 

When I squeeze my bulb in the fuel line, it gets firm if not hooked to the engine, however, when hooked to the engine, gas flows through the carb and out the bottom. Bulb does not stay as hard as I am used to. 

Engine did not want to run, lots of fussing with throttle position and choke. Once warm, a little choke would kill the engine. We also tried putting a little pressure on the bulb, but it seems like that had the effect of flooding the engine, especially in the end when the engine was very hot. 

When it was running, especially after getting warmed up, the motor was making some wicked rattling noises - don't know if that was knock or not... This carb was pretty simple - is it possible something funny is going on in the carb due to the bad fuel getting back into it after the rebuild? Would that cause it to run lean, hot and knock? 
Should I just pull the carb, dissassemble, clean and reassmeble? I should not need a new carb kit, should I?


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## huntingbronco (Jun 19, 2011)

Her she sits at the dock - trying to get her to start...





Here's a shot of her running on the water...





After this run, we tinkered for quite a while trying to get her to run right...nothing seemed to work. Man, was she hot when we got to the dock. Read my previous post for more details - need some advice here guys.


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## gouran01 (Jun 19, 2011)

just a possibility, if your just wanting tilt/trim to alleviate manually raising/lowering the motor for transport and shallow water and etc, i hooked a small atv winch to my 70hp chrysler and it works frickin great. had back surgery a few years ago and the manual system aint for me


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## Zum (Jun 19, 2011)

Have you done a compression check?
Never like hearing,"running hot"...burn your hand hot?


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## huntingbronco (Jun 19, 2011)

yeah - it was really quite hot, but you could put your hand on the outside. Compression was fine - it was 115-120. For it to get hot with pee coming out, it seems it must be lean? Don't know how else it could be so hot with water flowing.. Even the water in the pee stream was very hot.


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## gouran01 (Jun 19, 2011)

didn't read the entire post but possibly thermostat?


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## huntingbronco (Jun 20, 2011)

Thermostat - interesting thought. I eliminated because the water coming out of the engine was very hot. If the THermostat was stuck closed, causing overheating, don't know that it would be so hot coming out. Any other way to check?

Also - I pulled the carb last night. The one item I am not confident about is the float. I did not disturb the levers, but I did change out the float when I rebuilt. The carb was clean. I inspected all jets - none were clogged and the only debris I found was in the filter prior to the carb. So, I don't think my problem was the little bit of bad fuel. 

Here is why I am worried about the float. When I squeeze my bulb, with the line disconnected from the motor, it gets firm and stays firm. When I connect to the engine - fuel flows right through the carb and I can't get the bulb to remain firm. I am thinking the float is not coming up and shutting off the inlet valve. Should it be able to resist moderate pressure on the bulb? 

This may not be the cause of my other issues, but if this is not right, it too needs to be fixed. 

THOUGHTS - Should my bulb stay hard?


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## Derek (Jun 20, 2011)

Have you pulled the lower unit to check the impeller? If the water coming out is hot that is not good. The impeller could be pumping water even with broken vanes, although it wont pump enough to cool the motor. Your last question had me laughing. Yes your bulb should stay hard. Mine gets almost as hard as when disconnected.


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## wasilvers (Jun 20, 2011)

Yes the bulb should stay hard when connected to the carbs. I'm a big fan of adjusting these myself, though it only takes a little bit. 

If I read it right, you didn't remove the floats when doing the rebuild? If that's the case, you need to remove them and clean the fuel inlet - carb cleaner and clean rag. The main reasons your bulb doesn't get hard - 
float needle is clogged, dirty, your float isn't adjusted right, a float has a hole in it, a fuel line has a hole in it, or your bowl isn't put on right (lowest part of the float bowl goes away from the float hinge) and doesn't allow the float to work right. (been there, done that  )

I would start with pulling the carbs and checking the float needles, then making sure the floats hang the same, you can shake it to see if it has a leak. Check the fuel lines (that will cause some of your hard starting and weird running.) 

You did mix the gas with oil (sometimes you have to ask the basics).


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## wasilvers (Jun 20, 2011)

Also, your fuel line (and bulb) is hooked up the right way? There is an arrow on the bulb showing the direction of flow. Just some of the basics to check. I saw a boat with the bulb hooked up backwards. Gave the owner a good laugh.


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## huntingbronco (Jun 20, 2011)

wasilvers - I changed the float - just did not remove the levers - they looked right. So the needle and seat that operates by force of the float did not come out - just flushed a great deal. Confident there is no goop in there. Worst case is the prior rebuild put something together wrong - that's what I am looking at now. Yes, fuel has oil and lines are correctly assembled and working properly. No worries, no offense taken - only stupid question is the one not asked. 

BTW - does anyone know how compression relates to running hot? 

If a cylinder has bad compression - would it not draw enough oil/fuel to lubricate - there fore it would run hot? 

Thanks for the education.


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## wasilvers (Jun 20, 2011)

huntingbronco said:


> So the needle and seat that operates by force of the float did not come out - just flushed a great deal. Confident there is no goop in there.




Well, when this needle closes, it's what will cause the bulb to get hard and limit the fuel so it doesn't flow out the carbs and likely flood the engine.

As to compression and getting hot, I've not heard of compression affecting cooling (aside from a cracked head on car). You might have some clogged cooling channels, but I'm not quite sure how you'd get them clear. I had an old force that I pulled the power-head on to clear out all the channels, but that's a lot of work. Is the water coming out of the peehole fast - like you can point it in the air it would squirt a good 8ish feet?

Also when you run it, if it's on muffs, don't run the engine real fast.. I've heard that muffs cant get enough water to cool the motor if it's at higher rpms. 

Just trying to help - Will


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## huntingbronco (Jun 20, 2011)

Will - thanks. I took it to a shop today and they said not to spend any more money on it. Sad for me, but you have to consider it might just not be worth spending more on it. So, I guess I can start looking for a replacement motor. 

I'll make someone a great deal on this one - I just think the powerhead is going to require work that I am not willing to do. 

Bummer.


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## huntinfool (Jun 20, 2011)

I don't know that I would give up on it yet. When you squeeze the bulb the fuel should pass through the seat past the needle and into the float bowl. As the fuel rises it will raise the float and that will force the needle into the seat, thereby shutting off the fuel. You did not take the needle out and therefore can not say for sure there is not any trash in there. I have sprayed to check them and did not see any trash, but when pulled out....there was trash. Also I had one that the rubber tip of the needle came off and was sticking in the seat. Another one did not have the rubber tip. So Since you have nothing to lose, take the carb off. Take the float bowl off. With the fuel line attached give the bulb a squeeze. (you should get fuel out of the seat, so be prepared) Then lift the float so the needle is set in the seat. Squeeze the bulb. You should not get any fuel. If you do then that is the problem. You could be forcing extra fuel into the cylinders and that would cause it to run a bit hotter. I am not saying this is the problem, but it is a free test. If all checks out then put it all back together. If not fix what ever problems you have or post up here and let us help you. 
Now as for the running hot problem. Again it is free for you to take the lower unit off and check and see if the WP is in correct. I just did one where we put a brand new impeller in and hooked up the water and started the motor and no water. Took the lower unit off and the impeller was trashed. I finally figured out that it had pieces of impeller in the lower part of the lower unit, where the water intake is and those pieces were being sucked up into the new WP and eating up the impeller. Once I got it cleaned out it worked like a champ. Now if you have a thermostat, you could take the therm out and with it on the water or in the tank start it up. If water pours out of the therm housing then the pump is fine. Now the problem is aeither the thermostat or after the thermostat. Heck the thermostat may be stuck part way or even in backwards, although I doubet it if your getting water, but stranger things have happened. Some modle boats have a set of reeds that the wate has to pass through. If they get a build up of calcium they will impeede the flow of water to the cylinders and thus allow it to run hot. I am not familiar with that particular motor, so I do not know how it is designed. Along those same lines there is no guarantee that there is not some other calcium or limescale buildup internally and that is keeping it from running cool. I heard about someone pouring CLR into the thermostat housing and letting it eat out all the buildup. This allowed it to flow water better and cool better. But I have never done it, so I can not give you any more infoi. I think you would have to block off the pee hole and take the LU off and plug the pick up tube....but again I do not know for sure. Just some food for thought. I hate to see you give up, since you finally got it running. 

We are still here to try and assist you in getting it running.


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## wasilvers (Jun 20, 2011)

Right, I wouldn't give up. Since it runs, then the electrics are likely good and you just have some mechanical issues to work through. If the deal is good enough, I'd buy the motor. I could use a backup, or resell it, or package it with a boat and have a second tinny! I tore a 1996 40hp down to nothing and put it back together 3 days later. Then tore it down again a week later (to the crankshaft) and put it back together 2 weeks later. There's not all that much to these engines.

If you're replacing it, you have nothing to lose. Worst case, you can still part out the motor when you're done.


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## huntingbronco (Jun 20, 2011)

Well guys, you both make great points. I have come so far and the coin for a new motor could set me back a year. I'll try the float thing and try to figure out where the thermostat is... 

I was kind of thinking that if the compression is down between 110-120, it might not be worth much more effort, but you guys make great points about being able to chase the two key issues - float and coolant water. 

My work on my 1968 Montgomery Ward Snowblower went well tonight, so maybe things are going to turn around.


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## wasilvers (Jun 20, 2011)

Compression at 110-120 is fine - the motor shoud run on that. When you have fuel/oil, I always beleive it compresses better than testing when 'dry'.


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## Kago5938 (Jun 21, 2011)

That may be known as a Merc 402 what I found works to get it to pee with more pressure is a piece of silicon hose to join the metal water tube with the nylon one that sits on top of the water pump. I have some from a hobby shop packaged as replacement tubing for a Dave Brown 6 shooter fuel pump for RC planes also Traxx silicon exhaust tubing for RC cars.


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## Kago5938 (Jun 21, 2011)

Getting compression back- if possible get the motor positioned spark plugs vertical remove plugs set the pistons at TDC using a screw driver to check it pour in the plug holes Seafoam straight to the top screw the plugs back in check the level over the next few days top it off. Walmart and some automotive stores carry it.


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## huntingbronco (Jun 22, 2011)

Kago - you are talking about where the water pump hooks up to the metal pipe riser that goes up to the bottom of the engine from the lower unit, right? Does this stop leakage at that location or just give flexibility for a better fit/alignment up top? It has been several months now since I did my water pump - can't say I recall what it looked like. I just know that everytime I ever try to get the water pipes on any outboard lined back up, I have no confidence that they have actually sealed. There has to be a better way to connect water lines...


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## huntinfool (Jun 22, 2011)

Before I put a lower unit on I put grease on the tubes. This will help them slide inside one another. Remember, just because you have replaced something does not guarantee that it is perfect. 
Like I said we work on boats for a living. (mostly fiberglass, but some mechanical) And I have done several WP's. But I had one I just put together 3 times and it failed twice. NOT because of something we did wrong, but because of trash below the pump it ate the impeller up. We would put the water to it and pump the trash back through it and eat the impeller. Luckily we caught it and resolved it. So you could easily have had a problem similar to that and not even know it.

Also, the compression range your saying is just fine. I have run outboards at 95 psi on all cylinders and they ran great. So I really think your just fine there. Keep us updated on where you are and I am confident that we can help get your outboard running.


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## huntingbronco (Jun 24, 2011)

Can someone explain to me what sticking reeds and a dry cylinder means? Can sticky reeds be repaired by soaking in seafoam, similar to the suggestion about filling the cylinders with seafoam?


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## huntinfool (Jun 25, 2011)

The reeds are basically a one way valve, that let the fuel into the cylinder and not out during the compression stroke. While the cylinder is on the downstroke it allowes the fuel to be sucked in through the reeds and on the compression stroke, they close and do not allow the compression to blow back through the intake and carb.

A dry cylinder is just that. Dry. No fuel and more importantly no oil. That is why we always suggest when someone says they have a motor that has been sitting for a while, to remove the plugs and "lube" the cylinder. 

Are you still having troubles? Where are you at in the repairs? What have you done out of the suggested ideas?


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## huntingbronco (Jun 26, 2011)

I have pulled the motor off the boat. I am going to soak the powerhead with seafoam and take the needle above the float out. Then I'll bench test to see if it will run.

When I started with the motor, I think I shot the cylinders with oil...but nothing like soaking in Seafoam. Does it make sense to flip it over and soak the bottom side in Seafoam?


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## Derek (Aug 4, 2011)

having any luck?


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## huntingbronco (Aug 5, 2011)

Yes-I have to get some pics up of us on the water with the boat. I ended up stumbling into a good deal on a 1980 40 hp merc. So I swapped engines and controls and away we went. Now I have to decide whether to tinker with the 1979 or sell it to some enterprising individual. We got loads of compliments on the finished boat.


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## Derek (Aug 5, 2011)

awesome get some pictures up


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## huntingbronco (Aug 9, 2011)

Pics of boat with replaced motor on posted on the boat project page, rather than here. I won't work the camo painted '79 until this winter, if I don't sell it first. Price will triple if I get it running right!


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