Motor won't start when in water but starts fine with muffs

[phabej]

My Mercury 500 50 HP Four was leaking oil from the lower unit so I replaced the water pump prop and all of the water pump gaskets. Now the motor starts fine when I put on the muffs. But when I took it out to the water it wouldn't start. The engine crank but won't start. I took it back home and put the muffs back on and it fires right up on the first try. I also took a big bucket fill with water and submerged the entire lower unit into the bucket and then turn the key and the motor also start up fine. So, my question is why it wouldn't start when I took it out to the water? Anyone has any advice or idea what might be the issue? Thanks in advance.

 

[bigpoppakdog]

Re: Motor won't start when in water but starts fine with muffs

do you have an owners manual? There is a "under load" section explaining this scenario.

 

[phabej]

Re: Motor won't start when in water but starts fine with muffs

No I don't have any manual for it. Do you know if there is any free download manual for it? I hate to spend more money on it if it's toast. I've already spent closed to $200 replacing the bearing carrier, forward gear and water pump kit.

do you have an owners manual? There is a "under load" section explaining this scenario.

 

[carholme]

Re: Motor won't start when in water but starts fine with muffs

What is your engine s/n?

Gerry

 

[phabej]

Re: Motor won't start when in water but starts fine with muffs

Serial# 2406109. Thanks.

What is your engine s/n?

Gerry

 

[carholme]

Re: Motor won't start when in water but starts fine with muffs

Your s/n comes up as:

50 500 4-cyl 2305101 2514918 1968 USA

From here:

Mercury 2-takt, 4-cyl, 40 - 85 hp, produktions?r, modellguide

It is a model 1500108.

Parts listing:

MERC 500-7/8 - Mercury, Mercruiser, Force, etc. Parts Lookup

If you can start the engine in a bucket with the prop and LU submerged, there is no reason why it shouldn't start on the lake. However, if you do want an owners manual, I can send you one if you PM me with an email address.

Gerry

 

[phabej]

Re: Motor won't start when in water but starts fine with muffs

Today I tried starting the motor again with the muffs and it started great. It fires right up with no problem. I then switched it to the bucket of water and on first try it started and then dies after a few seconds. I could not get it to start again. Not sure why it was working fine in the bucket of water yesterday but no longer works today. Does it have anything to do with compression?

 

[bigpoppakdog]

Re: Motor won't start when in water but starts fine with muffs

Yes compression could be an issue. Buy a guage (I would never buy a motor every again without running a compression test no matter what the seller says) and do a test yourself. If the readings are all fine, then you can breathe a sigh of relief. I am not sure if the carbs are set up the same way on yours as they are on my 1983 115 hp motor? Clean carbs is an obvious recommendation. Idle mixture setting appears to be too lean and you might need to adjust your throttle a bit to bring up the rpm's.

 

[phabej]

Re: Motor won't start when in water but starts fine with muffs

What happen if it failed compression test? Is it junk then? Also how do you do a compression test? I've never done it and not even sure how to start. Are there any direction on how to do it and video showing how to do the test?

 

[mr 88]

Re: Motor won't start when in water but starts fine with muffs

Read a post recently where a guy had a similar issue. Turned out mice had built a nest behind his prop and it was enough to snuff the motor out. Pull the prop and try starting it in a bucket or see if there is any debris behind it.Don't worry about the compression test,thats not the problem in this case. After reading your first post I wonder if you installed everything correctly after you did the impeller,might want to re-visit that if it ran fine before..................

 

[bigpoppakdog]

Re: Motor won't start when in water but starts fine with muffs

What happen if it failed compression test? Is it junk then? Also how do you do a compression test? I've never done it and not even sure how to start. Are there any direction on how to do it and video showing how to do the test?

Yes, google outboard compression test. Easy as buttering toast. If it fails a compression test.....then toast could be a word used. Did you say your getting water circulating after you replaced the water pump? You never did say how this ran before you changed the pump.

 

[phabej]

Re: Motor won't start when in water but starts fine with muffs

This boat was given to me by a friend last spring and I was told that it ran fine before he winterized it. I was going to take it out to the lake this summer but found out that oil was leaking from the Lower Unit and there were clunking noises when I first started the motor. So I took the LU off and found out there was a crack in the bearing carrier and two teeth broken off the forward gear so I replaced them both along with new water pump props and gaskets. So, I'm sure there is nothing build up behind the prop. I did go back and check the water and prop and didn't see anything wrong with it. Are there anything else that I should check beside doing compression test?

 

[Mi duckdown]

Re: Motor won't start when in water but starts fine with muffs

Do a compression check. The cheapest(sp?) test. That will take alot of the equation out of the picture.

 

[bigpoppakdog]

Re: Motor won't start when in water but starts fine with muffs

Do you have water circulating through motor? Lower unit stuff is above me. If water is circulating fine after your fix and engine starts fine and engages to forward and reverse with mutts on, my bet is a too lean setting for idle mixture screws and maybe a little rpm increase on the throttle.

 

[phabej]

Re: Motor won't start when in water but starts fine with muffs

I'm going to go buy a compression tester and test the compression today but just a little information on what happened this past weekend. I took the boat out to the lake on Sunday and got the motor to start after three tries. I took it for a ride for about 10 minutes and then while idling the motor shuts down. I could not get it to start again so I paddle my way back to the landing dock. Each time I tried starting it sounds like it was going to fire but never got it to. Could this be the side effect of low compression? Or does it have anything to do with the carburetor or fuel? Also, does these model suppose to pee? I didn't see any water peeing out from the motor when I was in the lake yesterday?

 

[bigpoppakdog]

Re: Motor won't start when in water but starts fine with muffs

I don't know the specs on your motor. Yes poor compression can be a side effect. Could you tell us a little more specifically how it ran for those 10 minutes? Were you able to get to WOT? I am still leaning towards too lean of mixture setting and rpm could be cranked up a little bit.

 

[phabej]

Re: Motor won't start when in water but starts fine with muffs

bigpoppakdog, to answer your question the boat started fine and was idling fine the first 5-7 minutes but was not getting the speed that it should. While in the middle of the lake I shift it to neutral and just it idle for 3-5 minutes then it started to idle rough and slowly died. I was able to get it fired once after several tries but sounded like it was go to die again so I cranked up the rpm and it ran for about a minute then died again after I reduced the rpm. Could never get it start again after that.

Today I bought a new compression tester and ran the test on all four cylinders and they all read about 45 psi. From what I've read that is very low compression. I don't know if the battery had anything to do with the low compression but it also gotten weaker as I cranked the motor. I was not able to get it started today with the muffs like I used to anymore. I hope it was the weak battery and not fried motor. Anyway, how much will it cost to fix the compression? Does it even worth fixing if the compression is low? Are pictures I took on the Carb and Throttle Linkage. In one of the picture there is a wire sticking out from the distributor. Does anyone know if it should be connected to anywhere and what it is for?

 

[Mortamie]

Re: Motor won't start when in water but starts fine with muffs

that wire you are talking about is a ground wire. could have some to do with your problems...
I was having the problem of weak battery cranking on my motor so I cleaned the posts and connections on all my wires including battery.. this solved my issue could help yours... best thing you could do is get a manual for your motor.. also try moving your distributor by hand a little to the right before starting this will speed your idle speed up a bit and tell you if it is the idle speed.. this is based off what worked for me on my motor..

 

[bigpoppakdog]

Re: Motor won't start when in water but starts fine with muffs

not sure the specs for that old of a motor, but I would venture to guess, those compression readings are indeed very low. I will refrain from giving my thoughts, because I do not know if these compression readings are normal or not.

 

[Faztbullet]

Re: Motor won't start when in water but starts fine with muffs

Remove all the spark plugs and retest with a hot battery, if still 45 psi quit throwing $$ at it. Motor should have a minimum of 100psi to run correctly.