Need help with 1968 40 HP Big Twin Evinrude

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andreipou

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Hello,
'
Model 40853D.

I put it on the boat after the winter, put new spark plugs , new oil.
Started right away , ran it in the water tank for 15 mins fine, checked the water exhaust, temperature, everything was great.

Next day brought it to the lake, started fine, ran fine for a few mins and then stalled.
After that was very hard to start, runs roughly , sneezing and stalls.
Was not able to get it running.

Next day at home same story: starts fine cold, runs a few mins and then sneezing , chocking , stalls.

Tried different gas tank\hose, new spark plugs. Did not help.

Any idea where to start?

thanks.
 
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racerone

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What kind of fuel tank do you use ? A good original steel tank or plastic " junk " tank ?----Looked at the fuel pump diaphragm , yes or no ?-----Sounds like a fuel supply / mixture problem to me.-----Would be an easy fix for me.
 
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andreipou

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Plastic tanks, but I had them for years.
If I take rubber hose from carburetor and put it into jar and crank, will it test the pump?
The clear filter that sits right before the pump is filled with gas....


I do not think my fuel pump has a diaphragm.
This is a parts chart, can you point to the part number?

Thanks.
 
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racerone

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Really ?-----All those pumps have a diaphragm and your understanding is faulty.-----New diaphragm is available for your pump or you make one !!-----May take more research / looking at different models to find your diaphragm.----Also post a picture of your pump because it may not be the original !
 
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andreipou

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I have 2-3 years old coils there.
Sometimes when I play with choke it starts and runs like crazy on hight rpms , but then dies out....
 
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andreipou

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racerone said:
Really ?-----All those pumps have a diaphragm and your understanding is faulty.-----New diaphragm is available for your pump or you make one !!-----May take more research / looking at different models to find your diaphragm.----Also post a picture of your pump because it may not be the original !
Click to expand...

It looks like link with diagram was removed.
I am trying to upload picture as .jpg, .png, .gif and get "Unknown Error" message.
 
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andreipou

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Finally added image.
Which one is a diaphragm?
 

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racerone

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Do you understand that the fuel pump on your motor operates with a diaphragm, yes or no ??
 
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andreipou

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I know how usual pumps operate, but I disassembled this pump when I rebuilt this motor looking for diaphragm to replace and did not find it.
On the picture of the pump parts that I attached above , could you please point to the part number of the diaphragm?
This is exactly what I have and it is original.
 
Chinewalker

Chinewalker

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Your pump was deemed "non serviceable item" back when the diagrams were created, so they didn't dissect them for diagram purposes. Complete replacement pumps were preferred, so that's what they sold you, rather than the pieces to rebuild what you had.

The diaphragm is inside the pump housing - it's a thin, rubberized fabric. If it's cracked, which many nearly 50 year old diaphragms are, it'll need replacing and will do exactly what you're describing.
 
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racerone

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If it does not have a diaphragm then I believe you have come across the " smoking gun " on your motor issues !!!
 
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andreipou

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That sucks!!!
Motor was completely rebuilt and ran great.
Is there a way to take it apart and do a fix?
There is a bunch of very handy and inventive guys on this forum, maybe someone tried already.

Anyway, before I panic I will do a "jar" test with carb hose disconnected.
The fact that fuel filter gets filled with fuel gives me hope.
Also, I can get pump off my 1971 40 HP Ski Twin and do final test (hate to mess with working old motor).

Also, I just recall something ( I am old now and do forget things):

I had similar issue with my other motors and I think even with this one.
My theory was that it has something to do with RUBBER TIP carburetor fuel stopping needle.
Remember those needles used to be all brass fitted to the brass saddle?
Then they started to sell them with rubber tip and steel.
This is when this problem started to occur.
I understand that it is cheaper to make and no fitting needed, but I think when motor stand for long period ( and this is my case) it begins to get stuck in the sit.
Symptoms would be exactly like mine: First runs on gas in the bowl, then sneezes, stalls, then after hard pumping\starting starts and all over again.
I rebuild carb and everything runs fine until it stays for long again.
This is my theory , no hard proof to it.

One thing I am going to try: when it starts choking knock the spot on carb body above the valve with small brass hammer I have to see if it drops the needle from the sit.
 
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andreipou

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andreipou

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oldboat1

oldboat1

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Don't think it's a match (shape of the original pump and diaphragm is slightly different). Can pull out the diaphragm on yours and use it as a template for a new one. If the diaphragm isn't split or holed, chances are it has taken a set -- more like cardboard than flexible rubber.
 
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