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4hp evinrude 1977 stalling only during daytime

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curtisj

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I took the old motor out the other night. Launched at dusk and it ran 12+ hours straight (all night) with no problems. Once the sun came up and got hot about 10 am it started to stall if I didn't press the primer bulb every 30 seconds. As long as I kept pressing the bulb it would run fine, if I stopped pressing it then it would stall. Restarted immediately first pull every time. (After pressing the bulb obviously)

The primer bulb is new (cause it did this last time as well) but that didn't solve the problem. Temperatures outside at over 100 F when the stalling occurs.

A few days later it started in the morning fine and ran for about an hour perfectly, and then started to stall again once it got hot.

The vent on the tank is open.

Vapor lock? Fuel pump? Sucking air in somehow?
 
I'm going to think about this one for a few moments...BUT... by any chance was this engine manufactured in Transylvania?

Okay, I'm back.... Why the heat problem will remain a mystery... BUT... your description of the failure, regardless of the time, indicates a failing fuel pump.
 
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I concur with joe,just don't go out in daylight.LOL How old is fuel system? Hoses,primer bulb,tank,fuel pump,any filters, fuel pickup tube. Might be time for an upgraded system that can handle ETHANOL.
 
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I concur with joes reply,just don't go out in the daylight. When was fuel system last upgraded,tank,lines,primer bulb,any filters,tank pickup tube,etc. Might be time for a system that can handle ETHANOL!! Sorry about the double post folks.
 
I replaced the engine fuel lines a few years ago. The fuel lines for the tank are not terrible old (they are gray), maybe 15ish years old. I just replaced the primer bulb.

The problem is that I can't recreate the problem at home. It will run forever at home in a barrel. Then when I get out to the desert (over 100 degrees all day) It's like the tank swells up in the heat and it's sucking in air somehow.
 
It does sound like the extreme heat is affecting the fuel pump somehow.... Pumping the fuel primer bulb (acting as a manual fuel pump) allows the engine to continue running which proves this point.

If it were me, I'd install a new fuel pump if for no other reason to eliminate this possibility.
 
Would a loose connection between the bulb and tank (tank outlet fitting/hose connection) mimic a fuel pump failure because the fuel pump is sucking in air? Not sure how I missed that but that connection was swollen and loose. I cut an inch of hose off and re-tightened the clamp and it much more secure).

I think this may be the culprit because that is how it felt when I was constantly pumping it to keep it going. It felt like air was getting in.

Also, I have a good running 1971 johnson 4hp and a couple other 4hp motors I could use for parts(2 spare fuel pumps). Any way to test the pumps to verify that they are good or bad?
 
You should be able to blow through them one way but not the other,that is the only way I know of but maybe someone else can verify that.
 
An air leak would mimic a bad fuel pump. Vacuum leak we call it. Why not swap the 71 for the77 u said its running ok then work on the 77 later & go boating!!
 
I don't have an answer to the question, but I find the topic very amusing. When I bought my Honda motorcycle, it would not run in the wind. Yes, a motorcycle that wouldn't run in the wind. C'mon, wind is what motorcycles do, right? I took it to the very reputable local Honda dealer and they never heard of such a thing. It took me 6 months, but I finally figured out that if the wind was coming from around 2 o'clock direction it was blowing into the carburetor vent. Replaced the vent hose, which extends down below the bike, and it is fine now. And I wasn't crazy after all.
 
I decided to figure it out today because it was hot outside and I was able to recreate the problem with it running in a barrel. Ran fine for 10 minutes but once it got hot (combined with the sun beating down on it) it stalled as expected.

I put the gas tank on a ladder and shortened the gas hose so it was a direct gravity feed and it continued running with so sputtering or stalling.

So I either need to replace the fuel pump or bring a ladder along with me! My spare fuel pump from the parts motor leaked immediately on install so that won't work, but at least it got figured out and it's not driving me crazy any more.

Thanks for all the advice, I really appreciate it.
 
curtisj said:
I put the gas tank on a ladder and shortened the gas hose so it was a direct gravity feed and it continued running with so sputtering or stalling. So I either need to replace the fuel pump or bring a ladder along with me! .
Click to expand...

I'm amazed at the fact that none of our technicians with many years of experience arrived at that conclusion within one or two post replies. Looks like we need more schooling. :)
 
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