Help!!...Johnson 8hp dies after 20 min

[zebra7]

I have posted this issue in another forum but am still stumped
My 2000 8 hp Johnson dies out after running perfectly for 20 min or so.
I am able to keep the engine running near idle speed, after it starts to die, by quickly, alternately giving it choke and throttle, I am hoping that this fact would point to the problem.
I have:
-replaced the fuel hose and bulb from the tank.
-cleaned the fuel pickup in the tank.
-cleaned the tank vent (which is open).
-took apart and cleaned the fuel pump/filter, it all looked fine.
-took apart and cleaned the carb, top and bottom, blowing through all orifices, the float works fine. It all looked very clean before I started, the engine is not that old.

Pumping the bulb does not help when it happens.
The cooling water is still flowing fine, but if it is overheating, what is killing the fuel to the engine?

I assume it must be the carb and not electrics as I can usually keep the motor running with choke throtttle manipulations.
I am in Canada so no ethanol fuel mix issues.
I will get a carb kit but I am not sure what issue that this might solve.

What problem would cause this??
Thanks

 

[oldcatamount]

Re: Help!!...Johnson 8hp dies after 20 min

It sounds like a fuel delivery problem for sure. You have checked everything except the fuel pump. Try disconnecting the fuel line from the pump that leads to the carb, give the primer bulb a squeeze and see if a good squirt of gas comes out of the line. The fuel filter screen inside the pump may be dirty and that's easy to check. Look for any loose clamps or cracks in the fuel line all the way back to the tank.

 

[northwoodslivin]

Re: Help!!...Johnson 8hp dies after 20 min

Not sure what you mean by that you live in Canada and there is no ethanol here. Ethanol is in 99% of our fuel here "I live in Canada as well" Surely it is fuel related.

When you say it dies out after 20 minutes, is that from constant idle/trolling? It could be that your plugs are fouling, what plugs are you using and at what gap? I have an 8hp as well and mine takes the QL77JC4's and I gapped mine at 35 anything higher and it will sputter. Have you confirmed that the motor is not over heating?

Good luck.

 

[zebra7]

Re: Help!!...Johnson 8hp dies after 20 min

According to Wikipedia:
Ethanol fuel is ethanol (ethyl alcohol), the same type of alcohol found in alcoholic beverages. It is most often used as a motor fuel, mainly as a biofuel additive for gasoline. World ethanol production for transport fuel tripled between 2000 and 2007 from 17 billion to more than 52 billion litres. From 2007 to 2008, the share of ethanol in global gasoline type fuel use increased from 3.7% to 5.4%.[1] In 2009 worldwide ethanol fuel production reached 19.5 billion gallons (73.9 billion liters)

Ethanol is widely used in Brazil and in the United States, and together both countries were responsible for 89 percent of the world's ethanol fuel production in 2009.

This (often corn based) additive can be responsible for gumming up systems that are not designed to use it. As far as I know, this is not used in Canada where I live so it is not a factor in my engine trouble, as suggested by another commentor.

The engine runs perfectly for ~20 minutes at half to full throttle before it dies out, so I think that rules out a plug issue, although I did replace them tonight anyways. I also added a hose clamp to the fuel inlet line to the carb that I noticed was missing. Will take a 1/2 hour run tomorrow to see if there is any change.

Overheating is sill a possibility but I don't know how to check for it or what it to do about it.

 

[northwoodslivin]

Re: Help!!...Johnson 8hp dies after 20 min

Where in Canada do you live? because it is all I can get up here in Northeastern Ontario, there was some places selling pure gas when I used to live down south "Sarnia/London Ontario area, but nowhere to be found up here "non ethanol gas that is" it's nasty smelling stuff when people pass you on the highway, smells like a rotten fart but worse.. Either way, I had ethanol gas eat the fuel lines on my 20HP, and seen it do the same to snowmobiles. Which gas stations are your common ones here? Because the Esso and Canadian Tire gas bar here all sell ethanol gas, same in Quebec with the Shell and all the others "live on the Ontario/Quebec border"

Hope you get it resolved
PS

What year is that motor? might be a coil going bad or power pack? just a guess, but I have heard some stories on failing power packs and how they do weird things when they are going.

 

[zebra7]

Re: Help!!...Johnson 8hp dies after 20 min

I have taken the fuel pump apart and cleaned it, as well as the filter. Made no difference. Still dies after 20 min running wide open. All hose clamps are in place, all nuts and bolts have been tightened. I have had the carb on and off at least 3 times since this started happening at the end of last year and nothing has made a difference. Any other comments on why adjusting the choke enables me to keep the motor running at low speed after it dies out? This has enabled me to make it home a couple of times.

What would overheating symptoms be and how can I check for that? The cooling water has always been discharging.

I am at the point where I will have to drop it off at the dealer, which which could be expensive as I don't know if the problem will happen with the motor running in his tank. This motor is about 10 years old and just used for 3 or 4 months a year.

 

[northwoodslivin]

Re: Help!!...Johnson 8hp dies after 20 min

I am surely not a marine mechanic but I have done all my own repairs and upkeep myself with the help of some others. But I still tend to lean on carb, either it is dirty or something is not set right. It also sounds like overheating or fouling.

When your motor dies out after 20 minutes or so, is there a chance that you can pull the plugs and look at them when it happens? if you did, are they soaked with gas? sooty black? clean? Also, I am pretty sure your motor doesnt have a choke, that is a primer and you only pump that a few times on a cold motor. If you need to use the primer to keep it going then this tells me that the motor is starving for fuel and sounds like a carb problem or possibly your primer is not working properly or is sucking in air some where? Just some "guesses"

GL They are fantastic motors, have one myself accept mine is an 87.

 

[Vic.S]

Re: Help!!...Johnson 8hp dies after 20 min

I am pretty sure your motor doesnt have a choke, that is a primer and you only pump that a few times on a cold motor.

not according to the Diagram I am looking at

But it does sound like a fuel supply or carb problem. It sounds a bit like a non venting tank , but apparently not ... have you tried it with the cap off.

Or an air leak in to the fuel line, or a defective pump, or a partial blockage somewhere But then pumping the bulb would keep it going.

I would double check all these things first, but then I think I would be looking again at the carb. Keeping it running by playing the choke is a pretty sure sign of a dirty carb!

Is the little spring clip that links the needle valve to the float arm in position?

Like northwoodslivin just making a few guesses

 

[Al-53]

Re: Help!!...Johnson 8hp dies after 20 min

When it dies..have you tried to see if the spark is strong...also have you done a compression check on the motor when u return from having problems....start there first then

Use a spark plug air gap spark checker to see if u have a strong blue spark...

some times coils or a power pack if bad... malfunction when get hot.....when cooled down they function again....

to see if your motor is overheating it to be able to hold your fingers on the head area for about 3-4 seconds with out being burnt...proper way is to have a laser temp checker and measure your head temps...or a infra red one.....

also is this a 2 stroke or 4 stroke....

Al

 

[tx1961whaler]

Re: Help!!...Johnson 8hp dies after 20 min

I'm leaning towards Al's take on this. A clogged carb would not "run perfectly" for 20 minutes. Something in the ignition system may be getting hot and cutting out, and putting on the choke may richen the mix enough to keep it going with a feeble spark.
First check the compression, as it's good to start troubleshooting with that free test. Then check the spark with it running well, then check it with it behaving badly. As said before, make sure the motor is not generally overheating.

Luckily, the coil and power pack for this motor are still available fairly cheap.

 

[northwoodslivin]

Re: Help!!...Johnson 8hp dies after 20 min

not according to the Diagram I am looking at

But it does sound like a fuel supply or carb problem. It sounds a bit like a non venting tank , but apparently not ... have you tried it with the cap off.

Or an air leak in to the fuel line, or a defective pump, or a partial blockage somewhere But then pumping the bulb would keep it going.

I would double check all these things first, but then I think I would be looking again at the carb. Keeping it running by playing the choke is a pretty sure sign of a dirty carb!

Is the little spring clip that links the needle valve to the float arm in position?

Like northwoodslivin just making a few guesses

I find this interesting, perhaps you are confusing this choke for an actual primer, because on my motor which is older then his, I don't have a choke, I have a primer, or is this also classed as a choke as well? confusing me here

 

[Vic.S]

Re: Help!!...Johnson 8hp dies after 20 min

I find this interesting, perhaps you are confusing this choke for an actual primer, because on my motor which is older then his, I don't have a choke, I have a primer, or is this also classed as a choke as well? confusing me here

The diagram I linked to is for a 2000 8hp and that has a conventional choke as you can see from the diagram.

My 1984 6hp ( and the similar 8hp) also has a conventional choke. A couple of years later they were fitted with primer pumps instead. After a few years they reverted to the conventional choke.

If you care to trawl through the parts diagrams you will discover which years had what system.

 

[northwoodslivin]

Re: Help!!...Johnson 8hp dies after 20 min

Thanks for the informative post Vic, I wasn't doubting you what so ever, just found it odd how they would switch a tried and true system in the later years.

 

[zebra7]

Re: Help!!...Johnson 8hp dies after 20 min

Problem Solved, Finally

I felt that that this problem was caused by overheating of something, so even though there was a return of cooling water, I replaced the raw cooling water impellor and my problem has been solved. The impellor was not broken but it was a bit out of shape. It must have been deformed enough to provide an insufficient volume of cooling water to the engine. I have been out for 2 long runs now, and no stalling .

 

[AEROCOOK]

Re: Help!!...Johnson 8hp dies after 20 min

The diagram I linked to is for a 2000 8hp and that has a conventional choke as you can see from the diagram.

My 1984 6hp ( and the similar 8hp) also has a conventional choke. A couple of years later they were fitted with primer pumps instead. After a few years they reverted to the conventional choke.

If you care to trawl through the parts diagrams you will discover which years had what system.

My 1987 8hp has a primer but the knob has two functions, primer and choke. You pull it all the way out for prime (you can feel the tension as it's squirting the fuel into the carb) then leave it half way out for choke, after a few moments you push the knob all the way in and your good to go. I love the primer function, my motor starts first pull every time! I wonder why they went back to conventional choke in later years?.
Anyhow, glad you got it figured out zebra.