1986 Evinrude 8hp Yachtwin intermittent misfire

[Kulz]

Hello everybody!

I have a mysterious problem i have not been able to solve myself and was hoping to resolve the issue with the help from you people.

The problem comes and goes and it is not clear when and/or what makes the engine behave this way. See attached video for engine symptom.

Symptoms/info:

1. Engine starts
2. Engine runs on idle.
3. A little gas is applied and is held at a constant setting.
4. Something happens and the engine bogs down/dies.
5. The engine "re-ignites" at low rpm.
6. The engine revs up to correct rpm and "dies" again.
7. This cycle continues.

• Gas leaks from the primer/choke lever that sits besides the engine/carburator when priming.
• The spark of the spark plugs seem to "vanish" during the "bog down" phase.
• When spraying start gas around the cylinder gaskets and primer, nothing happens. However if sprayed directly into the air intake the engine bogs down.
• The compression is 130 psi for both cylinders.

Tried fixes:

• Changed spark plugs, tried 2 or 3 different types.
• Manipulated idle and fuel/air mix screws.
• Cleaned carburator multiple times.
• Changed float inside the carburator.
• Changed all fuel lines to new ones.
• Changed membrane inside fuel pump according to detailed instructions.
• Changed fuel filter and primer bulb for external fuel line 2-3 times.
• Dissasembled primer/choke and put it all together.
• Oil/fuel mix 1:100 ratio.

I think that was all, and would really appreciate some help from you experts on here. Thanks!

 

[racerone]

Step # 1 is to use a 50:1 ratio.------Ignore that 100:1 sticker.----Pull it off and throw it in the garbage !!----Factory bulletin came out many years ago on that issue.----I think throttle plate is opening too soon.-----Post video of it idling at slowest speed for 20 seconds.

 

[cyclops222]

Carburetor idle set too low. And or idle mixture set to lean.

 

[Kulz]

Thanks for your replies. I will certainly go to using 50:1 ratio from now on.

I didnt get a video of it idling today, however i managed to test the following (the engine ran really good today, however..):

1. I started the engine and it ran "good".
2. At higher rpms i clamped the hose that connects the primer/choke unit to the crankcase.
3. This resulted in the engine dying (presumable getting a too lean mixture.)
4. The reasoning behind this is that I think the crankcase draws fuel from the (faulty) primer instead of the carburator, and somehow that lets the engine run rather good actually.
5. I removed the primer unit and clamped the hose (still connected to crankcase)
6. The engine did not start, however i played with fully blocking and partially blocking the air intake of the carburator, at some point I think i got it to draw air from the carburator and the engine started. And i could manually adjust the ful mixture with my hand. I reckon it ran the best with ~1/3 of the air intake blocked.

What conclusions to draw from this new info I do not know. But can a faulty primer really create the symptoms this engine shows?

EDIT:
I forgot mentioning that i tried spraying start gas in front of the inlet as the engine was running in this wierd hand air blocking configuration. This time, the engine increased rpms instead of bogging down as before.. hmm

 

[racerone]

Repair primer as needed.-----Clean the carburetor.---Find / clean the high speed jet.

 

[cyclops222]

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