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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10964
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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, have a 1979 evinrude 4 cyl. cylinder three and four

Customer Question

Customer: ***** *****
JA: Thanks. Can you give me any more details about your issue?
Customer: have a 1979 evinrude 4 cyl . cylinder three and four are not working. have great spark. but after running engine, both lower cylenders are dry and plugs look brand new
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Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.

Hello. My name is Tan.

This is usually caused by a clogged carburetor. The top 2 cylinders work from the top carb and the bottom 2 cylinders work off the bottom carb. Now since you have spark that leaves the bottom carb as the possible issue.

Now it can be more serious the bottom crankshaft seal fails then the bottom 2 cylinders won't work correctly. Now what we can do is remove the bottom drain plug on each side of the bottom carb. Do you have fuel?

Post back with findings and questions.

We should also do a compression test to eliminate a possible compression issue.

Customer: replied 1 year ago.
fuel in carb. compression is 100 and 100
Expert:  Tan replied 1 year ago.

How long has the engine been sitting since it ran correctly?

Customer: replied 1 year ago.
started running weird about three month, has not been sitting. trying to get it right and running each month
Customer: replied 1 year ago.
when I put it in the water and start it up. I get raw fuel coming from around the lower unit and exhaust covers.
Customer: replied 1 year ago.
have to log out. will check shortly. thanks you
Expert:  Tan replied 1 year ago.

Raw fuel is caused by a flooding carb, bad fuel pump or weak spark.

If you squeeze the primer bulb does it get firm or can you continue squeezing the bulb

Customer: replied 1 year ago.
the problem is, I am not getting any fuel to the bottom cylinders , even with fuel in the lower carb. my plugs are dry.
Expert:  Tan replied 1 year ago.

Then you have a clogged up carb. I posted that in my first sentence. That is the purpose of squirting fuel into the bottom carb to be sure the cylinders will fire.

From here we have to verify. This is the purpose of the tests I posted. This is a process of elimination.

Customer: replied 1 year ago.
blub ferm
Expert:  Tan replied 1 year ago.

That tells us you don't have a bad fuel pump or flooding carb. Next is squirting fuel into the carb. If it doesn't fire then we have to check the quality of the spark. The spark must jump a 7/16" gap on a spark gap tester to fire the fuel.

Expert:  Tan replied 1 year ago.

Ok Bobby I'm logging off for the night. Let me know what you find after the tests I posted and we can continue tomorrow.

If the engine runs better when you squirt fuel into the bottom carb the bottom carb has clogged jets. Remove the carbs disassemble, clean and install carb kits.

Thank you.......Tan

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