How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Tan Your Own Question
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10746
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
Type Your Boat Question Here...
Tan is online now
A new question is answered every 9 seconds

Wont start, 120lbs of compression, plugs are firing fresh

Customer Question

wont start
JA: Sometimes things that you think will be really complicated end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so the Marine Mechanic can help you best.
Customer: 120lbs of compression, plugs are firing fresh gas, it just keeps turning over and over wont start, then after a couple of minutes it will start up then run for about 5 seconds and die.
JA: Is there anything else the Marine Mechanic should be aware of?
Customer: no
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Marine Mechanic about your situation and then connect you two.
Submitted: 10 months ago.
Category: Boat
Expert:  Jason replied 10 months ago.

Hello my name is ***** ***** am I speaking with?

What are we working on?

Customer: replied 10 months ago.
this is mark, 1970 Johnson 3 cylinder 60 hp
Customer: replied 10 months ago.
you dont have any suggestions? we wont it running today
Expert:  Tan replied 10 months ago.

Hello. My name is Tan.

Has the engine been sitting unused for an extended period of time?

If you squeeze the primer bulb does it get firm or continue to pump?

Customer: replied 10 months ago.
no it ran really good two weeks ago and went to go again last week and just shut down
and wouldnt start back running. the bulb gets firm
Expert:  Tan replied 10 months ago.

You say the plugs are firing how are you checking the spark? We need to check spark by using a spark gap tester. The spark has to jump a 7/16" gap for the engine to run.

Here is the type tester you need to check spark.

Customer: replied 10 months ago.
grounding them on the block, and yes they are jumping that much
Expert:  Tan replied 10 months ago.

I don't know how you can hold the spark plug against the block and make it jump 7/16 of an inch. It will only jump the gap of the plug.

If you can't do the spark gap test with a tester I can't help.

You have to do these test the way I tell you or I can't help. There are reasons for special tools to find problems. Short cuts don't work.

The spark has to jump a 7/16 gap and less of a gap will not fire under compression.

Customer: replied 10 months ago.
okay we have to go to town and get a tester and ck it. can you give about 30 mins
Expert:  Tan replied 10 months ago.

Sure take as much time as you need. I will be here all day.

Customer: replied 10 months ago.
great thank you
Expert:  Tan replied 10 months ago.

Your welcome. Could I get the engine model number please?

Customer: replied 10 months ago.
okay, got a tester and the spark is not jumping 7/16 of an inch. the firing starts at about 3/8ths and it quits past it.
Expert:  Tan replied 10 months ago.

Ok we need to test the voltage at the purple or red wire when cranking the engine. We must have 9.5+ volts. At the amplifier.

Expert:  Tan replied 10 months ago.

Do your spark plug wires come from under the flywheel or from individual coils?

I really need the engine model number to know which ignition system you have.

Customer: replied 10 months ago.
the plug wires come from under the flywheel there is one coil. MODEL #60ESL70D SERIAL #J3312962
trying to find my volt tester
Expert:  Tan replied 10 months ago.

Ok I had the right system. Just wanted to be sure. We need to verify that we are getting the correct voltage to the amplifier when cranking. This is the red or purple wire that is coming from the key switch. It could be either color. The wire can be accessed at the terminal strip where the amplifier wires connect. Amplifier.

Customer: replied 10 months ago.
found it checking now
Expert:  Tan replied 10 months ago.


Customer: replied 10 months ago.
we are getting 10.2 volts
Expert:  Tan replied 10 months ago.

That is at cranking speed correct? If yes then you have one of 2 things that are bad. The amplifier or the ignition coil. To test the ignition amplifier it requires a DVA adapter for your meter or a Peak reading volt meter. We have to test the voltage on the blue wire when cranking we must have 200 peak volts. If we have 200 then we know the ignition coil is the problem. So you have to get a DVA adapter or an ignition coil.

Here is a link to the ignition coil.

Here is a link to the DVA adapter.

If it turns out the amp is bad the amp comes with an ignition coil. So I would opt for the DVA adapter to test the amp.

Customer: replied 10 months ago.
i have a FLUKE ET73DMMA volt meter by MAC says on by do not exceed 4800 volts-amps
Expert:  Tan replied 10 months ago.

Will it read peak volts?

Customer: replied 10 months ago.
i do not thank so but i do have another coil on hand
Expert:  Tan replied 10 months ago.

Try the other coil. See we know everything is working as you do have spark but it is weak. So the only 2 things that make the spark strong or weak are the amplifier and the coil. Long as you have at least 9.5 volts when cranking you should have good spark. Be sure all you grounds and connections on the amplifier and the coil are clean and tight. A corroded ground can cause spark issues.

Related Boat Questions