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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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We've got a 2006 Yamaha two cycle 70hp. The third cylinder

Customer Question

We've got a 2006 Yamaha two cycle 70hp. The third cylinder isn't working so good. If you disconnect the second cylinder, the engine shuts down. Disconnecting the first cylinder makes it sound different. No noticeable difference disconnecting #3.
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. Is there anything else important you think the Marine Mechanic should know?
Customer: When we disengage #1 , the engine won't start.
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: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.

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

What is the model number on the engine?

When did this problem start?

Customer: replied 1 year ago.
Hey Jason, I'm Tim. It's a 2006 70tlr. The problem started after fueling up at one of the marinas. I also added Yamalube at the marina. We made our way through the no wake area and hit the throttle with very sluggish results. We decided to head back to the ramp and the motor would intermittantly run between 1) two cylinders at no more that 4300 rpm and 2) all cylinders at 5600rpm. Research showed the fuel pump as the issue, so I changed it. Put it back in the water and am getting 100% 2cylinder performance. i'm more of an auto mechanic, so I checked the coils, the plugs and wires, all electrical connections, fuel lines, and oil lines. pulled the #3 carb and checked for was clean and clear. So it's getting fuel and fire, the only thing I can think is that the control module or a sensor is bad, or there is a hole in the piston or a damaged valve, or rings? could the computer shut down one cylinder?Thanks
Expert:  Jason replied 1 year ago.

Hi Tim,

Steps one and two are going to be to check engine compression, and check spark output with a timing light. Are those tests something you can do and get back to me on?

Customer: replied 1 year ago.
you don't have to call. i can do both of those.
Expert:  Jason replied 1 year ago.

Okay let me know what you results are and we can take it from there.

Customer: replied 1 year ago.
It's raining, so it'll be tomorrow before I check. Can I get back to you tomorrow?
Expert:  Jason replied 1 year ago.

No problem

Customer: replied 1 year ago.
Rain stopped!! Ran the compression test on all three cylinders - they all came in at about 120 PSI. Spark was present on all cylinders. I think now the #2 cylinder is acting goofy - the only thing that I changed is the spark plugs. They got mixed up.
Expert:  Jason replied 1 year ago.

Good morning. What's going on with #2? How did you check for spark, did you use a timing light?