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Dominick
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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I HAVE A 2004 YAMAHA 40 HP TLRC CARBS HAVE BEEN REBUILT NEW

Customer Question

I HAVE A 2004 YAMAHA 40 HP TLRC CARBS HAVE BEEN REBUILT NEW FUEL PUMP, COMPRESSION IS 110 ON ALL 3 CYL. ITS CHUGGING AT AN IDLE AND SEEMS TO BE BACKFIRING AT WOT, I PUULED THE PLUG WIRES ONE AT A TIME, NUMBER 3 CYL HAS A DRASTIC EFFECT 1 AND 2 DONT SEEM TO EFFECT RUNNING AT ALL. I AM KINDA STUMPED
JA: Sometimes boat issues seem like they'll be really complicated, but 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: IT SEEMS TO BE SMOKING A LITTLE MORE THAN USUAL, THAT IT USED TO
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: 5 months ago.
Category: Boat
Expert:  Tan replied 5 months ago.

Hello. My name is Tan.

If you squeeze the primer bulb will it get firm?

What do the spark plugs look like?

Customer: replied 5 months ago.
the primer bulb gets hard, plugs look a little wet
Expert:  Tan replied 5 months ago.

Have you tried adjusting the idle jets # ***** to get the engine to run better? http://www.marineengine.com/parts/yamaha-outboard-parts/img/62/03/4972/0005.gif

Customer: replied 5 months ago.
Yep it runs best at 1 and 1/2 out on all three carbs
Expert:  Tan replied 5 months ago.

Ok is this with the engine in the water in gear?

Customer: replied 5 months ago.
it is it never stalls just chugs like its dropped a cylinder and when I go to wot it picks up and tachs out but sounds like it's backfiring. I even closed the primer circuit and unplugged the solenoid thought maybe gas was bypassing it
Expert:  Tan replied 5 months ago.

Try squeezing the primer bulb when it starts to act up. Do this at idle and when you are running at full throttle.

Customer: replied 5 months ago.
Ok give me 10 or so
Expert:  Tan replied 5 months ago.

OK. What we are doing is eliminating the possibility of fuel starvation. Chugging can be not enough fuel. The backfiring at full throttle leads me to believe we have a fuel delivery issue.

Customer: replied 5 months ago.
Ok here's what I have, there is no difference at idle, but throttling up it started to stumble in mid range and still pops at wot
Customer: replied 5 months ago.
Almost sounds like a mid fire
Expert:  Tan replied 5 months ago.

Ok this next test will require the use of a timing light to see if we have a misfire. Connect a timing light to the top cylinder run the boat watching the flash of the timing light. You should have a steady flash with no dead spots. Do this test fro each cylinder. If you find a misfire move that cylinders ignition coil to another cylinder check spark again. Does the misfire move? If yes you have a bad ignition coil if no then we have another ignition component failing. If spark is good on all cylinders then we have a fuel related issue.

Post back with findings.

Customer: replied 5 months ago.
Ok I am out on the water and I do not have a timing light on me so it probably will not be until tomorrow, I live 50 miles from the lake but I will do
Expert:  Tan replied 5 months ago.

Ok that's fine I will be available all week.

Thank you.......Tan

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