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Charles
Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3342
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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Hissing, high idle speed and engine dies under power.

Customer Question

Hissing, high idle speed and engine dies under power.
Submitted: 6 months ago.
Category: Boat
Expert:  Charles replied 6 months ago.
Hello, Kevin, my name is***** will assist youWould you please post the full model number from the engine?Do you recall what the compression numbers were?Were the carbs done before or after this started?
Customer: replied 6 months ago.
2004 F75TLRC Yamaha
150 on all four cylinders
after cleaning, engine would not start prior due to old fuel in the carbs and varnish.
Expert:  Charles replied 6 months ago.
Thanks, ***** ***** removed the carbs, did you take off just the carbs, or the entire intake?
Customer: replied 6 months ago.
the whole unit
Expert:  Charles replied 6 months ago.
Ok, now I am assuming all new gaskets and O-rings were installed as it went back together.Are you near the engine now and have a can of wither carb cleaner or WD-40, or something like them?
Customer: replied 6 months ago.
no, reused same gaskets and o rings
Customer: replied 6 months ago.
I have spray
Expert:  Charles replied 6 months ago.
Sorry, I had to step away for a few. Start the engine on a hose, allow it to warm for a minute. Then take the spray and use it around the flange where it intake runners meet the block and the point between the carbs and the intake. You are listening for a change in the engine tone.
Customer: replied 6 months ago.
Tried that and could not detect any changes...
Expert:  Charles replied 6 months ago.
With the engine running, can you identify about where you hear the air leaking?
Customer: replied 6 months ago.
At the entry of the air intake sounds like air is sucking.
Expert:  Charles replied 6 months ago.
Got it, After you rebuilt the carbs, did you hook a vacuum type gauge to the intake runners and set the sync on the carbs?
Customer: replied 6 months ago.
Kind of like an old steam train.cha cha cha cha cha
Expert:  Charles replied 6 months ago.
The thing that you need, looks like this one here. It is used to et the intake vacuum of each carb.http://www.amazon.com/Tecmate-Vacuummate-ME-Built-In-Battery-TS-71/dp/B0022WQL5M/ref=sr_1_1?ie=UTF8&qid=1464039165&sr=8-1&keywords=vacuummate
Customer: replied 6 months ago.
Thanks for your help, time to bring in a mechanic...beyond my ability...
Expert:  Charles replied 6 months ago.
Your welcome. What I feel that you have going on is that the carbs really need to be synced and the engine will smooth out. You cannot set up this engine correctly without it.

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