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Charles
Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3976
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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1983 Mercury 115 horse 6 cyl. I have rebuilt carbs, all new

Customer Question

1983 Mercury 115 horse 6 cyl. I have rebuilt carbs, all new gas, new trigger (not sure what that is) but it cost a 1050 dollars. Problem will not get above 4000 RPM.
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: it will only go about 13 miles per hour. seems to run good but runs out of throttle to make it go faster
JA: Is there anything else the Marine Mechanic should be aware of?
Customer: No
Submitted: 1 year ago.
Category: Boat
Expert:  Charles replied 1 year ago.

Hello, my name is***** will assist you.

Expert:  Charles replied 1 year ago.

Have you done a compression test on the engine, and if so, what are the numbers?

Customer: replied 1 year ago.
The boat mechanic did a compression test on it that the compression was fine. not sure of the numbers
Expert:  Charles replied 1 year ago.

Are you sure that it is running on all 6 cylinders currently?

Customer: replied 1 year ago.
it runs great but will only get up to 4000 rpm. the throttle lever bottoms out.
Expert:  Charles replied 1 year ago.

What size it the boat and the prop?

Customer: replied 1 year ago.
are u still there?
Customer: replied 1 year ago.
it is a jet boat
Expert:  Charles replied 1 year ago.

Yes I am

Expert:  Charles replied 1 year ago.

When was the last time it ran correctly?

Customer: replied 1 year ago.
aound 5 years it sat inside for that time
Customer: replied 1 year ago.
around
do you only answer by email? I do not want to pay for phone call?
Expert:  Charles replied 1 year ago.

We do either by phone or in the internet. Which ever you wish.

What was done when the carbs were cleaned?

Customer: replied 1 year ago.
internet
all 3 carbs were rebuilt last week
Expert:  Charles replied 1 year ago.

How was this done? There are several ways to do this.

Customer: replied 1 year ago.
new floats and carb kit
Expert:  Charles replied 1 year ago.

Ok, Has the timing been checked at WOT to see if it is advancing?

Has a spark out out test been done?

Customer: replied 1 year ago.
I do not think so
what is wot
Expert:  Charles replied 1 year ago.

Wide open Throttle

Customer: replied 1 year ago.
not sure how to do this
Expert:  Charles replied 1 year ago.

Remove the plugs, advance the throttle to WOT, hook a timing light to the top cylinder then have a helper crank the engine over while you shoot the timing at the flywheel. Should be around 24* ATDC.

Customer: replied 1 year ago.
ok I will try this
How do I get a hold of you again
this might take a few days
Customer: replied 1 year ago.
if it is not advancing what should do to fix it
Expert:  Charles replied 1 year ago.

Just reply back to me as you have been doing tonight.

Adjust the trigger to advance the timing.

While you are at it, do a spark test on all 6 cylinders. Make sure that they are all firing.

Customer: replied 1 year ago.
ok I will double check the compression numbers to the boat has an hour meter on it and it only show 100 hours
Expert:  Charles replied 1 year ago.

Personally would not reply on that hour meter. you do not know when it was added or if it works.

Customer: replied 1 year ago.
ok
thanks Charles
your answers are solid
I will get back to you and let you know the results
Expert:  Charles replied 1 year ago.

Thanks. Talk to you then.

Customer: replied 11 months ago.
Hello
I had a mechanic check the timing and it was set according to your post. We did a compression test and
we found one cylinder at 30 pounds compression the others average around 120. Could this be caused by a dirty fuel filter or lack of fuel getting to that cylinder? The boat has been sitting inside for at least 5 years and I know for sure it probably cannot have more than a 100 hours on the motor. It has been stored inside.
Art
Expert:  Charles replied 11 months ago.

Art, Sorry to hear about the engine. Most times a cylinder going down like that is either lack of oil due to a clogged carb or the engine got hot. You had wrote back on the 17th that a mech had done the compression and it was fine. Makes me wonder if it was or not. Although I personally have done one of these engines, rebuilt the carbs, water pump, and repaired some of the wiring, it was running great. We even test ran it on the river. Gave it to the customer, he blew it up the first day he had it out due to a design flaw in the exhaust back when the engine was made. It is prone to blow number 3 or 5 cylinder. In my opinion the engine is not worth the rebuild as it does take special tools to get done correctly, and the cost would be more than a newer used engine that you could just bolt onto the boat and be back out on the water.

Please let me know if you need any other information.