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Ask Dominick Your Own Question
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 1994 90 Hp Mercury. It starts well, but when I

Customer Question

Hi, I have a 1994 90 Hp Mercury. It starts well, but when I attempt to accerate from Idle the motor seems to bogg down. eventually the boat does plane off. but takes a long time. should tell you I has tried different Pitch prop. from a 21" all the ay down to a 15" neithwr pitch seem to be better tan the other when planning off.
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: I have checked compression. it is 125 on all there cly.
Submitted: 11 months ago.
Category: Boat
Expert:  Tan replied 11 months ago.

Hello. My name is Tan.

couold I get the engine serial number please?

Have you checked for spark on all cylinders?

Customer: replied 11 months ago.
Hi Tan,
I am sorry it is a Mariner 90 not a mercury.
Yes, I did check for spark on all cylinders and they are all firing.
The serial number is *****
Expert:  Tan replied 11 months ago.

When you are getting on plane choke the motor does it pick up and run? Squeeze the primer bulb when getting on plane. Does this help.

When was the last time the boat ran correctly?

Customer: replied 11 months ago.
I purchased the Boat used and it has this problem since I bought it. Squeezing the bulb does not seem to improve the situation. Also, I have replaced the diaphrams in the fuel pump. I have replaced the Carburetors with a another set which had been cleaned and rebuild kits installed. They gave the same results.
Customer: replied 11 months ago.
The motor runs okay once it is on plane. Does use a good bit of fuel for 90 hp.
Expert:  Tan replied 11 months ago.

Ok we are going to have to get a timing light and check that the cylinders are firing under load. Connect the timing light to the top cylinder run boat watch the flash of the timing light. The flash must be steady with no dead spots. If no misfire then move to the next cylinder. Do this test on all cylinders. If you find a misfire move that coil to another cylinder where there is no misfire. If the misfire moves then the coil is bad if the misfire stays then we have another failing component.

Customer: replied 11 months ago.
Okay will get back to you.
Expert:  Tan replied 11 months ago.


Customer: replied 11 months ago.
Your last response got me to thinking about something I have seen occurring on this motor, but never thought it was related. I have seen the Tachometer act erratic from time to time. Could this have something to do with the problem?
Expert:  Tan replied 11 months ago.

It can cause the stator to get real hot and cause ignition failure. But this would be a more dramatic failure.

Customer: replied 11 months ago.
Ok thanks. Just wondering.
Working on getting Timing light
Expert:  Tan replied 11 months ago.


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