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Ask Scott Martin Your Own Question

Scott Martin
Scott Martin, Marine Mechanic
Category: Boat
Satisfied Customers: 167
Experience:  Over 18 years experience in the water sports repair industry.
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i have a 89 60 hp mercury outboard. runs good at idle and has

Customer Question

i have a 89 60 hp mercury outboard. runs good at idle and has lots of power in neutral at full throttle but when you put it in gear it has low thrust.
Submitted: 4 years ago.
Category: Boat
Expert:  Scott Martin replied 4 years ago.

XXXXX XXXXX :

hello, how are you

Customer :

fine what do you think

XXXXX XXXXX :

has the boat been in storage for more then 60 days

Customer :

yes, probably longer

XXXXX XXXXX :

no problem we are more than likely dealing with fuel issues, but lets do it right and start from the first. when ever I see outboard enter the shop the first thing i do is, compression check and check lower unit for water and heavy metal particles

Customer :

did all that. compression is even on all cylinders at 125, lots of water on pick up and lower to top end seal was replaced. Engine was running at full on river and cut out and won't go now.

XXXXX XXXXX :

perfect information, this is rare thank you for all of that. Lets get back to the symptoms. she was running great after you did all those repairs and you said she just stopped. You restarted her and she had limited power correct? This type of question helps me to visualize your engine. the more info you give me ,even if it seems insignificant, the clearer I can see the problem

Customer :

still starts good and runs at idle, when you put it at full throttle in neutral it seems to have lots of power, lots of spark at each plug, when you pull the plug wires off on the bottom plug and top plug it wants to die, but not so much on the middle plug but stays running.

XXXXX XXXXX :

great test. you have eliminated top and bottom cylinders and carburetors. You and now I know that the power loss is contributed the the middle cylinder and carb. Are you near the outboard now?

XXXXX XXXXX :

oops need to proof read

Customer :

no but what are you thinking, i blew everything out with air, and flushed several times with fuel

XXXXX XXXXX :

You cleaned the carbs, but the delievery system to that carb could be a problem or the float level is off. the test I can have you perform will help us understand why number 2 cylinder is having problems

Customer :

so what can i do

XXXXX XXXXX :

I see your in Canada. The mercury engines in the USA have a drain screw at the bottom of the bowl. does you model have the same screw?

Customer :

yes it does but it looks like to me that there are two carbs feeding three cylinders, i drained the bowls and they came out clean several times, with no residue

XXXXX XXXXX :

I see, oops I should have asked for your model number and serial number that would have told me you have two carbs instead of our three. What your dealing with is a lean condition. You have already checked compression=good. when you pulled the plug wires while the engine running you verified that you had good spark=ignition test done. With the serial number information I will be able to go to my reference material and tell you the position of float drop and level. Air mixture screw settings if you have them and not a jet set system. Don't worry I will keep this ticket open for as long as you need. It doesn't matter how many days it takes to make your engine run right. I will change this application from chat room to email so it can stay active. Ok. send me the model and serial number as soon as you can.

Customer :

give me a few minutes

XXXXX XXXXX :

no problem what kind of fuel filter did you use after you did the carb clean?

Customer :

i think this is the serial #00A745772, cant find a model, clear pvc type

Customer :

system has two air fuel mixture screws, it doesn't make sense that it would run good and then cut out and have a fuel mixture problem

XXXXX XXXXX :

Thanks for the number. I get those numbers for you. Is the filter in the fuel line?Since your engine was running fine then failed. Something came loose after the after the filter. A piece of varnish or crumbling fuel line( seeing alot of that in the USA since ethanol was introduced). and went through your fuel pump (or came out of your fuel pump) and stopped up a high speed passage. The air mixture screw we will use as a tool to tell us which carb is stopped up. How while running the engine in a water tank or on the hose you can play with the screw at Idle speed and see by the turns what happens to the engine. The float setting are for when you tear down the carb again you can see where it is at now and see if there is a difference. I typed alot of information just now we can go through each in detail if you need.

Customer :

do you think it could be slippage in the drive shaft.

XXXXX XXXXX :

You would hear a loud grinding noise and the shaft splines would just come apart and spin freely. The plug pull test you performed told us alot. I still believe you have a fuel delivery problem.

XXXXX XXXXX :

plus doesn't your propshat have a shear pin for the prop?

Customer :

just thought i would check, when shifted in gear you can't turn the prop easily, and if you do force it the motor turns over, yes there is a shear pin. played with the screw while on hose, when you let the screws in and out it picks up or bogs down the engine

XXXXX XXXXX :

Very good, If your not convinced. are you close to a body of water to more test on the engine over the next day or so?

Customer :

yes, my concern is if the its the middle cylinder that not getting enough fuel, will it cause over heating problems and cease the cylinder, although when you pull the plugs out they does have fuel on it

XXXXX XXXXX :

very good question. if your running lean of fuel your running lean on oil on a pre mix system. The test can be done quickly on the boat ramp. or If you can take a person with you to control the boat while you test the engine. If you don't feel comfortable with those options. then we are back to pulling off the carbs and inspecting them completely. but this time we will install a filter after the fuel pump and before the carbs. I can get you a part number on a mercury filter that small enough to do this. I use it daily

Customer :

the filter is after the pump, i can have some one steer the boat while it runs. or at the ramp

XXXXX XXXXX :

good call. we have to get the engine under a load (simulating wide open throttle ). there are just two test you need to do. (test 1). At wide open throttle you need to get insulated pliers and pull then replace spark plug wires 1 thru 3 . As you did it before at idle. The engine will not die but should loose power equally. we are testing the high speed circuits in the carbs. (Test 2) shut off engine make sure all plug wires are back on firmly. If your carburators have a butterfly valve for choke (USA has injection) disconnect the arm tying them together so you can cover the intake of the carb slowly. This increases fuel flow down barrel of carb. start engine go wide open throttle.cover the top carburator with the choke butterfly. (if you have injection like us one finger than two. Does the engine decrease in power or loose power. Do the same with the bottom carb. This will help us identify the problem carb.

Customer :

so what the idea run it it gear and open the ports till she picks up speed and runs full out again

XXXXX XXXXX :

She may not run full again I would be surprised if she did. there will be a slight increase or a large decrease in power with the covering of the carburator barrel

XXXXX XXXXX :

we are just trying to find the problem carb. so when you clean them again you can pay extra close attention to that carb that had the slight increase of power when u covered the barrel. does that make since. I can try again sometimes i dont type clearly

Expert:  Scott Martin replied 4 years ago.
oops you fell out of the chat room No problem I will just change us to email so you can email me anytime. My cell phone will alert me when you have

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Edited by XXXXX XXXXX on 10/11/2010 at 3:53 AM EST
Expert:  Scott Martin replied 4 years ago.
Have a great night
Customer: replied 4 years ago.
had it running half speed on the river and opened ports wide open still no power change
Expert:  Scott Martin replied 4 years ago.
Did u do test #1 as listed? (plug wire pull at wide open throttle) Sounds like u just went to test #2 ? carb choking

Edited by XXXXX XXXXX on 10/12/2010 at 12:02 AM EST
Expert:  Scott Martin replied 4 years ago.
Did u do test #1 as listed? (plug wire pull at wide open throttle) Sounds like u just went to test #2 ? carb choking

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