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Thread: Where to start to find this problem?

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    Default Where to start to find this problem?

    A buddy of mine just purchased a used boat and it runs well on muffs but when you put it in the water wont get over 4000 rpm,s and not doing over 15 mph. I have done a little research but not exactly sure where to start. Some say possible clogged exhaust, possible stopped up high speed jets, and I had one once that I believe the brain box was weak and caused this same problem. It's a 50 hp Mariner on a 16 foot Bass Tracker so it should be able to hit more than the numbers it's doing. Wont even get on plain. Any suggestions? Thanks

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    Most likely high speed jets plugged up. Here is a inexpensive tip to try first. Find or borrow if you donít have one a portable gas tank that will hook up. About 3 gallons of gas and halt a can of seafoam. Mix that good with motor on muffs crank and let run about 15 minutes at idle. Shut off let sit overnight. Next day do same thing. Do this 3-4 hours with about 6-8 hour rest period for that stuff to work in carbs. Then take to lake and you can leave it hooked to trailer. Just back in enough to run motor in gear. Just put in gear and gas it up and let it run for a bit under load. Then launch and run the stew out of it. That should clean it out pretty good and loosen up any carbon on rings and some in exhaust. If that didnít improve it then you start deeper trouble shooting. I bet this used boat has been sitting up a lot with old gas.


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    My buddy bought it knowing it had a issue and from the conversation I heard with previous owner it was running fine and set over winter then started having this problem. Supposedly was taken to mechanic several times with no luck and the guy got tired of dumping money in it with no results.????? I'm just trying to help my buddy out so he doesn't get into a money pit.

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    Quote Originally Posted by Thomas Armstrong View Post
    My buddy bought it knowing it had a issue and from the conversation I heard with previous owner it was running fine and set over winter then started having this problem. Supposedly was taken to mechanic several times with no luck and the guy got tired of dumping money in it with no results.????? I'm just trying to help my buddy out so he doesn't get into a money pit.
    I would check the easy stuff first, make sure that the throttle cam is working and both carbs are opening equally, make sure that the timing is set properly, and make sure that the cable is not bound up or something and only opening part way.

    It would also be a good idea to run a compression and power balance test to see that all cylinders are contributing.

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    Thanks, he,s new to boating and bought it without my advice. My advice would have been drive it before you buy it! I've made that mistake myself in my younger years.

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    Quote Originally Posted by Thomas Armstrong View Post
    Thanks, he,s new to boating and bought it without my advice. My advice would have been drive it before you buy it! I've made that mistake myself in my younger years.
    Another thing to check is that the timing advance arm is moving fully.

    Had that problem on my boat and the dang mud bees stuck a mound right where the timing arm stop is, so it only opened half way.
    Last edited by CrappiePappy; 08-10-2019 at 02:00 PM.

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    I would also replace the Fuel separator Filter beside the tank.. then the Filters on the Motor, clean them also. Restricted flow from the tank can even be old Fuel lines collapsed on the inside
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    Quote Originally Posted by Fish on Line View Post
    I would also replace the Fuel separator Filter beside the tank.. then the Filters on the Motor, clean them also. Restricted flow from the tank can even be old Fuel lines collapsed on the inside

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    I had the same problem with a 40 mariner. Took carbs off and had them professionally cleaned and then rebuilt them. The bottom carb jet was bad. Looked like someone tried to modify it.
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    Start with the basics. Buy or borrow a fuel line and bulb, modern gas even "ethonal free " has a serious issue with delamination of the fuel lines. It's a VERY common issue that has cost way to many boaters unnecessary expenses. JMO as a retired mechanic

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