9.5 evinrude sportstwin no throttle past start

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allfordhouse

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Feb 20, 2015
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Solano County CA
So I took my new to me 9.5 hp evinrude sportstwin on the water first time yesterday. It's a 1972 I believe. Started one pull every time and ran great except after the throttle position "start" the motor wouldn't go any faster. Once at the "Fast" position it would start to bog down a little. But basically near the "Start" was the fastest it would go. I took the top off and watched it on the water the linkage is still moving from "Start" to "Fast" but there's no more acceleration. My first thought is it's not getting enough gas so I looked for kinks and found it was a little kinked where it attaches to motor but straightening that out made no difference. Out of the water it seemed to do just fine. I also recently added an inline fuel filter because I had it and thought it would help. Just wondering if this is a motor issue or could it be not getting enough fuel. Any ideas? Thanks.
 
Well, lets take a systematic approach to solving your motor issue or issues.

A good systematic process is to check compression first, then spark, and then fuel delivery. I will further explain the said process, but would like for you to do a couple of freebie checks first.

- did you make sure the fuel tank is vented. Most fuel tanks today need to be vented and have a screw release cap to allow air in the tank. If the tank is not vent then a vacuum state is created in the tank and the fuel pump has a very hard time to get fuel to the carburetor. Thus will start, but lug when trying to accelerate.

Running on one cylinder. Test is referred is the drop cylinder test.

- after you start the motor in neutral and let it warm up a few minutes, take a pair of pliers and unplug the top the cylinder spark plug wire from the spark plug. If it stays running we know the bottom cylinder is firing. If the motor kills then we know the bottom cylinder is not firing for some reason. Now replace the top spark plug wire snugly back on. Now unplug the bottom the cylinder spark plug wire from the spark plug. If it stays running we know the top cylinder is firing. If the motor kills then we know the top cylinder is not firing for some reason.

side note question: Did you remove your motor cover while running the motor? If you did, did it improve your performance??


Please let us know what you find and then I can add more information to continue evaluating your motor. Don't worry you will get your new to you motor running.
 

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