Mariner 20hp accelerating problem

[IrishSIB]

Ive got a 1998ish 2 stroke 20hp mariner. When i run it in the barrell it revs fully but when its on the back of my shetland and I try accelerate it wont rev much past 1500 revs i would guess. I think this is because it is having to push a weight when on the boat but it has to push no weight when in the barrell? I was told by a mechanic that its deffinitly the carbs and to clean the jets. I have taken them apart a number of time and blew them clean with an airline but still no luck. Any other ideas would be greatly appreciated.
Thanks.

 

[oldman570]

Re: Mariner 20hp accelerating problem

You can use a piece of clear poly hose and replace the fuel hose from the fuel pump to the carb and watch the fuel flow to the carb. If there are any air bubbles in the clear hose then you have an air leak in the fuel supply from the tank to the carb, and it will need to be fixed. If there is a dealer near you you can see if they have a can of Power Tune and follow the directions on the can and it might clean up the carb without having to take it off the motor. You need to check the compression of the cyclenders and they should be close readings , if not then the motor has internal problems. When in a barrel you can check the electronics by pulling one plug wire at a time and see if the motor is missing on a cyclinder. From the post it dose sound like the high speed jet is still pluged or resitcked and needs to be cleaned. If the Power Tune dose not work, you will need to clean the carb again. If you use ethenol fuel, the fuel lines could be deterated and will flake of the inter and plug the jets. If the lines have not been replaced with new ethenol resitant line you might want to do that also. JMO
Oldman570