Mercury 50hp red band

mdonni2000 · 11 September 2006, 12:10

Hi, can anyone help. I have a red band 50hp mercury engine. It is an old pull start.

You can start the engine select forward and it goes, it flies and will go forever, but when you stop the engine and select natural it ticks over fine. When you then select forward and accelerate the engines dies. You can restart the engine rev the engine then select forward and it goes or just dies again. If you stop select natural go back into forward and it dies again.

can any one help.

thanks Martin.

Pete7 · 11 September 2006, 12:59

Martin its an old engine but best guess could be: a: The throttle control box has a start in gear protection to stop you starting in gear. If the box is worn you may not be selecting netural properly, or b: its a fuel shortage problem with the carbs. Would be worth using a can of carb cleaner through the carbs with the engine running first. If that doesn't solve it you could take it to Pacer Marine around the corner from you.

http://www.pacermarine.co.uk/

Pete

mdonni2000 · 11 September 2006, 13:25

Thanks for the replay Pete.

The control box seems fine, I thought it may be fuel as you have to pull up the choke before the engine will restart, once started engage forward and it dies again. If you select forward and hit full throttle hard down if you catch it it picks up and flies. If I could keep the revs up I think it would be fine but that would just kill the gear box if selected at higher revs. This does not happen all the time. We water ski with this boat so I have to select neutral to allow the skier to sort himself out between runs. Someone mentioned that low compression could be causing it. I have checked this and all four pots are very close to 100psi should this reading be done when the engine is hot or cold ?

Thanks Martin.

Pete7 · 11 September 2006, 13:36

Martin, check the compression when the engine is cold, but if all cylinders are similar then its down to fuel and the carbs or pump.

Nos4r2 · 11 September 2006, 15:39

At 100psi compression that engine's well worn-they got around 140psi new but it depends on how good your gauge is too.I'd be looking at compression as being the likely cause.

You may well not have start in gear protection on it anymore- Do you have any wiring going to the control box from the engine? Most of them don't by now as the insulation falls apart. It's at least 34 years old now.

mdonni2000 · 11 September 2006, 16:14

Thanks, yes she is old but still pulls well. There is no wiring from the mercontrol box to the engine. If it's the compression the old girl has come to the end of her skiing life. It only does this when neutral is selected after its been running for a while if you don’t stop its fine you can slow down off the plain but just cant stop.

Is there anything else I can do. Thanks Martin

Nos4r2 · 11 September 2006, 16:38

Try and get the compression up with a decarb. It COULD be stuck rings.
A full bottle of redex in a gallon of normally premixed fuel will do it-don't load the engine heavily though as it'll weaken the mixture a bit.OR use Mercury Powertune (which is better). If you've got no wiring to the control box you don't have start in gear protection.