idles, but no forward or reverse

[badkarma]

I have a 1978?? mercury 700 70 hp that will idle fine, but when put in forward or revers will die. We had the motor serviced before this happened and the carbs were rebuilt, a new wiring harness was installed and the lower unit seals were replaced. Any help would be greatly appreciated.

 

[steelespike]

Re: idles, but no forward or reverse

Usually when they stall going into gear it is a fuel supply problem carbs could still be dirty or adjusted wrong.If idle is set too low it would stall when put in gear.On rare occasions if the drive shaft is seized it will stall.with it off and in gear see if you can turn the flywheel by hand.

 

[badkarma]

Re: idles, but no forward or reverse

Just a little history of how it dies. It was running fine fine on the water and then just lost all power. We took it to a local repair shop and was told it "might" be a broken reed valve. I'm thinking and electrical problem or carb problem. Any way way to tell which one it might be? If the drivshaft is seized what is the fix. Replace the lower unit??

 

[CharlieB]

Re: idles, but no forward or reverse

Slow down, you're jumping to conclusions and could well end up spending a LOT OF MONEY on parts you do NOT NEED.

It lost power, OK, how old is the impeller, was it beginning to overheat?

Check compression, check spark, repost the results.

You want to check and ensure that the engine is mechanically sound and rule out the majority of problems.

The carbs were cleaned, IF, the idle mixture was set for best idle speed while on a garden hose then the idle mixture is too lean once the motor is in the water an most be adjusted maybe a quarter turn out on the mixture screws, once it idles in the water THEN you can fine adjust while idling in gear, set them to best idle plus just about the width of the screw slot on the end of the needle.

NO MONEY SPENT ON PARTS, yet. PROVE THE PROBLEM first.

 

[CharlieB]

Re: idles, but no forward or reverse

Oh, yeah, how old is the fuel, any WATER in it?

Have you installed a water separating filter so that you don't suck some more right back into those clean carbs?

 

[badkarma]

Re: idles, but no forward or reverse

Carbs were last cleaned about five yrs ago. It was immediately after work was done to motor that this happened. I will probably rebuild the carbs "just to make sure" and replace the plugs at that time as well. Not to sure about compression, I don't have a manual yet but plan to buy one tommorow.