merc 650 65hp trouble

[jbrown270]

A friend of mine has an old merc 650 on a 15 foot fishing boat. the motor hasn't been run in the water in two years. here's the problem. from an idle, it accelerates hard to about 3000 rpms then it bogs down in the water. i cleaned the carbs and the fuel pumps but it didn't help. the motor has a rough idle. we started it out of the water today and the motor will accelerate but when the throttle is returned to idle it will almost stall but will slowly return to a normal idle. As far as i can tell, all this is caused by running rich. i can see a pool of gas in both the carbs while running. is this normal for an outboard? now i am thinking the carbs need rebuilt. the motor was tuned up and had a new impeller installed before it was put into storage for the two years. this is the first outboard i have worked on so i am open to any suggestions. thanks

 

[Starppy]

Re: merc 650 65hp trouble

First of all, we need more information. There were 3 versions of the 650. The ones made before 64-71 were 4cyl with the older style ignition systems (points and condensers) and the the ones made 72-75 were 3cyl with What I believe was refered to as type-III ignitions (electronic switch box, single coil) and the 76 3cyl with a type-IV ignition (newer style switchbox and 3 coils).

Find your serial number located (between the transom clamps or on the side of the engine block), look it up on the sticky post at the top of the forum and post back with that info. It makes a difference, trust me.

The fuel could be a problem, or a symptom so I wouldn't panic yet. Here are some typical things you can look at and will probably be recommended.

MAke sure you have fresh, clean fuel with the proper 50:1 mix of oil. I also recommend premium in the older engines. Not for the quality or octane level, but for the lack of ethanol. Ethanol is a corrosive and tends to eat at the older rubber seals and hoses.

You may want to clean the carbs. It's not as bad as you think. 2-cycle carbs are pretty simple. While you are at it you may want to put a kit in them while you have them off. Also clean the filter screens and check the floats.

There should be an idle adjustment screw on the front of each carb. If you really feel adventerous you can reset it. Turn it down to lightly seated and then turn it back open 1-1.5 turns for a base setting and adjust from there. Any adjustments made out of the water on the muffs will only be a rough setting. Final adjustment will have to be made on the water.

Those are just rough ideas. Get back with the serial and year and you can get more detailed info and troubleshooting from the guys here.

 

[jbrown270]

Re: merc 650 65hp trouble

its a 1969 model 4 cyl. i have cleaned the carbs and fuel pumps. it has fresh gas and a new tank. I tried priming it this morning and gas would just pour out the carbs. are the gaskets and the float the only things i need to rebuilt the carburetors or do i need additional parts?

 

[stubbstheman88]

Re: merc 650 65hp trouble

we had the same problem..... just order a rubulid kit and probally order a new float u will want to clean everything and replace anything that needs it. the float might be the problem because it might be stuck and not stop the fuel from flowing. mainly you will want to make sure the float can easily move up and down easily so as to stop the fuel flow. this is what i did for my 65 and it seems to work better. it is just a suggestion and i hope it helps

 

[jbrown270]

Re: merc 650 65hp trouble

new problem now. I rebuilt the carburetors and cleaned them again. now the boat has a fast idle. Starts good and and idles good at first but when i put it in gear it stalls. After that, i have to keep it idled above 2000 rpms to keep it from stalling in neutral. Got back home and started it out of the water and it still idles fast but doesn't stall with no load on it. could a small vaccum leak cause the motor to run lean enough to stall in gear?

 

[Starppy]

Re: merc 650 65hp trouble

I'm going to crawl out on a limb a little bit here. It is most likely an adjustment issue. You need a manual and go through the trouble shooting.

A very rough guess in order of ease to test would be one of the following...

1. fuel flow issue. It may not be lean, it could be flooding itself out as well. You can try squeezing the fuel line ball while it's running and see if that changes things. If it does, it might be a fuel pump issue.

2. Spark advance setting messed up. this one isn't so easy to test since it is linked to the throttle control linkage. Get the manual. It should have a procedure detailed on setting it back to baseline and tuning it to optimum.