TOPIC: 1964 Merc 650 - problems with wrap around cover on

This is a new one… had my 1964 Merc 650 overhauled (new upper/lower seals, 2 new pistons, etc...)... finally done with the 6 hours of 25:1 fuel mix… took the wrap around cover off to adjust carbs to 50:1 mix… found a sweet spot, put the cover back on, RPM’s drop and the engine either stalls, or stalls when put into gear. Take cover off, starts up, runs fine in gear. Put cover on, drops RPM’s and stalls. Hard to start with cover on.

All the wires, hoses, etc… seem to be in place, nothing lose or anything.

Any ideas?

Ran great the other night. Last night was giving me a bit of a hard time going from neutral into gear and not getting any power… took some time to warm back up – sometimes put it into low speed and it eventually picks up by itself. Water in the fuel perhaps?

Thanks.

Look for an exhaust leak most likely at the base gasket causing it to be smothered.

I'm trying to visualize this. Whereabouts on the engine should I be looking?

Thanks!

Are you running this in a barrel??? If so the fumes will choke it off in a barrel, expecially with the exra oil in the mix.

On a boat it can still do this, solution use a house fan to blow smoke away while testing static.

If does not work you have a leak.

My 500 leaks at the upper swivel mounts, (dynashocks) there are small seals that go bad and it sucks fumes back in easily.

Somewhere its getting exhaust back into the engine area and is sufficating it.

Conrad

Mine leaks at the pan gasket. At idle or trolling RPM you can see the exhaust shooting out. Where I am lucky is that it shoots out of the lower, vs back up into the block area.

Try running it with the cowl on, but the face plate off. If you are getting exhuast up there significant enough to choke it off, you should be able to see it.

Another thought. The air intake (at least on my 63 1000) is on the back of the top-hat. Make sure that that screen vent is not blocked off somehow. If it is blocked or restricted, I suspect she'll choke right off.

Yeah - no difference between the faceplate on or off. There is exhaust coming from the bottom of the engine.

On the other hand, it was a hot, humid day with no wind.

My 650 has the grill in the back of the top hat as well, but it's not blocked.

Hmmm. The weather could have been a factor. I ran my boat well into november last year. On the last day it was only in the 50's. She would fall flat if I put the throttle down to quick. The weekend before when it was in the 70's, no issue.

Now I am thinking a short somehow. With the face plate off, and since the carbs are right up front with clear air, I cant imagine she's starved for air. Is it possible that when you put the cowl on it's contacting a wire or terminal block somewhere? Maybe check the inside of the cowl for arc-marks.

Another random thought. Is the cowl moving the plug wires such that they are touching the mercury switch on the side, or terminal block on that side, causing poor connectivity.

Interesting problem (for us at least. for you of course it's just a big PITA)

Does your 650 have the holes in the lower cowling under the carbs like the early 400's and MK 55's and such???????

If it has the holes in the lower cowling for water/gas evacuation then a lower gasket leak would suck exhaust right up into the carbs trust me.

This is exactly what my 500 does.

A slow taper off and not wanting to idle is a good sign of exhaust ingestion problems.

Seriously this is a problem.

On the other hand, it was a hot, humid day with no wind.

it takes very little exhaust to ruin your idle.

If you were shorting your mag out by the wrap it would most likely not run at all.

Conrad

OK - finally had time to go down to the dock and tinker with the motor. I think I found the leak. It appears to be coming from the upper pivot under the lower cowl... see pictures. Any ideas how to fix (translation - without taking the boat out of the water and spending lots of money or tearing the whole thing apart).

There's also water gurgling up along with the exhaust from there as well.

And to answer a previous post, yes, there's a hole on the bottom of the lower cowl under the carbs and you can see when the exhaust smoke makes its way up there, the engine definitely behaves differently.

Exactly Nessman! just like my 500 did. Exhaust comes out that top swivel shock area and leaks right up into the carbs messing up your idle.


I belive to get that o-ring that is bad on each side fixed the darn block and leg have to come off.

THere is a rubber oring type seal that seals that mount area to the leg. Either it rotted out or was forgotten on re assembly at some point.

This year I took some carb cleaner and cleaned up that area well so that RTV/Silicone could be made to adhear to that area. Its a hard area to get silicone in to but it works as long as its clean. Mine I think will last years until I decide to pull it down to replace the seals.

Conrad