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Mercury 7.5 Running Problem, Please help.

C

CCMS

New member
Trying to help a buddy with his outboard...

Its an older merc 7.5

It was ravaged with ethanol seperation when i got it.

Cleaned the carb, put plugs in it, replaced the fuel lines, cleaned the tank, new primer bulb, new fuel connectors, etc..

Ran wonderful

He went and filled it up with gas. He primed it up and it ran for a second and died, and wouldn't restart. evidently the gas was nasty. Looks like a lot of rust and stuff..

the on carb filter was full of brown debris, i opened up the carb and it has the same brown debris.

Cleaned out the carb. flushed the fuel lines, cleaned the plugs, and now it starts, runs for a second then spits and dies...

Does this every time I try to start it. Any idea what this could be?

I'm thinking Reed valves are full of crap.

How do i get to the reeds? The online breakdown from merc looks like you have to take the motor apart.

Any help would be apprciated
 
Yes, if the reeds are crudded up you have to split the crankcase to get at them (and if you have re-cleaned everything else in the fuel system, your symptoms could well be the reeds).

They are located on a (donut) at the bottom end of the crankshaft - moving the cage to directly behind the carb was one of the major changes made on the small Merc`s for the 1986 launch of the new models.

And because this model is `headless` the reeds come out with the crank and the pistons as a whole unit - pain in the butt.

A Seloc`s manual can walk you through the process but this job is as much work as a total engine rebuild (in terms of the amount of time you will spend) - all components will have to be cleaned for reassembly, and since you are there may as well replace the crankseals while it`s apart (and of course inspect the bearing and rings etc).

Can turn into quite the can of worms, so hopefully it`s a good friend that owns this if you are contemplating the work.

This is the type of job that most shops would advise as `not worth fixin`- the labour cost could well approach the pricetag of a brand new portable outboard....
 
Thats what i was afraid of...

I have had the fuel system apart 3 times this morning just to make damn sure i have everything corrected, and it all looks good to go.


To be clear of the issue..


I prime it, start it, runs for a second, and then dies with a nasty spit out the exhaust, with the recirc lines not secured, it will actually blow the recirc line off the upper connection.

Sounds as if the reed is stuck open, or broken, do y'all agree?

Just want to make damn sure before I pull this thing apart.
 
And this like a 4 stroke/valve would affect compression as well right? because now i'm down on compresion on both cylinders
 
No effect on compression. It'll need a hone and re-ring job to fix that.

I've found out (the HARD way) that any dust sucked in will keep the reeds from closing all the way--and no amount of reving the rods out of it will remove it. Only ripdown and disassembly of the reeds for cleaning will get them back to normal.

Jeff
 
and when i say down, I don't mean rebuild down.. I'm at 120 on both, but was higher before this ordeal started.. may have been a misread to start out with, Thanks everyone for the help, looks like hes up the creek, without a motor
 
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