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Merc 70.

R

RJack

New member
Hey folks.
I've got a good one to pick your brain.
Have a late 80's 70hp. Can hook the hose up and run it all day. I've taken it to 2 Merc shops. Compression ok, carbs cleaned, plugs replaced, good fuel and ratio (I personally cleaned the tank, replaced lines, etc).
As I said, I can or the shop can run it on a hose all day, no problem.
Problem arises when I take it to the lake. Starts fine, accelerates fine for a while, half mile, mile, then I slow down and of course the front rises, rear lowers, then levels out and it starts sputtering and wants to quit. I can keep it running wait the warm up lever but it will not run good until I let it set.
Seems like when the motor gets water in the back rear when I slow down or gets too hot, I don't know.
Help if you can. Any ideas appreciated
 
Serial # is ?----3 cylinder motor with 2 carburetors.-----Test run with another tank and hose.-----Impeller replaced ?----Poppit valve inspected ?-----Run with timing light one cylinder at a time to see if there are ignition issues.-----Fuel pump inspected ?----Any sigh of water getting into cylinders.----Especially the top cylinder.
 
Thanks.
3 cylinders, 3 carburetors.
2 shops have tested it, both said internals were fine.
Impeller? What's that have to do with it running other than take off and speed?
Poppit valve? Not sure.
Fuel pump and carbs were rebuilt by the shop.
And, it runs good at the shop and in my yard. Just when I slow down from a run on the water does it show up.
 
Bummer.
Maybe the thing is haunted. Some previous owner ditched it or somewhat and it's taking it out on me....
There's got to be an answer.
 
Is it possible that you are getting water through the cowling or hood gasket when you slowdown.That could possibly cause the plug wire/spark plug to get wet and short out to ground.After you sit for awhile the engine heat dries it out and it runs could again.
 
I had similar issues with my 70hp, mine would sputter out 2 or three times then die but start right up, I cant say if this was what fixed it but after replacing every fuel line, carb kits, spark plugs, none of that did anything, i pulled the carbs to check the reed valves, at first they looked like reed valves should but after some measuring a few were a little gappier then the rest, apparently pushing/bending them to straiten them out is a stupid thing to do so when I got done doing that all are now showing about a 10 thousands gap evenly, the boats been running great since, but i wasn't having the issues common with bad reed valves backfiring, carbs puking gas, I really cant say that's what fixed it, this didn't help you at all, could also be a trigger going bad check the plugs if 2 look black one looks clean test the trigger
 
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