Old Merc 7.5hp low speed issue

Hello, I recently bought this older Merc 7.5hp and I’m having issues holding a low trolling speed. I can get the right speed but a minute or two later it starts to slow down and start to bog. Runs great at any other speed. I can’t tell what year it is as the serial number is not coming up online ( 7105558), I’m guessing it’s around 1975-1980

Pervious owner says spark plugs were changed before he sold it.

Sometimes when I throttle up in gear I can’t, I have to idle it back down and then it will throttle up all the way. Almost as if something is getting stuck. Don’t know if the two problems are related.

Anyone have any ideas before I attempt a carb rebuild.

thanks

That's a 1977 Canadian built model (Merc in Mississauga).

What you are describing sounds like some cooties in the carb.

Since it's "somewhat working" you could try running some seafoam in your gas and/or grab a spray can of Merc's "Powertune" (can get it at any Merc dealer) and just follow the directions on the can.

If the carb needs a clean/rebuild, parts are still available (including from the host of this forum).

A parts list/diagrams are available here: http://www.marineengine.com/parts/mercury-outboard-parts/75/7028598-thru-7111897-can

Canadian, eh? Did you check and change lower unit grease/lube. Why? I have seen this ignored and then bearings bind up. If this is the situation, the motor will be too expensive to repair.....good used parts for these transmissions are hard to find. Why? Very common....why? Driveshafts are not stainless.....like to rust under water pump, then seal goes bad.
If lower unit checks out, then do a spark test. 7/16" crackling blue/white spark. Do spark test in ALL stator/trigger positions....why? Bad trigger wires.