Old Merc with Thunderbolt Ign

[Rascal4now]

Anyone know anything about the old Merc motors with the Thunderbolt Ignition? I have a little 4hp. It runs steady but is really rough idling. Also hard starting. When she runs, it runs continuous. What mix is ideal? I put a new cap on it.

[Kokanee9]

50:1 is the proper ratio for oil/gas on that motor.

[sanjuanworm]

Time to either check the fuel pump or clean the carbs or both. My motor is doing the same.

[Rick.]

Could even just need new plugs. I'd do that first. Rick.

[Rascal4now]

I will check the plug but it was a new one when I bought it from my neighbor. It only has about a 3 weeks of say, 6 hour days on it. She is an old engine so maybe it is normal for those old ones to run rough?

[Rascal4now]

41030
this is not my engine but identical one. I don't know how to load images so hopefully I got it right

[Kokanee9]

Those should fire up on the first pull and about the third or fourth pull on a cold day. They will idle smoothly with no vibration. If the plugs are fine, take it into a marine shop and have them test it the ignition. The carb screws have a small amount of factory loctite to prevent them from moving due to vibration over time. If the carb has never been played with, now would not be the time to start.

[Kim473]

Well winter is coming, I would take the carb off and rebuild it, change the impeller in the water pump and maybe rebuild the fuel pump if it has one. Just all the stuff that needs to be done once in a while. You should be good next spring for less than $200 and about a days work. Good winter project.

[jim summit]

These little Mercs have a points set under the flywheel.
The points wear out over time as they open and close so the clearance changes. Pull the flywheel, and remove the points, take a small file and clean up the contact area. Install and adjust to about 10 thousand clearance.
Should run like new, or just sell to me....:sHa_sarcasticlol:

[Kokanee9]

Those were good motors. I used to have a 7.5. Mine was a 2 cyl and had 2 carbs. The only operating problem I had was a coil developed a hairline crack and it idled rough. At full throttle, it was fine.
The other problem was the weight/size ratio. A little heavy on the weight compared to the HP output. But it wasn't really any different from other manufacturers at the time.

[fishnab]

Anyone know anything about the old Merc motors with the Thunderbolt Ignition? I have a little 4hp. It runs steady but is really rough idling. Also hard starting. When she runs, it runs continuous. What mix is ideal? I put a new cap on it.

Rascal:

I have a 4.5 Merc and was told by the owner of a local marine repair centre the best thing I could do for my little motor was to run premium gas 50:1 and change to systhetic oil. Mine asperates and coughs occasionally when using for trolling into the wind. A lot less exhaust and fumes now.

[Rascal4now]

Lol. I love the old girl. She is just plain purty! My neighbor thinks I'm crazy. Possibly. I'm fairly handy but without a manual of some form, not sure I want to do too much. That said, short on pesos so may have to. Thanks much! Some super ideas

[Rascal4now]

I like the sound of that! I will do that next year for sure