Honda 15 hp four stroke help.

[fireman32]

Just bought a used Honda that had been sitting idle awhile. I’ve replaced the spark plugs, all the fluids and filters for the initial tune up. I’ve cleaned the carb twice along with all of the other fuel system components. It idles perfectly, but for a good while it wouldn’t rev unless I blocked the breather. It will now rev to full throttle without air restriction, but is backfiring through the exhaust while at full throttle. I’ve added some sea foam to the tank as well. Does this sound like a still dirty carb, or is it a bad fuel component? Also the prop isn’t on it so I can run it in a barrel, would that change its running?

 

[Kdog]

Sounds like you may still have an issue with the carb, but you need to test it with the prop on so it has a load on it.

 

[Whitefeather]

Just bought a used Honda that had been sitting idle awhile. I’ve replaced the spark plugs, all the fluids and filters for the initial tune up. I’ve cleaned the carb twice along with all of the other fuel system components. It idles perfectly, but for a good while it wouldn’t rev unless I blocked the breather. It will now rev to full throttle without air restriction, but is backfiring through the exhaust while at full throttle. I’ve added some sea foam to the tank as well. Does this sound like a still dirty carb, or is it a bad fuel component? Also the prop isn’t on it so I can run it in a barrel, would that change its running?View attachment 1214929

Yes as mentioned above it’s best to run it in water with a load. Sounds like dirty carbs, fuel lines or anything related to fuel system.

If it sat with ethanol gas in it for any extended period of time, just plan on replacing everything that’s made of rubber. That ethanol destroys rubber and it doesn’t take much to stop up the carb ports and jets.

 

[Hillbilly stalker]

Put it on the boat, take it to the lake and run it. Leave the front off and run it wide open and spray "Sea Foam" in it until it sounds like your drowning it. I have to do this to my Mercury about every other year. It will clear it out in about 5 minutes or less. It doesn't replace a total part by part cleaning, but it will get you fishing.

 

[Jim Baker]

Put it on the boat, take it to the lake and run it. Leave the front off and run it wide open and spray "Sea Foam" in it until it sounds like your drowning it. I have to do this to my Mercury about every other year. It will clear it out in about 5 minutes or less. It doesn't replace a total part by part cleaning, but it will get you fishing.

That will take some serious coordination. I have had pretty good luck using water muffs and the nuetral throttle lever using Seafoarm Deep Creep sprayed directly into carbs.

 

[fireman32]

After thoroughly cleaning the carb a couple times, we put it on the water. It was still back firing on the hose at home at half to full throttle, but she ran perfect on the lake. Had to be a back pressure issue.