Lycoming Back Fire

[manucanhunt]

I run a Lycoming 0-435 on a 16 foot boat. I have recently noticed that at idle I have a slight back fire. Once I rev it up it works great! It runs on gas pump fuel and I've been putting in 91 octane. That's the highest we can get here at the pumps. I run at about 4200 feet in elevation.

At my elevation, would using a lower octane help to retard the ignition or would the back fire at idle be something else. I didn't have this problem last year.

I appreciate all of the incredible expertise that I read about daily on this forum. You guys know your stuff!

 

[scottginfla]

you could have developed an exhaust leak, or intake leak, either would cause a backfire. cracked header would do it too.

 

[manucanhunt]

I'll check the intake and exhaust for cracks.

Do you know if the altitude makes a difference in the octane needed?

 

[ptr34]

take your carb off and clean out .it can get build up inside the carb and it will do that.

 

[manucanhunt]

Makes sense. I didn't run the boat from January to the end of September. May have some build up from sitting idle for so long.

 

[Rich Andrews]

never heard a continentals do that?

 

[hmgm123]

Sure you have just when the continental gets stuck and can't move anymore.

 

[Rich Andrews]

that's the sound of BEER popping

 

[hmgm123]

That a good one Rich.

 

[Moritz]

try using the discharge of the shop vac to pressure up the intake and test for leaks with soap water solution something you blow bubbles with to find the leaks

 

[manucanhunt]

Great idea. I do appreciate the great input. It gives me several options to check out.

Does a Continental have a different carb than a Lycoming??? I've pulled a few boats with Continentals out of the mud. Not bad for a 200 hp with a slight backfire.

 

[ptr34]

if a Continental has a carb it is probaly off of a Lycoming