Today I noticed my super cub back fireing. I have never had this happen before. I checked both mags and it seemed it would backfire more on the left mag. I tried burning off any carbon or lead. It stll would pop a little as I circled and checked for traffic. I thought about a no go, but decided to take off. Nothing was noticed after takeoff engine seemed to run fine. What is the most common cause of this? Thanks Mark
Backfire???
- Thread starter teeweed
- Start date
Greg Smith
Registered User
Merritt Island, FL
Backfiring or afterfiring ("backfire" through the exhaust)?
Backfiring is through the induction system, and can be from too lean a mixture or problems with the intake valve/valve timing.
Afterfiring is through the exhaust, and like Lance said is likely from a fouled plug. Inefficient combustion allows unburned fuel into the exhaust system. Other causes like valve clearance problems wouldn't have resolved on their own.
Backfiring is through the induction system, and can be from too lean a mixture or problems with the intake valve/valve timing.
Afterfiring is through the exhaust, and like Lance said is likely from a fouled plug. Inefficient combustion allows unburned fuel into the exhaust system. Other causes like valve clearance problems wouldn't have resolved on their own.
Clipwing_T
MEMBER
Sulphur Springs,Texas
Hi Teeweed, I would check your carb box for obstructions such as a
mud dauber nest a common problem in my part of the country (East Texas) . Several years back a guy treid to fly a backfiring Swift only to crash at the end of the runway ,the cause was found out AFTER removing the airbox. It was a "dirt dauber nest " as we call them around here that had obstructed the carb venturi. Get a light and a mirror and go check it sure won't hurt anything. Better safe than........... you know the rest.
Mike in Sulphur Springs TX
mud dauber nest a common problem in my part of the country (East Texas) . Several years back a guy treid to fly a backfiring Swift only to crash at the end of the runway ,the cause was found out AFTER removing the airbox. It was a "dirt dauber nest " as we call them around here that had obstructed the carb venturi. Get a light and a mirror and go check it sure won't hurt anything. Better safe than........... you know the rest.
Mike in Sulphur Springs TX
Dave Calkins
Registered User
Anchorage, Alaska
teeweed, the piece of your 'flametube' is likely a result of the afterfire, not the cause.
Keep looking.
Keep looking.
Could the flame tube pieces temporally block the exhaust as it bounces around and tries to escape out the exhaust? Could this cause a popping noise while doing a run up. I have located an intake gasket that looks like it is crumbling around the edges, almost looks like it is partialy gone, but can't tell for sure. Some discolored staining around this port and not on the others. I have not check it for leaks. I will tomorrow with the grease test. Would this cause my proplem if it was sucking air? Thanks Mark
While looking over my engine I found my rubber motor mounts to have cracks in them. I guess that's a sign it's time to replace them? I also noticed an oil leak ....I think its the oil pressure line. Small high pressure rubber line which has a curve in it, starts at the engine and joins up with a copper line that travels to the other side on the firewall and then into the cabin. It's leaking where the rubber and the steel crimp fitting is, so I don't think there is anyway to tighten this. I have owned my plane for 4 years and I am starting to look at some of the things I need to get done. Thanks Mark
Longwinglover
Registered User
Charlotte, NC
Uuuuhhhh Oooohhhh, Teeweed,
This is how those complete frame out overhauls start
.... Just a minor problem that gets you to start looking. One thing leads to another and then, well, you know.
Good luck!
John Scott
This is how those complete frame out overhauls start
.... Just a minor problem that gets you to start looking. One thing leads to another and then, well, you know. Good luck!
John Scott
Dave Calkins
Registered User
Anchorage, Alaska
Mark, yeah, check that intake gasket.
When the mount rubbers start to show cracking, it's coming up on time to replace them.
The oil pressure line is special, so don't just build a new one. The stock one has a restrictor in it.
When the mount rubbers start to show cracking, it's coming up on time to replace them.
The oil pressure line is special, so don't just build a new one. The stock one has a restrictor in it.
