Boulevard backfire?

[Rhubarb]

My 2005 C50T Boulevard keeps back firing when I back off the throttle.

I rode it for 500+ km two weeks ago and everything was fine. Took it out of the garage in the weekend for the first time since that 500km ride – now it back fires!

Sometimes there is a small burst of flame out of the exhaust. Mainly out of the lower exhaust but sometimes both.
The back fire can be anything from a ‘pop’ to a shotgun ‘bang’.

It starts first time every time regardless of whether it’s cold, warm or hot.

If I’ve been riding it for 10 minutes or 2 hours, it always starts easy and first time.

Acceleration up through the gears and out of the corners is smooth, consistent and delivers good power.
It runs nice around town at 50kmh and on long trips at 100-140kmh.
There’s no engine miss.

I rode to the Burt Munro in the weekend and it performed brilliantly there and back - except for back firing at every corner!

It’s not using anymore (or any less) fuel.

My first thought was an exhaust gasket or loose flange but the exhaust flange is tight and the gaskets don’t leak. There are no cracks in the headers.

Does anyone have any ideas what it might be?

Perhaps it’s the oxygen sensor or a mixture problem – maybe I just take it to a dealer instead of trying to fix it myself.

Any helpful contribution is much appreciated - Thank you.

[duckonin]

Try a new set of spark plugs.

[Rhubarb]

Try a new set of spark plugs.

That's a good (and cheap) place to start. It's probably due a new set anyway

Thank you.

[The Lone Rider]

My 2005 C50T Boulevard keeps back firing when I back off the throttle.

I rode it for 500+ km two weeks ago and everything was fine. Took it out of the garage in the weekend for the first time since that 500km ride – now it back fires!

Sometimes there is a small burst of flame out of the exhaust. Mainly out of the lower exhaust but sometimes both.
The back fire can be anything from a ‘pop’ to a shotgun ‘bang’.

It starts first time every time regardless of whether it’s cold, warm or hot.

If I’ve been riding it for 10 minutes or 2 hours, it always starts easy and first time.

Acceleration up through the gears and out of the corners is smooth, consistent and delivers good power.
It runs nice around town at 50kmh and on long trips at 100-140kmh.
There’s no engine miss.

I rode to the Burt Munro in the weekend and it performed brilliantly there and back - except for back firing at every corner!

It’s not using anymore (or any less) fuel.

My first thought was an exhaust gasket or loose flange but the exhaust flange is tight and the gaskets don’t leak. There are no cracks in the headers.

Does anyone have any ideas what it might be?

Perhaps it’s the oxygen sensor or a mixture problem – maybe I just take it to a dealer instead of trying to fix it myself.

Any helpful contribution is much appreciated - Thank you.

I had similar problems when I put on some exhausts I made. After running it a bit, the flames stopped and backfiring stopped. However, I still get the crackle and pop when I decelerate occasionally.

[munster]

On our 50's the pair valve (little chrome cover on left hand side) is designed to pump air into the exhaust to reduce the proportion of unburnt fuel coming out. Sounds silly, but it is to meet California emission laws. Apparently it's quite safe to remove with no adverse affect on the bike or performance. I plan to remove mine and go naked jugs eventually. If this is malfunctioning, it could be leading to an increase in the ratio of unburnt fuel in your pipes.

But I too would start with Spark Plugs.

[Rhubarb]

On our 50's the pair valve (little chrome cover on left hand side) is designed to pump air into the exhaust to reduce the proportion of unburnt fuel coming out. Sounds silly, but it is to meet California emission laws. Apparently it's quite safe to remove with no adverse affect on the bike or performance. I plan to remove mine and go naked jugs eventually. If this is malfunctioning, it could be leading to an increase in the ratio of unburnt fuel in your pipes.

But I too would start with Spark Plugs.

Thank you - I'll check that out as well

[skinman]

mine snap crackles & pops, could have something to do with the V&H pipes though, scares the crap out of cagers & newbe riders, I can tell cause they swerve all over the road looking in the mirrors

[munster]

mine snap crackles & pops, could have something to do with the V&H pipes though, scares the crap out of cagers & newbe riders, I can tell cause they swerve all over the road looking in the mirrors

The C&M50's tend to run a little rich anyway. You might be needing a fuel processor, though I've been told you can change one end (air aintake, or exhaust) without needing the processor. Change both and it's a necessity, if you give it more air it will run lean and that's not healthy if you value pistons.

[wainui]

Go on intruder alert plenty of advice for Boulevards

[Rhubarb]

On our 50's the pair valve (little chrome cover on left hand side) is designed to pump air into the exhaust to reduce the proportion of unburnt fuel coming out. Sounds silly, but it is to meet California emission laws. Apparently it's quite safe to remove with no adverse affect on the bike or performance. I plan to remove mine and go naked jugs eventually. If this is malfunctioning, it could be leading to an increase in the ratio of unburnt fuel in your pipes.

But I too would start with Spark Plugs.

I changed the plugs - no change.

Remove a faulty pair valve - problem solved.

Thank you.

[munster]

I changed the plugs - no change.

Remove a faulty pair valve - problem solved.

Thank you.

Glad I could help.