Topic: Back Firing, Popping, and Cutting Out

[campbmic]

So, I've put about 3,700 miles on my newly rebuilt engine. Rode it to Mexico and back. Last night me and a friend are out listening to Jazz and at about 2AM he tells me that he wants to take a ride down to Austin. I say sure and were off to Austin. During the 200 mile long trip there and back I noticed a few things about my bike that I would like to sort out.

My bike is a 1975 CB550 with EMGO pods, a 4-1 exhaust, and I think 105 mains?

#1 Issue - Bogging Down/Cutting Out
I first noticed this when I was in Mexico. Every once in a while my bike will kind of lose power like its bogging down to die. It tends to happen after I've been riding for about 50 miles straight without stopping. The bike's power seems to cut out and it makes kind of like a farting noise. 2-3 seconds later its fine and is pulling hard. This might happen as often as 5 times in a minute or as often as once in an hour. Was wondering if you guys had any ideas what could be causing it? It seems to me like one of my coils is possibly failing?

#2 Issue - Backfiring out the exhaust
On these long hauls I tend to move my choke around a lot. Since I have pods and did all of the carb work myself I have a fear of overheating my bike by running it too lean. Especially on these long trips down Texas highways. Most of the time I cruise at around 70-75 MPH and when I exit I roll off the throttle and the bike seems to backfire/crackle out of the exhaust. Whats is this a sign of?

#3 Issue- Popping from the pods
I also seem to be getting some pops coming from the intake side of the carbs where the pods are. What would cause this?

Thanks guys!
-Michael

[Stev-o]

I'm staying tuned as my 550 does #2 also [I think it is a carb issue]

[scottly]

On these long hauls I tend to move my choke around a lot. Since I have pods and did all of the carb work myself I have a fear of overheating my bike by running it too lean.
-Michael

Playing with the choke may be the main culprit for all 3 issues!

[cobra2411]

I just put Pods on my 750 and I went from 105's to 107.5's because that's all I had with me and it was popping under acceleration. I wanted to get a set of 110's but they only had 112.5's so that's what I went with and it's been fine. Not sure what stock jets are in a 550, 100's? maybe? Sounds like you might be a touch lean. I would do +2 sizes for the pods and +2 for the exhaust as a start.

The popping from the exhaust with the throttle closed; #2, sounds normal for a performance exhaust. The mixture goes rich because of the high vacuum and closed throttle and at the same time the exhaust is pulling air back up the pipes. Once the extra fuel and air mix in the hot pipes: Bang! It's odd to think of air getting sucked up the exhaust but in between the normal pulses, because of the high vacuum in the cylinders, little bits of air get pulled in. Open pipes do it best followed by straight though mufflers. Anything that's got to pass through baffles can't really pull enough air for the mixture to light off. So no gurgle with stock mufflers.

So as long as you can rule out any performance or running issues, it's not a problem if your bike gurgles or pops on decel with the throttle closed if you've got open pipes. That's just what they do.

[domer]

backfire out the carbs = lean
backfire out the exhaust = rich
the backfire (exhaust) on my 500 disappeared when i adjusted the a/f (after a carb sync)
Have you tried a plug chop?

[cobra2411]

Yeah mine was popping out the carbs with the 107's. The "normal" exhaust popping that I'm talking about is very different from backfiring. The best way I can describe it is a gurgling sound with some low pops while decelerating with the throttle closed. If you're popping from the exhaust under acceleration then you're likely rich. 

[TwoTired]

My bike is a 1975 CB550 with EMGO pods, a 4-1 exhaust, and I think 105 mains?

#1 Issue - Bogging Down/Cutting Out
I first noticed this when I was in Mexico. Every once in a while my bike will kind of lose power like its bogging down to die. It tends to happen after I've been riding for about 50 miles straight without stopping. The bike's power seems to cut out and it makes kind of like a farting noise. 2-3 seconds later its fine and is pulling hard. This might happen as often as 5 times in a minute or as often as once in an hour. Was wondering if you guys had any ideas what could be causing it? It seems to me like one of my coils is possibly failing?

Given your frequent choke operation while the bike is fully warmed, I'd say you have spark plug fouling issues, where they "sometimes" clear themselves.  Eventually, they won't.  Better carry some extra spark plugs in your unused filter box.

#2 Issue - Backfiring out the exhaust
On these long hauls I tend to move my choke around a lot. Since I have pods and did all of the carb work myself I have a fear of overheating my bike by running it too lean. Especially on these long trips down Texas highways. Most of the time I cruise at around 70-75 MPH and when I exit I roll off the throttle and the bike seems to backfire/crackle out of the exhaust. Whats is this a sign of?

What kind of deposits inside you exhaust?  If black sooty, too rich operation.  If none, too lean.  Light tan was always the best to find n the exhaust pipe.  It can take a long while to build up tan exhaust deposits.  (Doesn't apply to catalytic converter systems).
Backfire out the exhaust on decell is usually too lean.

#3 Issue- Popping from the pods
I also seem to be getting some pops coming from the intake side of the carbs where the pods are. What would cause this?

Take your pick:
Ignition riming.
Leaking intake valves.
Carbs out of sync.
Lean mixture.

Your bike's symptoms are common with induction changes and improper adjustment of the carbs to properly match those changes afterwards.

Trying to compensate with choke, is absolutely the wrong way to make an adaptation, imo.