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Offline rocco

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Popping and backfiring out of no where
« on: July 18, 2017, 07:35:07 PM »
I took the bike out today, drove for a couple hours, all was great, no issues.
I parked it to have a beer for a half hour, got back on, it started fine.

All of a sudden, I had almost total power loss, the bike was making popping noises and the occasional backfire.
At first the cutting out felt like it was running out of gas. I fueled up, no changes, it would occasionally pick up with full power, and then just cut out again until I had to park it.

I completely cleaned the carbs last summer. I realize it could be a number of issues from dirty carbs to timing and etc.
Just curious if there was a place to start because the bike was running completely fine beforehand.
It almost feels like it's a timing issue, like it's not firing properly but I don't know enough to be sure.
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Offline TwoTired

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Re: Popping and backfiring out of no where
« Reply #1 on: July 18, 2017, 07:55:25 PM »
Check the spark plugs.
If the spark plug center electrode insulator is coated with carbon deposits, that will shunt the spark energy away from the gap.
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Lloyd... (SOHC4 #11 Original Mail List)
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Offline PeWe

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Popping and backfiring out of no where
« Reply #2 on: July 18, 2017, 09:39:03 PM »
If you have dyna coils, check if an ign wire is loose.
All other wires/connections from points to coils.
« Last Edit: July 19, 2017, 09:05:43 AM by PeWe »
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Offline Don R

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Re: Popping and backfiring out of no where
« Reply #3 on: July 19, 2017, 01:10:07 PM »
 Loose points is my official guess.
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Offline Keith

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Re: Popping and backfiring out of no where
« Reply #4 on: July 19, 2017, 02:04:01 PM »
First things first, I say!  Check Dwell, both sets of points, if you have stock ignition. If off, reset and  then set timing. Don't even think carburation until all basics are set.
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Offline Bailgang

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Re: Popping and backfiring out of no where
« Reply #5 on: July 19, 2017, 02:35:41 PM »
Maybe a condenser going bad or is coming loose giving it a bad ground?
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Offline Bankerdanny

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Re: Popping and backfiring out of no where
« Reply #6 on: July 19, 2017, 02:41:50 PM »
Quote from: Keith on July 19, 2017, 02:04:01 PM
First things first, I say!  Check Dwell, both sets of points, if you have stock ignition. If off, reset and  then set timing. Don't even think carburation until all basics are set.

Honestly the first thing is juts to make sure that all your connections are tight. I experienced similar symptoms with my 550 k years ago and it was a loose connection at the points. It took me 2 days to track down and 2 minutes to fix.
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Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline flybox1

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Re: Popping and backfiring out of no where
« Reply #7 on: July 19, 2017, 02:46:21 PM »
Quote from: Bankerdanny on July 19, 2017, 02:41:50 PM
Quote from: Keith on July 19, 2017, 02:04:01 PM
First things first, I say!  Check Dwell, both sets of points, if you have stock ignition. If off, reset and  then set timing. Don't even think carburation until all basics are set.

Honestly the first thing is juts to make sure that all your connections are tight. I experienced similar symptoms with my 550 k years ago and it was a loose connection at the points. It took me 2 days to track down and 2 minutes to fix.
+1
Caps n ign wires.  Harness.  Block connectors.  Fuses...then pull the points cover and dig in.
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Offline seanbarney41

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Re: Popping and backfiring out of no where
« Reply #8 on: July 19, 2017, 07:50:09 PM »
condenser/s
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Offline Bankerdanny

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Re: Popping and backfiring out of no where
« Reply #9 on: July 20, 2017, 04:33:23 AM »
Quote from: seanbarney41 on July 19, 2017, 07:50:09 PM
condenser/s

Yep, that's where my problem was. Loose connection between the 2-3 condenser and the points.
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Offline greenjeans

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Re: Popping and backfiring out of no where
« Reply #10 on: July 20, 2017, 09:39:48 AM »
Don't forget the simplest options.   Double check your petcock and float bowls
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Offline rocco

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Re: Popping and backfiring out of no where
« Reply #11 on: July 20, 2017, 11:40:28 AM »
Thanks so much everyone, I've got today off so I'm into diagnostics.
The whole bike is stock set up. Condensers did come to mind because I swapped out the old ones for some new ones during the rebuild I remembered hearing people say the newer ones could go bad after 500 miles or less. I have the ones that came with the bike so I can put those back on and see if it changes anything.

I'll check the pet cock and fuses right now. I was having trouble with my main for a while.

I pulled the spark plugs and this is what I see, looks like definitely fouling on cylinder #1 and #2. Maybe all of them? Should lean out my mixture a bit? Is it possible they only fouled up after the problem started?
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Offline TwoTired

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Re: Popping and backfiring out of no where
« Reply #12 on: July 20, 2017, 03:15:29 PM »
Third from the left has deposits that interfere with spark.  Replace or clean and reinstall.  If it runs well, you found the immediate problem, but not the source cause, which is likely an over rich condition.
However, I would begin with a routine 3k mile tuneup checklist, and check carb sync.  How old is the air filter?  Then if it still fouls the plugs after a routine service, move on to carbs.

Cheers,
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Lloyd... (SOHC4 #11 Original Mail List)
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Offline rocco

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Re: Popping and backfiring out of no where
« Reply #13 on: July 20, 2017, 03:21:43 PM »
Okay, ya, I swapped out all the spark plugs and changed back to the old condensers. Bike started up fine, took it for a 15 minute ride, no issues.
I did notice while warming up, the second cylinder was missing every once and a while. Which is the same cylinder with the fouled spark plug.
Air filter is brand new, only about 300-400 miles.
I can't really check carb sync on my own eh?
I'll do the 3k mile tune up tomorrow
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1978 Honda CB550K.

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Offline TwoTired

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Re: Popping and backfiring out of no where
« Reply #14 on: July 20, 2017, 03:33:21 PM »
You can check carb sync on your own if you have a 4 manometer test set.
Pretty much every bike needs proper tools for maintenance.
The kids working in shops today are likely much younger than these bikes.  Do you really want them to use your bike as a training tool?

Really is best to do as much work on your own bike as you can, Imo.

Cheers,
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline Bankerdanny

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Re: Popping and backfiring out of no where
« Reply #15 on: July 20, 2017, 03:55:49 PM »
A Vacuum gauge set is a worthwhile investment and not a huge expense. You can pick up a set on eBay that will work adequately for about $60
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"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline seanbarney41

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Re: Popping and backfiring out of no where
« Reply #16 on: July 20, 2017, 04:16:28 PM »
yup, now you know not to buy those Daaichi condensers anymore
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Offline BomberMann650

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Re: Popping and backfiring out of no where
« Reply #17 on: July 20, 2017, 04:30:15 PM »
Quote from: seanbarney41 on July 20, 2017, 04:16:28 PM
yup, now you know not to buy those Daaichi condensers anymore


Where are the lotr condenser memes we made that one time?
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Offline rocco

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Re: Popping and backfiring out of no where
« Reply #18 on: July 21, 2017, 07:29:42 AM »
Quote from: TwoTired on July 20, 2017, 03:33:21 PM
You can check carb sync on your own if you have a 4 manometer test set.
Pretty much every bike needs proper tools for maintenance.
The kids working in shops today are likely much younger than these bikes.  Do you really want them to use your bike as a training tool?

Really is best to do as much work on your own bike as you can, Imo.

Cheers,

I guess I'll be investing in one, I haven't let a single shop touch my bike throughout the rebuild except for a cylinder hone haha. I had a member on this site help me with syncing the carbs last summer, but he did mention that should be done again this summer.
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1978 Honda CB550K.

"It is vain to do more with what can be done with less" - William of Occam (Occam's Razor)
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