Author Topic: 550k sputtering and backfiring - SOLVED  (Read 7590 times)

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Offline tylersilicate

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550k sputtering and backfiring - SOLVED
« on: July 15, 2011, 07:55:48 PM »
Hi all.

I was riding my 1978 550k tonight and was running absolutely great. I rode for about 50 miles and then out of nowhere I started sputtering and backfiring. It felt like no matter how much throttle I gave, it accelerated poorly and eventually stopped accelerating and conking out on me. I was able to keep starting it back up (sometimes I would have to wait a minute) and managed to make it back home.

The plugs are all still in good shape, and I put brand new gas (91 octane) in it before I started the trip.

Anyone have any ideas what could be going on?
« Last Edit: July 19, 2011, 06:04:29 PM by tylersilicate »

Offline DJ_AX

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Re: 550k sputtering and backfiring
« Reply #1 on: July 15, 2011, 08:02:39 PM »
50 miles?

Hmmm.. You'll need to provide more info to get better than just a guess.
But my fist guess would be gas tank vent.
It may also be the 91 octane fuel.
In the Fuel FAQs it says it burns slower and hotter... great if your engine was made for that.
But your engine was not.  :)

More info = state of tune? filters? timing? plugs?, what have you done recently?
Did it ride great before that 50 miles? for how long?
~ Vincent . . . '75 CB750 K5 . . . '97 BMW r1100rt . . . had; '75 CB550 K1 (sold) . . .  '73 CB350G (gifted) HELL YEAH!
Disclaimer: I could be wrong. :)

Offline tylersilicate

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Re: 550k sputtering and backfiring
« Reply #2 on: July 15, 2011, 08:10:27 PM »
I haven't really done any tune-up or service to the bike besides a new oil filter, and oil. I am a total novice when it comes to mechanical anything. It was running great. I started off in the day rode about ~30 miles to a wing place with family and ate. It was night by the time we came back and after about ~20 miles it started all this. It has been rainy here so it was a little chilly out. I bought it about 3 weeks ago and the previous owner said he owned it for about 5000 miles and didn't do anything to it. He said it has never really sat unridden. So I am not really sure where to begin.

Offline dave500

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Re: 550k sputtering and backfiring
« Reply #3 on: July 15, 2011, 08:15:55 PM »
start with the points,look in the faq section.91 wont hurt your bike.

Offline DJ_AX

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Re: 550k sputtering and backfiring
« Reply #4 on: July 15, 2011, 08:40:49 PM »
Cool! Another noob...  ;D I actually mean that in a good way.
Welcome... I'm no guru mechanic here for sure, but I've learned a lot in the last few years.

Are you ready to become mechanical then?  8)

If you don't have it already you should first get a manual. Download the one online here... but it's also really nice to have the Clymer printed manual. Or the Haynes but I like Clymer.
Amongst much other great reading in those you'll find the 3000 mile tune up list.
(You can also find it in past discussions here ... use the search box above  ;D .. lots.)
Generally it's...
Plugs
Filters
Oil
Timing / points
Valves
Carburators

Once you know all of those things have been made proper, then you can diagnose problems, if there are any  :-\ . ... Any of these things individually will make it run better, or not at all. All of these things together can make it run really great!

I myself have come to quite enjoy ALL of the above.
~ Vincent . . . '75 CB750 K5 . . . '97 BMW r1100rt . . . had; '75 CB550 K1 (sold) . . .  '73 CB350G (gifted) HELL YEAH!
Disclaimer: I could be wrong. :)

Offline bender01

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Re: 550k sputtering and backfiring
« Reply #5 on: July 15, 2011, 08:46:49 PM »
Did you seat the plug caps back on well? Run it in the dark to see if there is any electricity jumping around on the plug wires. Did you kick start it? The battery restarted it these times on the way home?
75 550 K1
74 750 K4
1968 450 K1 Super Sport
74 750k 836 project
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So, the strategy is to lie to people you are asking for help?

I think I'll be busy going for a ride.

Good luck!
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Offline Danno

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Re: 550k sputtering and backfiring
« Reply #6 on: July 15, 2011, 11:42:03 PM »
you need to adjust the valve lash it is over due and i would bet you need new condensers just did both those things to my 550 it needs to be done at least once a season but it is supposed to be done every 3000 miles for valve adjustment should dress the points every 1000 miles and you should replace the condensers about as often as you change your fuel filter or every 6000 miles the manual says you should change the oil every 1000 miles i change mine every 2000 but if you rag on it you should change it more frequently because your clutch will start slipping (sheared oil) and it will start shifting hard valve lash on the intake valves .003 inches and .004 inches on the exhaust  this will give you the longest time in between having to set the lash and not too much noise remember to also tighten the timing chain tensioner
when you own a motorcycle the wife does not have to find you handy she just has to find you

Offline Danno

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Re: 550k sputtering and backfiring
« Reply #7 on: July 15, 2011, 11:46:37 PM »
so you know if you do not have a fuel filter yet inline then get one
rust from the tank can also cause the problem you describe
 but the only thing that usually causes a backfire on these bikes is valve lash needing to be set
when you own a motorcycle the wife does not have to find you handy she just has to find you

Offline dave500

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Re: 550k sputtering and backfiring
« Reply #8 on: July 16, 2011, 12:19:58 AM »
the most likely cause of a backfire is retarded ignition,get onto those points,over gapped tappets will rattle,you dont have to use an inline filter,the fuel tap one works fine if its cleaned,if its blocked its doing its job

Offline tylersilicate

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Re: 550k sputtering and backfiring
« Reply #9 on: July 16, 2011, 07:42:15 AM »
Thanks for all the responses guys. I am trying to make sense of all of this! I will start off with the manual, because I have no idea what tappets or points or any of that is.

Offline tylersilicate

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Re: 550k sputtering and backfiring
« Reply #10 on: July 16, 2011, 07:46:50 AM »
Also. Yes the battery was electric starting it everytime last night. I did not kickstart it at all.

Offline tylersilicate

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Re: 550k sputtering and backfiring
« Reply #11 on: July 16, 2011, 08:24:59 AM »
I cleaned the air filter and the air box (probably didn't do anything lol) but I noticed there seems to be a knocking noise coming from under the gas vent. I can't really pinpoint it, I can hear it on both sides.

Offline tylersilicate

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Re: 550k sputtering and backfiring
« Reply #12 on: July 16, 2011, 09:27:03 AM »
I uploaded a video of the sound I am hearing. Hope this helps.


cb550k noise

Offline bender01

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Re: 550k sputtering and backfiring
« Reply #13 on: July 16, 2011, 10:13:42 AM »
Sounds good to me. A little camchain noise. Do the full tune up and see if your power comes back.
75 550 K1
74 750 K4
1968 450 K1 Super Sport
74 750k 836 project
http://www.bikepics.com/members/bender01/
So, the strategy is to lie to people you are asking for help?

I think I'll be busy going for a ride.

Good luck!
Two Tired Quote !

Offline tylersilicate

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Re: 550k sputtering and backfiring
« Reply #14 on: July 16, 2011, 10:25:51 AM »
I am running some sea foam through it. Hopefully that will help. Well that makes me feel better. I thought that was a bad sound.

Offline DJ_AX

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Re: 550k sputtering and backfiring
« Reply #15 on: July 16, 2011, 11:08:21 AM »
Looks like a very nice bike!  :D
Sounds pretty good too.

I think I can hear some clutch rattle too. Which is to be expected as it's common with these engines)
Does it change when you pull in the clutch lever?

I'm sure you'll soon have it running great.

And again ... as the above suggestions show.
It could be any one or combination of things on that 3k tune up list.

With my new poorly running 550.
I hit the list. It's a process of elimination. Debugging if you will.
As I'd go through and do each item on the list, if it didn't make it run better, at least I knew that part was good and done. And then I'd hit on one... two things that were off. Which did make it run better.  :) ... nice

For me it makes riding it even that much more satisfying!
~ Vincent . . . '75 CB750 K5 . . . '97 BMW r1100rt . . . had; '75 CB550 K1 (sold) . . .  '73 CB350G (gifted) HELL YEAH!
Disclaimer: I could be wrong. :)

Offline tylersilicate

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Re: 550k sputtering and backfiring
« Reply #16 on: July 16, 2011, 11:12:03 AM »
Well I left seafoam run through it for about 20 minutes. I tried riding it and it still had the same deal. Conked out on me in the driveway. Then the electric starter wouldn't start it. Neither would the kickstart.


Offline DJ_AX

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Re: 550k sputtering and backfiring
« Reply #17 on: July 16, 2011, 11:20:50 AM »
Did you let it sit and idle for 20 minutes?

These are air cool machines and need to be moving.
~ Vincent . . . '75 CB750 K5 . . . '97 BMW r1100rt . . . had; '75 CB550 K1 (sold) . . .  '73 CB350G (gifted) HELL YEAH!
Disclaimer: I could be wrong. :)

Offline tylersilicate

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Re: 550k sputtering and backfiring
« Reply #18 on: July 16, 2011, 12:57:08 PM »
Yes I did. Should I try to ride it around at low rev for awhile?

Offline TwoTired

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Re: 550k sputtering and backfiring
« Reply #19 on: July 16, 2011, 01:51:58 PM »
Check battery voltage.  At rest, while running, and then when reved up.  Turn off the lights and try again.
Charge battery if necessary.

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

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Re: 550k sputtering and backfiring
« Reply #20 on: July 16, 2011, 03:12:08 PM »
I drained the gas pulled off the tank rinsed it out. I pulled some gunk out of the petcock hose. I put it all back together, it is still running funky. And now the petcock has a slow gas leak.

I just want to yell!

Offline Bankerdanny

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Re: 550k sputtering and backfiring
« Reply #21 on: July 17, 2011, 07:17:29 AM »
Did you check the connection between the condensers and the points.

My bike did something very similar right after I got it. Didn't want to idle, wouldn't go over 45mph, a it backfired spectacularly, shooting fire out the #1 muffler.

The nut that holds the power wire on the 1-4 points had worked loose and was causing intermittent spark. It took 2 days to figure out and 10 minutes to fix.
« Last Edit: July 17, 2011, 07:19:09 AM by Bankerdanny »
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Offline Duanob

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Re: 550k sputtering and backfiring
« Reply #22 on: July 17, 2011, 01:12:10 PM »
I'm going to say that if he got 50 good miles out of the bike and then it sputtered out it's a fuel delivery issue. First thing is to pull your fuel lines form the tap and see if you got good fuel flow. It could be a cap vent issue or a plugged intank fuel filter issue. If all that is clear then move down the line to the carbs/floats.
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Offline tylersilicate

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Re: 550k sputtering and backfiring
« Reply #23 on: July 17, 2011, 03:31:28 PM »
Did you check the connection between the condensers and the points.

My bike did something very similar right after I got it. Didn't want to idle, wouldn't go over 45mph, a it backfired spectacularly, shooting fire out the #1 muffler.

The nut that holds the power wire on the 1-4 points had worked loose and was causing intermittent spark. It took 2 days to figure out and 10 minutes to fix.

I don't really know how to check the points or what they even are. Total beginner here.


I drained the gas from the tank. Ran water through it and saw great flow. I cleaned out the petcock which had a little bit of goop in it.

Didn't fix the issue. So I am moving on the spark plugs. I replaced #1 and #4 but #2 and #3 I can't seem to get them out.

Offline DJ_AX

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Re: 550k sputtering and backfiring
« Reply #24 on: July 17, 2011, 03:36:54 PM »
First thing I mentioned was the gas tank vent.  ;D

Try and take it for a ride and if/when it starts to sputter.. open the gas cap.
If you hear air ssssssss ... (you might not hear it even if it's there)
OR if it starts to run fine again ....
that that's it. You just need to clear the vent.

As gas leaves the tank, the vent allows air in to fill the emptying space. If that vent hole is blocked, the exiting fuel creates a vacuum thus making more difficult for the fuel to leave the tank.

If that doesn't do it .. then go on to check other things.

> Start with the most obvious and easiest things first.  :)

« Last Edit: July 17, 2011, 03:40:01 PM by DJ_AX »
~ Vincent . . . '75 CB750 K5 . . . '97 BMW r1100rt . . . had; '75 CB550 K1 (sold) . . .  '73 CB350G (gifted) HELL YEAH!
Disclaimer: I could be wrong. :)