Backfiring and rich

[Mikel8432]

Hi Guys, first time post on here. I have an XS650A and after riding it regularly, one day I pulled up at some shops, and when I came out to ride the short distance home, the bike started backfiring loudly and misfiring.

Since I hadn't had the bike all that long and have been a long time away from mechanical work on bikes (45years!!!) I took it to a shop.
They had it for a couple of days, got it running again and charged me $700+ labor but couldn't tell me what the problem was and replaced no parts. Just wondering whether it was pure luck it ran well again?

Fast forward a year after plenty of trouble free short rides, it did exactly the same thing......backfiring loudly and misfiring. This time I noticed black smoke out of the exhausts while it was popping and banging. I didn't notice whether it was out of both pipes or not.

I pulled the plugs and they were both black with soft sooty deposits. Cleaned them off with a wire brush but that made no difference.
Logically it would seem it's on the ignition side since it's obviously getting fuel if I'm seeing black exhaust smoke and carbon deposits on the plugs.

Any suggestions where I might start to look for the problem?

Thank you in advance,
Mike

 

[Raymond]

Hi Mike, welcome to the forum. Backfiring sounds to me like ignition. First thing I would check is the spark timing. Or the ignition not providing a reliable spark - can be checked with an in-line spark tester.



But fear not, plenty people who know a lot more than me will be along with more suggestions. You will be able to get 'er fixed.

Without resort to a shop - I'm not too impressed that they charged you an arm and a leg and can't or won't tell you what the problem was.

 

[JJames]

Welcome. With black, sooty plugs and black smoke it's possible that small pieces of junk/debris from the tank and/or lines are occasionally lodging in the carburetors needle and seat assembly, preventing it from sealing properly. Basically flooding the carbs and engine with fuel and leading to symptoms you describe. The shop may have "fixed" it with a couple of raps on the float bowl with a wrench, small hammer or screwdriver handle. Good luck.

 

[Melnic]

If you say cleaning plugs "made no difference" keep in mind that idling the bike will not tell you what you need to know because very often, the idle mixture can be set much richer than when your running the bike on the street.
Not sure of your year bike and if it has a bowl drain but checking the float height wet w/ a tube can be beneficial in troubleshooting.
My XJ650 has drains that make it really easy to spot check (even on the road) but my 78 XS650 I had to get these to check in the garage. (forum member recommended them)
https://www.ebay.com/itm/274881260720

 

[hovel]

As noted, an overly rich mixture is the cause of the poor running. It would be like running (or trying to) on full choke. The black smoke is the giveaway, I think you've got an intermittent fuel flow problem.
Wire brushing a plug rarely does much good. For a seriously fouled plug you must clean out all the crap at the base of the porcelain and around the porcelain and then blow out that recess with your favorite brake cleaner/contact cleaner/whatever and some compressed air. Dress the electrodes with a small file.

 

[Mikel8432]

Thank you for the prompt replies gentlemen.

Regarding cleaning the plugs....bear in mind that the motor only ran in this conditions for a couple of minutes each time (it was basically unrideable with the misfire), so when I pulled the plugs, the sooty deposits were soft and could be wiped away with my finger. I wire brushed them then sprayed with brake cleaner. Plugs are quite new so no carbon or any other deposits on them.

Yes, I agree an overly rich mixture is the likely problem (like running with the choke on as mentioned in one reply), but a bit much of a coincidence if both needle and seats became blocked at precisely the same time (plugs from both cylinders looked exactly the same with the soft black "temporary" deposits)

I plan to drop both float bowls and give all jets, needle and seat, etc., a thorough clean.

Here's the thing though.........the bike had been sitting for a couple of months untouched since this issue arose (I'd been travelling), so just for the hell of it I tried to start it yesterday.

Would you believe it started and ran pretty much normally.

I've yet to ride it, this was just a start up in my garage, but I'll give it a run in the next few days, but still clean the carbs and report back later.

Thanks again for all your suggestions. I owned a Gold XS2 as a young bloke but had been away from bikes for 45 years until my retirement three years ago. Always swore if I bought another bike, it would be something from my era, and the Yamaha was always a favorite. Not regretting it one little bit. This bike is very low mileage....and feels it. Still a nice "tight" feel and lovely to ride. My other bike is a Hayabusa and I enjoy both equally.

Thanks again guys,
Mike

 

[bosco659]

Thank you for the prompt replies gentlemen.

Regarding cleaning the plugs....bear in mind that the motor only ran in this conditions for a couple of minutes each time (it was basically unrideable with the misfire), so when I pulled the plugs, the sooty deposits were soft and could be wiped away with my finger. I wire brushed them then sprayed with brake cleaner. Plugs are quite new so no carbon or any other deposits on them.

Yes, I agree an overly rich mixture is the likely problem (like running with the choke on as mentioned in one reply), but a bit much of a coincidence if both needle and seats became blocked at precisely the same time (plugs from both cylinders looked exactly the same with the soft black "temporary" deposits)

I plan to drop both float bowls and give all jets, needle and seat, etc., a thorough clean.

Here's the thing though.........the bike had been sitting for a couple of months untouched since this issue arose (I'd been travelling), so just for the hell of it I tried to start it yesterday.

Would you believe it started and ran pretty much normally.

I've yet to ride it, this was just a start up in my garage, but I'll give it a run in the next few days, but still clean the carbs and report back later.

Thanks again for all your suggestions. I owned a Gold XS2 as a young bloke but had been away from bikes for 45 years until my retirement three years ago. Always swore if I bought another bike, it would be something from my era, and the Yamaha was always a favorite. Not regretting it one little bit. This bike is very low mileage....and feels it. Still a nice "tight" feel and lovely to ride. My other bike is a Hayabusa and I enjoy both equally.

Thanks again guys,
Mike

If you turned the petcock(s) off when you parked it last, the excess fuel that might have gotten by the needle valves probably evaporated. Then when you started it again, the flooded condition wouldn’t be immediately apparent. Just a theory and your next ride should tell you more.