I started up my 1980 XS650G last night after fitting new mufflers (long long
overdue). By the time I finished it was pretty dark in my garage, so I
couldn't help but notice that the left cylinder was backfiring... I could
see the blue flame inside the left muffler. My old rusty pipes were so
friggin' loud that the backfire may have been present last year, I'm just
not sure. What might cause this? I swapped the plugs between L & R
cylinders, but the backfire stayed on the left (damn!). The bike seems to
rev up okay, could it possibly just be an adjustment of my air mixture
screw? I'll throw a tachometer on the left plug lead tonight just to make
sure I'm getting spark.

Dave

On Jun 9, 11:09�am, "Dave" <dspear9...@yahoo.com> wrote:
> �The bike seems to
> rev up okay, could it possibly just be an adjustment of my air mixture
> screw? �

Maybe your carbs are getting a little plugged up inside. You might try
adding a few ounces of Berryman B12 Choke and Carburetor Cleaner to a
full tank of gas and going for a slow ride to clean out the idle
circuits.

There are two kinds of backfires related to dirty carbs. One is the
loud *bang!* associated with high fuel levels caused by dirty float
valves.

The other kind of backfire is a wimpy *piffle-piffle-snap!* on
deceleration, That's caused by dirty idle jets and passages.

"¿" <(E-Mail Removed)> wrote in message
news:d8519415-1757-47bf-b2ca-(E-Mail Removed)...
On Jun 9, 11:09�am, "Dave" <dspear9...@yahoo.com> wrote:
>> �The bike seems to
>> rev up okay, could it possibly just be an adjustment of my air mixture
>> screw? �

>Maybe your carbs are getting a little plugged up inside. You might try
>adding a few ounces of Berryman B12 Choke and Carburetor Cleaner to a
>full tank of gas and going for a slow ride to clean out the idle
>circuits.
>
>There are two kinds of backfires related to dirty carbs. One is the
>loud *bang!* associated with high fuel levels caused by dirty float
>valves.
>
>The other kind of backfire is a wimpy *piffle-piffle-snap!* on
>deceleration, That's caused by dirty idle jets and passages.

I'll try carb cleaner, I've got a bottle someplace, I recall I ran some
through last year or the year before. The other cylinder runs fine. I
think I'm going to end up pulling these carbs apart anyways at some point.
I would think that a plugged air jet might cause backfiring at idle, but I
really haven't worked on carbs enough to know...

On Jun 9, 11:56�am, "Dave" <dspear9...@yahoo.com> wrote:

> I would think that a plugged air jet might cause backfiring at idle, but I
> really haven't worked on carbs enough to know...

If you're fairly sure that the air jet has gotten plugged up, a shot
of aerosol carb cleaner would easily clean it out.

I buy both types, B12 in aerosol form and B12 in the handy liquid form
for adding to the gas tank.

Many Japanese ignition systems will fire both spark plugs at the same
time, using one sensor or one set of points to trigger the ignition.

When you have a waste spark firing, you'll hear rumbles in the exhaust
pipe on deceleration and you'll also get backfires when the carbs are
dirty because unburned mixture will build up in the exhaust pipe over
two or three exhaust strokes.

¿ <(E-Mail Removed)> wrote:

> Many Japanese ignition systems will fire both spark plugs at the same
> time, using one sensor or one set of points to trigger the ignition.

But the XS650 *doesn't*.


--
BMW K1100LT Ducati 750SS Honda CB400F & XBR500 Triumph Street Triple
Suzuki TS250ER
If you don't know what you're doing, don't do it. And RTFM.
chateau dot murray at idnet dot com

Dave <(E-Mail Removed)> wrote:

> What might cause this?

Incorrect mixture. Incorrect timing (I am not sure if the 1980 model XS
had points or electronic ignition, and I cba to check right now).


--
BMW K1100LT Ducati 750SS Honda CB400F & XBR500 Triumph Street Triple
Suzuki TS250ER
If you don't know what you're doing, don't do it. And RTFM.
chateau dot murray at idnet dot com

On Jun 9, 2:40�pm, totallydeadmail...@yahoo.co.uk (The Unflushable
Turd) wrote:
> � <macmi...@gmail.com> wrote:
> > Many Japanese ignition systems will fire both spark plugs at the same
> > time, using one sensor or one set of points to trigger the ignition.
>
> But the XS650 *doesn't*.

Well, take the time to *look it up*, you silly ****.

BTW, I'm a cracker. Eat me.

¿ <(E-Mail Removed)> wrote:

> > But the XS650 *doesn't*.
>
> Well, take the time to *look it up*, you silly ****.

Don't need to. I've rebuilt two.

But carry on posting erroneous information if you want to.


--
BMW K1100LT Ducati 750SS Honda CB400F & XBR500 Triumph Street Triple
Suzuki TS250ER
If you don't know what you're doing, don't do it. And RTFM.
chateau dot murray at idnet dot com

"The Older Gentleman" <(E-Mail Removed)> wrote in message
news:1j12esf.46eyv416hc4ydN%totallydeadmailbox@yah oo.co.uk...
> Dave <(E-Mail Removed)> wrote:
>
>> What might cause this?
>
> Incorrect mixture. Incorrect timing (I am not sure if the 1980 model XS
> had points or electronic ignition, and I cba to check right now).

The XS650G (1980) has electronic ignition, timing cannot be adjusted.

As for incorrect mixture, I'll try re-setting the air mixture screw on the
problem side for best idle although last time I used the "dead cylinder"
method I had quite a time just keeping the bike from stalling. I added some
carb cleaner and went for a spin last night, the bike runs just fine at
higher than idle rpm's.

Thanks.

Dave

On Jun 10, 9:38�am, "Dave" <dspear9...@yahoo.com> wrote:
> "The Turd That Won't Flush" <totallydeadmail...@yahoo.co.uk> wrote in messagenews:1j12esf.46eyv416hc4ydN%totallydeadmail (E-Mail Removed)...

> > Incorrect mixture. Incorrect timing (I am not sure if the 1980 model XS
> > had points or electronic ignition, and I cba to check right now).
>
> The XS650G (1980) has electronic ignition, timing cannot be adjusted.

Yes, and it only has *one* timing sensor and a 360 degree crankshaft,
so
both coils have to fire at the same time. One of the sparks is wasted
because the exhaust valve on that cylinder is open.

If there is a buildup of unburned mixture in the exhaust pipe on that
side, you'll hear a bang! out of that cylinder when the plug fires.

I advise you not to waste a lot of time debating with "The Turd That
Won't Flush". He loves to debate and argue instead of helping riders
find solutions to their problems.

Before you know it, he'll have you apologizing to him and thanking him
for giving you a ration of ****.

> As for incorrect mixture, I'll try re-setting the air mixture screw on the
> problem side for best idle although last time I used the "dead cylinder"
> method I had quite a time just keeping the bike from stalling. �Iadded some
> carb cleaner and went for a spin last night, the bike runs just fine at
> higher than idle rpm's.

OK, just remember that you can adjust the idle mixture screw all day
and it won't change a thing if the idle jets and air jets and passages
are plugged up with gum and varnish from evaporated gasoline.