From: Dave on
After a recent bout of twin-bashing on rec.motorcycles, I dragged out my old
XS650 parallel twin last night and took it for a ride. The ride was good, I
enjoyed the sound from those skinny chrome mufflers even if the 650 corners
like a pig compared to the sportbike I usually ride. Could do without the
enormous vibration too, particularly in the footpegs.

When I fired it up, naturally it backfired a bit not having been run since
last year. I had drained the carbs, blah blah blah so no worries. The
backfiring seemed (and that's all it was, seemed) to be coming from the
right pipe only. I put my hands behind the two pipes, and there was WAY WAY
more pressure coming out of the left pipe vs. the right. Intuitively this
seems very wrong. First suspecting rusty headers (couldn't remember just
how loud it was supposed to be) where they sweep up into the mufflers I
checked them carefully... no holes. Both pipes got hot at about the same
rate near as I could tell without an infrared thermometer. The temp of the
exhaust coming out of the pipes "seemed" about the same.

Anybody have any thoughts? Bad spark plug?

BTW the bike ran great, enough power to remind me that I never did get
around to replacing the front sprocket this winter... the engine sounds fine
and seems to run fine once warmed up marginally.

Dave S


From: Albrecht via MotorcycleKB.com on
Dave wrote:
>After a recent bout of twin-bashing on rec.motorcycles, I dragged out my old
>XS650 parallel twin last night and took it for a ride.

Well, how old is it? I can't tell you how to fix it if you don't say what
year it is in the first message.

>Anybody have any thoughts? Bad spark plug?

Could be, or maybe the points need cleaning and adjusting or maybe the carbs
are gummed up.

Remember that we were talking about 180-degree, 360-degree and 270-degree
crankshafts?

Here's a guy that has rephased his crankshaft to 277 degrees for a smoother
engine.

http://www.650motorcycles.com/XS277kit.html

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From: Dave on

"Albrecht via MotorcycleKB.com" <u33665(a)uwe> wrote in message
news:744a0f9032d76(a)uwe...
> Dave wrote:
>>After a recent bout of twin-bashing on rec.motorcycles, I dragged out my
>>old
>>XS650 parallel twin last night and took it for a ride.
>
> Well, how old is it? I can't tell you how to fix it if you don't say what
> year it is in the first message.
>

1980. Sorry.

>>Anybody have any thoughts? Bad spark plug?
>
> Could be, or maybe the points need cleaning and adjusting or maybe the
> carbs
> are gummed up.
>

I'll have a look at the points and check the gap after I stick a new plug
in. Never have replaced the plugs on that bike.

> Remember that we were talking about 180-degree, 360-degree and 270-degree
> crankshafts?
>
> Here's a guy that has rephased his crankshaft to 277 degrees for a
> smoother
> engine.
>
> http://www.650motorcycles.com/XS277kit.html
>
> --
> Message posted via MotorcycleKB.com
> http://www.motorcyclekb.com/Uwe/Forums.aspx/tech/200706/1
>


From: Dave on
"Dave" <dspear99ca(a)yahoo.delete.com> wrote in message
news:6Rdgi.11395$tB5.9153(a)edtnps90...
>
> I'll have a look at the points and check the gap after I stick a new plug
> in. Never have replaced the plugs on that bike.
>
I mean I WOULD have looked at the points if the bike didn't have electronic
ignition. Oops.


From: Albrecht via MotorcycleKB.com on
Dave wrote:



>I'll have a look at the points and check the gap after I stick a new plug
>in. Never have replaced the plugs on that bike.

1980 XS650 has an electronic ignition. If one cylinder gets a spark, the
other cylinder gets a spark, unless there's something wrong with the coil
wire or the spark plug.

http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=646010

#16 pickup coil.

That leaves the carburetor, or maybe a sticky valve as a possible problem.

http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=645995

The idle ports and passages in the carb may be plugged up with gum and
varnish for storing the bike without gas stabilizer in the tank.

The idle mixture screw cannot be seen in this drawing, it is underneath an
EPA anti-tamper plug in the sprue on top of the carb just forward of the
diaphragm cap.

The easiest way to clean out the carbs is to pour 4 or 5 ounces of Berryman
B12 Choke and Carburetor Cleaner into a fuell tank of gas and go for a slow
ride to make the engine suck the B12 through the idle jets.

Be ready to turn down the idle RPM when the engine cleans itself out.

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