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From: Bush on 2 Jul 2007 04:24
Hi I picked up a 1983 Yamaha XT200 for my wife to ride. It is in fair
shape with 2300 miles on it. After cleaning up the fuel system I got
it to start and idle, however giving it any throttle causes it to
start backfiring in the exaust. Any ideas about ignition or valve
timing are appreciated.

Bush

From: Albrecht via MotorcycleKB.com on 2 Jul 2007 08:51
Bush wrote:
>Hi I picked up a 1983 Yamaha XT200 for my wife to ride. It is in fair
>shape with 2300 miles on it. After cleaning up the fuel system I got
>it to start and idle, however giving it any throttle causes it to
>start backfiring in the exaust.

Wat kind of backfires, loud bangs or piffle snaps?

Loud bangs might be caused by rich mixture from a sticky float valve and
flooding. Piffle snaps are caused by fuel starvation.

The carburetor is still probably dirty inside. The carb is a slide valve type,
but the drawing doesn't show the typical pilot air screw on the side of the
carb, upstream of the slide valve. So the pilot air screw must be hidden
under an EPA anti-tamper plug that would need to be drilled out for pilot air
screw removal and cleaning.

You might try a chemical cleaning with about three ounces of Berryman B12 in
a full tank of gas.

The ignition system is electronic, you never have to set the timing, just
occasionally change the sparkplug.

There is probably a white sticker under the seat, on the air box or on the
inside of a side cover. This sticker has valve clearances and idle RPM
information.

Any ideas about ignition or valve
>timing are appreciated.

--
Message posted via MotorcycleKB.com
http://www.motorcyclekb.com/Uwe/Forums.aspx/tech/200707/1

From: Bush on 3 Jul 2007 21:25
I removed the carb again and blew out/ran a wire through evertyhing
accessible. I couldn't remove the low speed idle mixture screw
completely due to a small 'ding' in the housing however. Much better
for a couple of minutes, then became starved again and the subsequent
popping. I'll try the B12 and hopefully get it cleared out but getting
to the pilot air screw may be key here. Thanks again,

David

On Mon, 02 Jul 2007 12:51:33 GMT, "Albrecht via MotorcycleKB.com"
<u33665(a)uwe> wrote:

>Bush wrote:
>>Hi I picked up a 1983 Yamaha XT200 for my wife to ride. It is in fair
>>shape with 2300 miles on it. After cleaning up the fuel system I got
>>it to start and idle, however giving it any throttle causes it to
>>start backfiring in the exaust.
>
>Wat kind of backfires, loud bangs or piffle snaps?
>
>Loud bangs might be caused by rich mixture from a sticky float valve and
>flooding. Piffle snaps are caused by fuel starvation.
>
>The carburetor is still probably dirty inside. The carb is a slide valve type,
>but the drawing doesn't show the typical pilot air screw on the side of the
>carb, upstream of the slide valve. So the pilot air screw must be hidden
>under an EPA anti-tamper plug that would need to be drilled out for pilot air
>screw removal and cleaning.
>
>You might try a chemical cleaning with about three ounces of Berryman B12 in
>a full tank of gas.
>
>The ignition system is electronic, you never have to set the timing, just
>occasionally change the sparkplug.
>
>There is probably a white sticker under the seat, on the air box or on the
>inside of a side cover. This sticker has valve clearances and idle RPM
>information.
>
> Any ideas about ignition or valve
>>timing are appreciated.

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