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Re: Vespa Si Problems  Peter Staal
 Oct 11, 2001 17:17 PDT 
Hi ,
Since i'm not aware of the type of ignition of your moped, it could not be
the right diagnose. but generally spoken it sounds like a ignition problem.
Lets say the timing is wrong. And it fires too late.   what gives the
symptoms you are experiencing, lack of power and backfiring at high rev's.
could be caused by:
- wrong brakerpoint gap,
- wrong timing from the groundplate in relation to the shaft,
- wrong type of magneto (and / or mal adjusted)
- loose magneto
-damaged condenser, causing fast wear of braker points and even metal scrap
in the ignition room
-damaged/ wrong type sparkplug (changed this already? check needed type and
replace at first)
other poss.
exhaust sludged up, could give same symptoms (used the right mix gas/oil or
right oil at all?)
used oil at all? this could wear a engine in 1000 miles easy.
the only problem that i have is the low milage of your moped.
how do you use it, long rides? lots of short city driving? throttle full
open of always half open?
What is your weight (oops).
what is the gas consumption of the bike?
did you respect the 'brake-in' period since it was very new when you bought
did some one / some thing damage the exhaust port opening? (making it to
put on a high pressure cylinder head?
if the sparkplug cap is arching this will result in missfiring hardly ever
producing a backfire. more missing fire ;).
you can rule out that one ;).
more questions then answers i realize..
----- Original Message -----
From: "Curtis" <cdu-@autodocsys.com>
Sent: Thursday, October 11, 2001 7:10 PM
Subject: Vespa Si Problems
 I have a 1980 Vespa Si moped. It had 82 miles on it when I bought it in
July, and ran great. Around 800 miles there started to be some
backfiring at
high speed. Also top speed was slower (flat ground went from 29mph to
around the same time. The problem continued and at around 1100 miles I
going down hill when there was a BIG backfire which screwed everything
up to
the point where you could not accelerate at all. I took it to a local
engine shop, and they got it running again. There still seems to be some
small backfiring at high speeds and top speed is still not up to what it
used to be. The shop said I might try to replace the spark plug cap,
it may be arching, causing the problems I'm having. What are some of
opinions on how to fix this problem?
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