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From: curry@nsc.UUCP (Ray Curry)
Newsgroups: net.cycle
Subject: Re: bike "debugging"
Message-ID: <3742@nsc.UUCP>
Date: Tue, 19-Aug-86 16:11:06 EDT
Article-I.D.: nsc.3742
Posted: Tue Aug 19 16:11:06 1986
Date-Received: Thu, 21-Aug-86 06:49:37 EDT
References: <468@ucdavis.UUCP>
Reply-To: curry@nsc.UUCP (Ray Curry)
Distribution: net
Organization: National Semiconductor, Sunnyvale
Lines: 40
Keywords: Keep an open mind.

First bit of advice is to not try to lean toward carb or electrical yet.  When
debugging a bike, a general approach is that it can usually be anything.
From the sounds of the symptoms, it could be electrical or carb.  To eliminate
engine mechanicals, run a compression check first.  Piston/valve problems will
show up quickly then.  Assuming compression is okay, odds with Japanese bikes
favor electrical with older bikes, carbs with newer.  

I follow a ritual. First, examine the spark.  Put the wire on a loose plug,
hold it to the side of the engine and crank it over.  Used plugs are best for
this test.  The spark should be sharp and firm.  Multis are nice because they
will run and you can see if the spark falls off at speed.  Spark problems can
be caused by bad spark wires or worn/cracked/dirty caps.  The caps usually have
carbon resistors in them and go bad in a few years.  Other electrical problems
to check are the voltage regulator and the diode bridge.  The voltage regulator
especially will fail by causing lower battery voltage for a while, then none.
Check the regulator by unplugging it.  Measure the voltage at the battery while
running at idle and then at slowly increasing engine speed.  14.5V should be
min. increasing with speed.  Dont run the engine too fast without the regulator
though.  15.5 should be max.  Repeat with the regulator in.  14.5 min and 15.0 
is a good min/max.  This will point out problems with the alternator as well.
Since there are generally two sets of coils in an alternator, one for lights
and one for ignition, problems can crop up in one and affect the other.  Dirt
bikes ran the two seperately and a bad light would still affect the ignition.
If the charging voltage is high enough, and the battery won't stay charged,
the battery is probably bad.  They fail because of intermittant use.  My
street bike keeps a battery 3 to 4 years since I ride every day.  A bike 
that sits for a week at a time will kill a battery in as little as a year
depending upon the temperature extremes it sees.  One of the new nitrogen filled
long life batteries might be better for that case.
With the carbs, there are a few things to check.  The carb could have some 
internal passages blocked.  The main and idle jets can be removed and checked
for particles.  The needle and seat for the float should be checked as well
as float level.  The air screw and be removed and the slide taken out, and 
air should be blown into the idle hole in the venturi.  One last thing to check
is the sediment trap if there is one at the base of the fuel valve. If its
a vacuum operated valve, check the hose for leaks.
Modern gas has a tendency to grow crystals and flakes.  If the valve doesn't
have a sediment trap, you should add a filter. 
My last bit of advice is that bad parts can look good and vice versa. Shops
also don't take electrical stuff back.