mpg serious decrease...whats my problem?

[gsJack]

Low compression, bad coil?

I replaced the coils a while back and it didnt change anything. I swapped the cables back and forth too and it stayed with the left cylinder. It's probably a compression issue but I haven't had it checked, mainly because I am a cheapass and the shop wants 30 bucks to do it.

No need for a gauge to check to see if it's a valve problem.  Finger in the hole test will tell you.  Check cold compression, valve clearance increases as engine warms.  Pull plugs, tie clutch lever to grip to engage switch, crank engine with one hand while firmly covering a spark plug hole with a finger of the other hand.  Finger will be blown away from plug hole with a loud pop as you crank engine if you have compression.  Pop should be about the same for both cylinders..

[redhenracing2]

Finger in the hole test will tell you.

I have NEVER heard of someone doing this, but it sounds just logical enough for me to try it. Thanks pal 

[Dr.Sparkie]

whoa whoa whoa whoa..... remember that the throttle has to be WIDE OPEN before you do this test.

otherwise your finger will be pulled into the plug hole... you might just get a hickey, or it might be a bit more painful.

[sledge]

How to make a cheap go/no-go compression tester.......

Take an old sparkplug
Break the ceramic off leaving a hole all the way through it
Screw into the engine.
Stretch a baloon over the broken end of the plug.
Turn the engine over by hand ..............and see what happens 

[gsJack]

whoa whoa whoa whoa..... remember that the throttle has to be WIDE OPEN before you do this test.

otherwise your finger will be pulled into the plug hole... you might just get a hickey, or it might be a bit more painful.

I've used the finger in the hole compression test on bikes many, many times over the past 25 riding years and still have 10 fingers.  Could be my 77 year old fingers are much tougher than yours.     I can hardly remember what a hickey anywhere is.

As with checking compression with a guage, holding the throttle wide open gives a better reading or louder pop but it works either way.  I tend to crack the throttle some as I grab the right grip to hit the starter button I think but it's no big deal either way.  Try it, you'll like it.   

[Alphamazing]

20k since a valve adjustment? What about a valve check? Either way, get those valves checked!

Also make sure that one of the fuel lines leading from your petcock to your carbs isn't cracked/ripped and leaking fuel ever so slowly. Had that happen to me, and I saw a pretty significant dip in my fuel mileage.

[dadsafrantic]

20k since a valve adjustment? What about a valve check? Either way, get those valves checked!

Also make sure that one of the fuel lines leading from your petcock to your carbs isn't cracked/ripped and leaking fuel ever so slowly. Had that happen to me, and I saw a pretty significant dip in my fuel mileage.

It would be the valve check actually.  I did replace the fuel lines about a year ago when i had the last valve check.  I will look again.