On Mon, 31 Jul 1995 RLANCASTER@ntia.doc.gov wrote:
> Very informative guidance, John. I don't understand the part about
> "plug cuts" though, what is that and how does it relate to the SU
> tuning? thanks,
"Plug cuts" means you run the car in the mode you want to optimize
(highway, strong accelleration, or whatever) then right after you do that
you cut the engine off. Coast to a safe place and pop the hood. Check
the color of the plugs. One per carburetor is fine, although you might
want to switch off which test plugs you use (pulling the spark plugs will
wear out the external portion over time).
1) White deposits: Carb is set too lean
2) Black deposits: Carb is too rich
3) Brown or Grey deposits: Stop here, you are "close enough".
4) Oily Black: Valve seals/guides are shot. You won't be able to tell
from the color what the mixture is (and the oil being combusted will alter
the mixture and screw up the Colourtune as well). The car will run
better and burn less oil if you hustle the head down to your local
machine shop.
5) Just wet: Spark not firing on that cylinder
6) Dry with no deposits: Um... >really< complete combustion (riight!) or
you really aren't drawing air through that carb, or your intake valve
isn't opening. I had this symptom with my rear carb until I rebalanced
them... the fact that hardly any air was flowing also made setting the
mixture by the lift pin test >really< tough, and it didn't have any
effect on performance.
John M. Trindle | jtrindle@tsquare.com | Tidewater Sports Car Club
'73 MGB DSP | '69 Spitfire E Stock | '88 RX-7 C Stock
Home Page: http://www.widomaker.com/~trindle
"It sometimes seems as though we were trying to combine the ideal of no
schools at all with the democratic ideal of schools for everybody by
having schools without education. -- Robert Maynard Hutchins"
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