Lotus Elan

Checking Spark Plug Colour?

PostPost by: William2 » Sat Jun 24, 2017 11:24 am

What is the best way of checking mixture using plug colour as a guide? After a run to warm the engine up to normal temp for instance, if you left the engine idling for a short period would you expect the plug colour to be the correct brownish colour to show that the idle mixture is correct? The reason for asking is that I have used a Color Tune to get the correct Bunsen blue colour at idle but as far as I can tell the car is only doing about 22mpg when driven carefully below 3000rpm i.e. before the main jet circuit kicks in. I get the impression that there are mixed opinions as to the accuracy of the Color Tune method.
William2
Fourth Gear
Fourth Gear
 
Posts: 943
Joined: 20 Jan 2013
Location: West Sussex

PostPost by: billwill » Sat Jun 24, 2017 12:01 pm

As far as I am aware the colourtune should be used to set the colour to blue with flecks of yellow.

?

MPG is probably always low at idling speeds.
Bill Williams

36/6725 S3 Coupe OGU108E Yellow over Black.
billwill
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 4721
Joined: 19 Apr 2008
Location: London UK

PostPost by: Craven » Sat Jun 24, 2017 1:43 pm

Idle mixture adjustment is just that, low speed running mixture is set by the slow running jets via the progression holes.
Ron.
Craven
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1091
Joined: 14 Sep 2013
Location: south coast uk

PostPost by: RichC » Sat Jun 24, 2017 4:04 pm

so much more to mpg than just spark plug colour. how's your timing?
if spot on i'd go for weakening mixture until you get dropp off of rpm and then crank it open again 1/4 turn... this is only if your carbs are in reasonable condition and already have equal airflow balance
User avatar
RichC
Fourth Gear
Fourth Gear
 
Posts: 855
Joined: 28 Apr 2009
Location: Tendring Essex

PostPost by: RogerFrench » Sat Jun 24, 2017 5:25 pm

If you really want to check using plug colour, then get out on the open road, run at full throttle for a minute or so, then switch off and dip the clutch. Brake to a halt, remove the plugs and look at them, or put in different plugs and go home to look at them.
Way back when, it was known as taking a "plug cut". Tells you about mixture, and also if your plugs are the right heat range.
1967 Elan S3
1972 Europa Twin Cam
2005 Elise
User avatar
RogerFrench
Fourth Gear
Fourth Gear
 
Posts: 619
Joined: 01 Dec 2009
Location: Richmond, TX

Total Online:

Users browsing this forum: No registered users and 7 guests