Eric Russell p6rovers at yahoo.com
Tue Jul 4 01:10:54 BST 2006

Another Gunson's product which I brought back from the
UK is their CO Meter.  This was particularly useful to
get the Rover ready for the annual emissions test.
Tweaking the carbs created a digital readout from the
tailpipe and created a lesser burning sensation on the
fingertips that the colortune.  I was disappointed
with how much yellow appeared in the window and
difficult /impossible it was to achieve the "Bunsen
burner" blue they recommend.


--- Geoff Kirkpatrick <britcarnut at yahoo.com> wrote:

> I can vouch for the Gunson's Colortune.  I bought
> one on Ebay several
> years ago and have used it to set up one of my
> 3500S' carbs.  It was
> running very rich and popping and backfiring before
> I started.  Being able
> to watch the spark through the clear replacement
> plug that's part of the
> Colortune kit is a very effective way to get the
> carb mixtures balanced,
> and the car ran massively better when I was done. 
> One of these is well
> worth seeing out.
> Geoff
> Message: 6
> Date: Sun, 2 Jul 2006 20:43:44 -0400
> From: Glen Wilson <glenwilson at cavtel.net>
> To: rovernet at lyris.ccdata.com
> Message-ID:
> <200607022043.44921.glenwilson at cavtel.net>
> Content-Type: text/plain;  charset="iso-8859-1"
> (Eric, 1000 rpm sounds awfully high for a Rover...)
> Larry's question mixes up about three or four
> different issues. This is
> the 
> kind of stuff that drives me crazy about dual-SU
> setups because most of
> the 
> procedures and advice go out the window right at the
> beginning if the
> carbs 
> are not in tip top shape. Any leaks or worn parts
> can mess it all up.
> A calibration procedure must be broken down and
> performed in a number of
> steps 
> in a particular order because several of the
> adjustments are interactive
> and 
> affect each other. Sometimes when you are dealing
> with two adjustments,
> one 
> will change the other but not vice versa. Therefore
> you have to procede so
> that when you have one setting adjusted properly,
> you don't immediately
> screw 
> it up when you make the next adjustment.
> Correct me if I'm wrong in the following because I
> am not the guru. This
> is a 
> general conceptual description written as sort of an
> intellectual exercise
> to 
> refresh my understanding.
> 1. Basics...Get in the ballpark by setting the plug
> gap, static timing,
> point 
> gap/dwell angle, and set the jets to the same number
> of flats on both
> carbs 
> (how many, I don't know). When you do all of this,
> you should be aware of 
> whether or not you have the distributor vacuum
> timing advance disabled or 
> functioning, and you should make certain that the
> little weights in the 
> distributor for centrifugal advance are lubed and
> able to swing freely.
> The 
> weights change your timing curve and ignition timing
> depending on the
> speed 
> of your engine. Usually, when you use a timing
> light, the vacuum advance
> is 
> disabled and the engine rpms are kept low enough
> that the centrifugal
> weights 
> are not activated and changing the timing. The
> engine speed at which you 
> adjust the timing using a timing light may or may
> NOT be the same as the 
> basic idle speed of your engine.
> 2. Mixture...Regardless of the amount of air flowing
> through the carb, the
> ratio of air to fuel must be within a certain range.
> I would think that a 
> tool like a Gunson Colortune sparkplug thingamajig
> is the rational way to
> go 
> to get the mixture pretty close. Once you're going
> down the road, you can 
> check the color of the sparkplugs to see if any
> cylinders are rich or
> lean. 
> I would think that the mixture (air/fuel ratio)
> would have to be correct
> and 
> pretty much the same in each carb before you fine
> tune the balance,
> timing, 
> or idle speed.
> 3. Balancing...This has to do with balancing out the
> volume of air flowing
> through each of the two carbs in a given time at a
> given engine speed. I 
> guess the real point is to have all four cylinders
> firing more or less
> evenly 
> because they are getting about the same amount of
> fuel-air mixture. Loosen
> the link between the carbs before attempting to
> balance. If the carbs are 
> good, putting the jets to the same setting should
> result in a pretty well 
> balanced situation. Mixture-wise, this should make
> them pretty much the
> same 
> be it rich, lean or just right. You can use a carb
> balancing tool, listen
> to 
> a tube for equivalent hissing sound, or whatever.
> Regardless of what these
> techniques tell you, the bottom line is that the
> engine must run smoothly.
> To 
> my way of thinking, balancing the carbs is really a
> rather fine adjustment
> to 
> compensate for minor manufacturing differences
> between two carbs that are 
> both basically within spec and with the same needles
> and jets. You adjust
> the 
> jets to get the correct mixture, then adjust the
> basic reference throttle 
> opening of each carb separately to achieve balance
> between the carbs, lock
> the linkage between the carbs to keep them the same
> in relation to each 
> other, and then set the idle speed using the
> adjustment that adjusts both 
> carbs as one unit.
> 3. Timing...Haven't we established before on this
> list that there isn't
> all 
> that much difference between 92 octane unleaded on
> the current octane
> rating 
> scheme and 100 octane on the old P6-era scheme? I
> would think the best
> thing 
> to do without a rolling road would be to ballpark it
> and then adjust the 
> timing at the distributor until you just eliminate
> the pinging under load.
> No 
> matter what numbers you adjust to, you still have to
> get rid of the 
> pre-detonation under load, and adjusting much beyond
> that just reduces
> power 
> without gaining anything. You may then have to go
> back and fine tune your 
> idle speed, but your mixture and carb balance don't
> need to be readjusted.
> So, what did I leave out and what mistakes have I
> made in this general 
> description?
> Glen
> -- 
> ~ Glen Wilson ~
> http://stores.ebay.com/EasyAuctionServicesPA
> Adding new stock daily...
> "This is the final test of a gentleman: his respect
> for 
=== message truncated ===

The Rover Car Club of Canada -  www.roverclub.ca

Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 

More information about the rovernet mailing list