Well, I got to play with my new Colortune toy today. I looked at Cyl #1 and
4 for the rear and middle carbs. No problem, getting a good blue flame.
When I checked the #6 cyl for the front carb I could not get rid of the
yellow flame at idle (yellow indicates an overrich mixture), It stays
yellow regardless of RPM.
I checked the needle, it is seated properly and the float is adjusted
properly (Grosse Jets). These are the two items that the Colortune
directions mention that can cause this condition. The carbs bodies have
been respindled by Joe Curto and rebuilt by yours truely. There are no air
leaks (that would make a lean mixture). Somehow the carb is putting out too
much fuel. The question is, Where?
Valves are adjusted properly and the engine has 1500 miles on a total
rebuild.
Does anybody have any ideas as to what the problem might be?
Thanks in advance, all help gratefully accepted
Regards, John Walker
69 2+2, with a Series I 4.2 with triple SU’s
Are you saying that you turned the adjustment screw out the whole way
(that’s the direction on the 50s carbs) and it still showed yellow?
My first thoughts (there are probably many more) about where to look:
Do you have a starting Carb on that carb?
Worn needle, seat?
Same needle as other two carbs?
How about cylinder #5?----- Original Message -----
From: “Walker, John JR SSI” JW202035@MSXSSC.SHELL.COM
To: xk-engine@jag-lovers.org
Sent: Monday, December 27, 1999 10:57 AM
Subject: [xk-engine] Colortune Results
Well, I got to play with my new Colortune toy today. I looked at Cyl #1
and
4 for the rear and middle carbs. No problem, getting a good blue flame.
When I checked the #6 cyl for the front carb I could not get rid of the
yellow flame at idle (yellow indicates an overrich mixture), It stays
yellow regardless of RPM.
I checked the needle, it is seated properly and the float is adjusted
properly (Grosse Jets). These are the two items that the Colortune
directions mention that can cause this condition. The carbs bodies have
been respindled by Joe Curto and rebuilt by yours truely. There are no
air
leaks (that would make a lean mixture). Somehow the carb is putting out
too
much fuel. The question is, Where?
Valves are adjusted properly and the engine has 1500 miles on a total
rebuild.
Does anybody have any ideas as to what the problem might be?
Thanks in advance, all help gratefully accepted
Regards, John Walker
69 2+2, with a Series I 4.2 with triple SU’s
All: Thanks for the ideas, both on and off list. I rebuilt the carbs when
we rebuilt the engine. I am assuming the needles are the same. I will
check tonight. No starting carb. I am beginning to think I did not
centralize the jet properly and have slightly "reamed out the jet with the
needle. These carbs are so simple there cannot be too many choices for the
cause of the problem.
What it cannot be:
Air leak would cause a too lean mixture.
Needle seated too deep into piston. It was correct. I even extended the
needle about 1mm and there was no change.
Float level has been checked and is spot on.
Linkages are adjusted properly and all three carbs open together.
All are flowing the same amount per the Uni-Syn.
All carb pistons rise together but since this is a problem at idle that
shouldn’t matter. The fact that it shows at idle should also eliminate the
dashpots and dampers as a possible cause of the problem since they are not
operating at idle. .
What it might be:
Badly centered jet worn by the needle rubbing due to the misalignment.
a leak on the jet diaphragm causing fuel to flow between the jet bearing and
the jet. This is possible. right?
Wrong needle. If so, I got the wrong needle in the rebuild kit, easy to
check if I have the right one.
My plan is to check the needle for correctness; and check cyl #5 for with
the colortune. If it is the right needle and #5 shows the same as #6 I
guess I have no alternative but to pull and rebuild the carb being very
careful to properly center the jet. If this does not work I am stumped.
Also stumped if #5 shows a good mixture.