[TR] TR4A - This Seems Odd

[DAVID MASSEY]

 Well, Dr. Watson, eliminate the impossible and what is left, however improbable, is the truth.
1) An engine will not run without the proper fuel/air ratio.2) the only source for the proper ratio of fuel/air is the carburettor jet3) The engine continues to run
ergo: the throttle is not fully closed.  

Actually, the throttle plates do not fully close off since there is no point if you want the engine to at least idle.  The throttle plate is actually slightly undersized to allow it to freely rotate in the carburettor throat without binding.  Also, the plates must be properly centered on the shaft.  If they are not the top or bottom will hit the throat before the other end does and there will be a gap even at "in theory" fully closed.
If you hold a carburettor up to the light with the throttle fully closed you will see light leaking past the plate, mostly at the sides near the shaft.  If you see a lot more light at the top or bottom the plate is not properly centered.
But, if you get a decent idle, go with it as is.
 
Dave 

 
 
-----Original Message-----
From: G.D. Huggins <gdhuggins at genfiniti.com>
To: Triumph Mailing List <triumphs at autox.team.net>
Sent: Fri, Sep 6, 2019 9:35 am
Subject: [TR] TR4A - This Seems Odd

All,
Here’s another thing to ponder whilst I wait for my rebuilt lever shocks to arrive..
My engine will idle under the following conditions:   
   - Idle screws are backed off all the way, not touching the plate, therefore not opening the throttle plate.  (In theory, they are fully closed.)
   - Mixtures nuts all the way lean. (In theory, there should be ZERO fuel going into the carbs.)
   - Both the throttle and choke are loosened from the linkage, making sure jets are all the way up, and throttles are not sticking
For the record, these are professionally rebuilt HS6 carbs, with super throttle shaft bushing, perfectly centered jets, etc.
In what is ostensibly a ZERO fuel/air mixture, how is this engine running?Do these engines just have a magic power to idle when starved?
Has anyone else witnessed this on their own cars?If so, should I do anything?  If so, what?  (other than maybe looking to make sure the needles/jets are matched correctly)

Kind Regards,

Guy D. Huggins
gdhuggins at genfiniti.com
817.454.6415

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