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RE: TR4a engine timing: some answers

To: triumphs@autox.team.net (Triumphs List), "Randall Young" <Ryoung@navcomtech.com>
Subject: RE: TR4a engine timing: some answers
From: spamiam@comcast.net
Date: Thu, 03 Jun 2004 12:38:33 +0000
My impression was that he was referring to total advance including the vacuum, 
but I am not positive.  I think that I will leave the advance setting right 
where it is right now, at 30 total.

I, too, thought that leaking valve guides would only lean the mixture, and one 
could compensate as regain the correct mixture.

His thoughts on the subject were that the lower-than-normal flow across the 
carb bridge and jet did funny things at these low flow rates (idle) and forces 
one to set the carb rich because when you get it "right" it will not idle and 
just stalls.

I still have to check the valve train for proper rocker motions, but I would 
have had to lose both #1 and #4 the same way....

All in all, I find this entire issue distressingly difficult to solve.  Usually 
the problems are obvious once some basic testing is done.  It worries me that I 
am missing something and that "something" could be very significant.

-Tony


> > I consulted a local expert and picked his brain about the tuning
> > issue and he
> > had a few good things for me.
> >
> > 1)  26-28 degrees total advance should be enough.  30 as I have
> > it now at the outside.
> 
> Is your 30 vacuum + centrifugal as you described ?  I'll bet his 26-28 is
> centrifugal only.
> 
> > He thinks it is quite
> > possible that the
> > valve guides are worn enough to leak air during high vacuum states
> > sufficiently to mess up the ability to tune the carbs.  Yes, even
> > at 28,000
> > original miles, even when not raced.
> 
> I'll say only that I disagree ... I ran a head for awhile that had horribly
> worn guides and I was still able to get a good indication lifting the pins.
> After all, whatever vacuum the guides leak, they leak all the time.  Your
> problem is mixture too rich, not too lean ... and if it was sucking enough
> oil to change the mixture, you'd also get blue clouds out the exhaust (I
> did).
> 
> Good luck anyway ... sorry I won't be at VTR this year, but maybe next year.
> Randall





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