[TR] TR3A Choke Question

[Michael Marr]

Hmmm, now I think about it, I see your point Randall.  The heavier oil makes the piston rise more slowly, increasing the velocity across the jet, increasing the vacuum in the throat and sucking more gas in.  I was thinking purely in a mechanical sense, that if the piston rose too slowly, the annular space between the needle and the jet would be too small to allow sufficient fuel to flow, but I was forgetting about good old Bernoulli. I was basing this opinion on my own car, which had the same problem as Jim’s.  I tried replacing the 30 wt oil in the dashpots with household machine oil (3 in 1) and everything was fine, thereafter.  But, my carbs are worn and who knew what else was going on.

Thanks for making me think this through!

Mike

Michael Marr
Albion Technical Services
Mobile:  630-202-0065

Sent from my iPad

> On Nov 5, 2018, at 17:13, Randall <TR3driver at ca.rr.com> wrote:
> 
> 
>> What kind of oil are you using in the dash pots?  If the oil 
>> is too heavy, it may overdamp the pistons, causing them to 
>> rise too slowly and momentarily weaken the mixture, causing 
>> the hesitation. I find 3 in 1 is about the right weight. 
> 
> Actually, it's just the opposite.  Heavier oil makes the mixture go richer
> right after you open the throttle.  Using oil that is too light can cause a
> "lean bog" (like Jim described).
> 
> The book actually recommends 30 weight for temps between 40F and 70F; 40
> weight above that.  Optimum for you may vary somewhat, depending on engine
> condition and so forth; but I have always found that performance suffers
> with less then 20 weight
> 
>>  The choke cable is hard to pull 
>> out.  Takes two ands
>>> to pull out and then twist to lock.  That's to really get the choke 
>>> levers to move both jets down.  Is this normal or maybe I 
>> need a new choke cable.
> 
> Not normal, but unfortunately rather common.  Did you polish the jets when
> you had the carbs apart?  Originals were supplied polished, but the
> replacements I've seen have been dull.  Dull means a rough finish, which
> greatly increases the friction against the glands.
> 
> The linkage also goes together in an odd way.  If you put it together the
> way it seems it should go, it's harder to operate the choke.  The two
> clevises hang out behind the levers, rather than straddlings them.
> 
> I like to replace the gland sping (inside the jet housing) and the return
> springs during a rebuild, especially if you don't know the full history of
> them.  It's not uncommon for people to stretch the gland spring out a bit,
> in an attempt to get the glands to quit leaking.  The extra pressure
> increases friction, to the extent that often the jets won't return after
> using the choke.  So then they shorten the return spring.  Both actions make
> the choke more difficult to operate!
> 
> -- Randall
> <FIG 28 CARBURETTORS (LINKAGE) reduced.jpg>
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