Re: T'Quad mixture screws

[jlandry@domain.elided (John A. Landry)]

The black helicopters hovering over the house recorded
jmbrodsky@domain.elided whispering:

>     So the word from the other gear-heads at work here,(none of them ever 
>worked in a shop so their diagnoses are somewhat dealer oriented), is that the 
>fuel supply is low.  I'm gonna throw in a fuel filter just because, (it's an 
>inline between the fuel pump and the carb) and measure the output pressure 
>before and after the swap.  Maybe that's it?  It would seem that if the bowl is 
>full that it should pull till it drains, no?  I know that when I've had a low 
>float, the surges from the fuel pump can be felt, not the same here.  Is the 
>fuel pump a standard f@^d or a Ch@%y?  I hope the filter's the cause, since this
>thing just happened over the space of 4 days.  Total degradation in accelerative
>properties.  I s'pose that my mileage will go up now that the secondaries aren't
>using, but I *liked* the acceleration of 392 cubes.

Joel,

I have very limited T'Quad experience, but I'd like to offer this advice...
Definitely change the fuel filter.  It's cheap and can't hurt.  It should
be changed on a regular basis anyway.

Next, maybe the jets in one or more of the secondary throttle bores are
fully or partially plugged.  If the carb hasn't been completely
disassembled and chemically cleaned in a long time, maybe it's overdue?
Deposits from the fuel can reduce the size of a carb jet substantially over
time resulting in a significant leaning effect of the mixture.  Again, I'm
not familiar with the internal design of the T'Quad, but if it has some
sort of auxiliary enrichment or power valve for the primaries and
secondaries, it could also be at fault.  Under heavy load, an engine
requires a richer air/fuel mixture, and this is the job of the power valve
or other similar system.  If it fails, bogging under continued acceleration
is one of the symptoms, but normal cruising is unaffected.  It could just
be coincidence that the bogging begins at the same point you estimate the
secondaries are opening.  Typically a power enrichment system is activated
in stages by the dropping manifold vacuum.

The bogging you describe does sound suspiciously like a case of an
excessively lean mixture.  A lean mixture definitely results in low power.
In essence, it is a fuel delivery problem, though maybe not the fuel filter
or pump.  If the basic things don't help (fuel filter, etc.) and you have
the mechanical aptitude, you may want to rebuild the carb after
disassembling it and soaking it in a dedicated carb cleaner overnight (or
longer).  DO NOT put plastic parts in the carb cleaner and if possible dry
out all passageways with compressed air... even a bicycle pump would work
if you have a friend pump while you use the little nozzle attachment.
You'd be surprised at how well a carb works after being thoroughly cleaned
and reassembled correctly.  The resins and varnishes that build up inside
the carb really degrade its performance over the years.  I removed,
completely disassembled, cleaned and reassembled the intake air metering
and fuel injection system on our 100,000 mile 1987 Subaru Turbo-Wagon a few
months ago, and that alone *really* restored its original smooth idle and
acceleration.  The vapors entering the intake system over the years from
the PCV system formed a buildup inside the throttle body and throttle
plates that affected performance.  Once cleaned, it felt like a new engine.


I did the same cleaning routine to the *four* carburetors on my 1984 Honda
V65 Magna last summer and boy did it make a difference.  It had a lean
off-throttle stumble that was completely eliminated.  I didn't renew any
parts in that case... it uses rubber gaskets that were in fine shape.  They
didn't look all that dirty inside... it doesn't take much almost invisible
varnish buildup to affect performance!

Good luck,

John

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