I saw your message about simply replacing the butterfly valves with
those from an earlier HS4. I considered that for my carbs (AUD493/4 -
72 MGB) but found that the originals have a small square cut notch
(about 4-5 mm) at the bottom of the butterfly valve which corresponds to
a small jet orifice on the bottom of the carb body that sticks up above
the body of the carb.
I bought some HS4 butterflies and tried cutting a notch in them with my
dremel tool but I didn't have much success in making equal sized notches
between the two valves. This means I have a tough time tuning my
carbs. I can balance them OK but since one of the notches is a little
over sized, my engine RPM is higher than I'd like because that one carb
lets through too much air and I have to balance the other carb to match
it.
I also considered removing the spring loaded valves from the original
butterfly valves and soldering the exposed hole shut. I did this and it
came out OK but I read somewhere that a carb backfire could melt the
solder on these valves and I've been reluctant to install them.
Does anybody know of a source for an HS4 butterfly valve with a notch in
it? In looking through my BLMC parts book for the early B's, it shows
one and gives a part number. (if I wasn't at work right now I'd include
that number) Do you think I can trust the illustration and that the
part number shown is actually a butterfly valve that has a notch.
Should I try Lawrie Alexander and/or Joe Curto? OR should I send my
carbs to one of them for rebuilding and have them cut notches in a pair
of HS4 butterflies properly or as a more drastic step, modify the carb
body and cut down the little jet orifice that sticks up from the carb
body so the regular HS4 butterfly valves fit.
Thanks
Eric Zambori
72 MGB
Andrew Errington wrote:
>
> Hi,
>
> > >>expect to see an air leak around the throttle shafts, and I'll
> > be sad. I
> > >>also plan to solder the poppet valves shut.
> >
> > When I took my carbs off (HIF4s) earlier this week, I found
> > the rear valve
> > soldered shut and the front one standard (present and functioning). I was
> > going to ask the list but forgot until this discussion jogged my memory:
> >
> > Why would you do this?
>
> Well, as someone pointed out, why bother: just put new discs in from an
> earlier model, since I'll have everything apart.
>
> The reason for me to do it is because their springiness has gone and they
> hang open at idle, letting air in when the throttle disc should be closing
> the throat. Not only that but they kind of flutter, which leads to a rough,
> irregular effect on the idle speed.
>
> > Also, why would someone (I assume it wasn't the DPO, was
> > it, Mike ? :)
> > hehe ) only do it to one carb?
>
> No idea. Maybe never got round to finishing the job.
>
> > Further, is this what made it hard to balance my carbs at idle?
>
> Could be.
>
> > I was going to replace the soldered valve, but maybe I
> > should be doing
> > some soldering on the front one instead. Pros/cons, anyone?
>
> Well, you can solder them shut without disassembling them. If the springs
> are weak then you should solder them or replace both of them with new discs
> with working valves.
>
> Andy
> (dreading his first look at the carbs when they come off...)
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