Just to follow up, I took a look at my Weber Carburetor book, which has a
section
on manifold design and the use of different carbs. As you indicated Ron,
according to the book, a single sidedraft can cause some problems depending on
the manifold. However, if the manifold is designed to separate the throats of
the carb FROM THE VERY BEGINNING such that one throat is feeding two cylinders,
then it should work ok. The manual indicated that a plenum type manifold (which
does not separate the two throats from the very beginning of the manifold) would
cause problems because it would "permit excess mixing of pressure waves, cause
reversion and ruin tuning." So, Adam, take a look at your manifold and see what
you've got before you throw it out!
Greg Burrows
Ronnie Day wrote:
> >Adam Bradley
>
> > I recently bought a small DCOE (38DCOE25) for my PL411 w/J15. It'll be a
> > single DCOE on a stubby MGB manifold. I've opened it to see what jets and
> > such it has, and most look to be about right but one strikes me as
> > odd. Here's what it's got:
>
> >Idle jet 50F11 (40F9 or 45F9 would be better from what I've read)
> >Main jet 135 (I guesstimated 125-130 based on what I read online)
> >Air corrector 270 (this one alarms me; from what I've read it should be
> >approx main jet + 50)
> >Emulsion tube F15
> >Pump jet 90F
> >Choke 28mm
> >Aux venturi 4.5
>
> <snip>
>
> Okay, here goes. Been there, done that. Specifically a single 42
> DCOE/Warneford manifold on an L-16 almost 30 years ago, and it just didn't
> work. If the manifold centers the carb midway and the cylinders have
> individual ports fed by four separate manifold runners, there's just no way
> the middle two cylinders are not going to be way more rich than the end two.
> I know some of the older BMC motors use siamesed intake port so if that's
> the case with the J15 you might luck out.
>
> I can't get to my Weber books to check, but based on your observation that
> the air jet is 270 but should be around 185, it sounds like the previous
> tuner was trying to compensate for a rich bottom end by using a way too
> large air jet. I do remember that in order to tune any of these dual throat
> side drafts proper you gotta start from the idle jet and then work upwards,
> and that's after you've settled on a choke size and are starting out with
> the right emulsion tube (based on the phase of the moon and ritual voodoo
> and SCSI incantations!!).
>
> All this said, a pair of SUs in good condition are very hard to beat in most
> instances.
>
> FWIW,
> Ron
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