Geoff,
I assume you mean the jet inspection cover was missing when you refer to the
Micky Mouse hat.
You need a short lesson in how the DCOE works.
The engine via the DCOE draws air into the inlet manifold and induction tract
in two distinct places. The first is round hole about the size of a dime
that is on side of the carb (left hand as you look at the carb) above the l/h
barrel (a good book or photo might help). This hole is used to draw are into
the carb body, more of which later.
The engine gets the rest of its air through the carb barrels.
If the carb is correctly calibrated (like on a chassis dyno) and the jet
inspection cover comes loose or is missing (lost) the engine will run rough,
particularly so in mid range rpm (long time since that happened to me but I
think it is the 2,500 to 3,800 rpm range). At higher rpm there does not seem
to be a problem.
Back to the dime size hole. If you remove the carb top cover complete you
will see that the hole leads up to the top cover resticted by the top cover
gasket such that it gets to the area underneath the jet inspection cover.
This air is drawn into the gallaries that feed the emulsion tubes with air.
It is this air that is mixed with fuel drawn up in the jet (idle or main
depending on rpm) that is subsequently drawn into the air flow from the
barrels that is subsequently further emulsified.
If the jet inspection cover is missing then air is either drawn into the
emulsion tubes/holes in greater quantity than would be the case when air is
drawn in only by the dime sized holes OR... air is drawn in a lesser quantity
by virtue of a weaker vacuum. To be honest I don't know which it is.
BUT
Either the mixture leaving the jets (via the progression holes or aux venturi
is richer or it is weaker.
SO
Obviously your car is not correctly calibrated at some point in the rpm range
but I cannot say whether it is too rich, weak or just poorly emulsified.
However, if you provided a spec of the engine along with FULL details of the
calibration of the carb I ought to be able to guess and along the way add to
my knowledge of how the carb works (eg missing jet inspection cover leans/ or
richens mixture to detriment).
Finally, the jet inspection cover is there for a purpose (eg unfiltered air
enters directly into the jet system without it) so buy a new one
(aptfast.com) and then get the jetting sorted.
Daniel1312
PS. Most books on the DCOE aren't that good but you might find it helpful to
buy some anyway.
In a message dated 01/04/00 18:01:26 GMT Daylight Time, branch@valinet.com
writes:
<< And on another note: My 1275 had been suffering from a hesitation/misfire
at
low rpm and high load situations. Then it went away. Runs Great! So I went
a-looking for a reason and found the mickey-mouse hat on the Weber was
missing!!!!! For anyone with Weber side draft experience then:
1. Why would this improve the performance of this carb?? And what does it
indicate is wrong with it with the hat on?
2. Should I just leave the damn thing off?
>>
|