spridgets
[Top] [All Lists]

More carb/engine curiosities (longish)

To: "Spridgets" <spridgets@autox.team.net>
Subject: More carb/engine curiosities (longish)
Date: Tue, 27 Feb 2001 18:06:01 -0500
First, thanks to everyone who responded to my SU carb questions a week or so
ago. Unfortunately I'm still having problems, but have some new "evidence"
that may be relavant, but I can't really interpret what it means.

I have carbs from a 1967, but the rest is 1971 (I think, I can't swear to
the intake manifold.) I did one small mod on the intake manifold, though.
The connector coming out the top center (usually a right angle bend) was
broken off, plus there is no air pump, etc. (it was de-smogged when I got
it). So since I was installing the 1967 carbs I thought I'd as closely as
possible duplicate the 1967 emissions stuff - PCV mounted on the intake with
a connection to the oil separator on the timing cover. I'm assuming the
dizzy is 1971 and should be driven off the intake manifold rather than the
carb. So I basically have what looks like page 318 of Bentley. Ideally
should be what's on page 320.

(Looking closer at those pages just now, I think I may be getting to the
root of my problems)

Anyway, I discovered that if I take the oil filler cap off while running it
speeds up noticably. Disconnect the hose from the oil separator and it
really speeds up. Unhook the PCV from the manifold and it runs like a bat
out of he##. One think I JUST noticed in Bentley is that the 1967 used a
FILTERED oil filler cap, while the 1971 used a SEALED one. The connection
that would normally go to the carbon canister is open, btw. So it seems that
I have some kind of severe back pressure/vacuum thing going on in the
crankcase. Also discovered the sudden appearance of a oil puddle under the
car that wasn't there before. That's notable because I had been impressed
that it didn't have any major leaks before, and didn't notice it on Saturday
when I last ran it for a little while.

I do now have some 1972 vintage carbs that have the correct connections for
the crankcase ventilation and a carbon canister, so I believe I'll go ahead
and put them on ASAP and see what that does.

Couple of questions:

1) I remember reading somewhere (might have been in Vizard - haven't read it
all, just skimmed it a bit and hoping to really use it in the future) about
how crankcase pressures can cause problems if not handle properly. Can
someone explain why? And did what changed in the 1275s between 1967 and 1971
that would cause such differences in the crankcase pressures?

2) Does anyone have one of those Y connectors that goes between the carbs
and connects to the oil separator? The carbs I bought didn't come with that.
VB has it, Moss doesn't appear to. Rather send a few bucks to a list member
than to VB.

I have to admit, these A-series engines seem a little touchier than the
(older) American iron I've dealt with in the past. Not a slam, just an
observation. I just need to get used to the differences. Certainly newer
engines are touchier than the older. When they work, they're great. But let
one little sensor go out...

Eddie
1971 Midget (under pressure)

<Prev in Thread] Current Thread [Next in Thread>