Thanks for the info !!!
I don't think HIF's are that complex. Just think the ones one my car managed
to wear out in the last few months. Very frustrating - first I fixed the high
idle by changing the throttle plates (to solid ones) - car then idled fine at
500 RPM. Then the front carb needle valve stuck open. Then a week later the
idle went back up (to about 1300 RPM) and a couple of months (and a lot of
frustrating trouble shooting) later, I found the problem - one of the casting
plugs in the intake had come loose and was leaking (it, eventually fell out).
Idle back to 500 RPM. Two weeks later the idle is back at 1200 RPM. Then the
rear carb needle valve stuck open (removed the carbs and installed new floats
and grose jets). Re-installed the carbs only to find one of the grose jets
(needle valves) would not shut off the fuel with the engine running. Removed
the carbs and installed stock needle valves. Then I used the wrong picture in
the Bentley book and set the float level incorrectly (used the lower of the two
flat spots on the float instead of the bottom of the U - see second picture in
the book) - my fault. Removed carbs again and set floats correctly. Idle
still at 1300 RPM. Stuffed some grease in the outside shaft ends and the idle
dropped about 150 RPM. Removed the carbs again and packed all four shaft ends
with grease and the car idles at 300-400 RPM !! All this is not including one
removal of the carbs and intake to replace the gasket on the tappet covers -
which still leaks.
I have not driven an SU (HS) equipped car in an autocross. Do they have a fuel
starvation problem in the turns ?? I haven't heard this. I'm an engineer
(sometimes not a very smart one - see above) and IMHO all the changes I can see
between the HS carbs and the HIF carbs are for fuel metering reasons - for
emissions. I've never had mine working correctly, so I can't say if they would
perform better than the HS carbs.
Too Much Rambling, Skip '74 B
-----Original Message-----
From: Kai M. Radicke [mailto:kai@radiohead.net]
Sent: Thursday, April 08, 2004 14:15
To: Christian, Skip; MG Digest (E-mail)
Subject: Re: Carb & Trans Oil Questions
> I will probably junk the HIFs and install HS4s. The thing about the
> SUs I like the most is their simplicity and the HS series work fine
> and are the most basic. Unless someone can tell me why the
> HIFs are better (a lot of people have told me to keep the HIFs, but
> no one has provided a good reason), I plan to switch to HS-4s.
> Anyone - why are HIF4s better than HS4s (not including
> emissions) ?????
>
> Skip '74 B
The HIF series of SU carburettors is an improvement over the older H and HS
series. Here are the reasons:
On the positive side...
1) They flow more air, typically 5-10% more CFM than the earlier models.
2) The integrated float bowl means fewer fuel feed issues during extreme
autocross conditions or other race conditions.
3) The bi-metallic strip makes slight compensations in the fuel mixture
depending on air temperature.
4) I personally feel they are more durable and reliable year after year,
when in good condition, than earlier SU carburettors.
5) Better fuel economy when the carburettors are setup up correctly.
On the negative side...
1) Increased complexity, but, if you understand it, you'll get more out
of the HIF carburettors than the H/HS series of carbs. So this is a
positive, if you like the HIF series.
2) Increased cost. Replacement parts and rebuilds are more expensive.
Hope that helps your decision.
Kai
--
Kai M. Radicke
Wishbone Classics
www.wbclassics.com
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