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 Posted: Feb 10, 2021 02:03PM
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US
Quote:
Originally Posted by manila
Thank you for all the replies!  I guess the previous owner believed in strong adhesive, as I can't budge the cover.  Only tried for a minute after work.  I'll get after it tomorrow.  I've got  a cast aluminum cover.
A few well placed taps with a soft faced mallet does wonders.

 Posted: Feb 9, 2021 07:45PM
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Thank you for all the replies!  I guess the previous owner believed in strong adhesive, as I can't budge the cover.  Only tried for a minute after work.  I'll get after it tomorrow.  I've got  a cast aluminum cover.

79' pickup

"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about them."  -  Albert Eistein
 Posted: Feb 9, 2021 11:48AM
 Edited:  Feb 9, 2021 11:50AM
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I use rubber cement, called Permatex brush on gasket adhesive on just the valve cover side. If you have a sheet metal valve cover it's good practice to check that it's flat on the bottom face with a straight edge. If it has been over tightened the bolt locations will be high spots and prevent a good seal.

 Posted: Feb 9, 2021 08:22AM
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CA
You don't want to use anything that hardens (even over time) and end up having to carve the stuff off next time.
I used Permatex spray adhesive to coat both faces of the cork gasket and positioned it on the head, holding it straight until the adhesive set - it gets tackier and firms up. I said "used" because it was maybe 8-10 yeas ago and it hasn't leaked yet, even through one episode of coolant loss, which scorched the paint on the head.

I also use the same spray on carb gaskets etc.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Feb 8, 2021 12:34PM
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A lot of owners used a few dabs of gasket goo or grease on the cover to keep it in place while installing, I just fit the new gasket over the top of an old cover for a few days before fitting as it them retains the correct shape.
Do not overtighten the valve cover bolts as this will distort the cover and it will never seal correctly, also nip them up occasionally as the gasket compresses over time and heat cycles.

If in doubt, flat out. Colin Mc Rae MBE 1968-2007.

Give a car more power and it goes faster on the straights,
make a car lighter and it's faster everywhere. Colin Chapman.

 Posted: Feb 8, 2021 11:39AM
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Dan, "Thank you" for an incredible explanation of how it works. I knew about the oil, and can't believe I put the new carb on without it.  I guess as my grandfather used to say: "if it hasn't happened to you, you just haven't been doing it long enough." Car runs incredibly well now.  Got a small leak from the valve cover.  That'll be my next project.  I could only find cork gaskets. Are you guys using 'Gasgacinch' on them, or dry?  As always, thank you in advance.

79' pickup

"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about them."  -  Albert Eistein
 Posted: Feb 8, 2021 10:45AM
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CA
Thanks guys!

I suppose I should have added that SU carbs don't really have chokes per se. On a typical carb like a Holley or Rochester, when you pull the choke cable (or set a new-fangled automatic choke) you close a butterfly valve in the carb intake so the vacuum can't suck all the air it wants and ends up sucking more fuel.

With a SU HIF type, you turn a rotary valve that allows additional fuel to be sucked up a separate port channel in the carb,

With a SU HS type, it is even simpler and easier to see: pulling on the choke knob actuates a lever and rod that simply pull the main jet lower, allowing a richer mixture.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Feb 7, 2021 02:41PM
 Edited:  Feb 7, 2021 02:42PM
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I only have canola oil. ?? Will that work???? ?? Great explanation of an amazing piece of old technology. Thx!

 Posted: Feb 7, 2021 04:29AM
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Well written Dan. I could understand it all. Made sense too. 

"How can anything bigger be mini?"

 Posted: Feb 7, 2021 04:14AM
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To begin with, a SU carb does not have an accelerator pump at all. It has a different approach - a dash pot.

The dashpot is the large chamber on top of the carb. It has a small black knob on top that is actually a cap for the oil chamber. Remove the cap and when you pull it out, you will see a thin rod with a brass blob on the end. This is the dashpot damper piston. Look inside and you will see the bore of the damper. You fill that  about 3/4 full with oil. leaving enough room for the piston to go back in. Rerpalce the cap carefully - it has fine threads that are easy to cross-thread.

Here's how it works:

When you depress the gas pedal suddenly, you open the throttle suddenly. (Again no accelerator pump, so pumping the gas does nothing but open and close the throttle plate.) When the throttle opens, it allows manifold vacuum to extend to the place where the main jet is exposed to the flow of air. This is at what is called the bridge. If you look down your old carb from the intake side, you will see the bridge. At that time, the dashpot is down - it holds and regulates the main jet needle Kermy referred to. On an SU, you don't change jets to modify mixture - you change the needle.

When the vacuum extends past the throttle, it sucks on a tiny air port that leads to the dashpot vacuum chamber. The vacuum applied to the chamber causes the main dashpot piston (core) to lift up. This does two things.  When the engine is off, the dashpot core sits right on the bridge. choking off air supply and holding the long needle far into the main jet. As the vacuum lifts the dashpot core, it allows more air past the bridge AND allows more fuel to be sucked out of the main jet at the same time. The proportion is controlled bu the tapering diameter of the needle.

If the dashpot core rises too quickly, the engine stumbles because of a momentary leanness cause by the sudden inrush of air (like a carb with an accel pump would when the pump doesn't work) Here's the neat trick: To keep the dashpot from rising too quickly or oslillating (bouncing) the dashpot damper slows its action. This causes a delay in the rising of the dashpot with the result that the vacuum momentarily sucks too much fuel and presto! you get an extra spurt of fuel just like an accel pump provides.
As you drive along with steady throttle, the vacuum applied to the dashpot is in proportion to the airflow through the carb, so the dashpot is then held at the appropriate level to provide the right air fuel mixture.

So, back to Kermy's oil suggestion. The weight of oil you put into the damper can be anything from the engine oil (as suggested by the owner's manual), which might be 20W50 to something much lighter like 3-in-1 oil, automatic transmission fuel or even motorcycle fork oil. (Go figure!). So, you start with the engine oil you use and see how it works, If it is still hesitant, work your way through gradually lighter oils to see what works better. You may even end up with a mixture.

If you do over-fill the damper, don't worry. Any excess leaks down into the dashpot chamber and eventually gets sucked into the engine. It should only take between 5cc and 10 cc. (I've never measured.)

Side issue that may not be applicable: When I bought a new IF 44, I had problems getting it right. Even an expert Mini mechanic couldn't solve it. I removed the dashpot and disassembled it to discover there were TWO dashpot springs inside it. It should only have one. My guess is that the factory provided two for different applications of the carb.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Feb 7, 2021 03:48AM
 Edited:  Feb 7, 2021 06:41AM
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Weird double post deted

.

"Hang on a minute lads....I've got a great idea."

 Posted: Feb 6, 2021 02:24PM
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Thank you for the reply Kermy. You were correct. No oil in the dash pot. Can't believe I overlooked that.

79' pickup

"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about them."  -  Albert Eistein
 Posted: Feb 6, 2021 10:10AM
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Its leaning out. Do you have oil in the dash pot? If yes, maybe try a thicker grade. Also the needle might be too lean. You probably need a BDK needle.

 Posted: Feb 6, 2021 07:38AM
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I've recently acquired a 1979 Mini pickup.  It has a 1275 engine, and now, a new HIF 44 SU carb. Installing the carb brought immediate improvements in running.  Dialed it in as best I could after the engine warmed-up. If I try to accelerate fairly hard, the engine seems to fall on its' face, unless I've got a bit of speed.  If I release the accelerator slowly, the engine speeds up nicely, but if I put my foot back into it, it falls again.  If this was a different car and engine I would want to have a look at the accelerator pump on the carb. Anyone have any ideas?  It almost feels like a two stoke motorcycle not quite being on the power band. As always, thank you in advance!

79' pickup

"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about them."  -  Albert Eistein