MGB & GT Forum

I thought the idle screws on HIF-4 carbs (mine is a '74) were ALL supposed to have springs around them. But mine have springs around only the two "outside" or upper screws. The two inner or lower screws ('fast idle screws') are fastened very tightly with nuts. So, each carb has its upper screw mounted through a spring and lower screw tightened down with a nut.

With an a/c system on my car, the idle is too low so when I come to a stop, the car often stalls out. Moss says I need to increase the idle with a/c in the car. But with the nuts tightened as they are on the inner two screws, I can't adjust them.

So I ordered a set of idle screw springs from Joe Curto this morning and he said that on HIF-4's (or some HIF-4's) the factory installed the nuts on the two inner screws to prevent idle adjustment. Not sure why.

What do you think? Should I replace the two inner screws with springs--or leave as is? If I do leave the nuts in place, how do I adjust the idle?

And If I do remove the nuts, how? They're so tight, so small, and so close to the bell of the suction chamber that I can't get a socket or wrench to grip them. What should be a 10 minute job is taking me hours trying to get at those lower nuts. Any ideas?

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Drew Maddock, So. Calif. USofA



Edited 1 time(s). Last edit at 2014-07-29 02:55 PM by DrewM.

Having springs on all the HIF adjustment points is the best, I'm glad I changed all the old four screws and nuts with new screws and springs last year.

PS These nuts are not only very small but also difficult to reach. I had to modify a minute spanner set (on a ring) to get them loose. Problem gone now



Edited 1 time(s). Last edit at 2014-07-29 02:56 PM by Donthuis.

I agree. I switched my adjuster screws with lock-nuts out for Moss springs. They don't seem to ever slip.

D.

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Douglas Tourtelot
Seattle, WA

"Every education has a tuition"

I used needle nose pliers

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72 engine, hif carbs, black od, rest of car stock

Needle-nosed pliers didn't work. Too tight. What did work was realizing that the lower idle adjustment screw is on a pivoting lever just above the idle cam. Pivoting the lever raises the screw. I hadn't even thought of that.

That gave me enough room to carefully fit a small ratcheting wrench underneath where the screw head was and unscrew it. This is what surgeons get paid for. It's very fiddly.

Now with both lower idle screws both removed, I just need the new screws and springs from Joe Curto. Then I'll see if I can find the best idle speed for a car with a/c on. Sometimes I wish I had tiny girly hands!

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Drew Maddock, So. Calif. USofA

The screws are 4BA and will be set by the factory such that the first portion of choke application just lifts the butterflies to give a fast idle. They are not supposed to be adjusted subsequently and shouldn't need to be hence the reason they are fixed with lock nut.

The procedure for setting them is laid out in the manual but in a nutshell there is a marker on the cam which contacts them and with the choke cable pulled to that point the fast idle speed is set to 1100/1200rpm.

With an AC fitted it's inevitable that your idle speed is going to vary as it cuts in and out, in an OEM installation there would be some sort of mechanical compensation built into the system to cater for that but in this case your only real option is to pull the choke a fraction as and when required.

HIF4s can suffer idle problems in hot climates just on their own, particularly if set on the lean side, and putting a knats of choke on to prevent stalling can often be necessary anyway.