Correct me if I'm way off base. I have lost count of the number of HIF 38/ HIF 44s I have installed. I have had a few new 38s but all 44s were very dirty and used. I have cleaned and rebuilt all of the used ones. I have not yet had a reason to mess with the bi metal strip other than to clean/glass bead it. 

Seems I recall while tuning engines in a mini the idle speed will increase when moving the dizzy to advance the timing. The choke also has a fast idle screw which increases idle when adding choke. I'm not sure I have noticed much idle change when adjusting the mixture screw. You can use a dentist mirror and your finger and take a look though the carb and see it there is a burp/ poppet valve in the throttle disc. I have removed dozens of throttle disc with these soldered shut. All the twin 38s off MGBs are like that. 

Just wondering would you expect richer or leaner mixture to increase idle? This is just a slight change via the bi metal strip right? Steve (CTR)

Thanks Dan for the details.

I found the exploded view on this page:

//sucarb.co.uk/carbspec/carburettor/spares/id/1442/

#17

Pics are from this forum from many years ago. Original bimetallic lever is on the right. Modified version is on the left - dismantld and modified to remove the bimetallic effect.

If it is your bimetallic lever, your problem may rest with how oy set your idle mixture. The basic problem is that as you adjust mixture, the carb is warming up and the lever is ALSO modifying the mixture. Since you are doing it with the car stopped and the bonnet up, the heat from the exhaust manifold is over-warming the carb and lever, messing up your adjustment as you are trying to make it. You then set idle speed for an incorrect mixture setting.

When you get out on the road, air flow through the engine bay is better, the lever readjusts the mix and your rpms increase.

I did the modification on my carb and have never looked back. Tuning is much easier.

For those curious:

The lever sits with the end having the small slot pointing up. The mixture adjusting screw tip pushes against the slot. The main jet has an elbow at its bottom end, which fits into the keyhole in the 'toe'. The back 'heel' has a round hole through which a screw and spring provide a fulcrum point for the lever. So, as you screw in the mixture screw, it pushes the top leg inward, whcih moves the toe and jet downward, making the mixture richer (and confusing most people!).

The "toe" section is the bimetallic part. As it warms up, it curls upward very slightly, pushing the jet up and making the mixture leaner. Even though submerged in fuel, this is affected by heat off the exhaust manifold as described above.

If I recall correctly, the author of the photo (one of us here) dismantled the lever, removed the two outer strips of the bimetal bottom section, put in matching shims and riveted them all back together. I found it easier (?) to cut and bend a piece of stainless steel to match the shape, then cut out the slot and holes, all with hand tools. (The stainless steel was bl**dy hard stuff!)

I checked the return position on both choke and throttle pretty good, thinking it was sticking. Usually if it is slightly sticky a blip of the throtttle brings things down.

So I rechecked things, could not find a leak and went for a 40 mile or so drive including freeway time.The idle settled down at every stop light and stop sign on the way home after the freeway.

With the Burlen exploded view diagrams of the carbs hidden(at least from me), does some one have a picture of the bimetallic jet?

Terry

PS average 175 PSI compression per cylinder after the drive, all within 3-4 lbs.

I had virtually the same problem, as time went on, it got even worse (900 rpmm at start, 1500 warm, then went to 1800). Turned out to be the choke area of my HIF44. When I pushed in on the choke assembly, the RPM's would drop back down to normal. The choke assembly on my HIF44 still has a slight amount of play in it (in and out) but the rpm's stay steady now. Not sure if that play in the choke shaft is normal though. It was a simple .50 cent o-ring.....

I did not really confirm it until after you left in that cool twinky car.

I needed to do the basics before checking. I think that is how the SU book starts, "everything else must be perfect" before you mess with the carb.

I messed with the timing as well yesterday until I realized that fancy A+ engines have an external timing marker for the pulley. Reset to the Aldon/Calver suggested setting for a Yellow with vacuum as a starting point. Basically what it was at before. Re-checked all that this morning and now need to go for a drive...

Terry

Gee Terry, if I knew about this yesterday, I could have brought my Haynes carbbie book to you with the Monster
Eyebolts.  If you need it, let me know.

I think I loaned my SU book to someone and don't remember who. I have not worked on a HIF for a few years as I went to twins on the other car, but it has been off the road for almost two years.

Burlen used to have excellnt exploded view diagrams on their site, but I cannot find on the latest version.

I will check a few more things today.

Thanks for the help

Terry

The last time I ran into this problem, I also chased a number of ideas. In the end I removed the HIF 44 and sure enough the throttle plate had a burp valve. This is a tiny valve in the throttle plate with a very small spring. The idea is when the throttle is shut quickly this allows a little air to pass though the plate to avoid a stall. What happens ( my thoughts ) is the spring weakens and as it warns up it causes the idle to hunt. You can remove the throttle plate /disc and solder the valve shut or replace the disc with a blank one. I always order the big HIF 44 SU kit that includes the disc. 

The HIF 44s have throttle shaft seals which reduce wear and air leaks in that area. Steve (CTR)

check for a vacuum leak with engine running as follows:

start engine.

wave propane torch, UNLIT, along any gasketed areas and vacuum lines.

a leak will suck in propane and idle will increase as mixture richens.

Remember, DON'T LIGHT THE TORCH!

Worn throttle plate shaft.

There was a slight crack in the y branch,so that is why I replaced it and I was pretty careful about the replacement of the manifolds, but I will check tomorrow.

What you have in the picture Terry looks like a HIF 44.

X2 on the bi metalalic spring.

I would install an overflow hose on the port and run it away from the headers usually down the rear of the subframe next to the brake lines works.

Sounds like a vacume leak, or the bimatelic spring on the jet in a HIF carb. 

Did some of these have the popit valve?

Image Gallery

First how do you tell the metric HIFs from the older HIFs?

I have an inconsistent idle. I will warm it up with 10 minute drive, make some adjustments, get a nice 900 RPM idle, but when I go out on the road after 10-15 minutes, the idle is up to 1200-1300.

This has been consistently inconsistent. As it happened before I replaced the header last weekend and today after I replaced the rotor, cap and wires.

I believe this is a later HIF off a Metro

Terry