Hesitation with HIF6 carb on A+ engine

[AudreysDriver]

I have a '62 Sprite Mark II. She's named Audrey.
Back in the 70's she was set up for racing. Back in about 1993 I put an A+ (1300) engine in, and then I replaced the dual carbs with an HIF6 single carb. Then I had kids and put the car away for 15 years. Now we're getting it all going again. I'm following the books, but I have some questions that some experts might easily answer.
I see that Dan Lewis posted a similar question, but with quite a different carb. So I post this.

I've cleaned the carb. I haven't yet messed with the mixture screw. As far as I can see, the single HIF6 carb has only that one mixture screw.
I've gapped and static timed the distributor. I've adjusted the valves to 0.012" cold.

She starts pretty easily with the choke pulled out. But even warmed up, I can't get an even idle down to below about 1500 RPM. If I push the choke in farther, she stalls. Even when she's warmed up, I can't push the choke in all the way. Then when I step on the gas, the RPM drops like the engine will stall. If I baby the accelerator she'll run well at high RPM.
Does this sound like a familiar problem to anyone?

One thing that bothers me: The distributor on my A+ engine has a vacuum advance port, but there is no vacuum takeoff on the carb or manifold. I understand that this means I don't get any advance at idle. Could this account for what I see? Or does this sound like something that carb tuning can help? Or does it sound like something else wrong? If I'm going to install a vacuum port, where should I put it? I don't see any removable plugs on the carb. I was considering drilling into the spacer between the carb and the manifold. That seems like bakelite, so I hesitate to drill it. But the post about the weber implies quite different behavior with a vacuum port on the manifold rather than the carb.

When all of this was new, it worked better than now. The engine's got about 10000 miles on it, the carb has less.

 

[nomad]

If you had carburetor ported advance you wouldn't have advance at idle anyway. I don't think your problem has anything to do with distributor advance and I would first be looking for a vacuum leak. I'm assuming the carb settings are back to where they were before cleaning. If there is no provision for vacuum line hook up on the carb you could drill and tap the manifold for it. You wouldn't be giving up much to get the vacuum advance at cruise where it would do you the most good.

Kurt.

 

[dklawson]

Vacuum for the vacuum advance can be either ported (taken at the carb venturi) or manifold (taken after the throttle butterfly). The vacuum module on your distributor has to be connected to the correct one for it to work properly and I understand there are Lucas distributors set up for each type of vacuum. So... if you drill into the carb spacer and connect to it... the vacuum module needs to be for manifold vacuum or you will have any number of problems.

While your car is a Spridget, I don't know of any that were originally outfitted with HIF carbs. I think board member Gundy may have an HIF carb installed so he may be a good Spridget resource. Another place to ask is over in the MG part of the board. Later dual carb MGBs used HIF carbs before emissions dictated going to the Stromberg carb. There should be a lot of know-how among the MGB owners.

You said you cleaned the carb. How far down did you dismantle it? I remember that the HIF carbs have a more or less true choke where a rotary valve meters the amount of extra fuel available. There are a series of crossdrillings in the carb body to accommodate that gas flow. If those are blocked that could be part of your car's issue. The jet is supported by a bimetallic lever and even if you were careful it could be out of adjustment. It is also possible that the bottom of the jet could still be partially blocked with fuel varnish if you didn't remove the bottom of the float bowl and give the jet a good flushing through with spray carb cleaner.

 

[JPSmit]

Obvious question but is there oil in the dashpot?

 

[AudreysDriver]

Thanks! I agree it's an important question, and yes, I put oil in the dashpot.
It sounds like the lack of the vacuum advance is not the primary cause of the problem. More likely seems to be that the carb needs to be cleaned better. I will give that one a try next.

 

[LarryK]

Check throttle butterfly and make sure it is seating properly. Check passages for debris. Might still have old fuel in them. If this carb has diaphragm check for holes.

 

[RickB]

By all means make everything clean.
I have a pair of balanced HIF4's on my car, but it took a lot to get them dialed in.
After making sure everything is clean I'd definitely check the richening screw, I turned mine all the way in counting the turns then back out to where it was originally.
This gives you a frame of reference, knowing how far out the screw is.

If you don't already have diagrams you can get them online for the HIF carb.
I downloaded several and looked and looked and asked questions until I felt I really understood how they work.
NOT like the SU carb.
BTW turning the screw in makes it more rich.

Also - search HIF4 in Spridgets and you will see a lot of my own path of discovery...

For example:
https://www.britishcarforum.com/bcf/showthread.php?89916-SU-HIF4-fun-and-games&highlight=hif4

 

[Gundy]

I did indeed run a single HIF6 in the past. Then it was twin HS4s now it is twin HS2s.
I still have the HIF6 and intake. I'll look and see and take a pic or two.
I use an Aldon Yellow dizzy with vacuum advance. I'll take a peek when I get home to see where the carb/intake port is located
on the HIF6.
That HIF6 ran flawlessly on my 1380. No hesitation. I just wanted two carbs under the bonnet.
It's still for sale....but it is a bit pricey. The intake is for a big bore and the carb is setup for big bore as well.
Really a neat bit of kit. Complete with stub stack, K&N cone filter, all linkage and cable included.
Sounds like you may have an intake leak.

The pic is from the past when I used the HIF6.

 

[Gundy]

The vacuum port
Sorry for crappy I-phone pics

 

[BuggerAll]

I have an HIF 44 on my 1275 in my BE. I started with a BDL needle but ended up with a BDK for better top end. As to basic set up, remove the dashpot, set the top of the jet about .050" down from the jet holder (use your caliper) and it should run well enough to get it properly set up. If it won't idle then something is wrong. Double check the o-rings in the cold start valve -

 

[nomad]

Just picked up a couple of HIF6 carbs off a Volvo and both have a provision for a vac line. One is plugged but it is there. if you have the carb apart I would double check to see if a vac line hook up isn't there. Should have a feed hole right in front of the butterfly when closed.

Kurt.

 

[Morris]

A sticky dash pot or a small vacuum leak could cause the symptoms you describe. Does the dashpot rise and fall easily when you push it with a finger? What is the dash pot doing at idle? Is it steadily hovering just above it's seat? When you open the throttle, does the dash pot rise steadily? Have you checked thoroughly for vacuum leaks? A vacuum leak short circuits the dashpot so that it will not rise accordingly to engine speed.

Vacuum advance is a provision for fuel economy and emissions only. A ported advance allows you to have no advance at idle which reduces your NOX emissions. However, in my experience, having a lot of advance at idle can make it difficult to get a low smooth idle. What is your static timing set for?

Nail recommends setting your advance at speed rather than idle. Your dizzy reaches full advance around 3000-3500 rpm and this is the area where advance is the most critical. Too much advance and you get detonation. Not enough and performance and economy suffer. Depending on your setup, your max advance should be in the 25-35 range. Old schoolers would set advance with a vacuum gauge. You disconnect your vacuum advance, connect a vacuum gauge to the manifold, run it up to speed and adjust timing until you get the highest vacuum then back it off a few degrees. I cannot vouch for this method, but it has been recommended to me by several good mechanics. The best possible way to set advance is on a dyno... but I guess that is probably an unlikely option :friendly_wink: