HIF4 carbs - metering needles?

[RickB]

I'm posting here because MGB guys have more experience with the HIF carbs than anyone else.

I have owned several MGB's and MGC's but recently have been into the Spridgets.
The one that I put HIF4's on has a 1500cc Nissan motor which is really nice for power and fits well in the engine bay of a Midget being a slightly larger copy of the BMC A series motor.

My only problem is that the mixture screws don't seem to work and the setup runs rich all the time.
I've heard this likely means the o ring for the metering needle is damaged or perished.

I did a float and needle / seat refresh with new lower gaskets on these when I got them and they work very well except for the inability to adjust mixture.
Do they need to be disassembled to replace the O ring that is likely the culprit?
I realize they could use a total rebuild however I don't have another set to bolt on while they are being rebuilt, my plan at the moment is to get my 73 Midget with the 1275 on the road and then put this Midget in the shop and get the carbs rebuilt.
That's not something I can do very quickly.

 

[Sarastro]

There are loads of books on SU carbs. This one, https://www.ebay.com/itm/NEW-SU-Car...093?pt=US_Nonfiction_Book&hash=item5898da43d5, is one of the more useful. Rebuilding SUs is not difficult; the problem arises if you have worn throttle shafts. Then you need to have new bushings installed, and that requires a little machining, which you probably are not set up for. Just replacing some seals should be easy; just get a rebuild kit for the carbs, one without needles and jets so it won't be too expensive.

That said, there are lots of things that can cause them to run rich. If the float height is wrong or the fuel pump pressure is too high, that can happen. Also, if you are using them on a very different engine, you may have to experiment with the needle profiles, but, obviously, first you need to make sure that everything is operating correctly.

 

[PAUL161]

Rick, here's an exploded view of the HIF, which you might already have, but keep one thing in mind, if you change the jets, the front and rear carbs have their own jet and float and are not interchangeable. Go to the Moss site and get more info. PJ

 

[RickB]

Thanks guys, ok I see in the picture that #24, 25, 26 & 27 are what I'm dealing with.
Anyone know what # 24 does?

24 373-595 SCREW, adjusting
25 373-600 SPRING
26 373-585 SCREW, mixture adjusting
27 373-605 SEALING RING

 

[RickB]

Apparently if you are mixed up about the whole "clockwise" and "anti-clockwise" thing you might be running a bit rich...
Coulda swore it was clockwise to lean it and antiCW to richen.

Now that I look very closely at diagrams and cutaways I understand how this mechanism really works - there's a pivot in there and a spring and a lever and the screw lets that lever lean out toward the outside of the body or pushes it in toward the center. In toward the center lowers the jet while out toward the body raises the jet. Moving the screw ACW raises the jet and CW lowers it. Finally - I get it!
Currently running at one full turn out from totally turned in, I'll turn them anticlockwise a few more turns this afternoon.

Where's the emoticon that has the guy hitting himself in the head with a hammer? I really need that one.

 

[RickB]

After work I raised the bonnet and leaned both carbs out by two full turns of the screws.
Here are the first noticeable effects:
1.
Lifting the pins previous to leaning caused the idle to rise immediately and stay higher than normal.
After leaning when I lift the pin on each carb the idle falls off a few hundred RPM. Still runs, just falls off.
2.
The normal idle increased by a few hundred rpm, and I can't adjust it down because the idle adjustment screws are not touching the part that they would push against if they reached all the way. In other words they are all the way out.
I'd think this indicates a vacuum leak, but I haven't been able to find one.

The car runs good and there's no visible soot coming out the exhaust like there was before.
I won't know about gas mileage for a while, I filled it up after adjusting the carbs so after I put maybe 50 miles on it I'll fill up again and see.

 

[PAUL161]

Number 24 is the temperature compensator adjustment screw. These are a misunderstood part of the HIF by most people. Senses carb temp and compensates fuel flow accordingly. If your car starts too rich or too lean for the weather temp, adjusting this device will usually take care of the problem. That's only if the carb is in perfect working condition. PJ

 

[RickB]

Thanks Paul,
That is great information, so turning it in (cw) would make it richer and out (ccw) would make it start leaner?
Is this the "bi-metal' doohickey I keep hearing about?

 

[PAUL161]

Thanks Paul,
That is great information, so turning it in (cw) would make it richer and out (ccw) would make it start leaner?
Is this the "bi-metal' doohickey I keep hearing about?

Been so long I forget which way to turn the screw for richer or leaner. Someone else that's adjusted one recently might chime in on that.
And yes it is the bi-metal device you've heard about. Really been testing this old brain, but I think tightening the screw leans it out, but don't quote me on that.
The HIF carb is a little harder to set up, but once done, it's usually trouble free. PJ

I need to add, setting the float while on the bench to where it is supposed to be is extremely important, as once the unit is on the car, you can't adjust them, at least I've never seen it done!

 

[RickB]

SUCCESS!!!

After putting 94 miles on it (back and forth this week the 13 miles from home to work several times) I filled up the tank and kept clicking the filler handle until it wouldn't hold any more.

3.1 gallons

Roughly 30.3 miles per gallon!
Not driving any more sanely than ever and the engine is running really well.
The rpm of the idle is up a bit from before but the idle is smooth and strong.
No acceleration problems and no pinging.
I'm very pleased with this result!

Can't wait for the next road trip, in 2 weeks we will be going on our club's Tulip Rallye - the annual run that takes place around Mt Vernon and Anacortes Wa.
We should get some good gas mileage on the way up and the way back - I'll be sure to check.
Todays result makes me think that 35 - 40mpg is within reach.

 

[PAUL161]

Rick, A little higher idle RPM is not a bad thing! Seems to be a contest as to who can get their engine to idle at the lowest RPMs. Our 72 is set just under 1000 RPMs at idle. Last check we got 32 MPG on non ethanol reg gas. 30 MPG on 10% ethanol, which I avoid as much as possible. PJ

 

[Flash_Harry]

Um, I think I might have a different slant on # 24 in the photo. Both the regular Haynes manual and Haynes SU manual call # 24 in Paul's photo the "jet retaining screw". That # 24 screw is a shouldered screw which tightens to its shoulder, then the temperature compensator (# 23 in Moss diagram) can pivot on the screw, and the small spring on the screw kind of keeps the compensator in place after adjustment. Both manuals say that the mixture is adjusted using the "jet adjusting screw" (# 26 in the Moss diagram) on the side of the carb body.

Of course, I could be wrong - at my age, that's happened many times! As far as adjusting rich or lean, a saying heard was:

"Lefty - leany, Righty - richy" - kind of makes sense to me...

Harry

 

[RickB]

Yes #26 is the mixture adjusting screw.
In my understanding it works by moving the top of the L shaped piece #23 in and out at the top which lowers or raises the jet.
Screwed in pushes the top of #23 in lowering the bottom of #23 and thereby lowering the jet and richening the mixture.
#24 acts as a pivot point for #23. What function the spring has is still a bit of a mystery to me though.
I read that #24 can be adjusted to richen or lean at start-up, which would mean it wouldn't be tightened all the way but instead be tighter or looser depending on the climate needs where the car is used.

Lefty leany is something I should remember for my HIF carbs.

 

[Flash_Harry]

Just checked both Haynes manuals to see what they say about the jet retaining screw. Both say to assemble the L-shaped compensator and jet, get them correctly placed in the body, then: "secure the assembly with the retaining screw and spring" - sounds like it doesn't have an adjustment capability. I think maybe the spring is there to keep pressure on the compensator - keep it in place?

 

[RickB]

In that case the spring would be putting pressure on the bottom of the compensator.
I have to take one of these apart again soon and look closely at that area - what I need is a junk HIF carb to play with.
I'll check ebay.

 

[Flash_Harry]

I think that's just what the spring does - keeps pressure on the bottom of the compensator, maybe keeping it in contact with the tip of the mixture adjusting screw. That's my story, and I'm sticking to it.

 

[RickB]

Makes sense, I just want to get in there and look at it - see what it does with my own eyes.
No "junk" HIF's on ebay at them moment for cheap so I'll probably have to go look through my boxes in the shed and see if I already have some...