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MG MGB Technical - HIF4 Throttle Disc different on each carb

I have a 1974 mgb roadster, U.S. spec, with carb issues. I took the carbs apart and noticed one carb has a solid throttle disc and the other has the disc with a spring poppet valve operational. I've never seen this before, so I guess somewhere in the past, the PO replaced one of the carbs.
I've got the carbs apart for a complete rebuild due to them sitting for several years.
Is this going to present running issues? Should I leave them as is, or replace the disc with the valve with a solid one to match the other?
C


C Crews

Replace the one with the valve as idle balance will always be a problem. Denis
Denis4

I agree with Denis, I would change to two solid discs. At least the solid discs are cheaper than those with the valves!

I would also check that all the other parts are "paired" too. If you have an odd set of throttle discs, the chances are the springs, needles and dampers will be different, or at least worn differently.

Mike
Mike Standring

Whilst it's certainly better to have two the same, and the poppet valves are known to cause problems, when they are functioning correctly and the butterflies are fitted correctly having one of each won't cause idle balance problems, although it will result in a tiny difference when close to full throttle. They are only supposed to open under conditions of high manifold vacuum i.e. closing the throttle at higher rpms than idle, which reduces emissions on the overrun.

Changing a butterfly can cause its own problems if it isn't seated in the carb throat correctly, which was why I opted to solder mine up while still in-situ when they started sticking open on cold starts (racing idle) rather than replace them. To me the tiny performance improvement that might have resulted wasn't worth the hassle of changing them.
Paul Hunt

Okay, I'm a little afraid to solder mine shut, fearing someday a piece might get sucked in the engine. (just paranoid)
I have another question. Not being real experienced with SU, does part 15 move inside part 18? My two parts are still together and I was trying to remove the nut part 20, but can't get a wrench on it. I didn't know if part 15 was suppose to come out, therefore allowing me to put a socket on the nut part 20. See image.


C Crews

C,
Buy another solid disc. The poppet valves become unreliable AND when the throttle is open disturb and restrict the flow of air. Soldering them up solves the former not the latter!
Allan Reeling

Yes, part 15 (the jet) should come out when the bi-metal jet lever (not shown) is removed by undoing its screw.

I challenge you to detect the difference, Allan!
Paul Hunt

background info -

44 Secrets of the SU Carburettor Part 1 of 2 - http://www.youtube.com/watch?v=7GRAcqDySog&feature=plcp

43 Secrets of the SU Part 2 of 2 - http://www.youtube.com/watch?v=60Bj_2cZQnc&feature=plcp

35 Tuning HIF Carburetters - http://www.youtube.com/watch?v=ASeMfXfjNpw&feature=plcp

there are more if you find these helpful
Nigel Atkins

If you have the service kit part 15 comes with it, so you can use some force to remove it, they are usually stuck together with scale, my old car had one of each disc! we could have swapped!
Pat Gregory

If it shows on the flow bench and rolling road, that's good enough. Tuning and maximising efficiency is all about the small things, grinding off roughnesses, removing obstructions (noses of valve guides, poppet valves) matching chamber volumes and manifolds and ports etc., etc. Individually not major, but together really obvious. My last 1800 B showed 15% increase in BHP whilst giving 30mpg! That I could detect!!
Allan Reeling

Thanks for all your input.

I was reading on MGCARS.NET and saw an interesting comment by FR Filmore, where he says:
"HIF have tiny O rings in the cold start mechanism; when they die, the "choke" is effectively ON, and you get all the symptoms described. Since the choke effect diminishes with RPM, leaning out will help a bit at/near idle but kill performance and eventually the engine at higher throttle openings.
Rebuild the carbs, with special attention to the cold start".

After I soaked my starter valve in carb cleaner to get it apart, I noticed black goo in the areas on the shaft that look like O rings should occupy. There is no mention of O rings in this area for this shaft anywhere, that I can find, even on the SU website.

Attached is a pic of the two groves where I removed the black goo. If these grooves are not for O rings, what are they for?



C Crews

Hi C,
Moss US cattledog Carby section HIF4 shows part 52 373 715 seal starter valve X 2 for the carby. Also Moss UK part 27 AUD3602 X2. Punched the UK part number into a local suppliers web site came back $3.19AUD each. US is usually far cheaper than anything here.
K Stuckey

K,
I'm pretty sure those are the larger seals that go on the valve body, but not on the inside of the shaft where my arrows point. I could be wrong.
Looking at my picture, it just seems odd that SU would cut two grooves in the shaft and not put anything in them.
Cleve Crews

The Leyland Parts Catalogue only shows one of AUD3602 for each carb, plus a gasket, although it's not clear where the O-ring goes. However SU Carbs say late models did have two O-rings with no gasket. This http://classicmini.weebly.com/hif-44-diagram.html shows items 41 and 42 O-ring inner and outer, but they look too big for the spindle. It also shows 43 spindle seal which looks more like it goes over the narrower end than in the grooves in the spindle.

I was under the impression that failure of this latter seal results in fuel leakage from the spindle to the outside.
Paul Hunt

If you can wait till i shake off this chest infection i will remove the cold start assembly from the pair i have on the bench, and look.
Allan Reeling

Allan,
That would be wonderful. I don't want to put them back together until I get the answer, so I can wait, as long as you don't have something like Aspergilli, Blastomyces dermatitidis, Histoplasma capsulatum or Cryptococcus, which might take a while to get over.
Cheers and I hope you feel better soon!
C
Cleve Crews

I took this vid link out of my previous post as it is for HS but perhaps it does have a relevance to thetype of 'o'ring (?) (if in a different size/location)
- http://www.youtube.com/watch?v=Elgfc1xZkt8&feature=c4-overview&list=UU40j4KqUJPMVv4FQ29ro-xQ
Nigel Atkins

Hell Cleve attempting to write those, whatever they are, in my weakened state would probably see me off!
Allan Reeling

Nigel,
Great video, but not a HIF carb. Mine is an HIF 1974 USA spec.
Thanks anyway.
C
Cleve Crews

Cleve,
yes I know that, that's why I took it out before and put the vid is for HS but as you're posting about 'o' rings and if these come in contact with petrol they might need to be (Vitron?ol? /whatever John Twist said) - just the principle - if your 'o' rings don't come into contact with petrol then just ignore me as I must have misread a post

I think I may have the same illness as Allan and it makes me even more dozy than usual

Allan,
I'm in my fourth week of this, cough with nasties, tired and sleepy often, mostly I feel cold even when heated but then I sometimes get sweats all of a sudden - even my wife admits I'm ill as I'm off my food, practically unheard of!
Nigel Atkins

Nigel,
That's real man flu, and don't let anyone tell you otherwise!!! Still waiting for A B's to kick in………………………..have cancelled my friday night at the pub……………..now that is serious…………….off food AND off beer!!
Allan Reeling

"I'm in my fourth week of this"

Sounds like what my medic cousin called '100 day flu' which was what I had. While the infection part has cleared up I'm still coughing, sneezing and have other nasal issues three months later.
Paul Hunt

3 months???? I.m looking for a Stanley knife!!!
Allan Reeling

yes real man-flu, like you Ive also missed out on a couple of weekend runs to village pubs selling good quality ale

under 4 weeks and I'm beginning to feel better but I was in bed by 7.30 pm yesterday

100 days, I've had various coughs since mid-September but nothing like the last four weeks
Nigel Atkins

Have just spoken to a "camera" friend in Stockport, he thinks our real problem is not enough real ale!! But will have to start with halves, can't lift a full pint!
Allan Reeling

yes I'm sure you're right

when you have a lower limit to how much you can have the quality of the real ale is very important too - last weekend we went for a run in the midget to pub that normally serves the ale in very good condition and as I was limited because I was driving and hadn't had a drink for two weeks I was disappointed to find the ale wasn't as good as normal, of course when we got to the next pub their was a great local ale on and it was served in great condition and I'd already used up half my quote on the previous ale but I suppose that what makes the really highs so high because of the occasional dips (if you're selective about what you drink and where you drink it)
Nigel Atkins

"he thinks our real problem is not enough real ale!!"

I'm doing my best. It's always good to have a hobby in retirement, mine is chemical engineering ... converting beer, wine and whisky into urine.
Paul Hunt

Paul there are quite a few breweries that do that for you in their brewing process or finish

unfortunately the more new breweries that open the more that are not very good or very poor indeed

8 years ago we only had 5 micro-breweries in Northamptonshire now we have 19 but it's all of the older ones that are the better and not just because of experience

we have one part-time brewery that started in 1997 that is hard to get hold of in the county but does stand out ales, then we have two or three that consistently have very good beers, the rest of the brewers go from good to acceptable to bland to consistently poor

of course in the county town we have the mega-kegery, fizz-factory that may recirculate waste water but at least it's not Fosters, so the lager drinkers tell me
Nigel Atkins

That's it then, some on-line medical research. All sufferers to to get a designated driver and seek a good real ale establishment and imbibe, medicinal amounts of ale. NOT!!*** lager, which is contra-indicated for Man Flu. At least 4 weeks, but 100 days seems to be indicated as necessary by Nigel. I'm with him!!!
Allan Reeling

Beer is quick acting. Just dismantled the cold start. NO O rings on the shaft, just the larger one on the body of the unit and the shaft seal under the metal cap.


Allan Reeling

What was the problem again? (Been taking my medicine ...)
Paul Hunt

Allan and All,
Thanks so much for taking the time to get the answer for me!
You are fortunate to have local breweries. My wife and I just drove over 300 miles to Asheville, North Carolina to enjoy a night on the town and some of the local beer. Our favorite brewery there is Wicked Weed. Hops being the weed.
If you ever get a chance to visit North Carolina, be sure and pay a visit to this wonderful little city in the Smokey Mountains.
I sent you a picture of us freezing out buns off!


Cleve Crews

great stuff Cleve, the photo must have been before the brewery trip if you felt the cold :)

US brewers became more adventitious with the use of different hops and other ingredients sooner than most of our UK brewers - in fact some where paying for whole crops to be grown

if you ever get over this way we can let you know the breweries that really know how to use hops to make a hoppy beer that really tastes of hops

old joke - what's the difference between a dead frog and (selected beer) - there's more hops in a dead frog

Medicine
just for the record my severe man-flu is over, one day short of 4 weeks - so today I have an eye infection - this maybe because I've not partaken of proper medicine for a week
Nigel Atkins

My wife after a few beers in Dallas, TX
This is no stuffed animal. It's a real Texas long horn.


Cleve Crews

I hope she returned it when she sobered up :)
Nigel Atkins

This thread was discussed between 01/12/2013 and 09/12/2013

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