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MG MGB Technical - HS4 - '68 vs all the rest

Looks like I am developing a serious case of ship fitters disease. My 69B is all original - including well worn carb throttle shafts. I was pricing the carb rebuild kit, plus throttle shafts, machine shop service to ream the old carb bodies, etc. and I estimate that to rebuild would cost between $150 and $200, assuming I did my own assembly.
I used the LBC Quotation page and a set of new '68 AUD 265 replacements is only $315. Plus, these would have the fixed needle instead of the spring loaded needle of the 69-71 carbs, which is supposed to not wear as quickly. My 69B is de-smogged (well, its almost all original), so can anyone suggest why these wouldn't be a good replacement? And why are they $50 cheaper than than the earlier HS4 carbs?
Regards, Andy
Andrew Blackley

One word of warning. It seems like all new SU carbs now come with the spring loaded/biased needles. I expected the AUD135's that I purchased last year to have the fixed #5 needles, but upon opening them up found that they had the spring loaded/biased #5 needles. I believe Les B had mentioned this fact a couple of years ago, but it didn't hit me until I opened up the carbs. I can't address the reason behind the difference in pricing, but $315 is a good deal. Personally, I'd go for a brand new pair of carbs after having suffered through a not-so-great rebuild experience. I haven't heard any negative complaints about the new product, other than the cosmetics on some may not be quite as well finished as the originals.
SteveO

Andrew-
As those who know me are well aware, I have a near-terminal case of Shipwright's disease. I've rebuilt SU carburetors for years and have come to the conclusion that although I do as meticulous a job as I can do, they're never quite the same as a new set. I suspect that this may be due to the clearances between the piston/dashpot wall slowly becoming worn over the last 22+ years. When deciding to rebuild or purchase new one needs to be realistic. Since your carburetors are 33 years old, chances are the set you've got has already been rebuilt at least twice already. Add to this the fact that in this day and age $315 is not a vast pile of money. Unless you're just strapped for cash and have to get the car running right away, go with the new set.
Steve S.

I think I shall buy the new. I dont see a down side other than strict originality. But the 45D distributor I plan to buy aint orginal either. I was going through my old parts box yesterday and was remembering the "fun" I have had in the past with my previous rebuilding efforts. This car is a keeper and will be worth the investment.
Thanks for your opinions.
Regards, Andy
Andrew Blackley

What would be the best SU carb for an 1800V bored +.060 and stroked .035" ?

I've heard that HIF4s were good because the integral float solved starvation problems under hard cornering???

The 72 intake manifold I have has all kinds of fittings which look like they would cause interference with the airflow? Would an MGA manifold work better - with any MGB carbs?
Fred Horstmeyer

Fred. What do you intend to use this engine for? Peter Burgess lists such an engine using the -4 series carbs and one of his cylinder heads. On a road car, I think I would start out with a new set of 68 spec HS-4s, simply because they work and are less expensive than the other versions. On my bog standard (to the best of my knowledge) 68 GT, I had to re-needle the carbs for best performance when I bought the new set of SUs. Hence, I suspect that whatever carb you are going to start with, the operative words are going to be "start with" and you will have to change out needles and do some testing before you get your best results. HIF carbs do have a reputation for being slightly better around turns than the HS series. I, however, have never experienced fuel starvation on either road or track, with the HS-4s. As to the engine being "stroked .035", I hope you have checked con rod bolt head clearance with the camshaft to make sure you do not have interference problems. The last cam I installed was a CB spec cam from Moss of County brand. The shaft portion was oversize by .034", meaning it projected .017" further outwards on each side. Cam-bolt head clearance finally would up being .021-.022". You might want to find out what you have before running the engine. Les
Les Bengtson

Les, I would like to built the perfect street engine. Like Mark from Indiana, I am taking my time doing the research. I would also like to give my bbs friends lots of input.

Everything has 2-3 sides to it e.g. -
1. 3main= better revs, less friction
5main=stronger,smoother

2. Roller rocker=low recriprocating weight, less friction, higher rpms
std rockers=more reliable, cheaper

3. It's gotta idle in a traffic jam 90*+humid.
Alum flywheel hurts idle, but helps revs and weight, also quicker shifting

4. It's gotta have low-end torque.(I think that's what I want).
I'm not all that interested in rpms over 5-6 grand.

5. I want the largest displacement possible without getting the walls so thin they flex. prob. .060 over.

I currently have 3main 1800 block and a 72 18V.

I've got an 18 head on my cracked 1500(daily driver)and an 18L head on the V. I'm leaning towards the 5main with large valve head.

Won't use webers.

Lastly, I don't have big bucks to throw at it.




Fred Horstmeyer

Fred,
Rather than considering an MGA intake manifold, you may want to look at the APT offering. I've got one on order and will be putting it on in early June. I went from a pair of beaten-up but restored HIF4 carbs to new HS-4's. There are a number of threads in the archives about the stock intake manifold not being very efficient for flow because of the poor design on the cross-over tube. There are a few people out there running the APT manifold, and they seem to be impressed with what it delivers. I'm hoping that the new carbs, new Mike Brown reworked head, and the APT intake manifold will provide me a nice improvement on my current setup. Hope this helps.
SteveO

Fred, I don't think any MGA intake manifold will work with MGB carbs. The mounting bolt pattern is different between the MGA's H4 carbs and the MGB's HS4's carbs (the former at 12 O'clock and 6 o'clock and the latter at about 2 and 8 o'clock). I have had no personal experience with HIF series carbs, but it is my understanding that they use a different intake manifold than the HS series. I don't know what difference is; perhaps someone else could elaborate.
Marvin Deupree

Fred. To the best of my knowledge, the only difference between the HS and HIF intake manifolds is the thickness where it bolts to the head. The flanges on the intake manifold need to be the same thickness as the flanges on the exhaust manifold. As to the B intake manifold being inefficient, not that I know of. Most of the openings are in the balance tube and do not interfere with the flow of air to the carb ports. If you do not have "big bucks", why consider an aluminum flywheel? Lightening the steel one is less expensive. "The Perfect Street Engine" is merely a collection of words without defining what one considers the words to mean. For my purposes, a fully balanced, well built chrome bumper engine is about as good as it gets. I would give strong consideration to a Burgess "econo tune" head because it will give better preformance, still give good fuel efficiency and will have been rebuilt to use unleaded fuel. Whether the Burgess "Fast Road" head or Mike Brown's similar head is worth the money for street use is debatable. For all around driving, I believe, if on a budget, I would prefer an overdrive tranny to a tuned cylinder head. You need to define your requirements. Put them in a priority order then purchase them as you can afford them. When most of the money runs out, you draw a line and everything not yet purchased is "deferred" until later. It is easier to install a performance cylinder head with the engine in the car. Not so an OD tranny. Same thing about balancing the reciprocation and revolving parts of the engine. Hard to do once the engine is together. A valve job and an OD tranny cost about the same as a Fast Road head by Burgess or Brown. Les
Les Bengtson

Les, I'm doing this for my MGA.

I am leaning towards lightening the flywheel Vs alum. My experience with the old 3synchro tranny with worn synchros is that higher(even 4,000) rpm use is counterproductive because I need to wait for the rpms to settle b4 shifting. I've read that the lighter the flywheel, the quicker you can shift, but cost Vs gain favors the sightened std flywheel. I'd like to go as light as I can with it.

Steve O, above mentioned the APT intake manifold. I looked at the site and they purport it gives about 4hp. I wonder? If every part in the catalogs gave the hp they claim, we'd have a 300horse MG.

The British Automotive has great stuff on HIF Vs HS carbs. Bottom line, I think the bi-metal auto jet compensator will cause idle problems which I think will be my biggest challenge, therefore overriding any fuel surge problems. I think Hs4s are a less complicated design. I'm only considering HIFs because I have a set on the 72 18V.

I'd like to hear from you why the fast road head may not be a good idea. Why wouldn't the fast road be good for unleaded? How much worse might a fast road be for fuel economy?

Balancing the engine parts, chambers erc is a MUST. Friction reduction is a must, although I wonder about rocker spacers Vs springs. I do believe in the cumulitive effect re: weight, friction etc.

I would prefer a Mike Brown head simply because of access, shipping etc., although I curse Peter Burgess for writing the book that got me hooked on this kick!! It has replaced the Victoria Secret catalogs in my areas of the house. ;) I'd love to diy per Burgess but that is quite the point of contention here on the bbs!

I,d also love an od unit but installation in the MGA will be tricky as will be obtaining one, and they seem to be a high failure mode as are coils and fuel pumps. The 4 synchro that I have will be a challenge to squeeze in. I've got a salisbury 3.9 also. I'd like to cruise at 70-75mph comfortably, say 3500, but I will need to look into that.

Sorry to everyone for the loquacity.

Fred





Fred Horstmeyer

The HS-4 Carbs listed for the early 3-main MGB engines are similar but not quite the same as those for a 68. The needles for a 68 were orginally FX to meet the requirements for smog control. Also, OE HS-4s for 68 had the popoff valves on the butterflies, another dog I did not need for the applications I now had in mind.

When I ordered new SUs some years ago for both my MGA (18GA 3-main) and my 68 GT (for the very same reasons Steve S has mentioned), I ordered the earlier carbs since I am able to run with NO smog gear here in Idaho and still pass their smog testing.

The early HS-4s were correct for the 18GA engine used in my MGA, and they simply took the 18GF of my 68 GT back to a point where carburetion had been prior to smog. I then made sure both cams were spec'd for early use, and replaced the tired 25D dizzies with the "EuroSpec" 45D4 units, providing an ignition curve more similar to an early application than what came with my 68, and matching more closely the 3-main in the MGA. This combination is, at the least, satisfying to me, and I might suggest might provide somethings to consider in your quest for a decent and tractable setup for the road. FWIW.
Bob Muenchausen

Bob: I am not thrilled about the infamous poppet valves either. One could install the solid throttle disks and earlier needle, but by then the cost difference between the 68 carbs and the earlier ones will be eaten up. One thing that I would prefer is that on the carbs intended for the 18GH engine is that they use the simpler crankcase ventilation, i.e no valve.
Did your replacement carbs have fixed or spring loaded needles?
Andrew Blackley

Andrew,

I believe all the carbs are now coming with biased needles and plain throttle disks. I bought new carbs in December for my 71 GT, and that is how they came. You may need to experiment with needles anyway, as they are unlikely to be exactly what you need for your specific engine.
Paul Konkle

Paul. To the best of my knowledge, you are perfectly correct. On my 68 spec carbs, there were solid throttle discs and biased needles. Remember, these are Brit spec, not US spec carbs, at least on the 68. I did not bother to see if the later model carbs were the US or Brit specification for the applicable year.

Fred. Why would you not want to use a modified cylinder head. Cost. Simply by going from a stock MGA engine (about 79 hp) to a stock MGB engine (93 to 98 hp depending on whose spec you believe), you are gaining about a 20% in horse power. I never found my MGA 1600 to be wanting as a street engine. Increase the cars power to MGB levels and you should have a very fine engine. Add a Burgess "Fast Road" head or Mike Brown's similar version, new SU carbs with K&N filters and short velocity stacks and you will have far more engine than you really need. This goes back to my earlier "define what you want" question. You say you are on a limited budget, but are considering an engine which will require better brakes and upgraded suspension to be safe. My experience would lead me to believe that a relatively stock rebuild of an MGB motor, installed into an MGA would be "the ideal street motor". This means bored as necessary, fully balanced and carefully assembled. After I had a chance to play with the car and see how I liked it, I would decide whether it would be worthwhile to use a modified cylinder head or not. I would also have a chance to see how it handles and stops and decide whether more power would require modifications in that area. Finally, Peter Burgess offers several levels of performance cylinder heads. Andreas Pichler, on the A board, has tried Peter's Econo-Tune head on his MGA (working from memory). You might drop him a line and ask how he likes it. Performance is a blend of go, stop and what happens between the two. It seems that too many of us fixate on the go and only give lip service to the inbetween and stop. Since I am exactly at the same point as you--researching the engine that will be going into my MGA, my thoughts on this are more than idle theory or speculation. I am looking at a relatively box stock five main MGB motor with few "performance upgrades" but a strong, balanced, well assembled basic engine. I will "upgrade" as necessary and as I have time and money to do is. But only "as necessary". Les
Les Bengtson

Andrew:
My new carbs did NOT come with poppet valves, but they were also replacements for the early 18G-18GB engines. They did come with the biased needles as mentioned. I am also under the impression that for simplification of production, Burlen now uses the biased needles as this would simplify the range of air pistons necessary for the full range of HS-4 carbs. I would trust Les and Paul's comments otherwise.
Bob Muenchausen

Les, Whether or not you are in the process of researching your next engine, your opinions are highly regarded.

I always enjoyed my TR3A, which had pretty good power, but wasn't really pretty. I had a 67 MGBGT which could have used more power, I thought. The BGT taught me about single line brakes when a wheel cyl blew at exactly the wrong moment.

I admire the A as one of the most beautiful and well proportioned bodies of all the lbcs, thus my desire to stick to the spirit of the car i.e. no ford trans, stereos, or modern engines.

I will have ft discs, either 1600 or MGB with drilled rotors. Stainless brake and fuel lines. I WILL use the dual line non-servo brakes and master cyl.

I haven't yet looked into the oil cooler or the hoses. My wife loves to go motoring, and I would dearly love to have a functional roll bar. I want to try to create one that would be the exact height and shape as the top frame rail for the rag top, thus removing the need for the frame altogether. It just might work???


So, I am with you as far as the holistic approach is concerned. When I say a tight budget, I mean not going with the alum head, or the alum flywheel to cut cost. Using std rockers Vs rollers, std intake Vs ATP, or MGB brake sys Vs say Tilton, perhaps even trying a very conservative diy head,(against all advise).


I will weigh all these items one at a time as they arise, hopefully with your advise and the advise of our bbs community. Right now, I'm pulling my 72 5-main with L head, full synchro and salisbury 3.9, although I really would like to find a 3.9 banjo.

gotta run. as always, thanks for the feedback.
Fred Horstmeyer

Fred. Do you need the entire Banjo rear axle assembly or just the "pumpkin" to go into your existing axle assembly. Bob and Gil Schaulin at gbmg@aol.com used to have some early MGB rear axles and have mentioned the use of the pumpkin in the MGA rear axle. Do not have a clue as to what they charge for them. But, if all you need is the pumpkin, it should be possible to have one shipped to you. Les
Les Bengtson

This thread was discussed between 13/04/2002 and 18/04/2002

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