Welcome to our resource for MG Car Information.
MG TD TF 1500 - MGA Carburetors into TD MKII
|It's now clear that the 'MKII carburetors' that I've begun working on are actually from an MGA. (See thread 'Mystery Part on H4'.) It turns out that both carburetors are AUC 6020 bodies from MGAs. After a bunch of book/catalog browsing (and a look at a friend's MGA) I've decided to give something a bloody go -- I'm going to try to convert the MGA style to that of a TD MKII. The biggest difference is in the linkage/cams for advancing the throttle when the choke is pulled out. Since I'm going to be installing new throttle shafts, and will be drilling holes in the new shafts, I've ordered the MKII components from Abingdon Spares. It would be a real bear to try to resurrect the MGA choke linkages. Maybe I'm wrong as can be, but I thought I'd give it a try. I'll let you know what happens. Anybody else tried this?|
When I bought my TD it had 1 1/2 carbs from an MGA with Austin Healey linkage! Sent them off to John Twist for a rebuild (they were in horrible shape!) and he matched up the linkage beautifully! So now I have MGA carbs with TD linkage!
When I got my 52 TD it had MGA carbs on it. They had used the lower jet levers from the Td and the original throttle lever from the MGA.
The original owner used it this way for many years. I'm currently converting back to the original carbs. The original stile air intake manifold will not work the hole spacing is not the same. So they replaced it with two flat air filters. Now the horn is in the way so it had to be moved.
The MGA carb is deeper so the clearance to the hood is reduced.
They will work with a little modification. Also remember to plug the vacuum line port .
Bud - Before I would send them to John Twist, I would contact Gregg Purvis, Mich at firstname.lastname@example.org (gregg used to be be John's restoration guy and is finally now out on his own) or Joe Curto in NY. MGA 1 1/2" carbs will work fine but are different from MK II's. Did you try Mick for some rebuilt one's ? tom p
|Bud --- I long ago converted MGA carbs to work in my TD. I believe I put TD parts on to advance the throttle when the choke is pulled. If it stops raining tomorrow I could try to get some pictures if that would help. I recommend that when you order the new shafts you put the teflon bearings in the body of the carbs. I have the proper reamer setup for that if you would like to borrow it. Let us know how you are making out with this project.|
|R. K. (Bob) Jeffers|
|Tom, I'm pretty much a DIY type. I'll be doing the conversion myself. Bob - the bodies have brass sleeves in them. It looks as if standard shafts will seal quite well. I'm just trying to get this guy's carburetors functioning so that I can get back the set that I loaned him. (They belong to 'the53'. See http://www.ttalk.info/The53.htm)|
|Snafu! The carburetors are together after doing the various choke/throttle conversions. New throttle shafts are installed. Will idle fine, but boggles when asked to accelerate. Finally accepted the truth this afternoon -- the bodies are worn in the shaft areas. Darned near stalled when I gave it the spray-cleaner test --- both ends of both carburetors.|
Am in need of bushings/bearings, etc. Bob, I hope the offer is still open. Any leads as to where I can get the teflon bearings? TIA - Bud
|Bud - If you decide to try the teflon bushings in that Bb suggests, let me know. I have a number of the bushings that I have left over when our daughter picked them up from Burlen Fuel Systems a number of years ago when she was in England (I wanted 4 bushings and she got 4 sets of 4). Cheers - Dave|
|There you go Bud, Dave to the rescue. Boy don't we have nice bunch of guys on this BBS? Bob|
|R. K. (Bob) Jeffers|
|Dave, I'd be delighted to get a set from you. I'll email you off-list.|
|Just a question...is installing the MGA carbs alone enough to give you a big increase, or do you have to have larger valves installed as well...(how large and from what model)?|
|gordon lawson - TD 27667|
|Oh and what manifold would you use?|
|gordon lawson - TD 27667|
|Gordon --- Those hotroders of the early 1950's new what they were doing.|
I was chicken and used the larger valves from the MKII. The head needs to be opened up around the new larger valves. I opened up the intake manifold as described in tuning insructions for the XPAG, then opened up the intake ports in the head to match. The intake manifold can be opened to match the 1 1/2 in. carbs OK. You will have to check the exhaust manifold to see if it will flow smoothly into the larger sized exhaust systems now being sold (TF size) mine wouldn't so that got opened up as well. All of this just brings you to where the MKII was. BTW I found that the needles in the carbs worked better if changed to LS-1 needles. The GJ needles didn't seem to work as well as they do in the 1500 engine. In addition if your engine is out for any reason have the flywheel lightened and rebalanced.
Bud Did you say that there were brass bushings in the carb bodies? Standard 6020 bodies don't have brass bushings. That means somebody has worked those over before. The Nylon lined bushings are 3/8 in. OD. Are the brass bushings larger than that? If so then you will have a time opening up the bodies putting in new brass bushings then installing the Nylon bearings. (brass on brass isnt a particularly bearing).
|R. K. (Bob) Jeffers|
|"particularly GOOD bearing" Bob|
|R. K. (Bob) Jeffers|
|Bob - When Bud stated that you have a reamer to install teflon bushings, is it for the steel backed teflon bushing that Burlen Fuel Systems sells? These are a split steel bushing with a teflon lining that requires a 9mm opening as I recall. Dave|
|Yes, there are some brass bushings in place at this time. The throttle shafts that 'almost' work are ones for 1 1/2 carburetors from Abingdon Spares. I've installed LS1 needles in the carburetors. I'll have them pulled apart tomorrow to see what's what with the brass bushings.|
The intake manifold being used is a MKII manifold. There's a recent thread on the manifold issue. Interesting that the MKII head/manifold uses the same manifold gasket as the standard TD. I'm told that there's a knowledgeable article showing that a standard TD will gain little, if any' by simply converting to 1 1/5 in. carburetors. I'll be anxious to get these running so that I can try them on my 'upgraded' engine that is a bit beyond MKII specs. Lawrie Alexander matched my head to my manifolds.
|Dave -- Yes thats what I am refering to. I don't remember that they were split though.|
The counterbore that I use is 0.375", 9mm is about 0.354" I don't think the bearings would fit in the holes I ream. Can you mike the bushings (bearings) to verify the size? So far we have done carbs for four cars and have had good results on all four. Is it possible that Burlen makes two sizes of bearings?
Bud -- Maybe to get the brass bushings out you could start a tap in them and then put the body of the tap in the vise and whack the body of the carb with a soft mallet. If it proves that I have the wrong size counterbore I'll get the right size. But since they used a 5/16" shaft I don't think they used a 9mm bushing (bearing).
I think we are on to something here that needs to be explored to add to the archives.
|R. K. (Bob) Jeffers|
How are you getting on with the H4s? On a slightly different track the 'boggling' may be caused by too strong return springs in the dashpots. The TD mkII and TF used the lightest spring at 2 1/2 oz rate marked with blue paint. The MGA used 4 oz rate marked with red paint. On the mixture try the GL needles, they suit modern fuels better.
|The brass bushings are cast in place in manufacture. I think all H series were so made, but certainly all H4 I've looked at. If they have been rebushed, the bush or at least the hole for it will extend all the way into the throttle bore; the originals do not.|
|The latest is that I've opted to send the bodies out to Lawrie Alexander for new bushings. Discretion got the better part of valor. The brass bushings are as FRM describes them, i.e., stopped in the bores. Graham, the springs aren't colored. I've installed LS1 needles in both carburetors.|
Good move to sub out the rebushing, the folks doing the refurb work will get it right first time.
FRM - the brass bushings definitely indicate reworking when new H2 H4 carbies had the throttle spindle running straight into the cast zinc alloy body.
on the missing paint not at all unusaul to find it has disappeared over time, it was only ever a little splash.
worth checking on a small accurate kitchen scale 2 1/2 oz or approx 70g for one inch compression will show compared to 4 oz 115g. Sorry I'm not familiar with the LS1 needle.
I am sure you know but a word of caution; dont expect too much from the bigger carbs. Far greater power influencers are timing, mixture, compression ratio, general state of the engine etc. My MkII on full chat around 5500rpm only holds about 1/2 inch of piston lift on the H4s. Maybe you have a seriously tuned engine and are aiming for 7000rpm then the H4s will come into their own.
Hope to hear good news that you cure the boggling.
Not sure re H2 or H6, but I have been doing these since mid 60's, and I have seen a lot -hundreds- of H4s with cast in place bronze bushes which most definitely have never been reworked. I am not entirely sure that all H4s I've done have them, as wear here was not much of an issue back then. I have a number of bodies here, and all with the shafts out have the bushes; I'm not inclined to strip the still assembled ones!
I second your comments re the "paint" on the springs.
"My MkII on full chat around 5500rpm only holds about 1/2 inch of piston lift on the H4s" If this is sitting still under no load, it is a meaningless observation, as the engine is only producing the power required to turn itself, hence only drawing a similar amount of air. If it is on the road, real or rolling, at full load, then your carbs are seriously out of whack for the engine. See the recent Spridget tech thread "heavy misfire at 5500rpm" for an extensive discussion of how the SU actually operates.
|I'm planning a full report when finished, but here are a couple of images that you might want to see in regards to the present brass bushings:|
http://www.ttalk.info/mini-Inside.jpg shows that the brass bushing is stopped short of the end of the hole.
http://www.ttalk.info/mini-Outside.jpg shows the view at the outside of the hole. (Sorry about the fuzzy focus)
Yes, those are the cast in bushes. If you look under magnification, you can likely see that there is NO gap of any kind where the bush stops in the bore; and, on the outside, there are usually places where the alloy has run over the edge of the bronze, leaving no clean break between the two. It looks markedly different than even the best fitted "added later" bush.
Humble apologies I was clearly wrong about the brass bushes.
On the piston lift, we will have a difference of opinion.
Bud, any news?
|I'm putting together a full report, but here's the latest. I'm going to driving in today's Fourth of July parade using the MGA/MKII carburetors. Having them rebushed (by Lawrie Alexander) made a tremendous difference. I'm hoping to deliver them to their rightful owner next week. Can't really tell if there's any added performance. Any suggestions for a reasonable comparison test?|
|Since HP is rated at a significantly high RPM, I think time to 5000 RPM shifting from first to second to third in two directions (non wind aided) by the same driver will tell you if you are delivering more power. That test (absent a dynomometer) will tell you if you are developing more HP by getting you to your higher engine speed (and resulting wheel speed) quicker.|
Try to do the comparison tests (small and large carbs) under the same approximate temperature and humidity conditions.
Just my two cents
|DAve, I'm looking for a KISS test. My tachometer has an imaginary $$ stuck on at 4500. What I may try is a run on a flat section of the local divided highway. I'll probably use a stopwatch to measure the time it takes to get from 3000 rpm (~50 mph) to 4500 (~75 mph) by stomping on the go pedal in top gear. I'll try this with the MGA carburetors and then repeat it when I get my own back on the car.|
|Bud, that would work, except load the car as heavily as reasonable (take a 225 lb navigator/stop watch guy with you) because the heavier you are, the more the difference in power will show in a time trial.|
Without using a head with larger valves I doubt you'll notice any performance increase at all - in fact performance may suffer at different rpm ranges. Should be interesting to see what you find out though.
|For those not brave enough (like me).|
FYI Gregg Purvis is whom did mine for the TF in Ada.
He does excellent work! When I got them back ..bolted them on and fired right up!
David 55 TF1500 #7427
|Just to refresh (this thread's getting long). The carburetors are not from my TD. They're from a TD that was a MKII when it left Abingdon (TD/C 15185)whose engine has since been replaced by an early engine (XPAG TD 3265). These carburetors were on the intake manifold and we expected that they were fromthe original MKII. It wasn't until I started working on them that I learned that they were actually from an MGA. I have now modified them into thinking that they are from a MKII. I have been testing them on my TD (late 53 engine that has been brought to TF 1250 specs and then some). I would simply like to quantify their effect on my car before I hand them over to their owner (probably next week).|
This thread was discussed between 06/06/2006 and 06/07/2006
MG TD TF 1500 index
This thread is from the archive. The Live MG TD TF 1500 BBS is active now.