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MG MGB Technical - New burlen SU carbs

Has anyone installed the new Burlen made Su carbs, especialy the HS-4 carbs? If so, what has been your experience with them? Is there a notable improvement over the old, perhaps rebuilt carbs? Thanks, Kenn
Kenneth von Wolf Lewis

Kenn. Old, perhaps rebuilt carbs are, at the very least, 42 years old. The new carbs are--new! Thus, my decision, several years ago, was to replace the old carbs with a new set. That way, I know what I am starting with. I know how many times they have been/will be rebuilt. I do the same thing with brake master cylinders. New ones are available now. They may not be available in five years. I replace safety/performance parts with brand new parts when I can, then, keep track of them for the next owner so that he/she will know what they are getting. My daughter's car had such a history with previous owners.

When the people we bought her car from, for her to learn to drive on, handed me the receipts that they had kept, then, handed me the receipts the previous owner had given them, I knew we had an exceptional car.

Get the new parts while they are available and keep all of the receipts for the next owner. Someone will appreciate the trouble you spent to do so.

Les
Les Bengtson

Kenn - Anyone who has installed a new set of carbs in their MG since 1987 has a "Burlen built" carburetor in their car. I had an oportunity to tour the Burlen Fuel Systems facilities while in England three years ago and was amazed at the vast number pallets full of SU carburetor bodies. Burlen Fuel Systems put out very high quality products, parts and services. It is possible to get virtually any part that may be needed for any SU product regardles of it's age. They also have on display some really awsome SU carburetors. For instance, one for the WWII Spitfire fightee planes - it is a massive carburetor, measuring nearly 2 feet on a side. Cheers - Dave
David DuBois

Kenneth,

I purchased the Burlen units about 4 years ago, and have had no problems at all. Fit and finish of the carbs was very good. These were for my 67' GT, with HS-4 carbs.

Steve
Steve Brooks

Thanks to all. I, too, have rebuilt the HS-4 carbs in my 67 B-GT and still unhappy with their performance. Have ordered the new carbs and hope to install next week. At this point, while my car lacks some cosmetic touches, she is virtually new mechanically (and yes, I do have all the paperwork, but she goes when I go). As I use her as a daily driver, salty roads excepted, and just love a "brisk" drive thru the nearby hills, her on the road performance is most important. As an aside, this is my seventh LBC, which just proves the old saw, "there is no fool like an old fool" Thanks again, Kenn
Kenneth von Wolf Lewis

I purchased a set of new carbs in '95 to pass emmissions in CA. At first I couldn't figure out why the engine wouldn't idle properly. After dismanteling the piston assemblies, I found that the front piston had a large dent on the outer diameter of the suction chamber. I was able to polish it out but was quite surprised that such an obvious flaw could have made it past quality control. After repairing the piston the carb ran flawlessly. Ray

RAY

In 1999, I installed a set of the then new Burlen HS-4s. Almost immediately, I discovered that some annoying, but significant problems my well rebuilt, but OE (1968) carbs were never able to shake, disappeared without having done anything more than simply bolting up and correctly setting up the new carbs. Whatever the sources of those phantom problems were, they appeared to be related to the wear and tear on the old carbs that rebuilding had apparently not addressed. Others, having done the same have usually reported much the same luck (Ray's luck not withstanding). There is quite a bit of discussion about this situation in the archives.

After at least 30 yrs on any our cars, these carbs have been subjected to many things which simply aren't dealt with by rebuilding a carb, no matter how carefully the usual rebuilding procedures are followed or how well the typically replaced parts (like new throttle shafts/bushings, float valves, jets, gaskets, etc) are done.

We often forget that these carbs, especially on B-series engined cars like ours, are subjected to repeated heat cycles every time we run our cars, and that they sit, anytime we shut off the car, in close proximity to the exhaust manifold and its heat. Even with a heat shield, they take more heat than if they had been mounted on the other side of the head. This exposure can cause components to change shape to some extent. Not in a seriously bad way or we would have much more obvious sealing problems. But the cummulative effects over 30+ yrs, can be significant.

The other, probably more major factor is how any of our OE carbs were treated by any number of POs or PMs. Not every owner is as diligent as Les in keeping records of what has been done to them. That can be a real problem if the carbs have been dealt with by hamfisted mechanics, or folks who simply did not know that some aspects of SUs rely on the fact that components are not necessarily interchangable simply because they have been mass produced. With no clue what the history truly is, we can chase our tails around a carb tuneup for a long time.

When SUs are made the air piston/dashpot assemblies for EACH carb are matched so that the very finely machined clearances necessary (in the 0.0001" range) to give a specified air piston drop rate are maintained so that that particular carb functions as intended. Many times POs/PMs have swapped parts around or even replaced dinged dash pots and air pistons with others from "good, but used" carbs from their parts bin or pulled from a junkyard. It can become questionable after such work whether the carb will go on to work as it should. Ray should have probably returned the set he has for a replacement if he found this problem early. {All quality is a spot check at best, and depends ultimately on the care given by the assembler and by the time we get things, how they have been handled in transit to us.}

Add to this that dual carbs are sold as a matched set ~ matched for air flow. And air flow is determined by how each air piston/dashpot works ~ properly, we hope. If the sum of the parts of each carb ~ new or rebuilt, are working correctly and are/remain truly matched to each other, then you should have good luck in adjusting them and with their performance. But if you find that they no longer function as originally intended, then all bets are off. It is amongst this last group (and probably more prevalent than folks would like to think) of carbs floating around the MG car world that a new set of carbs will show the best contrast between brand new and simply rebuilt.

Remember, most SU rebuild kits don't include new air piston/dashpots, and yet most old carbs tend to show wear on the slide the air piston rides on. Also, some have been "polished", "touched up", "cleaned up", or "repaired" by well meaning workman/owners with abrasive cleaners/tools. Does that matter? Perhaps not that much, depending on the aggressiveness of what was used, but other aspects due to age which are not addressed by rebuild components can suffer eventually from cumulative wear and distortion and do seem to affect the ultimate performance compared to a new unit.

As has been said of other components, it is often hard for us to judge the genuine improvement of any component's rebuild or replacement with an alternative if all we have to compare the result to is a tired and worn out piece of gear and its dysfunctional behavior.
Bob Muenchausen

Bob, Many thanks for your meaningful input. My experience is very much parallel to what you describe. Having owned several LBC prior, including three MGBs, I have some feeling for how SU carbs should perform (in fact I passed my 2nd year of college French because I could balance and tune dual Su carbs on my instructors car) The current carbs on my 67 BGT have been rebuilt and continuously tweaked to my continued frustration. Your comments are right on. Thanks, Kenn
Kenneth von Wolf Lewis

Installed the new Burlen SU carbs yesterday. Due to weather, only got in a short test drive, but they look beautiful and run soooo smoothly. Also seem to have a few neat improvements over the originals.
Kenneth von Wolf Lewis

This thread was discussed between 07/07/2006 and 13/07/2006

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.