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MG MGB Technical - Easy 40 hp

About a year and a half ago I noticed that my 77 B just didn't have its original pep. I decided to replace the old Z-S and catalytic converter with a new Weber DGV and exhaust with header, purchased from a local mg specialist shop who did a turn-key intallation. They did a poor job and I have spent the intervening time trying to correct the new problems. When the car came back from the local shop it ran even worse than it did with the old set-up: running rich, excessive blow-by, no acceleration, vacuum leaks everywhere and the car drove like it was dragging a ton of lead. Corrective measures included rejetting the Weber, replacing the electronic ignition, distributor, and cam. All these were done step-by-step with a month or two of driving to analyse the effects. All to no avail. However, the engine idled well and ran smoothly with no other side effects.

I just returned from a short drive downtown. While out I hit a rough pavement joint at about 40 mph and the car lept forward like a dog off its leash. I don't know what broke loose, but the original performance seems to be back. So, I now reccomend driving over rough roads, just give the car a good shaking, before making any radical changes.

Doug
D. Cook

My father had that with his '71 GT after driving through a deep loading dock on the parking lot where the driving test took place!
Willem van der Veer

Excellent! I like a guessing game and I'm betting it was your right foot that hit the floor. Have you got twice as much throttle travel as before? A friend of mine bought a VW camper van a few years ago only to find it wouldn't climb the hills in the prettier parts of the Lake District. He came near to a nervous breakdown rebuilding the entire engine on evenings and nights getting it ready for a trip away, only to find no improvement. A few weeks later, he asked me to help tune the carb. It was quickly obvious (as it always is after the event) that the cable was only allowing the throttle to open half way. He didn't see the funny side for a while.
Steve Postins

Hey Doug,

Just a thought. Is it possible that when altering the exhaust system on the car, the shop which did the "poor" work, left some type of restriction in the system? This was a fairly common problem with late '70's GM V-8 products, where the inner exhaust pipe would collapse from being sprayed with the cold water off of a wet road. The outer pipe was fine, and disguised the inner pipe's collapse. This condition provided very similar symptoms.
As I said, "just a thought".
Good luck!!

JR
JR Ross

Doug you brought back old but not so pleasant memories of the Chevy exhaust of the 1970 chev. I was working at a GM dealer at the time and Ill never forget the look on the customers face when I put the Hacksaw to the almost new pipe. I promised him if this wasn't the problem I would pay for a new pipe. Needless to say he paid. Hope this is not too far off the subject, but the diagnosis of something left in the exhaust, well I have seen it many times.

Cec
Cec

You probably just needed a BFH. I have two different ones, a smaller one for the MG, a much larger one for my 245 Volvo.

I understand ones that work on Fords require two people to properly apply.

rn
RN Lipow

Sounds like you found the second barrel on the DGV. I had one of these, and while I found it easy to live with, I really had to burry my foot to get the second barrel to open. I would estimate that only the last 1/3rd of the pedal travel involved the secondary in any way. Maybe your linkage was binding?

Pete
Pete

Sometimes the obstruction in the exhaust system is in the front box muffler. As they rot, sometimes a baffle comes loose and in flopping around inside the muffler, it can either obstruct the flow or even completely cut it off. It is then that the "BFH" of serendipity (such as your rough road or a pot hole) can knock the offending baffle or other scrap loose eventually, and, Viola! instant gratification! All that to say that you may just need a new muffler.
Bob Muenchausen

This thread was discussed between 20/05/2004 and 23/05/2004

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