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MG MGA - Puzzler

O.K. folks!

Here's a "puzzler" that I had several years ago involving my MK II Deluxe. It took me nearly a month to figure out the problem and thoguht I'd pitch it out on a thread to see if anyone else can figure it out, not having the benefit of the car to diagnose, this is one you'll simply have to think out in your head.

The 1622 engine ran fine at idle. Smooth as could be. I'd get in to drive and at 2800 RPM, it felt like I hit a 100 MPH head wind and the power drop would eventually force me to pull to the side of the road. The engine would then simply die. I'd get out check fuel, spark, other obvious things and finding nothing, get back in and try starting the car. Fired right up and again would idle fine. Gunning it didn't seem to bother it and I would again take off down the road only to have the same issue develop at around 2800 RPM. Over and over again this happen until I finally reach home, just had to keep the RMPs under 2800! As I mentioned, it took several weeks to locate the offending issue.

Anyone who'd like to throw their hat in the ring, I'll wait about a week and let give the answer.

Good luck!
robert maupin

It's a lump of crap somewhere in ther fuel system that was forced into an orifice at a certain flow rate and so chopped the motor off. Stop the car and restart and the problem is no longer there as the lump has settled back. Up to 28oo rpm and the circle starts all over again.
Iain MacKintosh

Hi Robert. My guesses would be some sort of fuel delivery problem at high revs. Perhaps a bad fuel pump, or clogged fuel filter. Could also be an ignition fault, perhaps an intermittent condensor, pitted or burned points, or failing ignition coil. Could even be incorrectly gapped , or fouled spark plugs. I'm probably way off the mark, and the REAL fault was something really dumb, like a partially clogged exhaust pipe, or some other obscure type of failure. Cheers! Glenn
Glenn

By description, it sounds like a fuel related issue. However I have run into similar problems before. The first was related to engine speed vs load. It ran fine until I actually had to drive the car down the road. Idled fine, ran at RPM fine in first and second gear. But try to run down the road in fourth.......Cough, Wheeze, Hiccup. A general tuneup points/ plugs / wires fixed it for the several years that I kept the car.

The second time, was after rebuilding my A. It ran fine for a while but after a couple hundred miles it had a hard time running at highway speeds. Drop it down 5 MPH and everything ran fine for hours. Turned out to be a bad (new) coil.

My guess is ignition related. Maybe faulty coil or rotor.

Chuck
Chuck Schaefer

My guess ....restricted exhaust.
Gordon

Loose condenser or condenser wire?
mike parker

My 58 did the same thing. The coil bracket on the generator wore a hole in the coil and the oil went south. After you ran a bit the coil heated up and the spark broke down. Wait a few minutes and it would run fine for a few minutes. It acted just like a clogged fuel filter. Replaced the coil and no problems. Unfortunately it was an original screw-in lead coil. I will admit I cleaned the carbs, fuel pump, and blew the fuel lines prior to discovery.
Bill Haglan

I had similar problem on my TD. It was sucking a small piece of material that was used to reline gas tank. At low speed enough gas got passed but at high speed the fuel pump sucked it into fitting where line leaves tank. The car would die and piece wold go back into tank. The piece was actually attached to inside of tank and even blowing back through lines didn't help. Ended up pulling out fitting to get it out.
C Tarr

Had a very similar problem myself ... after a complete clean-out of the carb float chambers I added an in-line fuel filter under the bonnet, just ahead of the carbs. It didn't happen again.
Richard Ross

Hi
My guess would be a pitted or otherwise damaged needle, assuming you have SU carbies. If not, a blocked catalytic converter or exhaust will result in the same symptions.
Dave Godwin
David Godwin

Another explanation....
Maybe your tachometer was broken and you were really going 100MPH. :)
Jonathan


jonathan

I suspect that Robert would not have asked the question if the answer was one of the more obvious that we usually come across on this BBS. So it is time for lateral thinking and wacky ideas.

In my experience these types of problems are usually electrical rather than fuel. So that's fuel discounted! What moves (changes) at 2800RPM - Bits inside the distributer perhaps and the fan speed.

The distributer we have all talked about before and it has to be too obvious. It's the fan speed then that causing the problem!

Yes, it has to be an internally fractured (white) LT cable to the coil. It makes contact at rest and when the engine compartment is relatively benign, but at or about 2800RPM the draught from the fan is enough to deflect the LT cable sufficiently to intermittently break contact. Randomly, the contact remains broken until the starter is used to turn the engine again - the vibration re-establishing contact.

Steve
Steve Gyles

A loose baffle in the muffler in simple terms.
Denis
DENIS H

Great thread - like watching "Stump the Stars"!
Joe Cook

I agree with Steve that its got to be a less than obvious answer. Since all of the more logical causes have been covered, I'm going to take a wild stab and say that something was broken in the distributor and whenever the mechanical advance mechanism moved it caused an intermittant short.
How's that for a long shot?

Bill
Bill Boorse

Carburettor icing?
Nigel Steward

I had something similar which turned out to be an intermittent loss of the main ground at the chassis.
Al McMillan

To me it sounds like the mechanical advance in the distributor is frozen.

Don
Don Tremblay

I had a problem similsr to this and it was on my 1954 TF-1200. It would drop down to two cylinders when accelerating. It turned out to be a flat spot on the damper wall that was making the piston stick. Stop the motor and it would be fine untill picking up speed again. As I was on a trip far from home I had to revert to fine crocus cloth to free the spot.
Sandy Sanders
Sandy Sanders

I suffered a similar problem, which turned out to be the front carb needle had somehow come partially loose in the piston, and when the piston went up it only moved up a little but not the same amount, and obviously this reduced the fuel flow. For some reason it was all right up to about 3000rpm (must have lifted just enough to operate ok), but over that it was too weak to run. The problem was hard to find as that there was fuel AT the carb at all times but NOT passing through the jet proper.
Matthew
Matthew F.

Robert,
I just had the same problem with a old Ferguson TE20 tractor. It would run fine until it got under load and then it would sputter and stop. Only to start right back up again. After a carb rebuild, new plugs, wires, condenser, and coil, an old farmer told me to blow air up the fuel line from the carb. I did, and it has been working fine for the last two months. (there's no pump on the old tractor, just gravity feed) Something was in the fuel line, or floating over the line where it meets the tank, and was causing a shortage of fuel for high speed running.
Cleve

Is the problem at 2800 in any gear, or just in top?
Art

Hey Robert... did you resolve the problem?
skippymga

The flexy pigtail in the dizzy?
Tom

Gees,

I sure wish I had this tool when the problem occured originally. Thanks to all who provided their wisdom and realted experiences. I particularly liked Jonathan's 100 MPH explaination.

While Gleen, Gordon and David had the correct answer within their response, it was Dennis who had the problem pegged! Cudos to Dennis!!!

It was indeed a piece of rusted muffler baffeling that had broken free. The interesting part was appearently when it dislodged, it fell so as to balance on it's edge so when at idle, the exhaust pressure wasn't enough to tilt it. However, at 2800 RPM, the pressue flipped it up to block the exhaust flow. Once the car stoped, the baffeling returned to rest, on edge and allowed exhaust to pass freely. This thinig drove me nuts until I discoved the problem. Next time I run into a particularly difficult issued, you can bet I'll just defer to the great bunch of folks who follow these threads and save myself and trip the the mental ward! Thanks to all who sent in their answers! Great knowing you all! Safety Fast!
robert maupin

Wow. Learned something new. A variable restriction that is RPM related.

I did have a restricted exhaust in the past. Turned out to be peanuts. But that is another story.


Robert, great puzzle and glad it only took you several weeks to sort it out.

Chuck
Chuck Schaefer

This thread was discussed between 02/11/2005 and 08/11/2005

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