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MG Midget and Sprite Technical - Almost a brown trouser moment.

Hello all, apologies first, I’m posting this on a few lists just in case it saves someone else from a brown trouser moment – or even worse!

My ‘67 midget is used on AutoSolos and Sprints so is often driven hard. Fortunately it wasn’t in competition when the throttle stuck open last Saturday. I pulled over as soon as possible, popped the bonnet and saw just what I expected to see – two return springs and not three. I was a little surprised having replaced all three springs less than a thousand miles ago, but heck, these things happen.

I re-set the throttle on the front carb and drove CAREFULLY home using the lightest throttle possible. Even so, after just the mile or two to home idle was up at to around 3k. I’ve plenty of spares lying around especially just now as the “white” one (’72 RWA) is undergoing a minor rebuild so I set about replacing the missing spring. Then the fun started.

I fit the springs to the throttle linkage first and then stretch them down to the heat shield using thin nose pliers but no matter how careful I was the spring kept dropping off. Eventually I convinced myself that I wasn’t having serious senior moments and took a closer look at the throttle lever and got a nasty surprise, the spring had worn right through the lever. I’ve attached a photo so you can see what had happened.

Things went from bad to worse.

I’ve three full sets of carbs and a number of spare bits but every single throttle lever is showing signs of similar wear albeit that only one had worn through completely. With my son and son-in-law scheduled to compete in Abingdon CarNival Sprint on 11 June I thought it best to buy new levers.

I could not believe it when neither MGOC or Moss had stocks of levers. “We’ve never been asked for them” they told me. Are mine the only ones to ever wear?

Even SU Carbs website parts list doesn’t list them but I’m pleased to say that a telephone call to SU Carbs meant that I now have the last two throttle levers for the rear carb that they had in stock. No need to panic I understand that they will be making more soon and have five front carb levers still in stock.

I’m sure that some of you will be saying “silly idiot, everyone knows that they should check throttle lever wear to avoid a brown trouser moment”. But, if my experience prevents just one such moment – or even worse – for someone out there I really don’t mind if I’ve given everyone else a laugh!

Bill



BillMex

http://www.su-carbs.co.uk/

Speak to Andrew, he will have the spares you need and is an absolute pleasure to do business with
PeterJMoore

There's something more to this story. There appears to be a crack more or less opposite the worn through part, and there is no conceivable force that would cause that. I've worked with thousands of these and have seen some worn a lot but never through. Excess wear is usually a result of grossly over-strong springs as an attempt to cure a bad cable or other sticking problem. Further, correctly setup throttle linkage can lose either or both of the carb lever springs without much more than a somewhat fast idle, if the cable return spring is present. Or, the cable return spring can be and often is missing entirely without issue. Any one of the three springs should prevent runaway.
Can you get a picture of the assembled linkage on the car?

FRM
FR Millmore

If i can add my 2 pennies...

I really dont think loosing the spring caused your engine to take off and race to high 3K rpms.... my guess would be a worn out throttle cable ... aka bicycle cable.... esp the cheap ones... maybe 3 to 5 thousand miles.... are all those $3.00 cables that everyone seems to sell .... might have to order a good one off ebay. Which reminds me i need to order a good one also cause ive still got that cheapo cable from past year... i was using for a pinch



I wonder if a P.O. but some vise grips to that lever trying to rig up a spring... twisted it.. then fractured it un-knowwingly....i say that cause thats something id do

Prop
Prop

been there - not a linkage problem but the fold-on-the-floor pedal stuck down on the trim once while I was going flat out overtaking people...

something else might be a bit sticky as well if the single spring was that poor, I had one break on my 1 1/4s and it just made the idle a bit high.

as you say, lucky it didn't happen in a worse situation!
Rob Armstrong

Hi Bill, not doubting your reasoning for one minute however I confirm Prop's explanation as I too had a brown trouser moment and on investigation found that a single thread of wire on the cable had broken and had crunched up inside the cable jamming the throttle open. The bicycle accelerator cable should ony be used as a temp solution.
Mark Wilson

I'm with FR Millmore on this one. There is more to this scenario than, at first, meets the eye. The visible crack suggests excessive pressure has been applied to the linkage at some time in its life. And, as FR says, "Any one of the three springs should prevent runaway."

I concur - a photo of MillMex's linkage will be most interesting.
Andy Hock

I had a similar episode with a 1500 - the throttle cable snapped as I was overtaking.

Got home by wiring the throttle in the mid rev range. Stuggled to get up steep hills in top gear, but once over the top it was quite an exiting ride.

Dave
D MATTHEWS

Dave

Have seen a good friend finish a day of rallying (no servicing between stages) using all the shoes laces available to them to make a hand throttle which was controlled by the navigator whilst the driver did the rest

Madness
PeterJMoore

Just to correct the typo error "an exiting ride"

Mind you, there were times on the downhill sections where I did feel like exiting.

Dave
D MATTHEWS

This thread was discussed between 27/05/2011 and 29/05/2011

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