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MG Midget and Sprite Technical - Throttle control

Gentlemen may I seek your collective wisdom please?

I have a '78 GAN6 Midget that I bought in December last year - my first MG. I drove it home 186 miles from Edinburgh with the world's biggest grin, but it was obvious even then that all was not well with the throttle. I thought "sticky linkages" but subsequent events showed that to be false.

The throttle was not closing fully, but I could drive around the problem by flicking the pedal. I fitted a new cable, which improved matters but didn't cure the prob. Then I found that the hole in the firewall for the cable entry was dimpled over to one side, causing the wire to be deflected at a sharp angle so that it bound against the cable sheath at the "closed" end of the pedal travel. All the linkages and the pedal mount bushes were free and moved easily so a bit of bending of the panel with a short end of steel rod lined up the wire with the engagement on the pedal and removed that problem.

That's when I found that it had been hiding another problem, which is causing much head-scratching. I trawled the archive and found a gentleman called Richard Powell had posted about the exact same prob last year, but apparently had no replies. Basically the throttle is very stiff to move from the closed position, then when it does move it does so very quickly, so fine throttle control is extremely difficult especially at low speed. It's hard to pull out from a tee junction without wheelspin and utterly impossible on my gravel driveway - I just use tickover there.

I have been driving around the problem for a while but yesterday I gave my mate Dave a go in it and he nearly 360'd the car exiting a slightly damp roundabout. That's when I realised I really have to fix it. Dave's an ex-Met traffic cop and a bloody good driver so he caught it before there was anything to cry about, but it was an epiphany for me - I need to find a solution.

My car has the "Capstat" carbs with the front and rear throttles returned by rotary springs as opposed to the earlier linear springs and it seems the spring tensions are too heavy. Certainly the throttle has always been a bit on heavy side. As an experiment I disconnected the central linear spring from the anchorage on the the exhaust manifold to header joint to decrease the tension on the assembly and noticed an improvement (so I speculate that spring tension is the root of it), but it's still not right.

I can't see any obvious way of adjusting (reducing) the spring tension - can anyone help?

I did wonder if the butterflies were being held closed by induction vacuum - I don't think so because I can hear a healthy hiss from the intakes when I listen through a piece of aquarium hose and the engine ticks over very contentedly when warm.

I have noticed the problem is worse when the engine is hot, for whatever relevance that has. But I've discounted the linkages dragging by disconnecting the cable and opening the throttle by hand. It's smooth with no tight spots, but stiffer than I expected.

As always grateful for any insights. I've had to accept that this fault is potentially dangerous so I'm keen to get to the bottom of it. Thanks for your patience.

Goodnight.

Rod.
RS Hughes

This might be hard to fathom without a good picture, but here goes:
The centre link peices can be set up to be too far over and cause what you describe, basically the angles are wrong just off tickover and cause a massive pull to be needed to pass the point, then suddenly all is well. You need to slacken the linkage and cable to re-set the position of the 3 peice link set up and reduce the actuating angles just off idle position. Once this is done, re-set the cable position so it has no slack.
One thing, though, don't go too far with this or you'll run out of travel (either in the linkage or the pedal motion) to achieve wide open throttle.

Of course, this might not be the problem at all. But it's worked for me in the past.

Other things to look for:
As well as the above issue with linkage, the 2 bits that engage the indiviual throttle spindle actuators can be set too far apart causing a tightness between the carbs. Obviously it gets warm, expands and becomes worse with engine temperature as you describe. Just check there is a little side to side movement on the linkage shaft part.

Cable routing. It is better to have a longer cable than a shorter one so you can give it sweeping curves rather than tight corners. Mountain bike teflon cored cable works well here. The stuff the usual suspects sell is junk really and usually too short.

Grease everything that moves. Except the cable if you get a teflon cored one!

You don't say, but I assume the pedal itself moves freely with nothing connected? Grease that too for good measure.

One last thing to remember, the midget pedal motion, especially the 1500s poorly routed one, is never going to be as smooth as a modern car. It is to some extent something to get used to and develop a slightly heavier and more cautious right foot over.
Roadwarrior

I was also thinking it may be to do with the angle of the throttle linkage.

A good place to start.
Dave O'Neill 2

Roadwarrior, Dave - don't you guys ever sleep??
Many thanks for your input. I have photos and wiil post tomorrow but now my cot calls.
Roadworrier it sounds like there is a way to cahnge the angle of the central bell-crank ank compensate by taking up the slack on the cable.
This sounds promising - I'll be in The Shed first thing.
Guys - thank you. Sincerely.
Rod.
RS Hughes

this..
"Cable routing. It is better to have a longer cable than a shorter one so you can give it sweeping curves rather than tight corners. Mountain bike teflon cored cable works well here. The stuff the usual suspects sell is junk really and usually too short."

Had the same problem with my mates 1500. If the throttle return springs are doing their job correctly ie closing the throttle at rest, then fit a better cable. I resorted to oiling the cable and using cable ties to anything I could find to provide sweeping curves to the carbs. It finally worked but next time I'll be fitting a custom Teflon bike cable.

best of...
MGmike
M McAndrew

As MGMike.

My 78 did exactly the same. I bought a replacement stock cable with no improvement.

Then I bought a motorbike Teflon Coated one from Venhill. I bought a kit which adjusters and everything which allowed me to replace some of the connection bits like for like at the carb end as well.

Not much money and well worth it.

2 years on still happy as Larry as they say :-)
Dave Squire

Don't know if it's the same thing but there was an article in last month's mascot about adapting the throttle linkage on 1500 midgets. Perhaps someone can scan it and post it here. You'd think the editor would be able to do it, but he's at work trying to earn a living to support his hobby!
Anyone?
G Lazarus

To reinforce what has been already said, the 1500 for some reason is very sensitive to cable "stiction".

I suffered from it for a number of years and tried different cables, different routes etc but about 10 years ago I bought a Venhill kit and made up my own teflon cable and since then the transformation in smoothness has been amazing.

Everything else has to be in good order too of course, but I would advise making a proper car/motorcyle grade teflon cable.
I tried a push-bike teflon lined brake cable but while it was smooth enough in operation, it was a bit less robust than I would have liked.
JB Anderson

Though a worn cable will cause problems, a new cable will work perfectly well even with the sharpish angles it has to cope with. Much more likely is Roadwarrior's point. Adjustment of the linkages is what counts. Also, make sure everything is really clean. I don't use grease on the linkages or any carb swivels because grease will hold the bits of grit that cause the friction in the first place. Once clean and adjusted, I use a light oil regularly.
Nick Nakorn

Thanks for the responses, guys. It's categorically not the cable. There was a issue with the angle it penetrated the bulkhead, but that's fixed. Now the cable works freely and smooth as you like.
I should have mentioned that when I disconnected the cable I did so at both ends, so as to verify that the pedal and cable were not sticky and found both moving freely. I lubricated them anyway and I had carefully lubed the cable before I first fitted it so I'm reasonably sure the root of the matter is at the linkage or return springs.
Slight domestic drama this morning so I won't get into The Shed until this afternoon. Thanks again for the input - I'll let you know.
RS Hughes

You may be right RS but that is what I thought. My cables have always been absolutely free but the stickiness refused to go away-until I put a proper teflon cable in position.
It is a very well known Midget 1500 problem this jerky. not returning accelerator cable and over the years it is usually solved by making a proper teflon lined replacement cable.
However, I wouldn't stop you trying anything else! You may be lucky!
JB Anderson

I like all the above

But id start with the nuts on the end of the linkage for the butterfly....

check that they are not overly tight...just stiff, if there torqued down to tight then the throttle action binds up

Thats the 1st place id start because its the easiest and simplist and the most common reasons for what your discribing

Prop
Prop and the Blackhole Midget

Rod,
good clear photos can sometimes help others to highlight possible problem areas

as on a previous subject your car might not be as standard which could cause solutions to be missed because others are thinking of the standard set up
Nigel Atkins

Okay - I'm going to go the Teflon cable route and here's why.
One of the things I did this afternoon was thoroughly lube the cable again, this time using a PTFE spray lube and I'm not sure but I think it's better. Can't hurt to try - a cable isn't going to break the bank.

However..........

I was having a good headscratching session (maybe why I'm so bald 555) while I was looking at the linkage when I spotted something. There is another hole in the bell crank (photo) where the vertical rod attaches. So I shifted the rod, gave everything a bit of a skoosh with the carb cleaner and lubed all the bits and bobs again. Then I went for a drive.

SORTED!!

It's as docile as an old spaniel - you could send your Mum to the shops in it! Apart from a fast tickover caused by me being a bit impatient with the cable adjustment and which 30 seconds invested with a 7/16" spanner solved and Voila.

I took the opportunity while it was hot to check Roadwarrior's excellent point about the linkage between the throttle spindles and found it had a bit of freedom side to side, which is good to know.

In the picture the rod is in the hole I shifted it to - to the left is the hole it came out of. I speculate that a PO has tried to quicken the throttle action by increasing the operating radius. Maybe.

Thanks Prop for your good point - it's something I spotted in one of the archives and good idea. In my case all was well there.

But I will get a better cable anyway with the Teflon liner.

Thanks all - it's so much nicer to drive now. Sorry the picture's a bit fuzzy. I had zoomed the phone camera on it and magnified all the cack on the lens!

RS Hughes

BTW this is the spray lube I've been using for a while now in preference to WD40. When WD dries out it turns into varnish or something like it. This stuff also dries, but the only residue is nice slippery PTFE.
I have no connection at all with whoever makes or markets it, I just think it's Good Stuff.

RS Hughes

Congrats RS

Well done...they can be fiddly,but your correct a teflone core is essential...ive been using a high end bicycle cable this past year and will go ither a motor cycle or a high performance morrison cable when mine wears out

Prop
Prop and the Blackhole Midget

Cheers Prop - don't it feel good when you kill a gremlin? And thanks to all on the teflon cable sheath. I hear you and will comply..........
RS Hughes

Grimlins ....augh!!!

I hate them they breed like rabbits everytime they get wet and some are just down right viscous and hard to kill

Prop

Prop and the Blackhole Midget

Well - what else can you do when you get wet? Your weekend's f####d otherwise 555!
Thanks to all The tech advice is one thing and very good, but the best thing is knowing other peeps are helping with the thinking.
I'm grateful. Ta.
RS Hughes

Rod,
well done on sorting it

I think most use light oil (3-in-One type) to lubricate the cables - not that it matters if you're changing to Teflon - I like PTFE type sprays too

er, you *might* need to give your camera/phone lens a clean to get sharper photos

on the accelorater cable I've got an oversized (colour-coded) outer cable sheafing (forget the correct name for it) with an inner Teflon lining and inside that an ordinary twisted cable - works very well without further lubrication

I know others use pushbike cables with success
Nigel Atkins

Cheers Nigel.
Might need to get a better camera while I'm at it!
91 miles today. Top down, Irvin jacket on - HUGE grin!
Anyone got a spare flying helmet?
RS Hughes

I'm very glad you sorted it, but just for reference the outer hole is the correct one. No DPO throttle tweaking actions here.
I do wonder if what you've done, whilst fixing the low down jerkyness, will result in not achieving WOT with a pedal to the floor due to reduced arc of travel.
Regardless, well done!
Roadwarrior

Roadwarrior I'm sure you're right. Careful study of the sketch in an old Moss catalogue supports what you say as well.
It was only speculation on my part.
But the nett outcome is great, even if it's only a happy accident. I still get full throttle opening and the car is now a joy to drive.
I measured the throttle deflection in both positions. A bit crudely I admit - I put a cable tie on the crosslink bar and watched what happened when I floored the pedal with my left foot while standing beside the car and could see no difference. Which must mean that as I have it now the pedal moves a fraction further than before. Whatever; I count it as a win (and a lesson learned).
Thanks again for your help.
RS Hughes

Rod,
don't change your camera, if you didn't use flash for your photos this time then that might be the reason, I spent ages last month trying to photo something and get a clear photo and it turned out I needed even more light than I thought (my wife likes lampshades that stop most of the light) that and being ham-fisted I was pushing too hard on the 'shutter' button

I actually do have a spare (well, unused for many years) flying helmet, same as the one on the link below, brown leather chamois lining, medium size, with three clips for band on goggles and buckle on chin strap (but with quick release and fitting popper clasp) - item Ref: 0979 - http://www.mgocshop.co.uk/catalog/MG_Hats__Gloves_and_Scarves.html
Nigel Atkins

Nigel - I'm sorry I missed your response. I got distracted by the 6 Nations games!

The photo we're talking about was taken with flash, I reckon the problem was that I had it zoomed in and that magnified both the crud on the lens and the camera shake (even though I had it steadied on the top of the rad cowl).

When I punt stuff on eBay I take the pix with SWMBO's camera phone, which is much higher quality and has image stabilisation and yada-yada-yada. In future I'll do likewise for the BBS, but there is a file size limit for uploads.

I read on American site (which I now can't find again) that somebody fixed this problem by chucking away the radial springs and fitting old style linear springs to return the throttles. Even so he said he also used a teflon cable sleeve, so that's still pointing me in that direction.

Interested in your flying helmet if you want to part with it.
ssr98148@hotmail.com

Again thanks for your help. Car is still going great btw.
RS Hughes

Rod,
email 'in the post'

with the photos for posting here you can crop hi-res photos and if still required resize them or set the camera for less than the very hi-res

cheers
Nigel Atkins

RS,

That could have been me... when my springs wore to the point they had the springyness of a hot dog, I went to home depot and got some springs out of the bin that seems to have the strength and springiness I was looking for then just cut to length then bent the ends to the ends to the shape I needed

You have to be carful that the springs are.not over strong or they will.wear.out the carbs quickly

Prop
Prop and the Blackhole Midget

Cheers Prop. I've never thought of hotdogs in terms of their Young's Modulus value but it will be a crucial consideration from now on!

Seriously though, as things stand, with the vertical link in the wrong position (as confirmed by Roadwarrior) I get full throttle opening and no nasty surprises opening the throttles from idle. That means the Midget is safely driveable and as much fun as it's supposed to be.

When the PTFE cable kit arrives, hopefully next week, I'll make up a new cable and report back on any changes. For examole I'll shift the vertical link back to it's correct position to see if it's better there.

I don't understand why there is an extra hole in the quadrant. It's possible someone else had the same trouble before me - who knows. Anything could have happened - it's 37 years old after all! And that's part of the fun. Whatever - it saved the day for me

What's the latest on your plan to fit RWA rear panels? I'd like to see that.
RS Hughes


What's the latest on your plan to fit RWA rear panels? I'd like to see that.


Its in the "Im sort of thinking about it stage" haha...

Id love to, and waiting on warmer spring, ive got the panals to make the conversion, but I dont have alot of avialable cash,

My plan is to do the work, then turn it over to a pro to do the detail work and painting

The big problem I have, is im still stumped on how im going to cut the old out, and put the new in....so im in procrastinate mode big time

Id like to cut at the corners of where the square and round arch intersect each other, but its the inner round section thats really got me stumped..so im thinking about it just not sure how to see it thur

Prop
Prop and the Blackhole Midget

Hahahaa - not many of us have available cash. If we did we'd be on a Porsche BBS!
Good luck mate.
RS Hughes

Thanks RS

Prop
Prop and the Blackhole Midget

This thread was discussed between 04/02/2015 and 10/02/2015

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