MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Mallorca Midget woes

aaargh!
those who have been following my Mallorca midget story will know I gave up on the Weber & fitted an 1 3/4 single su.
Just picked the car up from my mechanic &
Shes missing really badly. Drove off on 2/3 cylinders & doesnt get better.
Standing still running, she seems to rev freely but then the revs drop off & it seems to start dying.
This doesnt seem to alter whatever the mix is.
My mechanic is stumped!
1430cc stage 2
luminition
no vacuume advance



Mallorcaben

Ben, sounds you need to take a holliday to Bligthy and bring the midget to get it sorted here cause I dont think your mechanics are good enough to handle your midget.

How about comming over at Midget 50?
Then again , how do you drive a bad running midget to Brittain...
My plans usualy are logic... not always tho. :)
Arie de Best

"This doesnt seem to alter whatever the mix is."
do you mean you've been monkeying around with the mixture?
what tools & methods were used to select the needle and spring to match your engine?
Who did the SU setup?
David Smith

Ben,

might be a good idea to find a qualified volunteer from the forum offer him a ticket to Mallorca against fixing your midget.. Might actually be money well spent instead on wasting them on having a shop trying to fix it. :-)
Alexander Sorby Wigstrom

Alexander, I'm up for that! Two weeks in the sun, a few beers, play with a MG in the morning, order parts for over night delivery while I'm on the beach! Sounds like heaven....
Ben, let me know if it works for you!!!!!!

MGmike
M McAndrew

Mike,

I wouldn't mind going myself unfortunately I'm not that keen on SU's, mine drove me crazy so I discarded them. But it's not season there now anyway.. I spent a couple of months living in Palma when I was seventeen working at a local bakery, it was a swell time indeed.
Alexander Sorby Wigstrom

Ben

I have 2 thoughts on this. My TR4 (no longer owned by me) used to misbehave like this. It was fuel supply not happening. There was dross in the area above the needle valve of the float chamber of the SU, limiting flow. This was not visible until the float and valce assembly were removed. The dross was the lining of the flexible fuel line which was breaking up. It was hard to fathom this out as when one took the top of the float chamber it was full of fuel. By the time one had stopped the engine and inspected the float chamber, fuel had seeped past the blockage.

The other though was the experience of a pal of mine who had similar experience with his sprite.

He had a misfire which did not get fixed by literally replacing everything on the top of the motor - fuel/electrics/mechanicals.

His fix was to set up the ignition timing dynamically - twist distributor until highest tickover is discovered.

No doubt with your long sorry tale there will be something completelt different wrong. Don't give up!!

Cheers

Roly
Roly Alcock

Is it fuel or electrics ?
You can tell by the behaviour of the rev counter.
Guy

If you have a working fuel pump and good lines I am convinced it is ignition related
Onno Könemann

I recall you thought there may have been a problem with the weber. Surprised about that. With the weber on did you previously track it down to a fuel problem. I'm assuming with the weber everything else was done i.e. ignition, valve clearances, fuel pump, air leaks, compression test etc and all that was ok?

So now do you think it's the same problem as before? Could also appear worse because as well as the initial fault the SU is not set up correctly?

So if it revs ok in neutral for a bit then dies suggests fuel not ignition. So what about blocked fuel filter, squashed fuel line, something in tank?

e.g. with it idling the supply is good enough to fill the float bowl in the carby but due to a restriction when you rev engine it can't keep up so it runs out of fuel and starts to die. Let it idle for a bit then it's ok because the fuel supply can keep up.

You can test the fuel flow. Take the fuel line off at the carby put it in a bucket, turn on the pump and check the flow for a few seconds. Will show you exactly what fuel is available to the carby.

but if doing this best be veeerrry careful because it's a very nice looking car in gloss black and I'm sure it wouldn't look so nice in matt black.
Greg H

I do remember that you have been fighting this for a long time, but I don't remember everything you have tried. That said, have you replace the lumination with standard point to rule that out?

Charley
C R Huff

Check:

Exhaust system not blocked... silencers can fail inside and block the system, this will give similar symptoms.

Is there good fuel delivery... disconnect the fuel line at the carb and watch it deliver at least a pint of petrol into a glass jar.

Is the petrol contaminated... inspect the contents of the jar.

Are the rotor arm, distributor cap, HT leads and coil in good condition and not tracking anywhere... try running the engine in the dark and look for ignition tracking.

Spark plugs all gapped correctly.

Tappet clearances all good... not tight, not slack...

All LT connections good... to ignition switch, to coil.

I'd be looking at an ignition problem first, then, once sure all that was working fine, then look at the fuel system...
M T Boldry

And don't presume that a leak in a fuel pipe would drip fuel. Mine only drew air in and never leaked fuel. Check your flexy.
Shawn

I got given the following advice, anyone care to elaborate?
"The petrol inlet and Vac are similar the vac pipe is slightly larger 5/16" dia if connected to the petrol infeed pipe the engine will run and rev but under load will misfire I know this because I've done it ! maybe because you had a Weber carb the pipe for the Weber is5/16" and will fit the vac perfectly the fuel pipe needs to be fitted to the smaller 1/4" pipe on the carb."
Mallorcaben

elaborate?
- some punctuation might improve general understanding but it sounds like whoever gave the advice is suggesting the fuel feed pipe might be wrongly installed.
As with most of your previous threads, we are only getting half the story, some photos with clear descriptions of what's what will help.
David Smith

no, it was all connected fine but the mechanic cant get it running right.
Not sure what to do now.
before we swapped to the SU, with the Weber 45 on it she ran fine on throttle, but missed as soon as you eased off.
She accelerated really well, it was just trying to cruise that it was a nightmare.
odd
Mallorcaben

Perhaps an airleak? Has greater effect the less the throttle is open. With it running spray something like Aerostart around the manifold and places where it could suck air. If engine revs change or pick up it's leaking air.

My advice... Find another mechanic!!!!! These cars really are extremly basic so if it's too complicated for him he can't be very good. Find an older guy that's got some experience. Young guys often have no knowledge of older cars that have carby's and distributors.

I'd even think about getting a weber manifold that's in better condition and put the weber back on because you at least know that it used to work with the weber on.

It really shouldn't be this hard!!
Greg H

The mechanic is an older guy who is used to working on older cars, ut he got made redundant & is doing it from home with no kit.
If I was in England it would be dead easy.
You just swap stuff to rule them out.
Thats the main reason I changed the Weber. I knew it was playing up, has been for years.
This all started 18 months ago when (the same mechanic) swapped my starter motor over. When I got the car back she was misfiring.
It was fine for 10 mins then started missing.
I tried everything (dizzy, put points back on, leads, plugs, coil etc) because I was convinced it was electrics.
I stripped the weber and found a float broken off, but it looked like it had been like that for years.
I bought a weber kit & put it all back together & it was worse than before.
I couldnt get the float set up right so I gave up and took her to a garage in Palma that services race cars.
They had it for just over a year! (welcome to mallorca)
When I got her back, she was un driveable.
I tinkerd again myself & got her running smoothly.
She was fine on throttle, but when you backed off, she misfired.
The power delivery was superb, but terrible on cruising gentle throttle.
Decided to swap the carb. Had a 1.3/4 single SU & manifold built for me in England.
My mechanic swapped it over for me.
I got the car back & took her for a spin. As soon as I pressed the throttle, she missed & it got worse the more throttle I gave it. Down to 2/3 cylinders.
On standstill, when I rev her, as I keep the revs up after a few seconds the rpm starts to drop.
She appears to be reving freely but its obviously not
Pic is before I swapped to the SU obviously



Mallorcaben

You might want to check these 3 things. 1) That the distributor baseplate center bearing is locked, 2) and has a good earth connection - check the continuity and 3) that the coil has the correct resistance and is wired the right way around. The coil is best mounted inverted so wants to be upside down in the picture. What needle is in the SU and how much advance have you got at 1000 and 3500 RPM? To check whether it's fuelling or electrical can't the garage run the car on the rollers with Sun diagnostics?
F Pollock

FP, you might have missed this in Ben's latest post:-
"The mechanic is an older guy who is used to working on older cars, but he got made redundant & is doing it from home with no kit."
I don't think Ben works on the car himself and doesn't seem to have access to anyone competent on the island...
David Smith

Yes,I saw that but also read 'and took her to a garage in Palma that services race cars'
I was assuming these people would have more than just a piece of rubber tubing and hose clips, and that all ITV garages have basic diagnostic clobber.
F Pollock


"On standstill, when I rev her, as I keep the revs up after a few seconds the rpm starts to drop."

With this statement it still sounds like it could be a fuel delivery problem.

There were quite a few suggestions made previously on testing the fuel supply. i.e. how much fuel actually flows out the end of the fuel line. Was this done?
Greg H

hmm, the fuel thing could be worth looking into.
I had a filter king regulator on it before but I took it off when trying to diagnose the Weber problems.
There seems to be enough fuel coming through the pipe when I take it off but I dont know for sure.
The car is fitted with a Facet pump.
Mallorcaben

I'm with Greg H on this one. It does sound like a fuel problem or to be more accurate a very lean mixture. Check the flow rate of the pump at the carb. You want to be lifting about one pint per min. I would also temporarily remove and/or block all breather/servo pipes in the intake system.
I have a slight niggle that the needle in the SU may not be right for your car. Did the supplier know it was going on a 1380? Do you know what needle is fitted?

I find it strange this started after fitting a starter motor, which should be totally unconnected. My engineering background tells me to look at the last change for the cause of the problem and this takes me back to the starter or the person that fitted it.. Call me suspicious but I would be looking at the electrics. But time will tell...

good luck

MGmike
PS. I'm still up for a paid busman's holiday!
M McAndrew

This thread was discussed between 13/04/2011 and 27/04/2011

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.