1966 MG Midget

[mg66]

I have a 1966 MG Midget which has been running perfectly up until lately. It was running in the garage on tickover for about 10mins, which i do reqularly, when it started to misfire or run lumpy. I knew it was low on fuel, so assumed that was the problem. After filling it up and re-starting it still ran lumpy and eventually stalled.

I assumed some debris from the bottom of the tank was causing a blockage so i've checked the pipe from the tank to the pump, the pump, the pipe from the pump to the carbs and the carbs, all are fine.

It still runs really badly and stalls after roughly 30secs. From cold it starts first time and runs well for about 5secs, then runs lumpy and then stalls as if its fuel starved.

Then is definately fuel getting to the carbs and the jets have been cleaned. The fuel pump it relatively new, plugs, points, cap and leads have only done 500miles.

Does anyone have any ideas please.

[v8250]

Have you checked fuel filters and reverse blown the fuel lines? Air clear the fuel lines from carbs back to the tank, a foot pump is ideal. What pump are you running as some pump designs are able to 'hold' crud, others[Facet] hate even the slightest crud ingress. The symptoms also sound like a coil breakdown, if you have a spare it's worth doing a changeover test and getting up to full temperature.

Edited to add, if the fault is subsequent to new ignition component changeover...replace new with old to ensure new components aren't faulty. I'd take a close look at the distributor arm and cap first.

Edited by v8250 on Friday 4th March 15:50

[Flying Phil]

Years ago I had a similar problem and eventually found that the pick up pipe inside the tank was clogging, but it allowed fuel to filter through when the pump was not working. (I only found out after rigging up a temporary fuel tank to the pump!) As V8250 suggests, try blowing through the system in reverse direction.

[mg66]

Thanks for your posts, i've reversed blown all pipework and taken apart the electic fuel pump and not come across any issues. After running real badly for 30secs and stalling i checked the bowls and both were approx half full.

The coil, points, rotor arm, plugs, leads and dis cap were only fitted new approx 300miles ago, i believe i still have the old ones, so i'll dig them out and replace them one by one to see if this helps.

One thing i have noticed is if i go out to the car now, switch on the ignition, the pump can be heard clicking, i then pull out the choke and the car starts straight away and runs normally for the first few secs. Almost until the first priming from the pump has been used and then it stutters.

Do you think this is the case or just that it takes a few secs for the electical component to break down?

[Flying Phil]

If the fuel bowls are half full (- I assume with no float in them) then it probably is the coil starting to break down as soon as it gets warm. As you say try swapping components one by one - starting with the coil.
Good Luck!

[v8250]

Just another thought, check/renew any flexible fuel lines. If the wall is collapsing internally it will cut off fuel supply resulting in engine splutter/shut down. If they haven't been replaced for a while, replace them as they're such low cost items. And do be sure to buy modern ethanol E10 compliant fuel lines.

[interloper]

Another idea, I had a mini that would start okay then within a mile or two would play up stall and die. Turns out the mixture setting on the carb was set too weak, so once warm it was drawing too much air and not enough fuel.

[awooga]

My B had a similar issue a few years ago, turned out to be the coil. I had appalling running last year after it had been sat in the coachworks for 6 months while I was abroad. Felt like the fuel pump was giving up, turned out to be blocked jets in the carbs.

Also check that the coil is getting the right voltage - got a mate with a westfield ford crossflow which drove beautifully for about 10 mins and then died. Changed the coil several times, new leads, new plugs, new rotor arm, dizzy cap etc etc. The coil was getting the wrong voltage and overheating as a result.

[mg66]

Thanks again for all your replies. This morning i changed the coil which seemed to make a little bit of a difference, but still lumpy. Then i changed the dissy cap, no difference and finally the rotor arm, again no difference.

With all these changed it seems to idle almost ok but begins to run lumpy when i try to rev it, i've ordered a colour tune kit to see whats happening with carbs, but could issues occur all of a sudden when running as per my original message?

Oh and the fuel lines are only 6yrs old.

[Flying Phil]

You must be getting frustrated!
I can only suggest you try a gravity feed of fuel to the SUs from a small bottle of petrol held above the carbs to eliminate the fuel side of the system.

[mg66]

OK, so the latest news is, that I've checked the cards with the colour tune and the front one is fine but the rear one is way to rich. So rich that there is not enough adjustment to bring it into spec. I believe the jet needle is worn and causing the problem. I've got one on order and I'll update the forum after I've fitted it.

[Flying Phil]

Thanks for the update.
On re reading the posts, I wonder if the rear carb dashpot/piston is raising properly? You could check by removing the air cleaners and just look into the carbs with the engine running to see if the piston in each carb is moving in a similar fashion. I would have thought even a worn needle would not, on its own, lead to such a rich mixture.

[Mr2Mike]

mg66 said:

OK, so the latest news is, that I've checked the cards with the colour tune and the front one is fine but the rear one is way to rich. So rich that there is not enough adjustment to bring it into spec. I believe the jet needle is worn and causing the problem. I've got one on order and I'll update the forum after I've fitted it.

Though it might well benefit from replacement, a needle jet could not possibly suffer enough wear in 10 minutes of idling to cause this problem.

The one part of the ignition system you haven't replaced is the condenser, a more likely suspect for sudden failure and bad running.

[mg66]

Thanks for your post. My thoughts were that the carb parts were original and just at that point the needle wear became too great. I had replaced the condenser only a few years ago along with other parts but I will try it.

At the moment it looks like my battery has failed, I keep it trickle charged when not in use, I'm just getting a click from a 2yr old started motor.

I'll keep my progress posted when I have an update.

[pss1]

Hello, not sure if it's any help, but I had what sounded like a similar problem a few years back. I eventually traced it to the float chambers. The tube running from the chambers to the jet has a small rubber seal at the bowl end and this was creeping as it warmed up and ended up partially blocking the line at that point causing rough running, cutting out and all that fun. When it cooled, it went back to normal. Strange, but there you go.

[mg66]

Hi, I would just like to say a big thank you to everyone that that posted replies to help me.

I did change the jet needle and the car was even worse and would basically not start no matter where I set the mixture.

I then had to take few days out as I really didn't know which way to turn. As a last ditch attempt I remembered a post mentioning the condenser.

I replaced it and the car started on the second try and after the carbs were set, now runs as it well as it used to.

Once again many thanks, especially to Mr2.

David

[Flying Phil]

Well done and thanks for the update.....Car electrics....work of the devil!!