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MG MGA - Poor running

Hi,
I wonder if someone can help point me in the right direction. My car was running very nicely last year, but I have only taken it out for two or three relatively short runs this year. I find that although it runs well at first, after about 20 minutes, it starts to run poorly. It seems as if the petrol is having trouble getting through.
Where should I start looking first? I have read here many times that most fuel problems turn out to be ignition, and vice versa, but am wondering if there is some dirt somewhere blocking the fuel, hence the intermittent fault.
I have a standard Mk2. The carbs were renovated a couple of years ago, and I have electronic ignition, I think Petronix. I do not have a fuel filter, could that be the problem?
Any pointers would be greatly appreciated, thanks.
Graham M V

Speculation is not going to solve the problem mate even though you will now be bombarded with different suggestions from change the coil to are your tyres flat. :)

You need to determine by diagnosis what is causing the issues. To begin with what do you mean by poor running?
Bob Turbo Midget England

Bob,
Yes of course you are right. Just hoping for a few pointers to give me somewhere to start. I know the solution will probably take a while to track down.
The strange thing is it is intermittent, so probably not bad timing etc.? Is that right?
The symptoms are as if I am suffering fuel vaporisation once the engine has heated up. Once it starts to misbehave, at idle it will stall, and when driving it runs rough, not firing properly. Sometimes, a few kangoroo hops when moving away at traffic lights, etc. But then at other times it runs fine.
It is not overheating, at least not according to the gauge. I have a heat shield for the carbs, and it has happened when the weather was not at all hot. But it certainly acts like fuel vaporisation.That's why I thought the problem is probably fuel related and thought maybe there is some dirt somewhere getting in the way of the fuel?
Would you recommend I open up the float chamber and take a look to see if there is any rubbish in there? I had always understood there was a small filter in the carbs, but looking at Haynes, I can't see it.
To be honest, I am a bit reluctant to open the float chamber if not necessary, as I find the banjo bolts a real challenge to tighten without fuel leaking out afterwards. Always frightened the pressure I put on them will damage the carbs.
I see Haynes suggests lifting the piston and flooding the float chamber to remove dirt. Should I do this by just pressing the piston lifting pin? That seems too easy!
Thanks
Graham M V

Graham,

As Bob has suggested you will get many opinions from well meaning enthusiasts

I suspect poor fuel flow (as opposed to vapourisation) would be more obvious at higher speeds when the engine it demanding more fuel rather than at tickover or low speeds.

You really need to work through every fuel and ignition component in a methodical manner.

I would check the dashpots have oil in them and then if you believe it is fuel related you can disconnect the fuel line just before the carbs, put the end that comes from the fuel tank in a jar and turn the ignition on.

You should get a steady flow from the pump. If there is a good flow of fuel, you could then turn your attention to the carbs

Regards...John
J Bray

Check that the plugs are not carbon coated. Then I would check that the pump is indeed running all the time and not intermittently (check the points in the pump if it is erratic)

You do have fuel filters: There is one in the pump, and one at each carb banjo. If you remove the bolt hiding the fuel line to the carb, you will find it as a coarse gauze thimble inside. They are so coarse that they are probably useless. The one at the pump is much finer. Check they are clear, but if it is running properly for 20 minutes, I doubt you are not going to find anything there.

Check for fuel leaks at the carbs underneath where the float bowls attach. Again if it is running correctly for 20 mins it is unlikely you are going to fine anything wrong here

The pertronix either works or not, so it's not going to be a problem there. If you have a different one with an optical sensor, check it is clean. How hot is the coil when it starts running badly?

Lifting the piston pin does nothing except lift the piston. It will have no effect on a non-running engine.

I suspect you will find an electrical fault somewhere.
dominic clancy

Graham, post a picture of your plugs so we can see what colour they are (firing end that is!). Dominic alluded to carbon coated plugs. Checking the condition of the plugs is a bit like taking the temperature of a patient and a good place to start.
Lindsay Sampford

Thanks for all the feedback. I have my son arriving in the morning from Australia, so please give me at least a couple of days before I report back
Thanks for the help so far.
Graham M V

I had a somewhat similar experience with my 1600 roadster in the UK some years back. It turned out to be the fuel pump and have since been told that the armature windings in this (then new) model get warm/hot and break down after some period of use and there is really nothing that can be done. I now have a new Fuelflo (electronic I think) in its place and these are, in my experience, practically indestructible. I also have one on my F-type Magna and am about to put one on my ZB Magnette. Fuelflos are so light that the rubber hoses are all that is needed to mount/support them.
Barry Bahnisch

I sometimes wonder about the poor quality of fuel from some of the supermarket forecourts. In the past I have had the odd occasion of poor running that has disappeared with subsequent refuels using a proprietary brand like Shell or BP super unleaded. Maybe you got the dregs at your last refuel that was, for instance, contaminated with water or the suchlike.

Steve
Steve Gyles

Steve may well be right! We took our MGA 1600 roadster to the UK in 1996 for, inter alia, the FIVA World Rally and the differences in idling speed after refuelling was sometimes quite noticeable. I concluded (rightly or wrongly) that this was due to differences in fuels, in any case the car returned to "normal" when we returned.
Barry Bahnisch

I don't see why fuel quality problems would only appear after 20 minutes. Also until the last few days the temperatures have not exactly been hot so you should not have had vapourisation. You should be able to rule out a fuel supply problem by stopping the engine after the symptoms appear and restarting after the fuel pump has stopped clicking. This should have refilled the carb bowls.

My guess, and without evidence it is only a guess, is the coil is starting to break down.
Malcolm Asquith

Malcolm

It was just a thought. The fuel would have settled overnight. It would then have got stirred up a bit after a bit of driving to then get sucked into the delivery system.

Steve
Steve Gyles

Hi,
Reporting in. Due to the arrival of my son from Australia this morning, I did not have a chance to carry out any checks.
BUT, I did take my son out for a spin to visit family. Again about a 20 minute drive. Car didn't miss a beat! But after parking, I decided to check on the car after about 7 or 8 minutes, and it ran really poorly
and stalled on idle. I then realised, on my two previous occasions, it ran poorly after having stopped for 5 to 10 minutes.So I imagine I must be suffering from the dreaded vapour lock?
It was Steve's posting that reminded me I read somewhere at different times of the year, the volatility of the fuel changes. So I am guessing that I need to get through the current tank and get some decent fuel on board? But doubt that will be enough and think it is probably time for the famous Sampford Carbs Cooling System that appeared on this forum last year.
Does that all make sense and do you think I am on the right track?
Lindsay any tips on installing a bilge pump?
Thanks for all the comments so far
Graham M V

Hi Graham

I was going to say the easiest way to determine if the problem was fuel or ignition would be to use a timing lamp routed into the car and when the engine started missing note the lamp flashing, an ignition miss is obvious by the intermitnt flash of the lamp or fuel problem if not.

With later vehicles such a my midget with electronic tachos this missing by ignition is easily seen by the tacho jumping.

However it does seem to be fuel related and could be vapour lock. Be aware that when stationary the arbs can "flood" just as easily as vapour lock, what fuel pump do you use?
Robert (Bob) Midget Turbo

I just wrapped my exhaust manifold with "racing tape" to insulate it.

See here:

http://www.jegs.com/c/Exhaust-Headers-Mufflers_Heat-Shields-Insulation-Header-Wrap/10261/10002/-1

I actually bought mine at a local auto store.

It works great - you can actually touch the manifold with the car running and it's only warm to the touch.

JIM in NH
AJ Mail

Graham..before installing the Judson in my car a few weeks ago I decided to do a belt and braces job on carb area heat reduction and loads of cool air to the filter.
I had to release the exhaust manifold during the work so I took the chance to wrap the exhaust with tape as per Jim's post above ,then installed a total wrap-around heat shield of a great composite material ..see pic..and then put a bilge pump in the short piece of air duct on the right of the pic.( radiataor is out in pic) . The blower blasts air onto the filter/carb area and is totally hidden...loads of air come out of local body vent. I used a bilge pump after reading posts on this site by Lindsay and Barney. Details of the unit and cost ( ex Amazon and shipped to Oz) below. It does need to be thermo or manual switch controlled ..I use latter . I did not have fuel vap. problems and installed it to get more air mols. into the cylinders.
You can see from the pic that I have a slight obsession about insulation in general....but cockpit stays cool even in Oz summer.
""Attwood Blower H20 Resist (White, 3-Inch)...cost $20 ..plus $8 transport to Oz..ex Amazon.""




Neil Ferguson

PS. I favour Bob's tyres running flat! Not getting up to speed in that first 20 minutes out of your centrally heated garage. You need to drive harder and faster to keep those tyre temps up.

Steve
Steve Gyles

I have decided to try out the bilge pump to cool the carbs and have ordered the Attwood pump.
I am hoping that will solve it, but would it be an idea to fit an electric fan too? Are these generally wired "live" so that they remain on even after the ignition is switched off, until the thermostat cuts it out? And do people generally leave the original fan in place, or remove it?

Lindsay, do I owe you royalties on the bilge pump?
Graham M V

Graham.....here is a pic of the short section of air duct containing the bilge fan..taken after all the judson kit was installed ..also shows the twin 9in fans I put in my car two or so years ago and thermo controlled ( you can just see the control unit under the hose on the left).
The fans turn off when the ignition is turned off.
One cautionary note..after I installed the fans I kept on having flat battery problems..even when stopping during a drive. I have replaced the original generator with an alternator and lo and behold...all is sweet and battery problems have disappeared.




Neil Ferguson

Hi Graham
Interested in your saga- As you know I have also the MK2 with 1622 engine also fitted with a Kenlowe. My car runs all day at around 170 occassionally going up to 190 when pushed hard The Kenlowe never activates unless stuck in traffic when the temp goes over 190.
However when parked after a run, when started again I also get a few moments of uneven running I find a bit of welly 4500 revs for a few seconds clears the carbs and restores normal behaviour. My kenlowe is wired live and does come on after ignition off when the temp rises
Paul
P D Camp

Hi Graham,
What did you son think of Australia - has he suggested that you migrate out here? Weather problems wont effect you car here and you can drive all year round!
Mike
Mike Ellsmore

Neil, Your bilge pump appears to be on the hot side of the radiator. Is that right? In Lindsay's design, it sits in the air duct in front of the radiator.

Paul, Maybe we can get together after I install the bilge pump, and compare notes? Be interested to see your Kenlowe set-up. I assume you kept the original fan? I will email you.

Mike, My son emigrated to Melbourne 18 months ago. Are you nearby? He is back here for his wedding using wedding cars tonbridge next week and then returns.
Graham M V

Graham...The bilge pump cannot be seen as it sits totally inside the black duct on the right of the pic adjacent to the radiator and pulls cool air entering through the grill and in front of the radiator ... and pumps out of the metal duct downstream of the radiator . ..otherwise it make no sense!!!! You must have assumed the casing of the Judson supercharger adjacent to the engine to be the pump.
I saw little use in installing electric fan(s) and keeping the original belt driven unit.......unless the electric fan is incapable of cooling sufficiently. ..in which case better to get a unit capable of doing the whole job and saving a load of wasted engine power as well as controlling the coolant temp in a narrow range.
Neil Ferguson

Neil, Yes you are right, I confused your Judson with the pump. As you say, the pump would be pointless there, but didnt want to sound rude!
Graham M V

I actually followed suggestion by Barney on his site ( CB-208 ?) re the 3inch blower and the use of the duct...and it works well. I am going to hook it up to the radiator fan thermo....at present on a switch.
Neil Ferguson

Now the big challenge. Get some pictures of the 3" blower inside the air duct, and explain how you mounted it in there.
Barney Gaylord

Barney..impossible to take a decent photo from either side ..especially with the Judson now in position. I also had to bend a short section of the metal duct to avoid interference with the Judson pulley . Following explains the installation.....
I removed all the concertina duct from the metal duct and I chopped the two feet off the Attwood 3in fan as you suggested . I located the fan inside the metal duct ( not the concertina air duct) and checked the fit etc and then drilled two clearance holes through the metal duct from the outside and then holding the blower inside I marked the outside of the blower housing through the two holes . I then removed the blower ,ensured the marked holes where in a part of the blower housing with good wall thickness( and not aligned with the fan blades ) , and drilled two small holes through the blower housing at the markings. I wrapped a thin strip of semi rigid foam around the blower at the position of the holes to pack up clearances . I then used two fat self tappers to fit through the metal duct holes and thread into the blower housing . It is very secure.
I also padded around the remaining annulus between the blower housing with semi rigid foam.
Finally I installed a section of concertina duct on the suction side ..mainly to totally hide the blower .
It is still noisy at idle so best to have it switched or controlled by a thermo. ....but the blast is really good .
Thanks for the suggestion on your site..I am very pleased with the result .
Neil Ferguson

Graham
Yes it would be good to meet up again-I have kept the original fan as well as the Kenlowe -yes I accept there is a bit of waste energy in the system but it all seems to work well and the Kenlowe only operates in extended traffic jams or after switch off to cool things down - perhaps this is why I dont have too many problems starting again.
A 1500 mile round trip to Angeloume last Autumn gave no cooling problems even on some very warm days.
It may be you have some "heat soak" problem causing fuel vaporisation- I am surprised it doesnt clear after a few moments as my slight hesitation after a stopover clears within seconds.My earlier problem with hesitation at higher revs was caused by a deformed rubber grommett between the float chamber and front carb which caused starvation to the front carb- replaced grommet no further trouble The Blower in the front air passage to carbs looks interesting will follow the progress and will look forward to seeing it when we meet up
Paul
P D Camp

Neil,
Sounds like a sophisticated set up. Planning that mine will have space for a beer chilling tray!
Graham M V

I installed a 4 inch Atwood bilge blower by cutting the consertina duct and installing the fan in the middle of it. I cut the feet off of the fan, and split the ducting in several places for about an inch to allow it to expand around the ends of the fan body. I used two 4 inch hose clamps to hold the ducting to the fan. After painting the fan black, it is not noticable unless you are looking for it. Now if it would quit raining and warm up I could find out if it helps prevent vapor lock.
Ed Bell

This thread was discussed between 23/05/2012 and 27/05/2012

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