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MG Midget and Sprite Technical - Engine Stalling

Yesterday afternoon we had a problem with our MK-III midget stalling. Petronix ignition the only real upgrade from stock (about 54K miles), and very healthy engine. Twice had to push her through intersections because she failed to move from a start. Much coaxing got her home a mile, or two at a time. No fun in that I'll tell you!

Symptoms are as follows: Cough, and sputter while moving in any gear with attempt to open the throttle. Stalling at take-off from a stop when throttle opened from idle. Felt like fuel starvation.

Suspects as follows: New SU fuel pump installed last year, but bench testing this evening proved the pump good (perhaps a bad ground?) Search for a vacuum leak so far has found no obvious problems (will check the throttle shafts tomorrow.) If that proves good, will pull the carbs off to inspect the spacers, and gaskets. Finally, ignition coil, cap and rotor, are the last on my list to check.

Suggestions welcome?

Regards,

Larry C. '69 Midget

Larry C '69 Midget

Larry. Fuel starvation is the first suspect. You mention that you have bench checked the pump. Also check the system out at the carbs. David DuBois has a good fuel system trouble shooting tech article which might be of use. If you cannot find his website with a Google search, go onto mine (www.custompistols.com/) and there should be a link to his articles from my MG articles.

An obstruction at the fuel tank (including a broken pick up tube) or an obstruction in the fuel lines will not show up when you bench check the fuel pump. (Bench checks are, by definition, performed on a test bench and only on a single piece of the system at a time.)

It would be possible to cut the rubber hose from the fuel pump to the carbs, install a T fitting and run a line into the cockpit where you have, temporarily, fitted a fuel pressure gauge. That would let you see what is happening as the problem takes place.

Ignition system problems can cause the symptom you describe (loss of power) and you need to check out the connections in the high tension circuit (coil lead, distributor cap, spark plug leads, and rotor) to see if there is any problem there.

Normally, if there is a low tension circuit problem (coil, distributor, points/points replacement system) you will see the tach operate funny when the problem is present--either dropping to zero or jumping between zero and some other value.

Please let us know what you find out.

Les
Les Bengtson

looks like les covered it all...


just a thought on something super easy to check And outside the normal. look at the pertonix chip where the 2 wires (Black and red) intersect into the chip, and see if the insulation has broken down (Exposed shiny copper when you bend back the wires agianst the chip)....I had a problem with my chip "Hinging" right at that intersection of the wire and the chip, causing the insulation to break down and making a nice little arcing ground. it was cased because of the vacume advance doing its job, On the re-placement, I drilled 2 small holes in the dissy cap and re-ran the wires to avoid the hinging effect.

Prop
Props Black Hole

Les,

Thanks for the input, I will checkout Davids fuel system article later today. Both carb float bowls were full, and the needles were moving freely so I think the flow between the pump and bowls may be good. Their was a small bit of sediment at the base of the bowls which may be an indicator of another problem, although the fuel filter (clear plastic) looks to be in good shape. This evening I will pull the carbs to check the main jet/s, and the flow through the tubes between the bowl and jet needle.

Prop,

Thanks also for your input, the distributor was next on my list. I had a problem earlier this year with the Petronix unit in our B/GT that we replaced.

Regards,

Larry C.
Larry C '69 Midget

Hey larry,

Back when I 1st got my car, I had some carb issues, there was alot of gunk in the little tubes between the float chamber and the jet, I had to use a pipe cleaner and a can of carb cleaner with a straw to clean it all out.

just a thought while your in the carbs

Prop
Props Black Hole

Removed, and cleaned both carbs, replaced front, and rear jets. Acceleration is back close to normal with only a slight (irregular) misfire at higher RPM's. Drove around ten miles this afternoon including several starts, and stops with no stalling. Perhaps every other run through all gears a slight misfire between second and third at around 4,000 RPM only.

Shift in my attention now to electrical. Will start with a new set of spark plugs, to be followed by plug wires, and then coil. Suggestions welcome?

Regards,

Larry C.

Larry C '69 Midget

Freash plugs and wires are always a good place to start. The coil mmmmmm. Not so fast, unless its just really old. It ither works, or it dosnt, or almost close to dying within a few days....IMHO.

Try puting the car in a dark garage and start it up in the dark of night, and see if you got a blue electrical light show firing away under the hood...look both cold an when engine is at temp.

Prop...misfireing engines at night is cheaper then a lazer light show
Props Black Hole

hi there a friend of mine has just had the same problem . . . He also changed plugs ,cleaned carbs etc . . He replaced the condensor last night with a new one and fired up straight away and drives lovely hope this helps . . .
n williams

N. Williams,

Thank you for that, but have pertronix installed in the car so no points or condenser. I have been thinking about the side entry distributor cap, and the modern 'silicone' wires I have installed. I will look at the cap screw connections to the wires possibly 'burning back' as part of the problem. I haven't been able to locate older style metal core ignition wires here in the past few years. Suggestions to source proper wires welcome?

Regards,

Larry C.
Larry C '69 Midget

There you go Larry !!!

Problem solved...Your dissy cap, is it the type that requires that you insert the plug wire into the cap and use the little sharp screw to attach it down, and are the plug wires the modern day type...so your cutting off the ends and sticking it in the cap and thightening down the little pointy screw on all 4 plugs and the coil wires?


Yepp, Ive been there and done that...I cant explain why, because its all mumbo jumbo electrical techy talk stuff, But what you have to do to correct it is, get some copper house wire, for wiring your house with ...has to be the solid copper thats in the black or white insultion, NOT the ground, cut off about 1-2 inches, strip the insulation so that its just the solid copper strand, and jam in into the vary center inside the filimet if possiable. push so its fairly flush, and re-cut off the end to give it a clean end/edge, stick it back into the the cap, make sure the pointy sharp screw is good and sharp, and screw it down. and do for all 4 plug wires and the coil ..if the coil is the same type as the plug wires...as to which gauge. not sure, bigger the better I guess that will still fit inside the inner filiment... a small dab of that electrical grease (vasoline) helps it slid into the plug wire a little better.

I think as long as the pointy screw is making contact ither thur the copper or on the side your good to go.

That really solved a lot of mis-fire problems for me, esp. higher up the range...Just a tip I got somewhere along the way....maybe some one can explain the reason why is works that has better knowledge then me on electrics...and thats not saying much.


Prop
Props Black Hole

As to why not use the ground wire from the housing wire...who knows why?, I sure dont! LOL.

Im guessing its a differant material composition, i just remember dont use the ground wire!...then agian, that could be a UK house wiring code thing, after all they like suped up wiring in there houses...240 volts systems If Im not mistaken...same as my electric dryer and stove

Prop... Whizzing into an electrical socket at 120volts dosnt hurt as bad as the 240 volts...Prop
Props Black Hole

Do replace the distributor rotor as a matter of course. I lost a day of my life cranking the 1275 until I realized that was where the short was.

I prefer the original side mounted distributor cap with the original copper wires. The radio picks up a little static but needs replacing anyway.
Glenn Mallory

Getting back to fuel, do you have a filter in your fuel line? I like having the clear type for two reasons; one, to filter fuel (duh), and two, so I can see if there's fuel in the line at that point when diagnosing running problems. I fitted one at the inlet side of the pump (mechanical on the 1500, and easily visible under bonnet), and another at the carb. This makes it pretty easy to see if fuel is making it from the tank to the pump, and then from the pump to the carb. Plus, the fuel line is double-filtered, hopefully keeping muck out of the float chamber.

Cheers,

-:G:-
Gryf Ketcherside

Just remember...The filters are exempt from the laws of nature, Just because the filters only fill up 1/2- 3/4 of the way does NOT mean you have a fuel problem


I do have a theory, as to why this is....my guess there is a pulse action creating a back pressure from the carb...tho minimal...an example a full 1 gallon of gas in a 1 gallon gas can, being poured out thur the small tube...at first its smooth then it gulps out, in a pulsating action...but if you pop off the small air tab it flows freely

I think the fuel filter acts as the small air tab, a chamber of sorts but because the carbs contantantly are opening and shutting off to inject the fuel, it creates a back pressure of sorts...kind of a "for every action there is an oppisite and equel,,,,reaction"


agian...I cant prove it, or point to any documents to make my case. its just a guess on my part as to why the fuel filters are never full.

Prop....Now if your filters do fill completely, you may be suffering from demon possiesion...Prop
Props Black Hole

Gryf,

New fuel filter was installed when I was checking the fuel system. Ultimately replacing the carburetor jets cured the stalling problem.

All,

I trimed back the ignition wire leads inside the cap, and this helped with the misfire. I drove to our club car show today without incident. PON307G ran smooth, strong, and placed second in the Spridget class.

Regards,

Larry C.
Larry C '69 Midget

Great, Larry! Sounds like you've got it sorted.

For now, anyway...

Cheers,

-:G:-
Gryf Ketcherside

This thread was discussed between 01/09/2009 and 13/09/2009

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