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 - Silly Q... Starting

Bit of a numpty question... but this has been bugging the other half for a while.

When starting her 1500 from cold, it will literally spin, fire once and stop, it will do this usually twice, and then 3rd time start perfectly.

To the best of my knowledge the carbs are set correctly as is the timing. Its got one of the cheap britpart ignitions as alot of people on here bought for a tenner! I dont think its that because its always been the same on points. I did notice when doing the timing after fitting the ignition that the dizzy is quite worn.

Once in a while the car runs on aswell.

Am I correct in thinking a new dizzy might cure the problems? I was contemplating a lumention optronic for it as a xmas present but really I cant see it improving things that much?? Shes also struggling to get a decent fuel consumption out of the car, would the lumention make any difference?
D Tetley

I doubt that the Lumenition would make much difference, either to the starting or the fuel consumption.
What is the fuel consumption like?...and what sort of trips is she doing - duration, traffic, choke?

Dave O'Neill 2


just my intial opinion and guess....might try opening the gap a bit on the spark plugs an see what happens also try some warmer spark plugs if you got a set of colder plugs, if you have the 150 stromberg carb, I know from gryfs postings there is a diaphram and o ring that tends to wear and has similar symptoms

BTW...Im not certian about the 1500, But on the 1275s you have to turn the key to the "ON" postion and listen for the tic, tic, tic sound from the fuel pump to stop (thus pressureising the fuel system) before turning the key to the start postion that engages the starter....also try spraying a little WD40 inside the dissy cap to keep mositure at bay...trytriming back your spark plug wires if they are the type that use the little sharp screw that holds them in place in the dissy

Anyway theres a few ideas...I wouldnt fault your ignition system so quickly without doing alittle extra looking around. it could be a number of things.

Prop.

Prop

If you mean it fires once, kicks the starter out, but fails to keep running, then that is typical of an engine with low compression in one hole. It never quite makes it to the next cylinder in line. As in, #1 fires and kicks the starter, #3 doesn't have enough comp and doesn't fire, and it then does not have enough inertia to compress #4 to firing point. Once it's fired a few times, things are warm enough to light up. Check compression. If not even, set valves and recheck.
Bad comp in one or two holes could certainly explain poor fuel mileage too.

FRN
FR Millmore

Prop, UK 1500 midgets dont have a single Stromberg carb but 2 SU's.(no airpumps, fuelpots or catalyzers either so have like 10 BHP more) :)
Arie de Best

Hmmmm I have not experienced that described by our resident expert but it sounds feasible so it is worth checking the compresion on each cylinder to rule it out (or in :-)}

Generally I have found that if the starter motor is being "thrown" out by the engine attempting to start then it can be a number of possibilities
The battery can be less than ideal
the starter motor itself can be substandard
The engine can be set up on the ignition timing badly.

How did you set up the timing?

The timing might well be poor as you mention that the engine tends sometimes to run on, certainly should not be doing that.

Finally a word about fuel consumption? First let me apologise to any women on these boards who drive a car and do not fit the person I am going to describe.. However both my wife and my daughter from time to time have complained about poor fuel consumption with their cars. Probably the best was my daughter when she changed 1 fiesta for a different one.
Because with the original one when she put £5 worth of fuel in the car the gauge would rise to about half a tank. The second one she bought when she added £5 to that the gauge only recorded about 1/4 of a tank, she told me the car was terrible on fuel based on that observation alone!!!!"!"

Anyway true fuel consumption can only be deduced by filling the tank a number of times and noting total fuel added over that time from FULL Tank to FULL tank and then as stated by Dave what kind of use has the car had. Aound town more than 25 to the gallon would be pretty good.
Robert (Bob) Midget Turbo

My suspicion - and it is only that - would be that the mechanical 1500 fuel pump is not working as it should.

There is enough fuel vapour drawn into the cylinder for it to fire, but until the engine has turned a few more times, the pump hasn't delivered enough fuel to keep it running. This could be a split diaphragm in the pump. It will still operate, but a lower delivery rate at least until the engine is turning at speed.

It may also be leaking fuel from the glands on the fuel jet delivery pipes. This would cause the float chamber level to drop whilst it was parked up, exacerbating the starting problem and also show up as poor fuel ecomnomy.

Guy
Guy Weller

That's the basic procedure I follow when starting my 1500... it cranks a bit, I let off the key, and then crank again, whereupon it fires right up. My guess is that fuel drains back from the carb, and it takes a few seconds for the mechanical pump to fill the chamber again.

It's done that for years, so I consider it normal. If it's been running and I restart it, it fires right up with a tickle of the key. Only when it's been sitting does it take a bit of cranking, but again, only a few seconds' worth.

Doesn't bother me a bit, actually - in those few seconds before it fires, the oil pressure has time to build a little.

Cheers,

-:G:-
Gryf Ketcherside

Not sure how fuel would drain back from the carb, but it might evaporate ;o)
Dave O'Neill 2

I first experienced the low compression thing on a dying Rover. At first it only did it when quite cold. As the valves got worse, the temp required got higher, as did the number of attempts to start. When a second cylinder started eating a valve, it got very annoying. Have since found the same on several other cars. It's easy to check, and a first step in the tuneup that might fix several other possible causes mentioned.

FRM
FR Millmore

Thanks for the replies guys! Hopefully together we can sort this!

I did check the compression last year, but since then a recon/unleaded head has been fitted. I will check the compressions tomorrow and report back.

I have a facet fuel pump/reg Iíve never got around to fitting so I will try and do this when Iíve a free weekend to plumb it in properly.

I strobed it at 10o BTDC, Now its been mentioned Iím not sure this is correct, can someone confirm what is correct when strobing a 1500?

Also can someone confirm the correct plug gap? It just so happens a new set of plugs came through the door this morning (thought it was worth changing for winter anyway)

thanks....
D Tetley

D T.

As you are probably aware the book says 10BTDC at ONLY 680 RPM and vacuum disconnected.

This means in laymans terms that with no mechanical advance the timing should be 10BTDC, thus if the dissy was fitted with a 11 or 12 degree cam then if that was all functioning correctly the timing would be about right.

However after 30 years or more our dissies leave an awful lot to be desired not least of which many have been swapped for other specs at various visits of previous owners to the scrap yards.

So with this in mind IMO there is only one sure fire method of setting the ignition timing to optimum. The method has been described 100s of times and is this]

Rev the engine to 4K RPM and with the vac disconnected set the timing to 32/34 degrees BTDC. Then see how the car performs.

The plugs are standard for most cars of that era and are NGK BP6ES set at 25thou.
Robert (Bob) Midget Turbo

Many thanks Bob, I'll do exactly that tomorrow after shes changed the propshaft as the UJ is knacked! Better not tell her I'll be reving it to 4K though, she will have a fit!

The plugs I got were the 6ES's so all good there.

I'll report back when I've checked the timing again.



D Tetley

This thread was discussed between 23/10/2009 and 24/10/2009

MG Midget and Sprite Technical index

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