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MG MGB Technical - persistent starting problem

Here is my 1966 MGB-GT’s tale of woe. I replaced the std. transmission with a black-label overdrive unit. This required a new rear-engine plate, a change from positive to negative ground, replacement of the starter with a pre-engaged unit, and some rewiring. I added a starter relay, and I made the necessary changes inside the tachometer and in its white-wire loop. The car originally had a positive ground pertronix ignition, which I replaced with a negative ground Pertronix.
The engine and transmission all fitted back together, and the car started and ran. With the back wheels off the ground, I was running through the gears and the OD. When I didn’t give the engine enough gas in top gear, it stalled. I haven’t been able to start it in the 2 weeks since.
A new battery is sending a full 12 volts to the new coil. There is spark at each plug. Each plug has been sand-blasted clean, and they were firing before I did the OD work. The fuel pump works fine: plenty of gas is pumped out of the hose to the carburetor. The carb is a Webber 32/36 DGV, which has been on the car for a couple of years and works well.
I have checked the white, brown, and white-striped wires for electrical continuity, and they all are good. I have hunted through the archives and done all of the suggested tests with a test light and volt meter. Everything checks out OK.
I have reset the static timing to 10 degrees BTDC as per the Haynes manual. The new starter turns the engine over rapidly, but it will not fire. In fact, it has never even coughed. The starter grinds on and on with no result, like the car was out of fuel. I have checked this, and there is plenty of fuel in the tank and coming through the fuel line to the carburetor.
I have 2 new neg. ground Pertronix ignitions, and I have put them in one after the other, with no result. I removed the Pert. Ignition and replaced it with points and a condenser, also with no result.
What am I missing?
Thanks in advance for your help!
Mike
M.E. Whalen

Some additions: (1)I have the spark plug leads in the right order. (2) When I remove the spark plugs, I notice that they have gotten black and wet-looking after only a few minutes of testing and engine cranking. The carb. sat idle for about 6 weeks while I did the other work.
M.E. Whalen

Hi Mike,

From your second post, I would surmise that the engine is flooding. Also this can be checked by smelling the exhaust pipe after cranking, a strong petrol smell.
Check the fuel level in the float chamber, maybe the float needle is stuck fully open. Clean your plugs again, try starting with no choke and the throttle fully open, DO NOT PUMP.

Good luck

Herb
Herb Adler

My guess is that the problem lies in the Pertronox units. They have a history of not matching up with the original mounting holes that the the points used. This will throw your timing off so much, that the engine won't even start. If you still have the point setup, I would suggest that you substitute them for the Pertronix assembly or try advancing the timing until you get some kind of results. I did the same conversion to my '67, several years ago, and it transformed the way the car drove. I went with a slightly more complex ignition system, but that was because I installed a supercharger at the same time. When I ran the Pertronix unit, I had nothing but trouble. It even burned a hole in the distributor cap, due to the misalignment of the pickup assembly inside the distributor. RAY
rjm RAY

If an engine has fuel, air, spark and compression in the right quantities at the right times it MUST start. If it doesn't you have to go back to first principles and see what is wrong.

If you have spark at the plugs then you need to check the timing to make sure it is occurring at the right time, i.e. a few degrees before top dead centre, and that is TDC on the compression stroke not the exhaust stroke as the carnk pulley mark indicates both. You also have to confirm that the timing mark is correct i.e. it really is TDC when it says it is, by seeing if the piston really is at the top of the bore. There is also no point checking wiring if you have sparks at the plugs and it is cranking.

What is your plug lead order? Tell us what it is and we will tell you if it is right or not. Simply telling us it is right is no good.

But as Herb says implies the simplest thing is to check for flooding. If you crank for several minutes, presumably with the choke out (or after repeatedly prodding the accelerator with a fixed-jet carb), without starting then you will flood it and this is immediately obvious as a strong fuel smell. If you aren't getting that take the plus out after cranking for a while and sniff them. They should have a strong fuel smell (fuel getting through) but not be soaked (flooded) or sooty (fouled), fouled plugs will still spark at the plug lead but not inside the cylinder. If there is no fuel smell then fuel isn't getting through to the cylinders, regardless what is reaching or inside the carbs.
PaulH Solihull

if i remember correctly, to check if there is current to the spark plugs and check timing at same time, remove the no1 plug at front with cord leave it on the chassis, switch on the ignition key, and turn the crank by hand with a spanner until you see no1 piston arrises and start to go down, you shoud would have a spark on that plug, then you know the timing is correct..
if the plugs are wet means there is fuel coming througt.. maybe a push will help to start the car..and burn all that excess of fuel..
regs
amf rodrigues

Just seeing the piston going up and down isn't good enough, that could be the exhaust and intake strokes. You need to make sure the spark happens at the top of the compression stroke by removing the plugs, putting your thumb over No.1 plug hole, and turning the engine until you feel the compression lifting your thumb off the plug hole. *That* is the compression stroke, and the spark should occur almost at the top of that.
PaulH Solihull

This thread was discussed between 31/01/2011 and 02/02/2011

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