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MG MGB Technical - YANS (Yeat Another Non-Starter)

Hi,

I've been battling with getting my 1973 B Roadster to start for a while. I've been following all relevenat threads and doing searches in the archive which has allowed me to dismiss possibilities for the fault. However, at this point I'm stumped.

First some history: the car has been laid up for quite some time (6 months) - with us moving, we push-started and drove her to our new home. Once there, she refused to start. Over the course of the last few weeks, I've done the following:

1. Checked the spark plugs: a spark is delivered to each of the spark plugs, as per the remove and put plug on block method.

2. Electronic ignition, coil & plug leads: Initially I thought the problem might be due to faulty sparks being delivered, so before #1, I swithed to an Petronix ignotion, new 40KV coil and new spark leads. As per #1 I think I can rule out this option.

3. Checked fule delivery: with the fuel line removed from the carbs, I switch on the car (quickly). A health dose of fule is delivered through the line. (So the fuel pump is operating)

4. Spark plugs again: checked the plugs for excess fuel or oil, nothing found. (So we are not flooding)

At this point it still doesn't start. The engine ticks over normally, definately not sluggish at all, but doesn't start. (Not starter related.) The battery is good and charged and definately delivers a spark to the plugs. In addition I've checked that the carb pistons are not sticking, i.e. pushing them up makes them come down nicely.

So I'm lost and have reached trhe limits of my knowledge. I've followed all advice, know that the electrics are good, fuel gets delivered, and by all accounts it should be ok. Any ideas?

Greetings,
Jaco
Jaco Greeff

Are you sure you haven't gotten the ignition timing way off somehow in the process? Or plug wires in wrong order? Just because you are getting spark doesn't mean it is arriving when needed.

I'm not sure if it is available in SA, but what I would try in this situation is a squirt of starting fluid down the carb after taking the air filter off. Starting fluid is just a spray can of ether; while it is not good to run an engine on it, it will at least fire (and clear wet plugs) if the ignition is close to correct. If it runs for a bit on starting fluid and then dies, you aren't getting fuel through the carb.
Tom

I would give it a shot of starting fluid into the carbs and see if she fires that way. If you are running dual carbs with the T in the line into each carb, could be that the T is blocked preventing fuel reaching the float bowls. Good Luck
M Holmes

Tom,

Looks like brillient minds think alike. My mind just moves a little slower. I was still typing when you posted :)

Cheers, Michael
M Holmes

> Are you sure you haven't gotten the ignition timing way
> off somehow in the process?

I hope not.

> Or plug wires in wrong order? Just because you are
> getting spark doesn't mean it is arriving when needed.

Agreed. I have checked and double checked the order of the plug leads before and after mucking with them so I'm pretty sure that is not the case.

> I'm not sure if it is available in SA, but what I would
> try in this situation is a squirt of starting fluid
> down the carb after taking the air filter off.

I'll locate a can of that and try it. (I seem to recall seeing it in a shop somewhere.) It was next on my TODO list anyway, moving it up a bit - my how-to-diagnose-and-fix problems book made a mention of that and I assumed that giving it a go won't hurt at all.

> If it runs for a bit on starting fluid and then dies,
> you aren't getting fuel through the carb.

My carb has the fuel line going in the bottom with a connector fuel line piece running between the carbs as well. Before getting my hands on the start spray, I'll just double check delivery to the second carb as well. I was hoping to rule out the fule delivery problem completely, seems like I have a bit more testing to do. (I have not checked the actual fule level within the carbs, with the HIF-4 carbs it seemed like a bit more work getting there than with the HF carbs which have easy access.)
Jaco Greeff

I'm a little suspicious of fuel delivery.

If it's getting gas and not firing there should be unburnt fuel in the cylinders.

After tryiing to start it by cranking it a while, try checking the plugs to see if they're wet and smell like gas. If they don't, try putting one end of a small hose in or against the spark plug holes and sniff for gas. Sounds weird, but if it's getting gas and not firing you should be able to smell gas.

If it smells like gas, I'd verify initial timing.

If you can't smell gas, I'd investigate as to why not.

Good luck.

One more thing...have you checked valve lash?

Glenn

Back in the days when I worked for a British Leyland dealer, we had a lot of newer cars that the float would stick in the shut position.
Usually it's the other way around, a stuck open needle and seat valve, causing fuel to flood over.
Check that!
Safety Fast
Dwight
Dwight McCullough

Some more things to check tonight, thanks. While I am still learning at a rapid rate, I'm not sure what Glenn means by "valve lash". I'll do a bit of scrounging on that one. (First to understand, then to check.)

As for Dwighht's suggestion on checking for the open seat valve, I'll need to follow the same procedure. (Read some more, then check.)
Jaco Greeff

If you have a non-starter then an extended period of cranking will usually dampen the plugs, if not flood the engine if the choke is being used. Wet plugs are flooded, dry plugs and no fuel smell means no fuel is getting through. They should have a strong fuel smell after cranking but not be wet.

Take the air cleaners off and blow in the float chamber overflow pipes and you should see fuel bubbling up out of the jet. If the float overflows are plugged the float chamber will not fill with fuel hence none will get into the jets.
Paul Hunt

Get a camping gas stove and direct the gas down the carbs as you turn it over. My MG ran fine on gas - pulled the gas away and it died. Did this for a few goes and eventually it ran on petrol....

I put it down to stuck compression rings and old petrol...Once it was warm it was happy with anything.

Stuart Robson

Jaeco- Did you possibly mis-connect the fuel supplies to the overflows on the carb bowls? If the starter fluid doesn't get at least a back fire, pull plug #1, crank until the pressure blows your finger off the hole ( I use a $5 trigger switch from Craftsmen) pull the balancer back to TDC notch on the timing cover, and check for a rotor position of 1-2 o'clock. Also check to make sure the rotor lug has the rotor captured and the dizzy is set into the drive dog slot sufficiently. Its real ez to get those eccentric centered drives off 180 degrees.
vem myers

Check the timing.

When you swapped over to the pertronix - the
ignition timing was altered far enough to make
starting difficult, if not impossible. I can't exactly
remember whether if installing the Pertronix
retards or advances the timing - but in anycase,
the timing is more than a few degrees off.

With the Pertronix, it's almost impossible to set the
timing statically. Switch on the ignition, aim a timing light on the pulley marks, and spin the engine a few times with a bump switch. Adjust
the dizzy. Repeat, if necessary. Once she fires up,
check and set the timing at idle speed.

If this doesn't work, still, I'd check the plugs, again,
this time, using the "hold plug against the block"
method. Some of the earlier (old stock) Pertronix
units had dodgy factory quality control, but this
seems to have been resolved in the years since.

I've had my Pertronix working happily in my car for
over 4 years without a single hiccup (...knock on
wood).
Daniel Wong

It seems that this issue was due to clogged float chamber overflow pipes. Last night I had the following experience:

1. Removed the air filters to check the overflow pipes. Blew into both of them until I could hear the petrol bubbling.

2. Repeated the exercise with my finger (hopefully clean) stuck underneath the carb piston, making sure that I really heard petrol bubbling. (Yes, indeed it was petrol, as my finger could attest to.)

3. Decided to put back the air filters to check for a damp plug or petrol smell on the plug.

4. On turning the engine, for some obscure reason it started. I was caught totally unawares, as were the dogs which ran around the garage for a full 10 minutes yelping at this new noise maker.

I think the timing might be a bit off, altough she starts very easily now she runs a bit rough, might be because she hasn't had that experience in a long while. Now that I'm over the first hump, I'll start playing in that area.

Thanks a lot for all the guidance, advice and help, it has made the experience worth-while.
Jaco Greeff

Playful dogs and a running engine - life is good.

Glad you got it running.
Glenn

This thread was discussed between 08/09/2003 and 09/09/2003

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