MGB & GT Forum

Hi Guys and Gals.

As a newbie, let me introduce myself. I live in Malaysia, ergo my MGB and I suffer tropical heat! Also I apologise in advance for what will be a lengthy post. In my lifetime, I have owned four MGBs of various ages and types but my current baby is an early 1972, chrome bumper roadster. As far as possible, I am trying to keep her 'factory original'. I never experienced this 'hot start' problem with any of my previous MGBs but then they were driven in wet, soggy England!

For the past four years or so, my B has refused to start when hot and I am fresh out of ideas as to why. For the first four years of her life in Malaysia, hot starting was never an issue. Even though living in a hot climate, from the get-go she has always needed choke to initially start, thereafter starting on the first turn of the key without choke. She runs like a veritable train with no misfires, accelerates with no lag and, as far as I can tell, has no issues. That is until I stop! If I stop when the engine is fully warmed (she generally runs just shy of the 'normal' mark on the gauge), then she will not start until the engine cools. Without teaching my grandmother to suck eggs, most of you will be aware the temperature in the block rises once the engine is switched off. Even so, the temperature gauge only climbs to 'normal' or slightly above. If I try to start within five minutes or so of stopping; no dice; wait a couple of hours and she starts at the first turn of the key and behaves perfectly - that is, until I stop again! The conclusion? The problem must be heat related. So the search began!

I have a pacemaker fitted so I have to be careful on the ignition side of the engine so the search began on the fuel side, ie looking for a vapour lock. All the braided fuel lines were replaced, the carb breathers were cleaned and checked that they were not blocked and the fuel pipe along the bulkhead straightened so there was no potential for vapour to collect in the pipe. Any vapour would migrate to the carbs and out through the breather pipes. I read on one of the threads here that ethanol in the fuel may be responsible so I checked with Shell Malaysia and they do not add ethanol to their 95 RON petrol here in Malaysia.

The problem still persisted so the search turned to the ignition side of the engine - new plugs, new HT leads, new coil, new dizzy condenser, new points. No dice - she still stubbornly refused to start when hot. I should point out the coil gets very hot but I don't know how hot is too hot!

Going to the weekly classic car meeting is not a problem - we are generally nattering for a couple of hours or more and the engine has cooled by the time the meeting breaks up. Doing longer trips is the problem. Being a gentleman of a certain age, moderately frequent pitstops are required and I do not relish the idea of sitting by the roadside communing with monkeys for a couple of hours each time!

If anyone has any ideas, I would be most grateful to hear them. By the way, all parts were bought from either Moss, Rimmers or The Distributer Doctor although, in the case of the former two, the parts probably came from China so I could have bought them locally for half the price! In addition, I should point out that, at each stage, the carbs, points and timing were checked and adjusted as required.

Cheers.



Edited 2 time(s). Last edit at 2024-04-16 11:21 PM by RHJ.

I had a similar issue with a 78 B. What I found was that by disconnecting and reconnecting the line from the carb to the charcoal canister and reconnecting it allowed be to restart immediately.
I have since cleaned the charcoal canister and haven’t had the problem since.

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1978 MGB
When diagnosing issues related to running and stalling, always check to see if you have gas in the tank first.

Thanks for taking the trouble to reply, Bob. Sadly my MGB is late 71/early 72 and manufactured to UK spec so does not have a charcoal canister or very little else controlling emissions for that matter. As I say, thanks for taking the trouble to reply to my post - it is appreciated.

Diagnosis is your friend...

Do the simple things first...

Arm yourself with a little jumper wire with alligator clips. Remove the fuse box cover. Immediately after shut-down, attach the jumper to the bottom fuse and to coil positive. Then see if the engine will start. This will bypass the entire low tension circuit, including the ignition switch and related wiring. If it now starts, you can dig into the switch and wiring. Heat can make an iffy electrical connection fail due to high resistance, so look closely at the related wire terminal connections. Also, check the integrity of the low tension connections at coil negative and at the distributor. Also check the connections inside the distributor along with the integrity of the small ground wire from the points plate to the distributor body.

Finally, check the center connection and carbon button inside the distributor cap.

If no joy, move to carburetion. Remove the air cleaners and gaskets. Have a helper crank the engine while you manually raise the carb pistons a little. If the engine starts, you'll know you have a richness issue in one or both carbs.

If no joy, raise the pistons and squirt a little starting fluid or carburetor cleaner into each carb and try again. If the engine now starts, you have a lean condition...

Report back...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Thanks for taking the time to reply, Dick.

Paragraph 1 - done that and engine didn't fire.
Paragraph 2 - I'll check the dizzy cap.
Carbs - fuel mixture has been checked many times and is correct.

Thanks again.
Rowan.

Carbs - fuel mixture has been checked many times and is correct.

You miss the point... Many things could still be wrong -- heavy float, maybe even something as simple as lack of oil in the dashpots...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Hi Guys and Gals,

The latest theory/diagnosis/guess is a faulty distributer rotor. In all my years of maintaining cars, I have never encountered a faulty rotor arm and in a list of 100 possible causes for the 'hot start' problem it would be in 99th place! However, from my research on the Internet, I understand a failed rotor arm is now quite a common occurrence - poor quality parts. The faulty rotor arm is causing the coil to overheat. I am not sure whether the coil overheating is the actual reason the engine doesn't fire and whether this has damaged the coil. The next attempt to solve the 'hot start' problem will be replacing the distributer cap, rotor arm and coil. I will post the results so, hopefully, others experiencing a similar problem won't expend a lot of money, time and energy solving the problem.

Rowan.

Just to close this thread, this morning the dizzy cap, rotor and coil were changed, which seems to have cured the problem. No sign of damage/wear to the dizzy cap but I changed it anyway. The rotor was changed to one of the new super-duper red ones sold by The Distributer Doctor. The brass on the old black one looked to have a goodly accumulation of oxidation. The coil was changed as a precaution - the old one got so hot it was likely its innards had been damaged. So there we are; duff rotor arms sometimes appear!

Rowan.