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MGB MGB does not start when hot

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Robi

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I know it is a redondant topic but i am stuck on the side of the road again. I have a 78B that starts nice when the car is cold, it drive pretty nicely but if I stop after 10 minutes or 1 hour, impossible to restart!! It cranks but nothing else. Sometime it seems to fire while i am keeping the key "on the starter" but stop immediately.

gas is coming and i have sparks. I changed the fuel pump, the coil, the wireset, the spark plugs, the distributor cap and i cleaned the carbu. I check a air leak, nothing.

i received tones of advices but I still have the same problem... And i am short of ideas now!

condenser?

thank you for your help.
 
Which carburetors do you have on the motor?

If they're SUs, it's a well-known issue that the fuel in the carbs gets too hot and starts to aerate, causing a lean condition and making starting hard or impossible. Something like heat shielding would be a step in the right direction if that's the case.
 
can you give us more information?

1. what are you using for a fuel pump?

2. Are you using a Zenith Stromberg carb?

3. How long does it take before it will restart?

4. to clarify, the car doesn't quit, you turn it off and then it won't restart - correct? (and is it running properly until then?)

we will get there I promise!
 
Condenser? Well it could be, but condensers usually work or not, especially the after market ones. I personally would look for a vapor lock situation first. I had to insulate the fuel line that goes behind the engine on our 72 to prevent vapor lock 5 years ago and I've not been bothered with it since. Ethanol gas will vapor off at a lower temperature than non ethanol. Have you tried using non ethanol gas? PJ
 
Thank you for your answers.

The carb is a ZS 175 and the fuel pump a SU AZX. The car drives very well and the idle is stable, but i mustn't stop. It takes 2 or three hours before i can restart!

I also use no ethanol gas! But i have a little run-on going when i stop. Anti-run on gas valve?
 
1, A 78 MGB has a ignition relay. If that is bad it will run when in the start position but die when released. (as mentioned in your first post). 2, See if the coil is wired properly. It will run wired wrong but may lead to a overheated coil breaking down and needs to cool. Whatever color the wire to the distributor is that should be hooked to the negative terminal of the coil. (points type distributor) 3, does it have a electronic distributor conversion? Maybe something going bad with that?? I hope this stuff leads you in a direction to get it fixed!
Bob
 
This could be electrical, but it sounds like classical vapor lock to me. Try pouring some water over the carbs when it's misbehaving, and see if you can start it then. If so, it's a heat/vapor problem at the carbs. Check the voltage at the coil when you are starting it--you could have decent voltage when you measure it when it's running, but when you run the starter, the voltage will drop to some degree. Electronic ignitions can be especially sensitive to this.

Anyway, I'd go back to basics. Since the problem occurs reliably, it should be easy to find the problem. Run the car until you encounter the problem. If the water-on-the-carbs trick doesn't fix it, check fuel flow by disconnecting the fuel line at the carbs, point it into a container, and crank. See if you get a good flow; I'll bet it's weak, probably from a vapor bubble in the pump's valves.

To check the ignition, connect a timing light with an inductive pickup, and make sure the plugs are firing. If not, work back through the ignition system to see where you're losing it.
 
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