Vapour lock

[Pellwood]

So we got caught in the tail backs on M5 over the weekend. We had been cruising up the Mway around 55mph for an hour or so then hit very slow moving traffic, we drove in a stop start fashion for around 2 hrs and then the engine got more spluttry then died and would restart. We got to the hard shoulder. I checked everything in the engine bay, all ok. Tried the engine again after about 20 minutes or so and it fired up ok. We only had 1/2 a mile to go, so crawled along the hard shoulder until our exit and we made it home ok.
Sorry for the waffle but I thought explaining symptoms might help. My initial thoughts are vapour lock?
If so any ideas on how to prevent it happening?

 

[Happystamps]

I suggest you collect some more data before jumping to a conclusion. If you can get the fault to happen again, pop around the side of the van and undo your fuel filler cap, and listen for a hiss, then try to start the van again. If the problem goes away, you need to clear out your fuel tank breathers.
Also might be a good idea to check the coil resistances- measure between the small metal connectors on the coil- should be pretty low- and one of those connectors and the centra HT lead post. Should be pretty high. It also shouldn't be oily (indicates leak), have cracks in it, or shoot sparks at your fan shroud when you crank the engine.
Other than that, the issues that come to mind are all "something's out of tune" so... give it a service. Get your valve gaps sorted, check the points dwell angle (I've always found using a feeler gauge on these things is fairly useless- for every 4 "good" results using feeler gauges I'd have one using dwell). Check your timing and your carb setup, your carb should be 3-4% CO.

 

[Pellwood]

Thanks for the advice re the tank & breathers, I will check. I had covered some of the other tests already. I should have mentioned before but to give you some background. I have completed a top end rebuild and replaced the coil, plugs and leads, plug gaps set. Valve gaps set ok, electronic ignition with an SVDA dizzy, timing 7.5 btdc, carb tuned. It had been running like a peach for the last 500 miles or so. I'm always on top of my servicing and have re-checked everything less than 100 miles ago but It doesn't hurt to check again

 

[Happystamps]

Good idea- especially as you've replaced parts. Not that you shouldn't, but if you've replaced something and then you get problems, that's probably a good place to look.