MGB overheating (possibly) problem.... any ideas?
Discussion
I have a 1974 MGB roadster (late chrome-bumpered jobby) which has a mechanical problem I have, thus far, had no luck diagnosing. It's been happening for ages now and several garages have looked at it and proudly announced that they've fixed it only for it to happen again next time I drive anywhere.
The symptoms are thus:
The engine starts fine and runs fine for somewhere between 15 minutes and half an hour (depending on what it's doing). Then I start to get a slight hesitation if a floor it from idle (in neutral)... the engine splutters and the revs drop slightly before it picks up and revs freely. This gets gradually worse until even touching the throttle lightly causes the engine to stall. Eventually it wont even idle. Once it's died it's a while before it'll start at all and hours before it'll run properly again.
Nothing is obviously overheating, the water temperature is fine and the underbonnet temperature seems normal. The fuel supply is fine and the carbs aren't getting hot so I don't believe it's vapour-locking. I'm pretty convinced that the fault is electrical but don't know how to (1) prove this and (2) work otu what component is at fault.
Any help would be much appreciated.
The symptoms are thus:
The engine starts fine and runs fine for somewhere between 15 minutes and half an hour (depending on what it's doing). Then I start to get a slight hesitation if a floor it from idle (in neutral)... the engine splutters and the revs drop slightly before it picks up and revs freely. This gets gradually worse until even touching the throttle lightly causes the engine to stall. Eventually it wont even idle. Once it's died it's a while before it'll start at all and hours before it'll run properly again.
Nothing is obviously overheating, the water temperature is fine and the underbonnet temperature seems normal. The fuel supply is fine and the carbs aren't getting hot so I don't believe it's vapour-locking. I'm pretty convinced that the fault is electrical but don't know how to (1) prove this and (2) work otu what component is at fault.
Any help would be much appreciated.
Headgasket: possible, I'll check this evening. I replaced the head about 5 years ago with a reconditioned (peter burgess) one. I'll check the torque on the head bolts and look for leaks, etc. and repost.
Coil/condenser: The last garage I took it to replaced these and it didn't solve the problem although they said it did allow them to restart it immediately after the replacement. That's what made me think it was perhaps something else in the electrical system damaging or overheating the coil.
Fuel pump: I don't think this is the problem - if I look at the fuel filter (it's a glass cased in-line one) there is fuel in there, although there's some gas (air?) too. The other thing that makes me doubt this is exactly how it fails. It initially stutters at low revs and full throttle which sounds like over-fueling (or a weak spark) rather than under-fueling to me.
Coil/condenser: The last garage I took it to replaced these and it didn't solve the problem although they said it did allow them to restart it immediately after the replacement. That's what made me think it was perhaps something else in the electrical system damaging or overheating the coil.
Fuel pump: I don't think this is the problem - if I look at the fuel filter (it's a glass cased in-line one) there is fuel in there, although there's some gas (air?) too. The other thing that makes me doubt this is exactly how it fails. It initially stutters at low revs and full throttle which sounds like over-fueling (or a weak spark) rather than under-fueling to me.
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