What are the symptoms of...

[Nunyas]

an incorrectly installed Head gasket? I was talking with the PO's of my B recently, and we got onto the subject of how the B vapor locks after driving for a while. They mentioned to me that they've had the problem with the car ever since they had the head worked on, and that no one they've taken the car to has been able to figure it out. They also told me where the soft fuel line that's routed from the tank to the carb (not in use) came from. They installed the soft line because they thought the vapor locking might be because of a blockage in the hardline, but using the soft line did not change anything for them.

What I'm wondering now is: How much coolant circulation will an incorrectly installed head gasket block? OR possibly, would a head from an earlier car not disipate heat correctly for a later car?

I have to wonder these things, because I clearly recall that there was a mix of "incorrect" parts on the rocker assy when I rebuilt it last year...

 

[DrEntropy]

Is it *clearly* a vapour lock? Meaning: when you experience the problem, the carb is obviously shy of fuel in the bowl? A classic vapour lock is hard to understand with a ZS carb, or an SU as they're "demand" carbs and as such the supply side is about the only place for fuel shortage to occur. Is the tank vented correctly? I seem to recall you'd checked the filler cap for the "whoosh" effect. You've put a heat shield on it, the pump works up to snuff... very perplexing.

 

[mgb4tim]

my 70 used to suffer from the same. One day I was starting to put gas in the car. ought, and fought to get the gas cap off, and I got the crazy suction sound, too. Inspected the car, and drilled a vent hole (1/8") in it, and was never an issue again

 

[tony barnhill]

1. Early head can be used on late engine with no ill effects.

2. If head gasket were blocking water jackets, I would think the car would run hotter than normal.

Off the top of my head, if it is a vapor lock....head was rebuilt & not cleaned properly so there could be some blockage....does your early head have the little automatic choke outlet in the rear of the head behind the valve cover.

...do you still have the ZS?

 

[Nunyas]

Yes, I still have the ZS on the car, and there is a water outlet at the back of the head behind the valve cover, but it's plugged with a rubber stop. Stock ZS equipped MGB heat shields are in place.

I'm gonna have the cooling system flushed or reverse flushed (is one way better than the other?) relatively soon. This heat thing is really annoying me. The car doesn't over heat, but it can get nervously hot at times. It will stall from fuel starvation before the engine over heats, and it happens a lot faster on hot days than it does on cool days.

I'm 90% sure it's something akin vapor lock. When the fuel starvation sets in the carb itself is darn near too hot to touch.

I've inspected the vapor sepparator system and it seemed "ok", aside from there being fuel IN the sepparator that is. I cleared the sepparator of fuel, mounted it in its proper spot, and then checked the lines for air flow. Both seemed "ok" to me at the time, but thinking back I recall in-haling quite a bit of fuel vapor when I was checking the charcoal canister line. So I'm sort of thinking there might be some fuel in that line blocking air flow. However, I've never had any "suction" from the fuel cap area when I take the cap off.

 

[tony barnhill]

So, you have a manual choke on your carb?

I prefer backflushing the engine block but you'll probably have to make a little modification to do that.

How's the catalytic converter?

 

[Nunyas]

Yes, the ZS has been converted to manual choke.

The catalytic converter is an aftermarket free flow/hi-flow cat mounted under the driver's floor pan (directly below the driver's feet to be precise). I guess in stop and go traffic some of the heat from it collects in the engine bay, but while in motion I think it's too far from the carb to directly radiate heat on it.

What sort of modification is needed to back flush the engine?

 

[tony barnhill]

I always replace one of the freeze plugs with a 'faucet' - so I can hook water to the back side of the engine...guess you really don't need to do that though...there are kits you can buy for backflushing.