When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Given how close they are to the fuel tank, is this possible? ...since I noticed a buildup of pressure inside the tank, I'm just wondering if this is a possible cause of the issues I've been having with rough running after shut off - restart, and fuel dumping out of overflow pipes...I could be pretty easily persuaded to imagine that the puny little breather hole isn't large enough to displace a moderate amount of pressure.
Before changing the tank, I considered it, and afterward, since I had to fiddle a fair bit to find a sweet-spot thru re-torquing all the clamps in order for the tailpipe section to not rattle against the bottom....well, I'm wondering if this just may be the cause.
Last edited by Chris Scott; Dec 16, 2023 at 04:27 PM.
Try putting some heat shielding between the exhausts & your fancy stainless steel tank. You could be building up vapour pressure above the liquid fuel.
I would still start with a gravity feed direct to the carbs as discussed in your other thread on this issue. Otherwise you are going to keep chasing your tail.
Since an exhaust pipe is hot, it's not impossible. On the other hand (there always is one), considering the number of Mk2s that have run happily with their exhaust tail pipes under the fuel tank, it seems unlikely to be a real problem. When the car isn't moving and the engine is idling, the exhaust gas from the tail pipe isn't very hot. When the car is in motion and the gas is at a higher temperature, there's also a lot of cooling air flowing past the tank.
Since an exhaust pipe is hot, it's not impossible. On the other hand (there always is one), considering the number of Mk2s that have run happily with their exhaust tail pipes under the fuel tank, it seems unlikely to be a real problem. When the car isn't moving and the engine is idling, the exhaust gas from the tail pipe isn't very hot. When the car is in motion and the gas is at a higher temperature, there's also a lot of cooling air flowing past the tank.
I tend to agree with you, on both counts.
....it's just that my lack of first-hand experience with these cars has me considering all possibilities.
I've also not verified whether or not there's a section of (in my case copper) fuel line that's being heated by some part of the exhaust system....a mate of mine happened to mention that this is an issue when inexperienced installers run fuel supply lines too close to exhaust systems...we'll see when I get back and get the car up off the ground to do a thorough inspection.
The other thing is that I had a very brief convo with a well-known mechanic in L.A., and after explaining the "runs fine until shutting off for a spell" scenario, he said "...yeah, it's "heat soaking" "
....anyone know what he meant by this?
As always, thanks in advance for any ideas!
Last edited by Chris Scott; Dec 17, 2023 at 09:43 AM.
I would still start with a gravity feed direct to the carbs as discussed in your other thread on this issue. Otherwise you are going to keep chasing your tail.
The other thing is that I had a very brief convo with a well-known mechanic in L.A., and after explaining the "runs fine until shutting off for a spell" scenario, he said "...yeah, it's "heat soaking" "
....anyone know what he meant by this?
When you shut down an engine after a run it suffers what is known as "heat soak" where the temperature initially rises due to no airflow & then starts to cool down. Heat soak is a frequent cause of fuel vapourisation in the fuel lines around the carbs causing vapour lock and hard starting.
When you shut down an engine after a run it suffers what is known as "heat soak" where the temperature initially rises due to no airflow & then starts to cool down. Heat soak is a frequent cause of fuel vapourisation in the fuel lines around the carbs causing vapour lock and hard starting.
Hey Glyn,
Yeah, pretty much what I expected.
The entire fuel system will soon be scrutinized...all shall be revealed.
For most cars or at least most Jaguars, a prod on the throttle when starting a hot engine is usually sufficient to clear the vapour from the fuel line.
For most cars or at least most Jaguars, a prod on the throttle when starting a hot engine is usually sufficient to clear the vapour from the fuel line.
Just to be clear, starting the car in this condition isn't the issue, it's that it runs rough and won't pull cleanly until around 5 minutes or so, when it runs normal again.
Just to be clear, starting the car in this condition isn't the issue, it's that it runs rough and won't pull cleanly until around 5 minutes or so, when it runs normal again.
But still spews fuel out of the Plenum drains from time to time which is why I suggest you start with gravity feed direct to the carbs & isolate the real problem. Post No 3.
Tailpipes heating fuel in tank Mk2.
