TR2/3/3A rough running after 20 min shutdown

[TFB]

My TR3 runs great,no issues except one.
On a hotter day say over 80 if I shut the car off and then restart after sitting about 20-30 min. the car starts up easy but wont idle and runs rough for about 30 seconds and then goes back to normal smooth idle.If it sits longer it doesnt happen.If I shut the car off for few minutes it doesnt happen.
Today I came home let it sit about 20,same symptom.Water temp gauge crept from 185 to 200.Infared temp gum showed intake manifold 170,float bows about 115,I pulled off one bowl top and fuel was about 3/4 full.I think gas may be vaporizing or flashing until the manifold cools down but not sure.
Any input appreciated.
Tom

 

[NutmegCT]

Problem occurs only after a short shut-down when the engine is hot.

I'm thinking *vapor lock* due to engine bay heat vaporizing fuel in the lines near the carbs.

Quick check might be putting a wet cloth onto the fuel lines when this happens; that should condense any vaporized fuel in there.

Hope this helps.
Tom M.

 

[Hamish Racing]

yes agreed - sounds like fuel vaporisation in the carbs or lines
do you have a race style 4 branch exhaust manifold.
i changed the fuel line routing to the back of the engine and into the rear carb first- just swap the float bowl tops over.

but i do abuse my car in my short sprints etc..

 

[CJD]

+1...mild vapor lock. The fuel boils out of the lines, so you are starting on what's in the bowls. It runs rough until enough fuel passes into the lines to cool them and refill the bowls.

 

[TFB]

Thanks for replies.
I was thinking not the lines but manifold and cyl. head temp because bowl seemed pretty full.I will do some more experimenting with keeping the lines cool.I have a stock ex. manifold partially wrapped along with the pipe,steel line from stock pump to rubber fuel hose from just before the rad. neck to the bowls .I dont think its normal in 80 deg.Maybe Im a little lean.
Thanks
Tom

 

[Madflyer]

OK mine is a TR6 but, so more heat. I added heat shield at carbs replaced rubber gas lines with braided lines and add a screen door spring over gas line from fuel pump around head as cooling fins

 

[poolboy]

Maybe a little too rich for restarting a hot engine.

 

[TFB]

Maybe a little too rich for restarting a hot engine.

Thats an interesting possibility.The car runs great,always starts with just a push of the buton,good plug color no pinging etc.
I need a little choke for about 1 min. from cold star to smooth no choke idle in even 70 deg. garage temp so I dont think thats the case but some more troubleshooting is ahead.
Thanks
Tom

 

[NutmegCT]

Tom - try the wet cloth suggestion in my first post. That should tell you if there's vapor lock going on.

I think that too rich/too lean would be indicated by plug appearance.

 

[TFB]

Tom - try the wet cloth suggestion in my first post. That should tell you if there's vapor lock going on.

I think that too rich/too lean would be indicated by plug appearance.

Thanks,I am going to try that .Hopefully getting out again soon.
Tom