Won't start if hot, suspect vapor lock, options?

[Steve1970]

gents...

the car won't start after running the engine hot for fifteen minutes or so. the engine <span style="font-style: italic">does</span> indeed turn over after 10 or so tries but it will not stay running unless i rev up the rpms. if i keep the rpms up for about a minute, the engine will stay running beautifully.

this only happened after (1) the weather got hot, and (2) i adjusted the fuel mixture. both events occurred the same day. i decided to lean the mixture on the carbs because of sooty plugs; i backed off the needle a 1/2 turn to the left.

i hesitate to restore the mixture back to rich because it actually runs soooo much smoother at the current leaner setting.

so i'm guessing my fuel is evaporating before it gets into the cylinder. almost every component in the fuel system is 2 yrs old or newer.

i'm currently going off of this supposition: when i replaced the jets + floats a couple yrs ago i had a little trouble adjusting the floats. i'm thinking that i have the floats set such that bowl is not filling enough. could this plus the new lean mixture setting have caused the fuel evaporation problem to now render? tomorrow i plan on adjusting the floats so that the bowl fills higher.

does anyone have any other ideas i could try?

 

[poolboy]

I'd check the float level if you have any doubt. But even when they are right (.625 to .627 inch) you might have trouble starting under those conditions.
I attribute the problem to some gas in the float chamber vaporizing.
One thing that helps is holding the accelerator pedal down about 1/3 of the way (steady) while cranking the starter.
With the throttle disc open, the suction fron the intake cycle promotes clearing the vapors and gets some real gas coming up the jet.

 

[pjsmetana]

Sounds to me like the carb(s) are getting too hot. I don't know what kinda your running, but I'm pretty sure theres heat shields out there that should help. If not, then wrapping your header(s) should help. I would do both personally. Check that float level as well.

 

[TR3driver]

https://www.the-vintage-racer.com/webroot/Heatshields/

 

[NickMorgan]

Modern fuels are far more inclined to vapourise than good old leaded.
I have had similar problems with my TR3 since having to run it on unleaded here.
I tried moving the fuel lines a little further from the engine block, but what really has made a difference is getting the timing and ignition spot on. I wouldn't have believed that this could make such a difference.
The heat shields available should help, too.

 

[Steve1970]

thanks, will start by re-adjusting the floats; i remember having a tough time getting this right with a small 'L' ruler, i like the looks of that tool poolboy is using.

good call on the heat shield and manifold shield. the order is going in today.

nick, along the lines of fuel formulation being the problem... i've recently switched my brand of gas (from gulf 92 to shell 93); maybe there's some additive in the shell that it doesn't like.

 

[poolboy]

It's a dial caliper, Steve. As the jaws open at the top, which you don't see in the picture, the slide projects from the bottom the same distance.
I have the ARE heat shield and it helps, but on a really hot day, like today, it's a good idea to follow the owner's manual suggestion about holding the pedal down 1/3 of the way.
Nick Morgan's points are well taken and I'd like to reinforce them.
I ,too, once rerouted my fuel line from the pump to the carbs just to see if it made a difference. Nope, so to me, it's the heat affecting the float chambers, more so than the fuel line itself.
Timing and carb mixture being spot on for your engine always contributes to a better start-up particularly in adverse environmental conditions. Try a Vacuum gauge for the timing.

 

[startech47]

You can purchase a 6" digital caliper from Harbour Freight for around $20.00.