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69 Dart Hard to Start When Hot, Starts Fine Cold. Possible Vapor Lock?
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Author:  indetrucks [ Tue Jul 12, 2022 1:33 pm ]
Post subject:  69 Dart Hard to Start When Hot, Starts Fine Cold. Possible Vapor Lock?
Hey guys, long time lurker turned member today.

My 69 Dart Slant 6 runs like a top but has a VERY hard time starting when hot (lots of cranks). I heard it could be fuel vapor lock based on what I've read here. Something about the fuel line being close to the exhaust manifold? Starts almost instantly cold and only gives me starting issues after I've been driving for a long time.

Is this what's happening based on this pic? If so, what is the fix?
A/C car, has been removed and choke functions correctly.

Image
Image
Author:  SlantSixDan [ Tue Jul 12, 2022 6:52 pm ]
Post subject:  Re: 69 Dart Hard to Start When Hot, Starts Fine Cold. Possible Vapor Lock?
Probably not vapour lock. Percolation is more likely. Do the Fuel line mod, make sure you're running the correct 5/16" thick carburetor-to-intake gasket, make sure your maniflold heat control valve works all the way correctly, and be very suspicious of the condition of your carburetor. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.
Author:  indetrucks [ Tue Jul 12, 2022 7:19 pm ]
Post subject:  Re: 69 Dart Hard to Start When Hot, Starts Fine Cold. Possible Vapor Lock?
SlantSixDan wrote:
Probably not vapour lock. Percolation is more likely. Do the Fuel line mod, make sure you're running the correct 5/16" thick carburetor-to-intake gasket, make sure your maniflold heat control valve works all the way correctly, and be very suspicious of the condition of your carburetor. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.


Thank you Dan, I came across your link in the past and forgot where that Fuel Line Mod post was. Cheers!
The carb is freshly rebuilt with new bushings at the throttle plate "Butterfly Valve?" due to a previous vacuum leak. I also sprayed the manifold heat control valve with copious amounts of special MOPAR penetrant spray . The valve opens and shuts freely, however Im not sure how tight the spring is supposed to be wound on that valve? Looking it over, it's pretty loosey goosey as it is, but if I wind it one more turn, it's stiffens up but still operates freely.

I'll start with the Fuel Line Mod. Thanks for your time. I appreciate you.
Author:  SlantSixDan [ Wed Jul 13, 2022 11:26 am ]
Post subject:  Re: 69 Dart Hard to Start When Hot, Starts Fine Cold. Possible Vapor Lock?
Glad to help out. The heat control valve, when cold, should turn by itself into the fully clockwise position (as viewed from front). Unless it is very cold, it shouldn't snap forcefully into the clockwise position, but neither should it lazily just sort of barely drift to the clockwise position. A good test here is to start the engine and rev it; the valve should move anticlockwise with each rev, then spring back clockwise as the engine RPM goes back down. When the valve is hot, the spring-loading should go away and it should remain in the anticlockwise position. That's assuming you've still got a '70 or earlier exhaust manifold, with the rectangular heat valve counterweight. The '71-up valves with the bigger round counterweight will tend to spring themselves clockwise at engine idle even when the engine is warm; they have to get very hot before they relax completely.
Author:  FrankRaso [ Sun Jul 17, 2022 6:05 am ]
Post subject:  Re: 69 Dart Hard to Start When Hot, Starts Fine Cold. Possible Vapor Lock?
I've found that I had a vapor lock problem that prevented my car from restarting when hot. I found that pouring a gallon of water over the fuel pump would help get me going again.
Vapor Lock
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