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Starts great cold, not so great warm
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chrismwood
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PostPosted: Mon Nov 16, 2009 4:41 pm    Post subject: Starts great cold, not so great warm Reply with quote

I've recently gotten my 74 super tuned up and running, and when it's cold it starts up great. I've found that after I drive it around a while, though, it's not easy to start back up. I have to crank it for quite a while and really nurse it to get it to turn over. Any ideas where I should look?

Thanks!
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Matt Wilson
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PostPosted: Mon Nov 16, 2009 4:47 pm    Post subject: Reply with quote

Sounds like the valves could use adjusting.
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chrismwood
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PostPosted: Mon Nov 16, 2009 4:50 pm    Post subject: Reply with quote

Matt Wilson wrote:
Sounds like the valves could use adjusting.


That's interesting. I just adjusted them, but it was my first time and I could very easily have made a mistake. Why would out-of-adjustment valves cause problems only on a warm start? Wouldn't I have problems starting period? Thanks for the quick reply, by the way!
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Matt Wilson
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PostPosted: Mon Nov 16, 2009 5:10 pm    Post subject: Reply with quote

When the car is dead cold the compression is higher and the valve adjusters are loose (you can usually rock them the .006" by hand and hear them click when both valves are closed). This guarantees that the valves will be fully closed when the engine is cold.

When the engine is driven and warmed up to operating temp (or overheated), the valve adjusters will not click. (heat makes metal expand). If the valve adjusters are too tight, say .001 or .002, the valves will not fully close, as the adjusters are holding the valves open. This means that when the piston is sliding in the cylinder outward, instead of compressing the fuel mixture, the mixture is getting pushed out the open valve.

Adjust the valves when the engine is overnight cold. Make sure they are set to .006" ("six thousandths of an inch"). An aircooled (lawn mowers, scooters, motorcycles etc.) engine will always start better when dead cold (with a choke) than hot. The engine actually gets a little hotter after just being shut off before it starts to cool. The heads are soaking heat from the exhaust (aluminum soaks heat). So unless your valves are adjusted to ensure the valves are always closing all the way, the engine will not easily start.

You can avoid this more easily by not running all out on the highway and then abruptly shutting the engine off. Let the engine idle and cool down a little bit before you park. Then when you come out of the grocery store on a hot July day, the engine will start with no problems.

A lot of people don't know how to start a car with an automatic choke. You should gently depress the accelerator pedal once to the floor to set the fast idle cam. Push in the clutch and fire it up. I've seen people frantically pump the gas until the engine is almost all bogged down. With the auto choke working you can get in and go. Some people recommend warming it up and others disagree. If you sit and warm up really slow with an excessive rich condition (choke closed all the way) it can act as a solvent, washing the oil off of the cylinder walls. But some people will say not to load up the engine when things aren't warmed up. The compromise is that you can start the engine and drive gently until the engine warms up. It will warm up quicker than sitting in your driveway.
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chrismwood
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PostPosted: Tue Nov 17, 2009 12:00 pm    Post subject: Reply with quote

Fantastic explanation. Thanks for the replies!
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