Engine won't start when warm

[thor13]

Sorry if this has been posted, but I have an 81 c10 step side 350 th 350 tranny. That when it gets warm it's nearly impossible to start.

I kno it's not the starter the other one went out 2 weeks ago so it's new. I know it's getting fuel because when I got it the fuel pump was shot so that's new as well. I've been getting mixed answers so I thought id bring it up here.

[454Man]

What's the initial timing?

[thor13]

shoot i honestly couldn't say. i got the truck from a guy who couldn't really tell me anything about it. he said he had recently replaced plugs and wires.

[Fairlane514]

Does it "grunt" when you try and start it?  454Man is suggesting too much advanced timing.   

[thor13]

not really a grunt so to say, but it just tries to turn over but wont get all the way there. if i pen down the gas and hold it for about 2 or 3 seconds and do that a few times it will eventually crank. starts first crank every time before it gets hot though,

[Fairlane514]

What I mean by "grunt" is, it sounds like a weak battery. 

Check your initial timing, it should be safe a t 10 degrees advanced. If you are too far advanced, you may also experience some pinging or detonation. If you are experiencing detonation you should immediately retard the timing to avoid major damage to the pistons.

Also, do you know if your alternator is charging?  Maybe you are just running down the battery when driving and thats why it wont start.

You can place a multimeter on volts and and touch the probes to the battery terminals while the motor is running and it should read 13.5-14 volts.

[Lt.Del]

check for fire?
if no fire, i'd say its your module or pick up coil in the distributor.  My 79 did that when it was hot, couldn't restart til cooled.  No spark.

If it gets fire at the plug, i'd say choke adjustment. Probably stays closed when engine is warm. Open it with a screw driver and turn it over and see.

[sbx22]

Mine did this too. What I did was I put in a heat shield for the starter and I also put a heat insulator between carb and intake. I did both simultaneously so I couldn't tell you which one did the trick for me.

[Irish_Alley]

if it does grunt or slow turn, easiest and fastest thing is to retard the timing, just turn the distributor 1/2" to 1". see how that works. if that doesnt work test for spark. if you have spark then the only thing left is the starter being heat soaked. new starters can be bad out of the box or go bad fast. chances are its just the timing or a spark problem tho

[bake74]

     I would start with what everyone says, most likely heat related.  If not you might have to tune the carb, the carb acts differently when on a cold engine to a warm engine, vacuum inside changes which changes the internal venturi's and how they operate, if out of adjustment that might be why you have to hold the pedal to the floor. (or dirty)
     Like I said start with what has been stated, the easy stuff first, then if need be move on to the advanced stuff.

[VileZambonie]

You said engine won't start when warm so obviously it's not your starter if you are stating it cranks but will not run. Am I correct in this assumption or are you stating it won't crank when it's warm?  Clarify

If it's in fact a crank no start condition check for spark. GM HEI pick up coils are prone to heat failure. If you determine you are losing spark when the engine is hot I would suggest replacing the distributor. It's no longer worth replacing a pick up coil or module. You can buy a replcement distributor with cap, rotor, coil, module, and pickup for under $70 now.

http://www.ebay.com/itm/SB-SBC-GM-CHEVY-HEI-Distributor-Clear-Cap-65K-Coil-350-/330588689439?pt=Motors_Car_Truck_Parts_Accessories&hash=item4cf89f141f&vxp=mtr