HOT! Start Problem

[Sooner1970_K10]

I have a stock (1970) 350 no mods.

Before anyone tells me I need to do a search for my answer, I already tried. Must posts were about a carb that is hard to start when cold. Also several about needing a spacer inbetween carb/intake so that gas does not boil over. In either case, I dont think my truck carb problem fits into any of the other posts. Granted I dont know the boiling point of gas?

Simptoms:

1.) The truck starts easier in colder temperatures i.e. <80 Degrees
a.) When started "cold", I turn ignition, give half a pedal tap, it starts & runs rough, untill what looks to be "flooded smoke" from tail pipe goes away aprox 5 mins. During this time I might tap the gas pedal a couple of times to adjust engine rev.
b.)Once the engine is warmed up it idles and runs fine. I can kill the truck and restart with ease. Almost always smell gas during initial start.

2.) The truck either refuses too or starts hard in hot temp i.e. 90+ Degrees
a.) Hot truck temp can be reached either by driving the truck (started cold), turning off and leaving it for 30mins - 1hr or trying to start it during the day (Summer Oklahoma 95-115 Degrees) so block/carb are already "HOT" in this scenario I cannot get the truck started.
b.) Doesnt matter what I try, doesnt matter if I havent started the truck in 1 hr or 1 week, if the block/carb is hot 90+ degrees it wont stay running. It might turn over and initially attempt to come to life but it feels like gas chokes it out almost as soon as its started.
c.) When the truck is hot I have learned to just give up on getting it started or I will drain the battery... because it will just turn over and over without ever restarting.

Conclusion:

I strongly believe my truck is flooding itself wether I step on the gas peddle or not. It smells of gas every time its started (cold), it smells of gas if it wont start (hot). I havent advanced the timing, the timing cap, wires and plugs are new. My truck only gets 1,000 miles a year and doenst get driven a heck of a lot. The truck has 72k original miles on it so I guess things could go bad just from idle sitting around. I checked compression last year all cylinders were 140-160. Im pretty green when it comes to troubleshooting a vehicle, any suggestions or help would be greatly appreciated. Thanks!

[jacobs]

I've never had that type of problem with my pickup in over 300,000 miles BUT I do have a similar problem with an older Subaru. I finally started changing thermostats every spring and fall. During the summer I use a 160° thermostat and during the winter a 180°.

Here's some things you might try/check

1. A insulated carburetor spacer under the carb may help.
2. Check to make sure your heat riser valve isn't stuck closed.
3. Make sure the plugs in the bottom of your Q-jet aren't leaking
4. Check your carb float to see if it's full of gas. To do that, remove the float and set it on a level surface. If it doesn't fall down from the weight of the arm, REPLACE it.

[jhow66]

You have CHOKE problems.
1--cold start problem= choke pulloff not working (when cold remove breather and block choke in the open position-start engine -if it runs without any black smoke you found your cold start problem-replace choke pulloff.)
2--hot start problem= float and needle problem ( before trying to start hot remove 2 or 3 plugs to see if they are wet with gas-if so rebuild carb.)

[johnnyp]

You might want to consider a new coil. I recently had similar problems with the truck not running or starting well, especially when it was hot. one day I happened to notice that the coil was leaking and had a hair-line crack. I replaced the coil and the truck now starts and runs great. Not much to troubleshooting these old trucks -- it's either spark or fuel (or both).

[bryanw1968]

jhow66,

You're probably right. Choke might need adjusting.
First, what kind of carburetor are you running?
I had the EXACT same symptoms on my truck running a barry grant demon.
The choke was adjusted wrong and it would choke itself no matter how hot or cold it was. Loosen 3 screws and a small turn and that took care of it.

[SB406]

Check for spark when Hot/ Acting up.
If you have spark......It's either choke (no air) or carb (fuel)
Air + Fuel + Spark =