My mostly stock 350 with a 600 cfm holley DP runs very good for the most part. It starts right up cold and after sitting for 10 minutes or so, but is hard to start after sitting for 30 minutes or more and runs extremely lean (over 16 to 17) for a few minutes. I have to fiddle with the gas pedal to keep it running. I've checked fuel pressure and float level and everything seems to be OK.The engine runs cool (1/4 up on the console temp guage) so I'm kinda stumped. I've adjust the idle AFR to about 13 when the engine is warmed up. Any ideas would be appreciated.
Hard starting after 30 min sit!
reelknots
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I would try another carb. Ask a buddy if you can swap with him for a day or even a couple of hours and see what happens. I prefer carbs with chokes!! I drive mostly on the street with an occassional track run. Unless you see more track time than street time, IMHO you should have a choke. Yes I read it starts up easy in the cold, or when cold, so I'm not sure if you have a choke or not? I've had this problem years ago and changing carbs worked for me. Of course this information is useless if what you are describing is "Hot Starts". Good Luck.
Yep been there done that...it is not uncommon to drop an old car engine in a run about boat....sort the cooling grab a coil laying around, then head out for a day fishing ....
Get about 20/30 mins out it starts to splutter and dies...nothing makes it fire, clean plugs leads check carb, all look good, pull the fishing lines up and fire up away you go...and does it again.
Classic of a ballast ign system running on a 12v coil or visa versa....
Either throw a ballast resistor in (they are ceramic blocks about 2 1/2" long, 3/4" x3/4") with a heavy resistance wire coiled up inside, or change the coil to one that has 12 in the part number stamped on the bottom.
Oh man, Thats a great carb too! Are you sure its not a Hot Start problem??
Just for comparison....my carb is a 600 cfm 4150 Holley double pumper with mech sec and mech choke. I'm picking up the spacer tomorrow so I'll let you know if this cures my problem. When I took the carb off today, I did notice that the fuel level was low in both bowls. I've checked them several times when the car was running and they were fine. I hadn't run the car since yesterday, so I'm thinking that the fuel has contracted since being hot yesterday. I believe this could lead to a low octane fuel when hot hence a warm start problem. Sorry, thinking out loud. I'll know more tomorrow.
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I had the same issue with my 68 396/350. Being the purists, I added the factory optioned heat shield and it seems to have helped. (maybe you can see it in this pic)
OK, I installed the 1/2" phenolic spacer that Holley agreed should help with my problem. Well the problem is still there although not as bad even though it's in the 90's today. My next step will be to install the heat shield that you guys recommended. I found out that some models of camaro actually had this installed originally. It's a Holley model 108-70Thanks for the help, it's off to see the wizard!
Reelknots - keep us posted. I would love nothing more than to have you solve your problem and my problem as well! 
It's encouraging that it helped some, but discouraging it didn't completely fix the problem. If the heat shield doesn't work it's got to be something electrical/timing related. I'm frustrated for you!
It's encouraging that it helped some, but discouraging it didn't completely fix the problem. If the heat shield doesn't work it's got to be something electrical/timing related. I'm frustrated for you!Nice Pic, when I first saw the picture , I said how the hec did he get a picture of my car??? LOL Mine is almost identical.I had the same issue with my 68 396/350. Being the purists, I added the factory optioned heat shield and it seems to have helped. (maybe you can see it in this pic)
![Image]()
I'm trying. I believe it's definately a hot carb problem. I can pull the choke closed and pump it a few times and it'll start but it runs extremely lean for the first couple of minutes. This bothers me almost as much as the embarrasment from the excessive cranking of a 'new' old motor.Reelknots - keep us posted. I would love nothing more than to have you solve your problem and my problem as well!
Attachments
Are you controlling the choke manually with a cable ??
Since you have a Type K thermocouple and meter, if the pigtail is long enough, maybe run it out through the cowl, and rest the thermocouple next to the carb after a run and record the temps.
Today's fuel with ethanol/alcohol, evaporates quicker than the older fuel we've known in the past. Ever think about making an insulated chamber about the carb for a science project?
Today's fuel with ethanol/alcohol, evaporates quicker than the older fuel we've known in the past. Ever think about making an insulated chamber about the carb for a science project?
I've taken temp readings of the carb bowls while running and after sitting for 30 minutes. The bowls run about 30 deg hotter after sitting 30 minutes. They'll go from about 100 to 130 - 135 degrees. When it cools down, it starts right up.
Yes, the starter is fine, the engine just cranks too much when warm.
Timing is 13 initial with 22 centrifigal @ 2700 r.p.m's and 14 vac advance degrees. I don't know what my cam is but I believe it's pretty much stock.
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