Ever since I put the factory style air cleaner on my engine I've been having hard starting issues when the engine is warm and off for anywhere from 2-3 minutes at the earliest. I think the housing is trapping excess heat and percolating the fuel in the carb and either boiling/evaporating all the gas out (or just enough to where it needs throttle/pump shot to start) or the percolation is partly flooding the carb and the excess air/engine speed (again, by cracking the throttle open on hot startup) is allowing it to swallow that gas. It didn't do this when I had a 14x2 cheapy parts store deal on there. What did the factory do to combat this? Both carbs I've tested (old one and new everyday performance one, purchased for separate reasons not related to this issue) are M4MC carbs. Also the car runs dead at 195* (195 thermostat in it) in ALL types of weather, and has never overheated. Current carb is brand new from everyday Performance as said. Due to the engine being a '70 and me having an M4MC carb with Th350 nub, I have a 1/2" phenolic/laminated wood spacer installed under the carb, two 1/16 "thin" gaskets, one underneath carb, one underneath spacer.
I am also running stupid corn laced gas, this weekend I'll try straight gasoline and see if that changes anything. I do love the way my engine looks with the filter on it when I pop the hood to show those curious, I'd hate to have to not use it for such a stupid reason. I was thinking of getting a K&N filter instead of the paper one in the housing, maybe one a little taller so the lid is off the base so it can breathe a little better...
I would put in a 180 stat and that will help cool down the engine. I never went over 180 unless I had to drive in the winter and the 180 will hold you to 32* below that you would need the 195 stat. Could be float is too high and when you shut off the engine the heat is pushing the gas into the intake.
A taller filter will need a longer threaded rod or you can simply flip the lid. Sounds great with the lid flipped when you go to WOT with a Q-jet!(just try not to do it with any cops around, don't ask) With the lid flipped for driving, you can un-flip it when you know you might be opening the hood if you like the look of the factory housing.
Flipped lid and a hole in the muffler, yeah that will get the coppers after ya. lol come on tell the truth works with a 2bbl too
No, not even half as loud with a 2bbl, gotta have a 4bbl Q-jet for that big BBBWWWOOAAAA sound when the secondarys open, not even a Holley 4bbl double pumper will make the Q-jet sound when all 4 barrels are opened!
Cooler thermostat won't do anything for heat soak. Trouble is todays gas is formulated for use with fuel injection (pressurized). It evaporates more quickly than older fuel blends. Anything that traps heat around the carb will make it worse. Run the open air filter if that stops the problem. Or try a tank of leaded race gas.
I have the same problem as the original poster..... I have a mild build 350, TA aluminum intake, ram air cleaner but Holley carb... 195 stat, runs fine.... 30 minute drive. Shut it off for 3 minutes it starts right up.... wait 10+ minutes it cranks for a while before it starts..... curious on other responses.... would non-ethanol help? Not many pumps even close to me.... thanks
I think A lot of our problems are from the ethanol laced gas.I can go to A local about 40 miles away and get non ethanol 87,89 octane, but not in that area very often .
Just some added thoughts... Its interesting that "back in the day" the factory suggests depressing the gas pedal half way on warm engine starts. Some of what your experiencing may be inherent in the technology of the time ; you may be able to lessen the effects of heat, fuel volatility or improve air intake but end the end, you still may have to compensate with added gas anyway. I'm sure timing and engine condition also play into it so tune up basics may also help improve condition to where the hard start is minimized. You probably know all this anyway, so I'll go back in my hole..
I just had the same thought after about 10 minutes or so the carb probably needs a little pump shot to start, just touch will do it. No, a thermostat may not help with heat soak but 10 degrees is less when you shut off the motor. The temp can rise over 200 after you shut the car off then it will cool off. You can always put a wrap on the gas line from the pump to carb that will help keep the heat away from the lines when you shut it off. Summit has a nice one I used on mine. I use 5 gal of race gas all the time each tank.
Filled up with non ethanol gas, problem is a little better, but over 85*f outside, still does it. Oh well. Half pedal, starts right up. I'll still test the chrome deal and see if it goes away.
