Strange starting problems on 1972 Chevy w/307..

Guys and Gals,

I have a puzzler for me (although I bet it's easy for some of you). I own a 1972 Chevy C10 stepside pickup which I have spent the last 2 weeks rebuilding the top of the engine and I'm having some intermittent strange problems now. Here's the scoop.

First off, we have a new Edelbrock Performer Intake manifold, 4-BBL Edelbrock carb, Summit Racing HEI Distributor and built-in coil, new plugs, new plug wires, new gauges, etc. The engine does not smoke, idles around 700 warm, runs great under normal conditions. I drive it back and forth to work every day with NO problems after it warms up.

Here are the oddities 1) It takes around 3 to 5 minutes to warm up before it will idle without any help (this might be normal for a 307). 2) It runs JUST fine going to work and coming home from work. The temp gauge indicates around 200 degrees for normal temp. Here in Atlanta in the afternoon it gets up to around 210 or so. 3) The truck ALWAYS cranks on the first time, EXCEPT when it has been running in the heat for 30 minutes and I shut it off, then it doesn't fire at all. This happened 1 time and I was able to advance the timing enough that it fired over and then I reset it with a timing light. 4) The air-fuel mixture seems to be about right, it doesn't run rich. 5) The problem when it doesn't fire (usually after getting home from work) seems to be a spinning and spinning without any spark. I can't figure that part out. It has gas, but won't fire. 6) The truck has a brand new radiator and thermostat, so it shouldn't be boiling.

I suspect the HEI coil is getting too hot, should I call summit and try to get some help? Is the truck running too hot? Am I missing something obvious? What are your thoughts?

I turn this over to the Truck and Engine Guru's....

brian 'sparkless' in Atlanta.

First, I'd look at the fuel lines... are they away from anything hot? You might be getting vapor lock. The cold idle thing sounds unrelated, maybe you need to play with the fast idle adjustments on the carb, OR, is there too much choke? August in HotLanta, shouldn't see much choke action at all......

Good Luck, Scotty *****************************

Thanks for the reply scotty, I put in new fuel lines and fuel filter, they are not NEXT to the manifold, but I'll check to make sure. Also, I haven't hooked up the manual choke yet, though I've bought the cable. I wonder if that is causing some oddities. I'll also check it.

Vapor lock? Good theory, I'll look into it.

Thanks for the post!

The hard starting after it has run awhile can be the gas in the carb is boiling off from underhood heat. Try lifting the hood when you park it next time, see if it starts ok then. Another way to tell is to open the throttle full while cranking to clear out unburned fuel, don't pump the throttle, just hold it open. Be ready to close it when it fires though. This is SOP for a flooded engine. Bob

Hey Brian, without the choke operating, you'll have too warm it up a few minmutes before taking off. A cold engine needs a slightly rich condition when it's cold to run properly & since you don't have the choke hooked up, it's not getting the extra fuel when it first starts. I put the same setup on my 65 Chevy pu & I didn't want to hook up the manual choke, I just have to warm it up first thing in the morning or whenever it sets for a long time. You didn't say what kind of fan or if you're using a fan shroud or a clutch fan or ? Are you using coolant? If so, are you using it mixed 50- 50? You didn't say what temp your engine ran before. What type radiator are you running? 2 row/3 row/4row, standard cooling fins/ hi-efficiency cooling fins ? Mine runs 180 degrees unless it's a 100 + day, then it might creep up to 190 degrees. I put a 4 row crossflow radiator/ standard cooling fins & fan shroud originally designed for a 68 Camaro in my truck & I run the original 4 blade fan. I have my coolant mixed 50% coolant/50% water, you should never use coolant only on the older cars/trucks. Your temp of 200 to 210 should be fine if it runs that temp all of the time. When it starts fluctuating you'll have problems. Your starting problem sounds like vapor-lock or the carburetor fuel bowl is boiling all the gas out of it. Chevy pickups tend to get pretty hot under the hood. Did you install headers? If so, they tend to cause even higher underhood temps, though they will cool off faster than the castiron manifolds. Yes aluminum dissipates heat faster, but it also heats up faster too. So your engine is running 210 degrees & you shut it off, the engine temp climbs to about 230 to 245 degrees, the intake manifold absorbs that heat too, then it transfers to the carburetor & causes the gas to boil out of it. Even if you think the fuel lines are far enough away as to not get hot, raise the hood 5 minutes after shutting off the engine & put a thermometer on the fuel line or filter, it'll surprise you just how hot it gets. If it's possible, raise your hood after you shut the engine off & leave it open until you're ready to leave again. If it starts OK, then you'll know it's getting extra hot under the hood. Chevy had the same problem with the fuel boiling out of the carb back in the late 60s & early 70s & they came up with a very easy solution, they made an aluminum plate that went between the carb & manifold that kept the manifold heat from rising up & heating the carb/fuel. It didn't take much. Good Luck & Have Fun...ManxManiac

Sent via Deja.com http://www.deja.com/ Before you buy.

If you believe it is a spark problem, check to see if you have a full 12 volts to your new HEI distributor. The old points system used a resistor wire to reduce the voltage. If you don't have 12 volts you need to replace that wire. I don't know if that would cause your problems but lots of people have trouble switching to HEI and that wire is the main cause.Good

Dave & Joann Harms wrote:

Dave, Thanks for the message, Fortunately, I found out about the wire BEFORE putting the new HEI in, so I went ahead and ran a brand new wire from the fuseblock. I don't think that would be problem in this case, but i can put a meter on it and let you know. Thanks for the advice!

With the advice that everybody else has given, I'd time the engine by ear - advance the timing until the engine starts running rough at hot idle and then retard it a bit until it is running smooth again. Put it in gear and put a load on the engine (auto trannys just put the pedal down about half way) and see if it pings and if it does, retard until it stops pinging. Take it out for a drive and see if it pings at any point, pulling over and retarding a little bit more until it doesn't ping anymore. Mark that point and use that as your timing point. I don't know if you put the exhaust gas restrictors in the intake gaskets or not but you should have and you are going to have to do that if you didn't as that will make your carb too hot otherwise. As far as the cold problems, you need to have a choke for anything less than a 100 deg. day or the thing just won't idle until it gets warm enough.

<< Subject: Re: Strange starting problems on 1972 Chevy w/307..

What color is that wire? I have a different problem on my car, but it is very close. My climate is cold, car will sit and spin some times for no apparent reason.

Most of the time, hot or cold, it will fire on the first click.