'72 350 Quadrajet 4MV hard start when motor is hot
July 7th, 2011, 09:51 AM
#1
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Join Date: Jul 2011
Posts: 13
'72 350 Quadrajet 4MV hard start when motor is hot
This is in a '72 GMC Custom 1500 P/U, but I'm hoping someone can help me on here.
Sometimes when motor is hot, it drags and acts like it isn't gonna start. Sometimes, it starts right up, no hesitation.
Starts fine when motor is cold.
Tried advancing and retarding timing, but neither makes a difference.
I put an HEI [computerless] distributor in several years ago, but have recently seen where the hot wire was suppose to be changed to a 12volt wire. Apparently, the wire going to fuse box is not big enough [7,9volt, or something...I believe it was referred to as a 'resistor wire'].
Could this be causing my starting problem?
Any help,advice and information would be appreciated.
Keith
Sometimes when motor is hot, it drags and acts like it isn't gonna start. Sometimes, it starts right up, no hesitation.
Starts fine when motor is cold.
Tried advancing and retarding timing, but neither makes a difference.
I put an HEI [computerless] distributor in several years ago, but have recently seen where the hot wire was suppose to be changed to a 12volt wire. Apparently, the wire going to fuse box is not big enough [7,9volt, or something...I believe it was referred to as a 'resistor wire'].
Could this be causing my starting problem?
Any help,advice and information would be appreciated.
Keith
July 7th, 2011, 10:51 AM
#3
Registered User
Join Date: May 2011
Location: Melrose FL 32666
Posts: 425
This is in a '72 GMC Custom 1500 P/U, but I'm hoping someone can help me on here.
Sometimes when motor is hot, it drags and acts like it isn't gonna start. Sometimes, it starts right up, no hesitation.
Starts fine when motor is cold.
Tried advancing and retarding timing, but neither makes a difference.
I put an HEI [computerless] distributor in several years ago, but have recently seen where the hot wire was suppose to be changed to a 12volt wire. Apparently, the wire going to fuse box is not big enough [7,9volt, or something...I believe it was referred to as a 'resistor wire'].
Could this be causing my starting problem?
Any help,advice and information would be appreciated.
Keith
Sometimes when motor is hot, it drags and acts like it isn't gonna start. Sometimes, it starts right up, no hesitation.
Starts fine when motor is cold.
Tried advancing and retarding timing, but neither makes a difference.
I put an HEI [computerless] distributor in several years ago, but have recently seen where the hot wire was suppose to be changed to a 12volt wire. Apparently, the wire going to fuse box is not big enough [7,9volt, or something...I believe it was referred to as a 'resistor wire'].
Could this be causing my starting problem?
Any help,advice and information would be appreciated.
Keith
July 7th, 2011, 10:59 AM
#4
Registered User
Join Date: Dec 2007
Location: Fort Pierce, FL
Posts: 1,124
Is the problem that the cranking is slow, like it has a weak battery, or is the engine/Carb just not letting it start?
The slow cranking is usually a bad battery connection or ground. But it might also be because of too small a gauge battery cable. I had a terrible problem on a 70 Bonneville with 455 after a restoration. I had new everything, including battery cables. Found out I had a 4 gauge negative cable that was provided by one of the restoration parts companies. I think the original was a 2 gauge. I wound up using a 1 or 2 gauge and it started perfectly with just a touch on the starter. I read that a 2 carries 10 times as much juice as a 4, and when a cable gets hot, it has more resistance and carries less current. It works when cold, but carries less when hot and cranks slower.
The slow cranking is usually a bad battery connection or ground. But it might also be because of too small a gauge battery cable. I had a terrible problem on a 70 Bonneville with 455 after a restoration. I had new everything, including battery cables. Found out I had a 4 gauge negative cable that was provided by one of the restoration parts companies. I think the original was a 2 gauge. I wound up using a 1 or 2 gauge and it started perfectly with just a touch on the starter. I read that a 2 carries 10 times as much juice as a 4, and when a cable gets hot, it has more resistance and carries less current. It works when cold, but carries less when hot and cranks slower.
July 7th, 2011, 02:59 PM
#6
Old(s) Fart
Join Date: Mar 2007
Location: Northern VA
Posts: 48,229
With the key in the START position, the ignition switch bypasses the resistor and sends the full 12V (actually, 13.8V) to the coil, so while you do not have it wired properly, that is not the cause of a starting problem.
Unfortunately, your description of the problem is not completely clear. If by "dragging" you mean that when hot the engine turns over more slowly when cranking with the starter motor, well, that could be many problems. Certainly check all electrical connections, especially the battery cables. Resistance goes up when the wires get hot, so that's one possible problem. Also, this really sounds like the common GM hot starter problem. I'd pull the starter and check the brushes and the contacts inside the solenoid. Usually the copper contact disc inside the solenoid gets pitted, increasing resistance and lowering cranking speed. I'd opt for a high-torque starter (not necessarily a mini-starter, just a high torque stocker). I'm also a skeptic of the Ford starter solenoid wiring, since the stock GM solenoid is STILL in series with the Ford solenoid. Good quality wiring and starter parts usually make the difference.
Unfortunately, your description of the problem is not completely clear. If by "dragging" you mean that when hot the engine turns over more slowly when cranking with the starter motor, well, that could be many problems. Certainly check all electrical connections, especially the battery cables. Resistance goes up when the wires get hot, so that's one possible problem. Also, this really sounds like the common GM hot starter problem. I'd pull the starter and check the brushes and the contacts inside the solenoid. Usually the copper contact disc inside the solenoid gets pitted, increasing resistance and lowering cranking speed. I'd opt for a high-torque starter (not necessarily a mini-starter, just a high torque stocker). I'm also a skeptic of the Ford starter solenoid wiring, since the stock GM solenoid is STILL in series with the Ford solenoid. Good quality wiring and starter parts usually make the difference.
July 7th, 2011, 08:35 PM
#7
Registered User
Join Date: Dec 2005
Posts: 511
On the starter issue, another common problem is that GM didn't design engines with headers in mind. If you have headers, they run very close to the starter motor and solenoid.(at least on a big block) I had this problem on my SX many moons ago. After an hour or so of driving and shutting the engine off and then trying to restart within 20 minutes or so.....very slow cranking, as if the battery was almost dead. If you have headers, you might try some insulating wrap on the pipes near the starter. Chumley
July 8th, 2011, 11:16 AM
#8
Registered User
Thread Starter
Join Date: Jul 2011
Posts: 13
Is the problem that the cranking is slow, like it has a weak battery, or is the engine/Carb just not letting it start?
The slow cranking is usually a bad battery connection or ground. But it might also be because of too small a gauge battery cable. I had a terrible problem on a 70 Bonneville with 455 after a restoration. I had new everything, including battery cables. Found out I had a 4 gauge negative cable that was provided by one of the restoration parts companies. I think the original was a 2 gauge. I wound up using a 1 or 2 gauge and it started perfectly with just a touch on the starter. I read that a 2 carries 10 times as much juice as a 4, and when a cable gets hot, it has more resistance and carries less current. It works when cold, but carries less when hot and cranks slower.
The slow cranking is usually a bad battery connection or ground. But it might also be because of too small a gauge battery cable. I had a terrible problem on a 70 Bonneville with 455 after a restoration. I had new everything, including battery cables. Found out I had a 4 gauge negative cable that was provided by one of the restoration parts companies. I think the original was a 2 gauge. I wound up using a 1 or 2 gauge and it started perfectly with just a touch on the starter. I read that a 2 carries 10 times as much juice as a 4, and when a cable gets hot, it has more resistance and carries less current. It works when cold, but carries less when hot and cranks slower.
July 8th, 2011, 11:18 AM
#9
Registered User
Thread Starter
Join Date: Jul 2011
Posts: 13
On the starter issue, another common problem is that GM didn't design engines with headers in mind. If you have headers, they run very close to the starter motor and solenoid.(at least on a big block) I had this problem on my SX many moons ago. After an hour or so of driving and shutting the engine off and then trying to restart within 20 minutes or so.....very slow cranking, as if the battery was almost dead. If you have headers, you might try some insulating wrap on the pipes near the starter. Chumley
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