Timing and Carb problems
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Timing and Carb problems
So I managed to get my 1972 Ford 390 running. Barely. It used to not run at all, but it turned out it was because my PCV valve was just pulling vacuum straight through. After capping it off, it started up and ran.
Now here's the issue. I was fairly certain that the balancer hasn't slipped because it ran fantastic at about 10° advanced and I think that's fairly normal. Now that I have a 4 barrel intake on it and a 4 barrel Holley 600 I rebuilt (the first time I've ever rebuilt a carb), it's at something like 40° advanced to start up, except it seems to stop a little on every stroke starting, and I have to screw in the idle air screws all the way in for it to idle smoothly. It pulls good vacuum with the choke all the way open, but when it's driving it wants to die with any touch of the throttle and has no power at all.
If I move it back to 10° it doesn't start. What could I have done wrong rebuilding the carb? Or is the balancer indeed slipped.
Now here's the issue. I was fairly certain that the balancer hasn't slipped because it ran fantastic at about 10° advanced and I think that's fairly normal. Now that I have a 4 barrel intake on it and a 4 barrel Holley 600 I rebuilt (the first time I've ever rebuilt a carb), it's at something like 40° advanced to start up, except it seems to stop a little on every stroke starting, and I have to screw in the idle air screws all the way in for it to idle smoothly. It pulls good vacuum with the choke all the way open, but when it's driving it wants to die with any touch of the throttle and has no power at all.
If I move it back to 10° it doesn't start. What could I have done wrong rebuilding the carb? Or is the balancer indeed slipped.
Fleet Mechanic
Joined: Oct 2005
Posts: 1,369
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From: Gainesville, GA
If it's 40* advanced the starter will do as you said. Set it back to 10* and check elsewhere. Does the carburetor squirt fuel when pumped? Are the idle screws 1 1/2 turns out? Is there a vacuum leak? Seal all the holes in the vacuum tree behind the carburetor. Does it start when you put gas into the carburetor? Only put a bottle cap worth in. Did you check compression, although I doubt that's your problem. Has the distributor broken the roll pin that holds the gear on and slipped? You already know this but when you pull the distributor don't lose the oil pump shaft down the engine. Let us know.
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Holley 4160 600cfm
Measured with a timing light, yes. I have a nice little digital advance light.
It does squirt fuel when pumped. There was a vacuum leak but I fixed that when I plugged the EGR, which was leaking straight through. Compression is good, I checked that a bit ago. The distributor is one of the newest things on the truck. I will turn it back to 10° and try a little gas.
The idle screws are screwed all the way in at the moment. I can try 10° with them 1 and a half out.
Thank you for your help.
Measured with a timing light, yes. I have a nice little digital advance light.
If it's 40* advanced the starter will do as you said. Set it back to 10* and check elsewhere. Does the carburetor squirt fuel when pumped? Are the idle screws 1 1/2 turns out? Is there a vacuum leak? Seal all the holes in the vacuum tree behind the carburetor. Does it start when you put gas into the carburetor? Only put a bottle cap worth in. Did you check compression, although I doubt that's your problem. Has the distributor broken the roll pin that holds the gear on and slipped? You already know this but when you pull the distributor don't lose the oil pump shaft down the engine. Let us know.
The idle screws are screwed all the way in at the moment. I can try 10° with them 1 and a half out.
Thank you for your help.
Lead Driver
Joined: Jan 2003
Posts: 9,893
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From: Ohio
I think you have issues with the rebuild of the carb. Did you match the gaskets exactly? There are a few variations and you need to make sure you used the right ones or the carb will not work right. It should not idle with the mixture screws turned all the way in. Depending on where you got this carb, it may have been messed with and will need to be set up correctly to get you in the ball park.
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I think you have issues with the rebuild of the carb. Did you match the gaskets exactly? There are a few variations and you need to make sure you used the right ones or the carb will not work right. It should not idle with the mixture screws turned all the way in. Depending on where you got this carb, it may have been messed with and will need to be set up correctly to get you in the ball park.
Can I pull everything apart without having to replace the gaskets or is it a once you tighten it up you want to use new ones?
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Fleet Mechanic
Joined: Oct 2005
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From: Gainesville, GA
You can reuse the gaskets. I'm afraid Freightrain is on the right track. I've been using the same 600 cfm Holley for over 40 years and sometimes it has giving me fits. When it's apart make sure all the passages are clean with compressed air.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
Holley makes blue gaskets, can be reused. Coating conventional gaskets with vaseline or chapstick helps keep them from sticking and tearing upon removal. Then soak them overnight in water, and let dry. This sort of rejuvenates them. Can usually get a few uses out of them if careful. Gaskets are easy though, just buy gasket material and cut your own. Cereal boxes work fine too.
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I started the truck up, let it warm up a little, then turned the idle air screws to 1 and a half out and then timed it to 10°. It got really shaky and didn't want to rev at all without coaxing. I turned the screws in more to almost all the way in and the idle stabilized and I am getting good vacuum, about 20in hg at 750-800rpm. Thinking I may have been in the clear for a little bit, I took it for a little test run.
It still presented the same symptoms. No power, bogging down and backfiring through the carb when I try to give it any gas.
With it getting good vacuum I don't think it has any leaks. Could the 1 inch spacer I have be causing problems? The old carb had a 1 inch spacer so I replicated that. WD-40 didn't cause the idle to raise spraying it so I think that's okay.
So it has to be a problem with the carb, right? I'll pull it off tomorrow and see if I can spot anything. Am I just looking for gaskets covering something or anything else?
It still presented the same symptoms. No power, bogging down and backfiring through the carb when I try to give it any gas.
With it getting good vacuum I don't think it has any leaks. Could the 1 inch spacer I have be causing problems? The old carb had a 1 inch spacer so I replicated that. WD-40 didn't cause the idle to raise spraying it so I think that's okay.
So it has to be a problem with the carb, right? I'll pull it off tomorrow and see if I can spot anything. Am I just looking for gaskets covering something or anything else?
Tuned
Joined: Jul 2019
Posts: 464
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From: Evansville, Indiana
Sounds like the idling circuit is clogged. I had the exact same thing happen with an old Holley 600 cfm 4 barrel. We rebuilt, twice, and soaked the idling circuit twice, cleaned all orifices with compressed air and never could get the truck to idle. Started to look at buying a new idling circuit... After buying the rebuild kit, carburetor cleaner, new secondary diaphragm, and wasting days trying to get a 40 year old mystery carburetor to work, I threw in the towel and bought a new Holley 600 cfm Brawler for $270.00. The truck doesn't even crank in the morning...you pump the pedal once, turn the key, and it is running. I get a lot compliments on how fast it starts. Good luck.
Lead Driver
Joined: Jan 2003
Posts: 9,893
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From: Ohio
The big thing with Holley's is there are plenty of holes and most any of the gaskets will match up to something. But is it the RIGHT passage? Many kits come with 2-3 metering gaskets and you need to confirm, even if it means matching the gasket up before scrapping the old one off.
Going to Holley site I was trying to find the correct picture for the correct metering plate gasket, along with base gasket.
I think this is what you need for metering gasket:
https://www.holley.com/products/gask...parts/108-89-2
I think this is the base gasket:
https://www.holley.com/products/gask...ts/parts/108-7
A buddy had a Demon carb on his race car. Local guy did a rebuild on it. It suddenly had idling issues that it never had before. Luckily my buddy kept the old gaskets. I pulled it down and compared everything. I found the base gasket was incorrect by one hole and that screwed up the calibration. Once I put the old gasket back on, it ran perfectly.
I use brake clean and compressed air to make sure every orifice is clean if it is an unknown carb.
Going to Holley site I was trying to find the correct picture for the correct metering plate gasket, along with base gasket.
I think this is what you need for metering gasket:
https://www.holley.com/products/gask...parts/108-89-2
I think this is the base gasket:
https://www.holley.com/products/gask...ts/parts/108-7
A buddy had a Demon carb on his race car. Local guy did a rebuild on it. It suddenly had idling issues that it never had before. Luckily my buddy kept the old gaskets. I pulled it down and compared everything. I found the base gasket was incorrect by one hole and that screwed up the calibration. Once I put the old gasket back on, it ran perfectly.
I use brake clean and compressed air to make sure every orifice is clean if it is an unknown carb.