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Lurching Issue


DSwan
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Having a pretty severe issue with my car lurching when I'm just trying to cruise. If I'm under throttle it is much better but it's bad if you're just maintaining at a steady throttle. It's a 351-C that has an Edelbrock 630 carb, 4-speed, stock manifold, Pertronix ignition, new wires, new cap, new plugs, good gas. It's got a slightly lopy cam, not sure specs because it's the way I bought it. Any ideas would be helpful.

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What Pertronix module is it? If it's a P3 that's likely what your problem is.

Another thought, how long did it set before you bought it? The gas may have dried in fuel bowls, plugging the circuits with varnish making it run too lean, accelerating opens the power valve, increasing the fuel into the engine.

Final thought, maybe this guy was a previous owner

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Lurch from Addams Family

Edited by Don C
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“If you can't explain it simply, you don't understand it well enough.”

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Not sure which model Pertronix it is, going to look into that today. I'm not sure how long it sat before I bought it, the guy I bought it from had other cars he drove and didn't drive this much at all because he was 74 yrs. and the 4-speed scared him. I'll take your advice and go through the carb, never worked on a Edelbrock before but there's plenty of stuff on the web about them. It's been having this issue since I bought it, but I really couldn't pass it up for that because the price was right. I'll try to update as I find out more.

Thanks for your help.

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I like Edelbrocks myself and have had good experience with them but I seem to remember that they are sensitive to too much fuel pressure. I had one bogging at higher speeds once and had to add a pressure regulator. 
 

I wouldn’t take this as suspect number one, but something to keep in mind if after a pertronix fix or carb rebuild you have the same issue. 

Edited by Lazarus
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Lazarus

 

9-C51-EEB4-A25-A-4-F27-8-D01-0-EB879931296.jpg

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59 minutes ago, DSwan said:

I'm not sure how long it sat before I bought it, the guy I bought it from had other cars he drove and didn't drive this much at all because he was 74 yrs. and the 4-speed scared him. 

 Heck, I'm 74 and I LOVE driving the 4 speed. Doesn't scare me one bit, but it does scare the wife!!

On the Pertronix, the simple way to tell is color. A Pertronix Ignitor I is black, a P II is red and a PIII needs to be in the garbage. pic below. Not that the PIII is bad electronically, it's the construction of the moving plates, unless of course Pertronix have redesigned it finally.

Pertronix III.jpg

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Geoff.

 I learn something new every day!

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Some guys are young at any age, and you're one of those guys! I'm not that far behind at 65, but in my mind I'm still 18, although my body doesn't appreciate me trying to do the stuff I could do back then!

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2 minutes ago, DSwan said:

Some guys are young at any age, and you're one of those guys! I'm not that far behind at 65, but in my mind I'm still 18, although my body doesn't appreciate me trying to do the stuff I could do back then!

Yeah I know what you mean. I have a hip replaced, but that doesn't stop me doing anything. I ride a road bike (bicycle) about 2K miles each year. My surgeon, also a road bike rider, gave me the "sports model".

 I always say " I see what I saw when I was 20, I think like I thought when I was 20, I just don't recognize the old fart in the mirror"

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Geoff.

 I learn something new every day!

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Jokes aside, personally I don't like Edlebrock carbs, but as I've never had one, it's just an opinion based on the fact they just don't "look right", Sound dumb I know, but I prefer Holley's or Quick Fuel. On mine I run a Holley Street Avenger 670 with some tuner mods done by a specialist. My distributor is a factory Autolite with a Pertronix II (red) and , this is where it gets tricky, a modified slot plate, springs and a fine tuned "curve". I run this on timed port on the carb, not full manifold vacuum. There has been much discussion in the past on that. My timing is 14 deg. initial + 20 deg. crank and only about 4-6 deg. vacuum advance on top. This is on a 4V 71 with CC heads. The cam is a Melling MTF 2 which is just over a stock cam. I thought I'd give you my specs as a guide only. They're all different it seems.

Good luck sorting it out.

 

Geoff.

 I learn something new every day!

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I've had two Edelbrocks, one on a FE (390) in a '64 F100 and the other on a Y block in a '55 Willys 4x4 wagon. They ran too rich out of the box, and even a small amount of very fine debris in the bowls had adverse effects on them (the kind of stuff that gets through the filter), plus they weren't daily drivers, so set for a while in hot weather, and didn't like getting dry fuel bowls. That was several years ago, never had one since.

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“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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1 hour ago, DSwan said:

Thanks for the info guys. Now I just need to squeeze some car time in between the wife thinking doing stuff on and around the house is more important!

That damn "honey-do" list again! 

Geoff.

 I learn something new every day!

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Well, I went through the carb (Edelbrock 1406), cleaned everything up, paying special attention to the jets and metering rod setup (didn't seem too bad but cleaned it anyway), reinstalled it and it still has issues. I don't have a calibration kit for it so I did the best I could adjusting the idle mixture screws. I put the timing light on it and now I'm confused even more - the vacuum advance from the distributor is on the manifold port and while watching the light on the damper I pulled it off and it didn't change at all. My understanding is that the manifold port gives you vacuum at idle and the timing port doesn't, so like I said I'm confused. I'm setting initial timing at 16* BTDC because that what the Ford info says, but I know this motor isn't stock so maybe I need to do something else with that. I don't have any info on the motor other than it was supposedly built to boss specs. The other thing is that it does have the Pertronix II ignition, so I'm not suspecting that at this point.

Should I start looking at Holley?

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The vacuum diaphragm has probably failed, connect a vacuum pump to it, see if it moves the distributor breaker plate and if it holds vacuum. I would also connect a vacuum to the intake, see what kind of vacuum you're getting at idle. I would also verify that your timing marks are accurate on the harmonic balancer and the ring hasn't slipped.

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“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Found something that was definitely an issue: When I took the car around the block, not only was it bogging at throttle, it also didn't want to start before I pulled it out of the garage and I had to prime it. I got to thinking last night while trying to fall asleep - while cleaning the carb I was spraying it down and noticed something fall out, it was the small brass piece that goes under the primary squirters, so I had put it back in and put everything back together.  When I got up this morning I got an exploded diagram of the carb off the net and lo and behold, there's a small BB type ball that is supposed to be under the brass weight called the pump discharge ball; it keeps the gas from being sucked out of the accelerator pump. Knowing I didn't have anything like that around, and also knowing I would be hard-pressed to find one at an auto parts store, I resorted to using a large magnet on a string to drag the cement apron outside my garage and with God's help I found it! Just put everything back together and will try it out in a little while.

I haven't done anything with the vacuum advance yet, but will after I make sure the carb is good to go. I also ordered a  calibration kit to really dial it in. Thought you guys would get a kick out of that - I sure felt good about finding that little needle in the haystack! I wish the videos I watched on rebuilding the carb would've mentioned to be careful of that when disassembling. Thanks again everyone for the advice.

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