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Ford 302 Shakes mildly at idle

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Old 01-08-2012, 02:06 PM   #1
umfan92
 
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Default Ford 302 Shakes mildly at idle

Hey everyone. I'm new to this forum. I have a 1966 Mustang Coupe and I just finished swapping the engine for a rebuilt 1987 302 HO. It has an Edelbrock 500 cfm carburetor, an Edelbrock Performer 289 intake manifold, and pertronix coil so no points.

The problem is, it has a cyclical shake at idle. It's not a big deal but I don't think it's supposed to run that way. It's an HO, but I still don't think it's supposed to shake at idle. It was rebuilt to stock specifications so the cam should be stock and I think the cylinders were bored .030 over. What could be causing this shake?

I had an old 1985 302 in it before and it would do the same shake but worse. The only things I reused on this engine were the distributor, the carburetor, and the coil. I don't think it could be the carburetor, and I doubt the coil is causing this. Or can it? I have tried messing with the timing but I can't get it to run smoothly.

Does anyone know what might be causing this? I'm leaning toward the distributor, but someone told me a cyclical shake doesn't sound like a distributor. Thanks.
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Old 01-08-2012, 02:36 PM   #2
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generally when an engine shakes like that it's becuase it's idle is too low. Do a vacuum test and make sure you don't have any vac leaks. Check and make sure all the adjustments on your carb are where they need to be.

Otherwise it could be a missfire. Check all your plugs. Make sure they're firing and getting fuel. A fast way to check for misfires is to get the engine up to operating temp and take a temp gun to each cyl and see if one or more is firing hotter/colder than the rest.
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Old 01-08-2012, 02:44 PM   #3
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Thanks jojobanks. I don't think it's a big enough shake for a misfire though. And my vacuum is good. Here is a link to a video of what my vacuum does. http://www.youtube.com/watch?v=OoWX27024OY
And this is the acceleration: http://www.youtube.com/watch?v=SxwjjmDOs4U

I think the gauge is off. The needle is less than 0 when not connected to anything so I think my vacuum is a little higher than that but you can still see what the needle does.

I'll still try to check the temp of each cylinder. Should I take the spark plug off? Or can I just point it around the spark plug or the header pipe?

Thanks.
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Old 01-08-2012, 02:56 PM   #4
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Quote:
Originally Posted by umfan92 View Post
Thanks jojobanks. I don't think it's a big enough shake for a misfire though. And my vacuum is good. Here is a link to a video of what my vacuum does. http://www.youtube.com/watch?v=OoWX27024OY
And this is the acceleration: http://www.youtube.com/watch?v=SxwjjmDOs4U

I think the gauge is off. The needle is less than 0 when not connected to anything so I think my vacuum is a little higher than that but you can still see what the needle does.

I'll still try to check the temp of each cylinder. Should I take the spark plug off? Or can I just point it around the spark plug or the header pipe?

Thanks.
I usually just point at the header pipe. look for a difference of about 150* or greater between cyls.
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Old 01-08-2012, 03:53 PM   #5
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Check that your pcv is working and not causing a vaccum leak. Could just ne low idle in gear..
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Old 01-08-2012, 03:59 PM   #6
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You may just reset your idle and check timing. Block the front tires and make sure in gear when tuning. It will be higher rpm in park but will level you out in gear and warm. make sure your tune the carb for highest vac. With the car warm. Check for vaccum leaks. And you say you took the points out.. did you shim the magneto with the plastic feeler gauge when you put it in?
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Old 01-08-2012, 04:32 PM   #7
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De ja Vu.
My engine shakes also at idle...on my build...have about 500 miles
302 roller cam 30 over built to 1985 gt specs.
Early 70s 4 barrel intake. Holley 600cfm elec choke
Msd pro billet dizzy..
Stock 65 mustang exhaust manifolds.
I get about 15" vacuum.
running a auto c4 tranny.

I have no idea how to get this engine to idle smoother...
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Old 01-08-2012, 04:36 PM   #8
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Quote:
Originally Posted by boogerschnot View Post
Check that your pcv is working and not causing a vaccum leak. Could just ne low idle in gear..
I bought it not too long ago but I wasn't sure if it was working correctly. How can I check if it's working right? The PCV valve is a controlled vacuum leak, so plugging it will make the engine run better even if the PCV valve is running well in the first place right?

Quote:
Originally Posted by boogerschnot View Post
You may just reset your idle and check timing. Block the front tires and make sure in gear when tuning. It will be higher rpm in park but will level you out in gear and warm. make sure your tune the carb for highest vac. With the car warm. Check for vaccum leaks. And you say you took the points out.. did you shim the magneto with the plastic feeler gauge when you put it in?
I'm sorry I didn't take the points off. It's a 1987 302 and I'm not sure which distributor it is but do I still have to do that magneto thing? I'm not familiar with that. Thanks

Quote:
Originally Posted by jojobanks View Post
I usually just point at the header pipe. look for a difference of about 150* or greater between cyls.
I will try this later. Thanks for the tip. I don't think it's a big enough shake though. If a cylinder wasn't firing, shouldn't it be a bigger shake? Thanks.
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Old 01-08-2012, 06:12 PM   #9
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Quote:
Originally Posted by umfan92 View Post
I will try this later. Thanks for the tip. I don't think it's a big enough shake though. If a cylinder wasn't firing, shouldn't it be a bigger shake? Thanks.
not really. Some misfires are actually worse than others. If you're having problems with your ignition system somewhere you could just be getting a weak spark.

Personally i think your vac should be higher than that if you have a stock cam. it's a steady reading but it's borderlining on the bad side. The lowest your vac should ever steady is about 16. Highest I've seen is 21-22.

In fact, if your previous engine did this as well, I think it's very likely that the problem got carried over in one of the parts that you swapped over.
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Old 01-08-2012, 06:37 PM   #10
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not really. Some misfires are actually worse than others. If you're having problems with your ignition system somewhere you could just be getting a weak spark.

Personally i think your vac should be higher than that if you have a stock cam. it's a steady reading but it's borderlining on the bad side. The lowest your vac should ever steady is about 16. Highest I've seen is 21-22.

In fact, if your previous engine did this as well, I think it's very likely that the problem got carried over in one of the parts that you swapped over.
Yeah the vacuum is higher than that. The gauge is broken. It functions but the needle sits at below zero when there is nothing connected to the gauge. So I'm pretty sure the gauge is giving a lower reading than it really is. I'm pretty sure it's around 18 or 19. I'm going to buy a new vacuum gauge and see what reading I get.

Quote:
Originally Posted by Xring01 View Post
De ja Vu.
My engine shakes also at idle...on my build...have about 500 miles
302 roller cam 30 over built to 1985 gt specs.
Early 70s 4 barrel intake. Holley 600cfm elec choke
Msd pro billet dizzy..
Stock 65 mustang exhaust manifolds.
I get about 15" vacuum.
running a auto c4 tranny.

I have no idea how to get this engine to idle smoother...
Hey I didn't even see your post. Yeah I know how you feel. If you figure it out, let me know! I have no idea what's going on.
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Old 01-08-2012, 07:40 PM   #11
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I would bump the idle up a bit and see what happens, my 289 would shake when i was at stop lights since I liked my idle low since it sounded better raising it by 100 rpm fixes most of the time.

If its not that or a misfire I heard a trick from my gramps the other day, crank the car in a dark garage/on a dark night and if you see sparks along your spark plug wires then it's time to replace em.
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Old 01-08-2012, 09:02 PM   #12
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I would bump the idle up a bit and see what happens, my 289 would shake when i was at stop lights since I liked my idle low since it sounded better raising it by 100 rpm fixes most of the time.

If its not that or a misfire I heard a trick from my gramps the other day, crank the car in a dark garage/on a dark night and if you see sparks along your spark plug wires then it's time to replace em.
Hey, thanks for the suggestion. My idle is already pretty high. I like the idle to be low as well and it's already too high for my taste. I'm getting a tachometer soon and I will see what it's at currently. I wouldn't want to raise it because that just hides the problem.

And I have tried running the engine in the dark and it looks fine, no sparks. The spark plug wired are relatively new. Thanks though. I appreciate it.
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Old 01-08-2012, 10:22 PM   #13
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Once you get that tachometer tell us where your at, a stock 302 should be at 1k give or take a couple hundred rpm, some engines need to run higher to stay smooth, the competitive drag cars with big cams can idle around 3k, imagine that sound D:
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Old 01-08-2012, 11:03 PM   #14
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mine idles great at 700 but that's a manual..if its auto then 1000 in park is about money or 750ish in drive
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Old 01-09-2012, 12:58 AM   #15
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I allways set it aroud 800 when warm in gear or as low as i can with it running smoothly.
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Old 01-09-2012, 07:23 AM   #16
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Is your engine balance right?

If the harmonic balancer, the flywheel, or both are 28 oz balance, (like the car would have come with), they will be wrong for your engine that PROBABLY wants a 50 oz balance flywheel/32 oz harmonic balancer (1982 and newer engines). One or the other of these being wrong will cause a mild shake, both being wrong will cause a shake that is more than mild.
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Old 01-09-2012, 01:29 PM   #17
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"JMD
Is your engine balance right?

If the harmonic balancer, the flywheel, or both are 28 oz balance, (like the car would have come with), they will be wrong for your engine that PROBABLY wants a 50 oz balance flywheel/32 oz harmonic balancer (1982 and newer engines). One or the other of these being wrong will cause a mild shake, both being wrong will cause a shake that is more than mild. "

JMD, your comments confuse me... how can a 32oz balancer work with a 50oz flywheel...

Not to high jack this thread... but we might be on to something hear... My engine built to 1985 GT Mustang specs,,, but is does have a 50oz Balancer and Flywheel... Does a Roller Cam engine have to have a 28oz balancer and flywheel.?
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Old 01-09-2012, 01:45 PM   #18
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Quote:
Originally Posted by Xring01 View Post
"JMD
Is your engine balance right?

If the harmonic balancer, the flywheel, or both are 28 oz balance, (like the car would have come with), they will be wrong for your engine that PROBABLY wants a 50 oz balance flywheel/32 oz harmonic balancer (1982 and newer engines). One or the other of these being wrong will cause a mild shake, both being wrong will cause a shake that is more than mild. "

JMD, your comments confuse me... how can a 32oz balancer work with a 50oz flywheel...

Not to high jack this thread... but we might be on to something hear... My engine built to 1985 GT Mustang specs,,, but is does have a 50oz Balancer and Flywheel... Does a Roller Cam engine have to have a 28oz balancer and flywheel.?
No it does not, I have a late model 5.0 as well and run a 50oz balancer and flywheel. I have no problems with it and this is my 2nd late model 5.0.
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Old 01-09-2012, 09:58 PM   #19
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Ok well I'm not going to reply to every comment individually but I'll try to cover everything.

I have a T5 transmission. I would like the idle to be around 800 but I'm pretty sure it's higher than that. I bought the tachometer today. It's garbage. It said my RPM was at 130. Then I tried it on a Volkswagon Golf and I revved the engine and held it at 2000 and it told me it was at 500. So I'm returning that. I need to get another one so I'm still not sure what my idle is at right now.

Also, I bought the harmonic balancer from Summit 3 weeks ago. I specifically made sure it was a 50 oz. imbalance. The flywheel came with the transmission and is a 1986 Mustang flywheel that we pulled out of my dad's 1986 Mustang, which had a 5.0 in it.

I hope I answered all the questions. Could the distributor be doing this? I pulled the cap off today and there was a lot of moisture in it. I'm not sure why. What could be making it shake like that?
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Old 01-09-2012, 10:03 PM   #20
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There shouldn't be any moisture. Make sure you set the tach to the proper number of cylinders, there's usually a switch with 4/6/8 options.
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Old 01-09-2012, 10:03 PM
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