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Canadian Poncho Homepage -> Canadian Poncho -> 65-70 Full Size Power Train Tech Forum -> Slight Stutter every 5 seconds at idle, can't figure it out.
Post Info TOPIC: Slight Stutter every 5 seconds at idle, can't figure it out.
Glenn Musgrave


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Slight Stutter every 5 seconds at idle, can't figure it out.
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A couple of things I use when diagnosing engine related issues. If you think there may be a vacuum leak take an unlit propane torch, acetylene would also work. With gas on for the torch hold it close to areas where you suspect a vacuum leak. Pay particular attention around the carb, carb base gasket, around the intake where it bolts to the heads and any vacuum lines. If the idle increases or smooths out you found a problem; fix that problem and continue testing to make sure there isn't more than one cause.

As a check on the timing you can use a vacuum gauge in conjunction with your timing light. If the vacuum is out of wack, i.e., low, it may be that your timing chain needs to be replaced. Before you rush to replace the timing chain and gears you should check for vacuum leaks and that the issue isn't carb related. If all else checks out then I would physically check the timing chain and consider replacement.

To help diagnosis and setup the carb use a tach and vacuum gauge, you may have an air screw that needs tweaking. If your car is stock, especially the cam, you should be able to adjust the air screws and get 20" of vacuum.

A vacuum gauge is a very useful tool, can also indicate if you have a sticky value etc. I use one with every tuneup.

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cdnpont


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As SD 396 stated, you never had anything major apart. 

It ran 100% fine before the body job. So don't focus on anything internal. 

You changed the wires and plugs I assume, added a pertronix and rebuilt the carb.

It's ignition related I bet. It's not intermittent, you report it as a timed miss. Can't see the carb or a external vacuum line leak causing this.

 

Start with a new quality set of plugs and a Cap. After that, if no change, find another long ignition wire and start pulling wires one at a time and putting the temporary one in.

 

 



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 67 Grande Parisienne 4 door HT. 69 Parisienne Convertible.
 
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ABC123


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I ran a 12 gauge wire from the battery to the coil,

What a difference !

Overkill but now it's sawdered to the ignition wire at the steering Colum.

However, I had the carb apart with that dirt in the needle.

That float may be not set properly.

Now that its running better, it bogs down on a 0-80 stop sign run.

Let off the gas an it recovers.

mild acceleration, no problems.

The cap is the only thing I have not changed.

I'll get one today.



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timbuk


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change cap fill tank with premium THROW IN A CAN OF SEAFOAM

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ABC123


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I called Barry at Performance Unlimited in London where I bought the Pertronix system.

I know he wasn't there the day I bought the system.

He always recommends a cap with copper connections.

Of course I have an cheap aluminum style cap.

He said that oxidization can cause problems.

Picked up an MSD cap off him.

He also insisted that I call him, when I have the cap on, to let him know what happens.

Love these small shops !

I'll pick up some Seafoam, couldn't hurt !

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ABC123


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That MSD Street Fire cap & rotor made a huge difference.

This car has never been this powerful !

The old cap was definitely a week link in the chain.

But,

That stutter was still there.

Found a YouTube video about the float.

He basically stated if you turn the top of the carb upside down, the float should be parallel to it.

This is my original carb.

006a.jpg

 

Sure enough the other float wasn't set like this and not allowing the bowl to fill.

When I had it apart to get the dirt out of the needle, I must of did something wrong.

Got it back together and,

yep,

The stutter is gone.

Thanks for putting up with this novice biggrin

I think I will still take it in to get it checked over by one of the best.

 



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cdnpont


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Good to hear!



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Canadian Poncho


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wink
Canadian Poncho wrote:

As mentioned full 12V is important for the Pertronix to work properly. Any slop in the distributor shaft? Is your float level set correctly in the carb?

 



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Glenn Musgrave


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It's always nice to get the opinion of a pro but nothing feels as good a solving the issue yourself, CONGRATS!!!!

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ABC123


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Reposting for Mark,

 

 



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65 SD L79


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I am thinking replace that 350 part with a 496 part and see if the shutter goes away



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ABC123


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Troublemaker !

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cdnpont


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Im putting a big block points distributor in it lol!



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65 SD L79


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ABC123 wrote:

Troublemaker !

 No No ! I am a Troubleshooter



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65 SD L79


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ABC123 wrote:

I called Barry at Performance Unlimited in London where I bought the Pertronix system.

I know he wasn't there the day I bought the system.

He always recommends a cap with copper connections.

Of course I have an cheap aluminum style cap.

He said that oxidization can cause problems.

Picked up an MSD cap off him.

He also insisted that I call him, when I have the cap on, to let him know what happens.

Love these small shops !

I'll pick up some Seafoam, couldn't hurt !

 i bought the Pertronic distributor for the 66 but only have the stock coil. I looked at the flame thrower coil and there is a number of them with different ohm rating what one do I need? help would be great thanx



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DonSSDD


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Buy the Pertronics coil to match the ignition you bought, their site says which matches.

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cdnpont


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I'm going to add to this thread in that I've had 100% success tracking down this strange mis. And learned a lot since the car became mine.

The thread has over 3000 views, so it obviously comes up in searches. Worth to post a conclusion.

 

North (John) was onto something.

It was carburetor related.

A loose and worn throttle shaft and perhaps fuel bypassing the accelerator pump discharge check ball likely was the cause of it.

 

A rebuild along with a temporary repair to stop the throttle shaft vac. leak and that mis was gone. Now, back up a couple of weeks ago. Then the car was exhibiting signs of flooding after sitting, so the carb had to come apart. A loose float needle seat was the cause of the flooding.

I don't think Randy had the flooding issue, I feel it just started this spring.

 

As far as the rebuild goes, it is possible that the accelerator (power) circuit discharge check ball (the one under the venturi cluster, under a small light spring and retainer "T") simply may have not been seating. At idle, fuel could be drawn past the check ball during a high vacuum condition (idle).

This bypass could cause raw fuel to drip from the two venturi discharge squirters. Raw fuel drips or droplets happening at a fixed rate could certainly have caused a timed miss. I did replace the check ball, and as recommended by pro carb guys, I did give it a tap when it was in it's seat. This is said to create a clean seat for the ball in it's soft metal base. Maybe that was it...

 

Anyway, this was what cured it!

 



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ABC123


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This car deserves you, Mark.

I'm so glad you got this done.

It's a motor that has never but hurt.

Enjoy the fruits of your labour !




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