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Post Info TOPIC: Slight Stutter every 5 seconds at idle, can't figure it out.


Poncho Master!

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Slight Stutter every 5 seconds at idle, can't figure it out.


I just changed the plugs and wires with all AC Delco

Pertronix conversion.

The plugs taken out all showed even burn.

You have watch carefully for the slight shake.

When you are driving you can feel the slight shake.

The re-manufacture carb was put on last fall but the car sat in that dusty body shop.

Yes I know the idle is a bit high but I worry about stall at a traffic light.

85,000 miles on engine.

Timing chain ?

dirty carb ?

I did find junk in the needle a week ago.

Let me know what you think.

after that, enjoy my bus driving videos from 2015 biggrin



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Randy(Muttwood)



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If you sit in the car, hold the brake and put it in drive, does it do the same thing?

If you load the engine (still holding the brake, in drive) does it still do the same thing?

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Poncho Master!

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So now the neighbour is wondering why I am doing brake stands in my shop biggrin

Yes, shake is still there under load.



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Randy(Muttwood)



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Is the shake always at the same time interval?


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Canadian Poncho Superstar!

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When you did the Pertronix conversion, did you run a new +12V line to it? They need a full 12 volts, and the original wiring harness has a resistive wire in it going to the coil. The resistive wire serves the same purpose as the old ballast resistors on the firewall.

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- Slop in the timing set should be obvious when you put a timing light on it. (The mark will "walk" noticeably.)

- I am not a fan of ignition conversions... though many persons like and recommend them, many others have problems and complaints about Petronix products. (Only GM's HEI is a true H.E.I. in this context.) Having said that, a conversion is only as good as the components it's mated with. Check the condition of everything and follow Petronix instructions to the letter, including coil resistance, which is critical...

- Assuming you have an otherwise healthy engine, most carburetor problems are ignition related.

Just my knee jerk reactions... 





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Poncho Master!

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Canadian Poncho wrote:

Is the shake always at the same time interval?


 Like clockwork !



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Randy(Muttwood)



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ABC123 wrote:

So now the neighbour is wondering why I am doing brake stands in my shop biggrin

Yes, shake is still there under load.


 Ok, that rules out a vacuum leak pretty much.



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Poncho Master!

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seventy2plus2 wrote:

When you did the Pertronix conversion, did you run a new +12V line to it? They need a full 12 volts, and the original wiring harness has a resistive wire in it going to the coil. The resistive wire serves the same purpose as the old ballast resistors on the firewall.


 Wow,

That was not in the instructions.

It did run fine after the conversion.

I am tempted now to put the points back in to see if that solves the problem.

I am using the pertronix coil but I kept all the old parts.

Trying to figure this out myself first because of what Covid-19 has done to my job,

I have lots of time to play.



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Randy(Muttwood)



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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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ABC123 wrote:
seventy2plus2 wrote:

When you did the Pertronix conversion, did you run a new +12V line to it? They need a full 12 volts, and the original wiring harness has a resistive wire in it going to the coil. The resistive wire serves the same purpose as the old ballast resistors on the firewall.


 Wow,

That was not in the instructions.

It did run fine after the conversion.

I am tempted now to put the points back in to see if that solves the problem.

I am using the pertronix coil but I kept all the old parts.

Trying to figure this out myself first because of what Covid-19 has done to my job,

I have lots of time to play.


Was just looking at the Pertonix instructions online.  The requirement for +12v is in the Wiring Instructions on page 2, including Recommended Installation which addresses bypassing the resistive wire.    



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Poncho Master!

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seventy2plus2 wrote:

 


 



Was just looking at the Pertonix instructions online.  The requirement for +12v is in the Wiring Instructions on page 2, including Recommended Installation which addresses bypassing the resistive wire.    


 I must have missed that completely !!!

Clint, I think you are on to something.

I have a plan now for Monday.

I hope it is this simple.



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Randy(Muttwood)



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As a trial, I ran a jumper wire from the fuse box to the coil.

There is a definite difference !

Thanks Clint !

However, the shake is still there.

I'll stop in and see Tiny this week.

My timing gun is very old so I think it's best to have him look at it.

I'm thinking at this point, timing chain.



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Randy(Muttwood)



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Jeff (Tiny) will figure it out. He's one of the best old school techs I know. Say "Hi" to him for me.

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A Poncho Legend!

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I know this may be a dumb (obvious) solution but did you check the gap on all the plugs when you installed them?

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4SPEED427 wrote:

I know this may be a dumb (obvious) solution but did you check the gap on all the plugs when you installed them?


 0.035 Gap

The plugs I took out were gapped the same.

Tiny said he would have to have it for a day.

He would start with a compression test.

 

and go from there.



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Randy(Muttwood)



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Before I'd be worried about tearing in to the engine for an almost indiscernible shutter, I`d be looking at the ignition wires and making sure there is good contact at coil and plugs, look for cracks and arcing, are the boots good and not soft and cracked or melted. After that I'd be going at that carb, make sure its clean and then set the idle mixture properly followed by curb idle. How about your fuel filter, I mean these are all easy things that cost little or nothing make your baseline right but they eliminate a lot of things too. If you don't trust your timing light its gotta be timed after Petronix switch.

I keep a spray bottle in my garage for ignition misses, have a look:

https://video.search.yahoo.com/yhs/search?fr=yhs-symantec-ext_onb&hsimp=yhs-ext_onb&hspart=symantec&p=spray+bottle+test+of+s%5Bark+plug+wires#id=1&vid=52231d50f249289f46674922fe3a4412&action=click

 



-- Edited by 73SC on Monday 8th of June 2020 11:36:32 AM

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Number 8 cylinder camshaft lobe is round common occurrence. ps wild guess



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Canadian Poncho Superstar!

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thought this thread was about the PM.....

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Poncho Master!

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timbuk wrote:

thought this thread was about the PM.....


 Shhh !

No politics

But,

Haircuts allowed in Ottawa as of Friday.



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Randy(Muttwood)



Canadian Poncho Superstar!

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ABC123 wrote:
4SPEED427 wrote:

I know this may be a dumb (obvious) solution but did you check the gap on all the plugs when you installed them?


 0.035 Gap

The plugs I took out were gapped the same.

Tiny said he would have to have it for a day.

He would start with a compression test.

 

and go from there.


 I am not saying that this will fix your problem but with Pertronix you can run 040 to 045 on your plugs. A wider gap is better with that amazing conversion. I have had Pertronix on all my oldies for over 20 years and swear by it. Never and i mean never had any issues at all with that wonderful system. Good luck fixing your situation there. 



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Poncho Master!

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Did your engine have this issue before the conversion? If not you should be able to rule out everything other than what you swapped. Give the tech working on it as much information as you can to help him with the diagnostics and save him some time. 

 Good luck.



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Poncho Master!

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SD 396 wrote:

Did your engine have this issue before the conversion? If not you should be able to rule out everything other than what you swapped. Give the tech working on it as much information as you can to help him with the diagnostics and save him some time. 

 Good luck.


 I did the conversion last fall and everything was great.

Sat for 5 months in a body shop with me having the motor out for a few weeks.

It has never really ran right since I got it back.

First dirt in the fuel filter and  then a piece of something stuck in the needle.

New filter, fuel lines and float seems fine.

Remanufactured carb last fall.

I'll get Tiny to set the timing.

I'm sure his equipment is better than mine wink

In the mean time.

0.040 - 0.045 gap coming up !

Excuse for another test drive biggrin

 



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Randy(Muttwood)



Canadian Poncho Superstar!

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ABC123 wrote:
timbuk wrote:

thought this thread was about the PM.....


 Shhh !

No politics

But,

Haircuts allowed in Ottawa as of Friday.


 i meant the Power Modulator......good luck!



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Sometimes vacuum leaks around worn throttle shafts can cause that periodic hiccup. Bushing kits can correct it.

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