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Does your idle timing bounce around?

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JeffS

JeffS

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There was a post on this before, but has been hijacked with a bunch of other stuff, so I decided to reply in a new post.

If your timing bounces around at idle while checking it with a timing light, there are 3 main causes.
1) The timing chain tensioner is worn and loose.
2) You have solid core plug wires which are messing with the timing gun signal.
3) The springs are worn in the distributor. Most likely the lighter (primary) spring has fatigued and is allowing the advance weights to swing around uncontrollably at idle. This is eaily remedied by replacing the springs - if you can find the appropriate replacements.

Please note that it is quite unusual for wear in the distributor to cause this "jumping" action. It IS possible for the weight pivots and pivot holes to be elongated and worn. It is also possible for the pivot pins to become loose or bent. These issues create more problems with timing consistency at different (accelerating and descelerating) rpms than at a relatively stable idle. The most common cause is definitely fatigued springs!
Jeff
 
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1) The timing chain tensioner is worn and loose.


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And if it looks as bad as mine did.....
Not only does the timing bounce around.
It makes this really cool "gear drive" sound. /ubbthreads/images/graemlins/thumbsup.gif
(Like a hopped up Nova)
PVGPSchenleyPark011.jpg
 
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3) The springs are worn in the distributor. Most likely the lighter (primary) spring has fatigued and is allowing the advance weights to swing around uncontrollably at idle. This is eaily remedied by replacing the springs - if you can find the appropriate replacements.


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---So where do you get them??--Keoke

--Please note; anything that changes the dwell angle in the Dizzy such as Wear will also cause the timing to jump around.- /ubbthreads/images/graemlins/yesnod.gif
 
Well, something unusual happened with my '79 the other day (Crane system in original distributor)...after over 100,000+ miles of enjoyable driving, it started running real rough & wouldn't get up to top end on the RPM's....on the side of the road I tried to reset the timing - it doesn't matter how advnced or retarded I make it, she still runs rough & has about a 3,500rpm max (at most & that might be a wish)....got her back to the garage & am going to check another distributor w/Crane in it to see if my original distributor is bad.

So, is that bad distributor springs?
 
Let me know what you find, Tony... Sounds sortof similar to my Alfa problems... You still got a cat on the 79? My dad seems to think that my cat is clogged, and it makes sense based on the 2 cars that I grew up with that had cat internals melt down for no apparent reason. But I still think it might be elctrical/ignition, or possibly fuel pressure related in my case.
 
Yep, cat's still there - actually, if you remmber, its all stock...not a cat problem...its in the timing somewhere...just out of nowhere as I was driving down the road she wnet "fluddddreerrr" & started running rough & lost her power...I immediately thought the timing had gotten off (my distributor was a little loose) since I had just been playing with it....but, I can turn the distributor as far forward or backward as is possible & it doesn't change anything.
 
Loose a spark advance spring maybe? or a weight?

Or do those actually even do anything on an electronic setup? Sorry, I have a 25D on mine with points.
 
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it doesn't matter how advnced or retarded I make it, she still runs rough & has about a 3,500rpm max

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My WAG is coil, pump or battery.....
 
Not in the fuel system - she's pumping great; battery shows good & fully charged.
 
coil or electronic control box then.
 
That's why I've got a second distributor with all its Crane stuff ready to drop in...the distributor in it is original but I put the Crane in it back in early 90's...coil at same time.
 
does the Crane use a light wheel sensor or the magnetic one? My wife's eagle talon eats light wheel sensors (factory) about once every 10-20k miles heat degredation of the sensitive electronics.
 
"So is this bad springs" I doubt that Tony it sounds like something has caused your timing to severly retard. Check all those little Crane brackets and screws up under the Dizzy cap to be sure something did not just come loose.---Keoke- /ubbthreads/images/graemlins/grin.gif
 
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3) The springs are worn in the distributor. Most likely the lighter (primary) spring has fatigued and is allowing the advance weights to swing around uncontrollably at idle. This is eaily remedied by replacing the springs - if you can find the appropriate replacements.


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<u>It was asked before but I didn't see a response. Where can you get new springs for a dizzy?</u> /ubbthreads/images/graemlins/crazyeyes.gif PJ
 
Springs are NLA. If you don't get replacements out of a donor distributor, your best bets are 1) eBay for the rare NOS parts offerings, and 2) Cambridge Motorsports in the U.K. (they have a web site). Cambridge has the only "set" of dizzy springs I've ever seen advertised.

Before investing in springs though, I'd like to offer my own observation. I have seen on more than one occasion where very badly adjusted carbs (dual) (with mixture problems) caused a good dizzy to have bad timing scatter at idle. Going through an iterative adjustments of the carbs, then timing, then carbs... eventually resulted in rock steady idles. Obviously this won't correct the mechanical wear this thread started out discussing and I'm not suggesting that it's a panacea. I'm suggesting it as a process to go through before spending money unnecessarily.Springs are NLA. If you don't steal replacements out of a donor distributor, your best bets are 1) eBay for the rare NOS parts offerings, and 2) Cambridge Motorsports in the U.K. (They have a web site). Cambridge has the only "set" of dizzy springs I've ever seen advertised.

Before investing in springs though, I'd like to offer my own observation. I have seen on more than one occasion where very badly adjusted carbs (dual) has caused such mixture problems that even a good dizzy will have bad timing scatter at idle. Going through an iterative adjustments of the carbs, then timing, then carbs... eventually resulted in rock steady idles. Obviously this won't correct the mechanical wear this thread started out discussing and I'm not suggesting that it's a panacea. I'm suggesting it as something a process to go through before spending money unecessarily.
 
I would also suggest that air leaks around the carb throttle shafts would produce much the same symptoms. Idle high or fluctuating.

To much air getting in thus carbs further open to adjust for it thus more fuel in the engine at idle as the shaft would could move around this would change as you watched.
 
My car has a single Zenith Stromberg...but I am going to check all vacuum lines.
 
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My car has a single Zenith Stromberg...but I am going to check all vacuum lines.

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OH MY God!,That would even make me jump around a bit and not for joy.---Keoke- /ubbthreads/images/graemlins/grin.gif
 
New springs are available in the form of recurve kits for HEI chevy distributors, or I have them custom made. The original springs truly are NLA, with the exception of a rare set that shows up once in a while. I make my own prototypes and have replacements made in bulk from those.

You may never see replacement springs or a recurve kit commercially available for your distributor, because the design tolerances are so loose that they may never be accurate.

Tony - have you tested your spark plug leads, cap, and rotor? It sounds like you are completely missing on at least 1 cylinder. What do the spark plugs look like? Chances are good you have one or two that are black?
 
Next thing to check after the vacuum & switching distributor - I don't think its in the plugs because she was running great & just started doing it all of a sudden....& everything looks good.
 
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