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Posted by: Ferg Aug 24 2009, 11:37 PM

Dwell is 49 at idle, jumps to 50 just off idle and goes all the way to 53 at full advance (3500 rpms), advance and retard hoses were hooked up for dwell check, I know to unhook them for timing. Is that right, or do I need to unhook them for dwell, as well.

Possible dizzy advacing plate issue?

Car has a miss at 3kish, I'm trying to squash.



Stock 74 2.0 djet. timing is set at 29.

Posted by: brant Aug 24 2009, 11:45 PM

thats weird
I'll let the experts jump in

but the dwell is measuring the point gap
that shouldn't change with rpm
(maybe a wobbly shaft?)

the gap shouldn't change with timing... it should always be the same gap.

I'd pop the cap and check the gap with a feeler guage while at the peak of the lobe... may need to roll the car forward or back to find peak.

hmmm....

Posted by: Ferg Aug 24 2009, 11:56 PM

Yes, strange indeed.

I did check gap again, seems spot on, and still get a solid 49 while idling. Just jumps to 53 when I take it to 3500.

Posted by: SLITS Aug 25 2009, 08:40 AM

The points are a spring. If you activate the spring in enough cycles per minute you can get spring bounce just like a valve spring (kinda like floating the valves) in which the dwell would change with RPM.

Try a new set of points for fun or just get an electronic module (I prefer Led trigger, but your experience may be different) that would not be subject to dwell changes.

Ferg, you are WAY to anal.

That's 3 cups of coffee thoughts.

Posted by: ME733 Aug 25 2009, 08:56 AM

And as suggested ,the shaft in the distributor....may have some wobble, due to it,s age and it,s old and all the perfect is gone!!....bouncing points , at 3000 rpm,s...guess what they are doing at even higher rpm,s.!!...this is probably the cause of the misfires when driving....replace the points,and condenser, with a new bosch set.....if the problems persist/ dwell changes/...it,s probably time for a NEW distributor...and trigger it with led...put these problems behind you as it ain't likely to heal itself....good luck.

Posted by: jaxdream Aug 25 2009, 09:06 AM

I've heard of circle track racers that run a Mallory dual point dizzy to solder a second points arm spring on top of the primary arm to help eliminate point bounce , supposedly works very well.

Jaxdream

Posted by: Ferg Aug 25 2009, 09:10 AM

These are brand new points (second set) and new condensor. I'll try swapping them out again with my spare set, but both are new.

I'll wiggle the shaft (he he) tonight as well. I did it once before and didn't remember any slop.

Posted by: Cap'n Krusty Aug 25 2009, 09:22 AM

Worn out breaker plate. The condenser, BTW, cannot and does not have anything to do with dwell.

The Cap'n

Posted by: Ferg Aug 25 2009, 09:28 AM

Thanks Cap'n, just got off the phone with my local wrench and that was what he said as well.

Are they still available? Or do I need to start looking for a used dizzy

Also, in the short term should I lower the dwell to 45ish, so when it jumps it stays in range, will that help?

Posted by: Joe Sharp Aug 25 2009, 09:41 AM

Hey Mikie, put some 30 weight on all the stuff below the points and grease the points. The oil is to see if it helps with the woble of the shaft and the grease is to keep the points from bouncing. If the shaft wobles less then get a new dist. Weather or not the points are bouncing replace them with something electronic.

Posted by: McMark Aug 25 2009, 03:25 PM

Cap'n, what wears out on the breaker plate? Does the advance plate become loose?

Posted by: ME733 Aug 25 2009, 06:45 PM

WHEN he replaces the points,...don't you think a new condenser is in order..?...the condenser CAN have something to do with misfiring.Lets suggest doing it all right..ONE #@&%**# TIME.

Posted by: Ferg Aug 25 2009, 09:36 PM

reset the dwell to 45 tonight, and retimed it to 28 degrees.

Runs a little happier, initial throttle tip in is smother and my miss at 3kish is less pronounced.

oiled as joe suggested, and more dizzy grease on the shaft. dwell is still jumping to 49 at full advance. that's a bit much. no slop that I can tell in the shaft, gotta be the plates.

Found a crane optical (thanks slits) so that will be going in this weekend.

Ferg