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> Still a miss at 4,000 RPM..., Backfiring at WOT, even with all new ignition components
old dog
post Jun 14 2013, 09:58 PM
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QUOTE(edwin @ Jun 14 2013, 06:20 AM) *

If you can pull a plug off and it isn't affecting performance then I'd be really looking at firing order. That start up seems like leads going to wrong cylinders
Have you tried stopping by a mechanic and getting one to take a spin around the block? Surely worth a couple of dollars if they can shed any light at all as to what's happening
My money is on firing order or timing
Edwin

I think I have to agree that the firing order has to be off in some manner. To kick back through the carbs like that just isn't right.
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ThePaintedMan
post Jun 15 2013, 10:45 AM
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Below is a picture of the firing order on the distributor cap, as I have it set up. I'm pretty confident this is correct, but you can take a look for yourself.


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mepstein
post Jun 15 2013, 10:58 AM
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Time for a 6.
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904svo
post Jun 15 2013, 01:41 PM
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Try this remove the cap and turn the rotor my hand and see if it returns. This will check the mechanical advance. It may be stuck.
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ThePaintedMan
post Jun 15 2013, 02:15 PM
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QUOTE(904svo @ Jun 15 2013, 03:41 PM) *

Try this remove the cap and turn the rotor my hand and see if it returns. This will check the mechanical advance. It may be stuck.


As mentioned before in this, now quite lengthy thread, the mechanical advance is operating as it should (recently cleaned and relubed). But thanks.
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904svo
post Jun 15 2013, 03:34 PM
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Have you check the resistance of each plug wire? They should be 5k ohms.
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r_towle
post Jun 15 2013, 03:50 PM
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Move every plug wire on spot clockwise.
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timothy_nd28
post Jun 15 2013, 05:24 PM
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QUOTE(r_towle @ Jun 15 2013, 01:50 PM) *

Move every plug wire on spot clockwise.

(IMG:style_emoticons/default/agree.gif)
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r_towle
post Jun 15 2013, 07:53 PM
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And reset the timing by turning the distributor clockwise till the edge of the vacuum can , the small top portion, lines up with the wire clip on the oil filler..
That should be close enough to start it and get a timing light on it.
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vw505
post Jun 15 2013, 10:07 PM
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Have you got the springs changed out yet?
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ThePaintedMan
post Jun 16 2013, 06:01 PM
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Pulled both springs on the suspected cylinder (#3) with the handy tool that Bill sent me. Pulled the exhaust lifter as well to inspect - couldn't get the intake lifter to come out due to the ridge that forms.

Long story short, I compared the springs with known good springs and they look fine - same height. The lifter showed a little sign of pitting, but nothing major. I'll post pictures of that once I d/l them off my GoPro.


Took a drive, and it didn't make a difference.

Then went to Rich and Tim's suggestion about rotating the plug wires one spot clockwise. Tried to align the dizzy the way Rich suggested, but now it won't fire at all. If I continue moving the can a little further, I can get an occasional pop/loud bang out of the exhaust, but it won't fire. Here's what it looks like currently:


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ThePaintedMan
post Jun 16 2013, 06:46 PM
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Nevermind. I got it by going back to the basics and setting it at TDC #1 and turning the dizzy till the rotor pointed at #1 wire. Which now means the vac advance can is wedged almost up against the tin/oil pressure sender wire.

Drove it around the block, same thing.

Are you sure you guys didn't mean rotate the plug wires counter clockwise?
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vw505
post Jun 16 2013, 07:12 PM
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Dude, time to pull the heads of and look for cracks.
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vw505
post Jun 16 2013, 07:12 PM
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Or swap out the motor.
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r_towle
post Jun 16 2013, 07:16 PM
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remind me, what distributor is that again?

How are you determining TDC at number one cylinder?

Can you post a few pics of this process?

Every stock distributor is set as I stated...or damn close to the pic you posted above with the number one plug wire nearest the fan.

It still seems like an ignition issue to me....considering everything you have done so far.

Rich
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ThePaintedMan
post Jun 16 2013, 07:41 PM
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Vw505, I'm getting dangerously close to that. I've got a spare engine, I just want to know WHAT the problem is before I pull the trigger, since compression and leakdown numbers are both pretty good. However, dicking around with this thing has mostly just wasted my time and money so far.

Rich, TDC determined via the markings on the fan and verifying that both intake and exhaust valves are closed on #1 (rockers rocking).

It's an SVDA distributor - more info here: (scroll down about 1/8 of the way, or search for "SVDA.")

http://www.ratwell.com/technical/FAQ.html



Could you elaborate as to why moving the spark plug wires 90 degrees would potentially solve a backfire on *one* cylinder though? In theory, if the plug wires are moved and the dizzy moved along with it, nothing else changes on that one cylinder, correct?
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r_towle
post Jun 16 2013, 07:50 PM
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I would suggest that at the point of TDC you have the valve covers off and see what valve opens on the number one cylinder as you continue to rotate the engine.

If its the exhaust valve, then you were at tdc, if its the intake valve, almost right away, you were not.

Rich
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Bills914-4
post Jun 17 2013, 03:23 AM
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Hey George ,
I got nothing except maybe 1 dumb question ,do you got the spring in there between the distributor and the drive gear ( it keeps the drive gear from twisting
up&out and changing the timing ) maybe I miss that part of this post (IMG:style_emoticons/default/confused24.gif) ,
sorry other then that I cant think of anything , watching that video ,it seems to
appear theres somthing to this timing Ignition thing , Good Luck Bill D.
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rhodyguy
post Jun 17 2013, 08:32 AM
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does your distributor have a notch in the top edge of the body? the positioning of the #1 cap terminal pictured doesn't seem as i remember.
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ThePaintedMan
post Jun 17 2013, 08:36 AM
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Rich, I'll give it a shot, but again, I don't see how my timing marks (this is the correct fan and it is bolted on properly) could point to TDC and the rockers be loose on that cylinder if it was not truly at TDC. I guess as you mentioned, it is theoretically possible that the engine was not assembled correctly and the valve gear is off. But this is a problem that seems to have developed over time - when I first got the car running, I never had a backfire. Which is *more* frustrating, given the decent compression and leakdown numbers. One would think that any problem that develops over time is a result of something mechanically wrong with the engine, or an incorrectly installed/broken part (read: dizzy, etc, but remember, I've replaced just about everything that isn't internal to the engine)

I do believe that you guys are on to something with the ignition timing, but I'm just having an issue conceptualizing why I would have a problem with one cylinder, but not others if it is indeed a timing problem.

Bill, that's a good point, but I do indeed have the spring installed in the drive gear.
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