Twin plug weak spark after dizzy ?

[haasad]

I'm struggling with the concept of phasing so need educating, here's my understanding,

I set the dizzy at a rough start with rotor pointing at No 1 pin.

I time the car with a light which indicates a spark at 6 degrees BTDC on number one at 900 rpm.

Checking the physical rotor position after this with No 1 at TDC comp identifies the rotor neatly aligned with No 1 dizzy pin.

I rev the motor to 3000 and can clearly see an indicated spark at No1 at 30 degrees BTDC.

Surely this would indicate correct phasing ? When I designed the dizzy I made sure the rotor location was as original with reference to the dizzy shaft.

With regard to using a scope I did hook it up to a Crypton analyser which did indicate low spark volts also the spark trace was leaning back which we didn't understand.

I think I'm out of my knowledge depth now but am very confused by the simple symptoms that the RHS bank runs fine and smooth the LHS not. The only thing not common to both sides are the cams which are timed at 5.4 mm dead equal
(now)and the carbs.

?????

[chris_seven]

Originally Posted by haasad

Jag Marelli Cap and custom 120 deg rotor

120 degrees?

[Mark Henry]

The phasing question is are you sure that it not only is on the pin at rest, but that it is also still well on the pin at full advance?

The 120 degree rotor I doubt is the issue, I'm assuming by 120 degrees you have the contacts spaced by 4 pins?
The JB and Jarvis are both one pin short of 180 degrees.

[haasad]

Yep 120 degrees. Bang on. And as I understand it if I have the spark occurring at 6 BTDC 900 rpm and at 30 BTDC 3000 rpm. the rotor must be staying in "contact " with the dizzy pin. There is a clear grey track on each rotor tip and each dizzy pin there is no evidence of tracking in the cap.

Also the spark intensity is not varying with revs and hence ignition advance all this leads me to believe my "phasing" is correct.

To the eye the spark plug to the eye is clear and consistent just a bit yellow white not a cracking blue.

I'm going to try to get an expert to look, if I can find one nearish who won't just assume my dizzy etc is all scrap on the basis I designed it and want to spend money on a process of parts replacement till the fault goes away ( which seems to be a "modern approach")rather than diagnostic steps to identify then solve the problem.

I'll keep you posted ...could still be carbs

[tctnd]

Since you have two essentially independent ignition systems you might try separating them for testing. remove the low tension lead from one coil and pull all the associated high tension wires (coil pigtail & plug) from the cap. See how it runs. Replace these and do the same with the other set. The engine should run very nearly the same in all three configurations; if it does not you have something to explore. As a last resort, pop in a stock dizzy and see what happens. I will say the bank to bank disparity sounds suspiciously fuel or vacuum related but to troubleshoot this successfully you need to separate the various systems and check each one methodically.

regards,
Phil

[LJ851]

I found on the 3.2 distributor that i converted to electronic (magnetic) pickup , it makes a huge difference in rotor phasing depending on which way the the two pickup wires are connected. It changes the pickup from leading edge to trailing edge and although the car ran it was not happy. If you can spare a cap i highly recommend drilling a hole and verifying rotor phase.

I could not even see the tip of the rotor in a 1/2 inch hole directly under a terminal, switched the wires and it was bang on, just like i designed it.

[haasad]

Thanks,

Phil, I have tried running it with each ignition circuit disabled to make it single plug , no change in symptoms either running on top set or bottom.


LJ851, I don't understand how drilling a cap will help me "see" a phasing issue can you advise further.

I have an accuspark trigger which shares the 12 v feed to the CDI and has its other side connected to the points connection into the CDI I'm worried to swap the connections in case I pop the trigger ?

I wonder if from Phils test I am coming down to carburation and am doubting "My Dizzy" as crap since I designed it !!!!

I've had the carb off at least 3 times and can't find any blockage or air leak, I've done all the carb cleaner around the flanges tricks and also neat fuel into the trumpets on tickover with no change in affect.

It doing me in this ...

[LJ851]

Originally Posted by haasad

LJ851, I don't understand how drilling a cap will help me "see" a phasing issue can you advise further.

Dill a large hole in the side of the cap directly under a high tension wire where the tip of the rotor is visible when it passes by. A vertical stripe of bright paint on the plastic tip of the rotor can help you see it. Hook your timing light to that HT lead, start the car and point the timing light at the hole. What you will see is the exact position of the rotor when the ignition is firing.

Here is my test cap.

[haasad]

Ahh got it now.. Thanks a lot even though the Marrelli type caps are a bit pricey at £150 sterling I think that's worth while to get this right or at least remove any doubt.

So if the phasing is adrift , and I'm thinking I should see the rotor initially in direct line with the timed pin then as the ignition advances with revs move away from it, clockwise rotating so that the spark happens earlier up to 30 degrees BTDC,

OR

I could send the dizzy off tho get it curve checked which would save scrapping an expensive cap?

[Mark Henry]

IMO if you can build what you have already you should be able to do this job with a protractor.

If you did drill a hole I'd use a cheap ebay cap

[LJ851]

The rotor doesn't move in relation to the cap as timing advances. The trigger and the rotor are connected, the advance happens between the upper and lower halves of the distributor shaft.

[haasad]

Thanks for the compliment but look how long its taken ....now a protractor that's an idea.

The thing I'm struggling with is that rotating the dizzy body around the shaft should change this phasing thing within the limits of the slot in the dizzy casting so effectively the rotor angle is 120 degrees and the spark is triggered by the accuspark unit at a predetermined point governed by the magnetic ring. This spark is transmitted to the dizzy through the rotor and sent out to the relevant plug, I can adjust the initial relationship between rotor and the relavent dizzy pin at 900 rpm timing setting, then the centrifugal advance takes over and moves the relationship to make the spark happen earlier as rpm climbs.

Thus surely the phasing is established as correct ?

So as long as the rotor is not past the relavent pin or at its limit of contact at 900 rpm all should be fine.

[haasad]

Thanks for the compliment but look how long its taken ....now a protractor that's an idea.

The thing I'm struggling with is that rotating the dizzy body around the shaft should change this phasing thing within the limits of the slot in the dizzy casting so effectively the rotor angle is 120 degrees and the spark is triggered by the accuspark unit at a predetermined point governed by the magnetic ring. This spark is transmitted to the dizzy through the rotor and sent out to the relevant plug, I can adjust the initial relationship between rotor and the relavent dizzy pin at 900 rpm timing setting, then the centrifugal advance takes over and moves the relationship to make the spark happen earlier as rpm climbs.

Thus surely the phasing is established as correct ?

So as long as the rotor is not past the relavent pin or at its limit of contact at 900 rpm all should be fine.

Now I can see a perfect grey track line on the leading edge of each rotor tip extending about 2/3 the way of the available length of the tip all indicating to me that I have got it right .

Still checking wont hurt

[LJ851]

Originally Posted by haasad

Thanks for the compliment but look how long its taken ....now a protractor that's an idea.

The thing I'm struggling with is that rotating the dizzy body around the shaft should change this phasing thing within the limits of the slot in the dizzy casting so effectively the rotor angle is 120 degrees and the spark is triggered by the accuspark unit at a predetermined point governed by the magnetic ring. This spark is transmitted to the dizzy through the rotor and sent out to the relevant plug, I can adjust the initial relationship between rotor and the relavent dizzy pin at 900 rpm timing setting, then the centrifugal advance takes over and moves the relationship to make the spark happen earlier as rpm climbs.

Thus surely the phasing is established as correct ?

So as long as the rotor is not past the relavent pin or at its limit of contact at 900 rpm all should be fine.

Rotor phasing is entirely dictated by the relationship of the rotor to the trigger on the upper (moveable) part of the distributor shaft. It does not change by turning the body or timing advance.

[LJ851]

Unless you rotate the rotor or the trigger on the upper distributor shaft (not both together) your phasing will not change.

[haasad]

Ok I think I'm beginning to get this. I need to physically check or otherwise measure that the rotor tip maintains contact ( close proximity ) to the dizzy pin throughout its ( the rotor ) range of movement. I and that its initial position is properly set with relation to the trigger point for the spark ie points opening or mag switch making ?

Finally I think I understand phasing... thanks so much, I'll get busy checking should be able to do all that on the bench with protractors and meters .

[LJ851]

When the distributor is rotating on the bench in the normal direction of travel, if you can with a meter, verify the rotational position of the the rotor when the triggering actually occurs, then you could see how well it aligns with the terminals in the cap at that position.

This would confirm your rotor phasing.

[haasad]

Excellent , thats what I thought to do. I'll contact the Accuspark maker here in the uk and establish how to check the trigger point using a meter and or power then I should good to go.

Thanks so much for all the help so far. I'm at the body shop tommorrow helping fix the thankfully slight hood damage then back on the fault .

[Steve@Rennsport]

FWIW,...

I use an old cap that I've cut away on the sides to observe phasing in my (Sun 504) distributor machine. In that way I can see the rotor-to-cap position and triggering while rotating it by hand.

I would recommend finding someone with one of these old machines so you can confirm/adjust the triggering point where the rotor tips pass the cap contacts.

[haasad]

Steve thanks a good tip. A final piece of this checking jigsaw for me....when correctly phased should the rotor tip line up centrally on the dizzy pin or with its leading or trailing edge. This is a clockwise dizzy?