Vacuum advance on a PI car

[pgee]

Steve, thanks.

 

Earthing is good, also when I move the advance plate. Advance is working correctly with the strobe.

I'm going back to the store tomorrow and change this one.

 

Peter

[John L]

Steve

I have the same unit as yours, could you take a look at your rotor arm please and see if its black on the heel of the rotor arm as mine is.

I still believe that the ignition unit needs to be in a slightly different position, so at full advance on the base plate the rotor arm is in a better contact position with the points on the distributor cap.

John

[TriumphV8]

The simonbbc locates the finger in a different position still with timing proper set.

It is worth a test if the finger meets the pickup contact when spark fires.

For that I made a cutout in the cap, connected the strobe to the ignition cable

belonging to the naked contact point and let the engine idle and rum at higher revs

and strobe the finger.

[John L]

I have cut holes in a cap to see what happens, and its firing on the heel of the rotor arm, so how can I change that? It must be the position of the module on the base plate surely?

John

[pgee]

Steve, yes, it is black on the heel.

Andreas, you think on higher revs it doesn't meet the pickup contact

 

When I drive and give full throttle the car immediately stutters firmly, no power. Until 2500 rpm all works fine.

When I drive and slightly rev up I can go to 3500 rpm before it stutters. 4000 is impossible.

Peter

[Peter Cobbold]

I'd put a timing light on the engine and check that the distributor was smoothly advancing/retarding as you rev the motor.

Yes.

Compare the curve when on points with the the electronic version. NB keep hands well away from the fan !! I'm not keen on electronic points. Especially now that DD sells the orignal fibre tip points.

Peter

[pgee]

I compared the curve, it is different. Contacted supplier and I will get a new one.

 

One strange thing I saw using the strobe when the normal points are back in. The flickering of the strobe light is not constant. Every now and than it misses. I think (stationary) at least ones every one or two seconds. It does that on all leads. When driving (cruising speed, not under load) it runs but I can feel a very slight hesitating now and than. It feels like the ignition every time is missing one. This is the reason I wanted the electronic ignition.

I put an extra earth cable from the battery directly on the distributor but it didn't fix it.

I checked the leads, they are good.

Rotor and distributor cap are new, also points and condenser.

Battery is good.

Could it be the coil?

Or alternator? Amp meter stays steady.

 

Or is it a fuel problem?

Edited June 25, 2018 by pgee

[Peter Cobbold]

I compared the curve, it is different. Contacted supplier and I will get a new one.

 

One strange thing I saw using the strobe when the normal points are back in. The flickering of the strobe light is not constant. Every now and than it misses. I think (stationary) at least ones every one or two seconds. It does that on all leads. When driving (cruising speed, not under load) it runs but I can feel a very slight hesitating now and than. It feels like the ignition every time is missing one. This is the reason I wanted the electronic ignition.

I put an extra earth cable from the battery directly on the distributor but it didn't fix it.

I checked the leads, they are good.

Rotor and distributor cap are new, also points and condenser.

Battery is good.

Could it be the coil?

Or alternator? Amp meter stays steady.

 

Or is it a fuel problem?

Missed sparks: check the short braided cloth-covered wire.

Peter

[TriumphV8]

I have cut holes in a cap to see what happens, and its firing on the heel of the rotor arm, so how can I change that? It must be the position of the module on the base plate surely?

John

 

There are two different Things:

The rpm advance will move the finger as well with advance

so the position of finger to pickup will be the same.

 

Vaccuum advance will move the baseplate and that will change position

of finger to pickup. For that the finger has not a point but a ring located

towards the pickup point. Under max vaccuum and no vaccuum the finger

must meet the pickup point properly.

 

If there is no vaccuum advance often the PI has a fine tuning nut to move the baseplate.

With that it is easier to move the finger to the pickup. I found it helpfull to turn the nut

fully in what retards the ignition. With moving the dizzy case that must be corrected

for proper timing.

 

If there is vaccuum advance or no fine tuning it will be difficult.

The base plate must be moved, that is the easiest way. The magnets

under the finger should not be touched, it is a quite precise thing

and plastic can break easily.

I see a slight chance to move the baseplate in the area where the plate

has the finger that connects it with a somewhat spring to the vaccuum box.

[John L]

Now had a chance to do some resetting.

Mine is a PI so no vacuum advance.

I have cut holes in a cap to see whats hapenning.

First look the firing is on the heel of the rotor arm, to number 1 lead, noticed before as a black mark on the heel.

I turned the thumb screw on the A/R to the fully advanced position, this has corrected the firing position on the rotor arm, but now have to reset the timing to 10 - 11 degrees with a strobe and voilla the rotor arm stays put at the firing point, now nearly in the middle of the rotor arm pickup.

Something I have learnt from this is that the rotor arm doesnt move its position, (irrespective of engine speed)even when you rev the engine, but the marks do change on the pulley increasing engine speed, so it must be advance working correctly inside.

From this it must be the position of the hall effect unit on the base plate itself, so the thrum screw is now redundant.

The rev counter cable how has to be on the inside of one of the injector fuel lines to be in good alignment.

Will be driving to the south of France tomorrow, so will be able to report improvement...….

John

[DaveR]

The vacuum unit is an fuel economy device. On light throttle loads it will advance the timing and improve the fuel burn. To stop pinking under a heavy load when the throttle is open wider the vacuum unit reduces the advance it had applied on half throttle. This is achieved by driving it from the vacuum present in the inlet manifold.

 

The factory couldn't get to 150 BHP PI engine to run without pinking on light loads if it had a vacuum unit fitted. As it was all about power and not economy no vacuum unit was fitted.

 

Dave