Distributor woes

Phil Robson

Phil Robson

Well-Known Member
My V8 has been seriously jerky when under load, particularly at higher speeds for a while now so I decided to investigate.

I've replaced the fuel filter which seemed to be less than free-flowing, but that didn't help a great deal. I then deduced (with my limited technical knowledge :LOL: ) that it may be the vacuum advance on the distributor, because if the car was 'coasting' there was no issue; only problems under acceleration. Having a closer look, there were splits in the rubber elbows of the vacuum pipe & also sucking on the pipe saw no resistance!

I have a spare engine with distributor attached, which I have now removed & put into my car. However, whilst sucking on the pipe clearly now has vacuum resistance, it does not move the baseplate. Should it? Am I on the right lines?

Of course, now I can't start the car :oops: although I suspect, as with a lot of things in life, that's just a matter of timing!
 
Hello Phil,

The vacuum advance module plays no part when the engine is under load such as when accelerating, only when under very light loads such as when cruising along an expressway with very little pedal being used.

When you suck on the vacuum module you will feel suction against your tongue but you do have to suck really hard in order to move the base plate. If in doubt there are three nylon pads that the base plate rests on and these can be lubricated with some light machine oil or even some engine oil if you prefer. The oil will soak around and lubricate beneath the pads aiding in free movement of the base plate.

If the problem only occurs under acceleration at higher road speeds, then it could be a lean fuel mixture or your ignition coil is breaking down, but the vacuum module won't be the cause.

Ron.
 
I'm still unable to start this car.. :oops:

I've been told that the timing may be 180 deg out & to verify that I've been advised to remove the plugs & feel when No.1 piston is compressing. Presumably I can tell with the rocker cover off, when the valves are both closed, but this seems to happen every time the rotor arm is lined up with No.1 cylinder... :?

Clearly I'm not what you'd call an expert at this. Can anyone help, please? :(
 
If its 180 out then removing the dizzy and putting it back with the rotor arm pointing in the opposite direction will do the job.... Think I'd just try it!

Rich
 
rockdemon said:
If its 180 out then removing the dizzy and putting it back with the rotor arm pointing in the opposite direction will do the job.... Think I'd just try it!

Rich
Click to expand...

A far easier way is to move all the leads to the opposite side of the cap. It won't look very neat, but it will prove the point and is a lot easier that removing and refitting the distributor, especially if it turns out not to be 180 out in the first place. Incidently they tend to spit back through the carbs when cranking if they're 180 out.
 
Thanks guys..... it's started! :LOL:

rockdemon said:
If its 180 out then removing the dizzy and putting it back with the rotor arm pointing in the opposite direction will do the job.... Think I'd just try it!

Rich
Click to expand...

I actually lifted the distributor out of its 'mesh', turned the engine once & then slotted it back. It started almost on the first turn - much easier than ever before! I'll set the timing properly now & then get on with the jerking problem....
 
Just to update, I have now reset the timing using a strobe & set the dwell correctly per the factory manual.

Not only does it run very smoothly (even though it's a £143k engine) but the jerkiness under load has totally gone :D . I've done nothing to the fuel side :?.
 
I have read Phil's comments about his distributor with interest.
I have now checked mine and find that whilst I have suction the base plate does not move.
However the engine runs smoothly throughout the rev range and I get about 24 -25 mpg on 95 octane fuel.
I'm tempted to leave well alone although I will lubricate the pads as suggested by Ron.
As an aside I found that the timing pointer on the crankcase was hopelessly out and if used as per the manual gave me a hopelessly retarded engine. This misplaced pointer is mentioned in the manual as a possibility on some engines.
I timed mine by running up and down the road and adjusting the timing until I got a smooth running engine. A bit primitive but it worked.
 
Nothing primitive about that! Essentially that is what a rolling road tune is doing, albeit with rather pricier kit involved. If you have "the ear" to correctly asssess an engine you will get excellent results like that.

I'm told that the vacuum advance packing up is one of the most common defects affecting engine running on the V8. The normal symptoms are exactly as Phil describes. And most non experts also always go for the carbs in error!

Chris
 
6Bcygnet said:
I timed mine by running up and down the road and adjusting the timing until I got a smooth running engine. A bit primitive but it worked.
Click to expand...

I set the timing on my 1966 2000SC in just that way but rather than judging it by a smooth running engine I timed how long it took to go from 30 to 60 on full throttle in top gear. Adjusted timing to get quickest time without pinking :D

Having done that I tried the same test in the V8 and the time over the same stretch of road was considerably quicker :D

Dave
 
Thanks for the feedback.
My next query. I see Phil didn't see the base plate move when he sucked on the vacuum pipe.
Neither did I.
Is it possible to move the base plate by just sucking or does this require more effort ie considerable manifold suction.
I removed the base plate and could move the vacuum diaphragm by hand although it required quite a bit of pressure.
Cheers
Frank
 
Hello Frank,

You do have to suck pretty hard in order to make it move, and there won't be a great deal of movement when it does. If you can't feel suction on your tongue, then chances are that the rubber diaphragm within the module has perished.

Ron.
 
6Bcygnet said:
I timed mine by running up and down the road and adjusting the timing until I got a smooth running engine. A bit primitive but it worked.
Click to expand...

I have now used this method to fine tune 'Hazel' & the timing is about 3 deg BTDC per the strobe. It's running beautifully, with only the very slightest hint of pinking under severe load. :p
 
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