Bucking at 2500 rpm

I am trying to resolve my problem with my Series 1 4.2 E Type (1966)

I have installed Pertronic ignition in the 22D distributor but have not been able to solve the farting problem under load between 2500 and 3000 RPMs. I moved from points/condenser to electronic hoping that it would solve the problem but no.

Would a defective vacuum advance unit have anything to do with this? I did notice that the vernier adjustment is frozen.

Dash pot oil OK. Timing OK. Plugs look OK. Using the Flame thrower coil with the original distributor.


Many thanks,

I had bucking at 3000 rpm. Very annoying. I was changing everything, coils, plugs, wires, but solved it when I bought a new 123 to replace the existing 123. Send the 123 back to the factory, and they returned it saying it was fine. Haven’t tried the old 123 again, but the car never bucks since I put in a new distributor.

It could be anything, but on mine, of all things, it was the spark plug wire not connected to the plug, it was pulled back in the boot. Just close enough for the spark to arc most of the time, but start coughing on revving above 2500.

Sounds to me like the traditional problem of the “curve” not being set to the correct degree for that particular range. That is a problem that is prevalent to all the 'vacuum Retard" distributors made for the late sII’s.


Wherever space and time interact, there is information, and wherever information can be ordered into knowledge, and knowledge can be applied, there is intelligence.
Pavel Mirsky, mid 21st Century Russian General

You might also verify that the advance weights are freely moving (i.e. you are getting proper advance at higher RPMs).

A quick check is to flip the rotor and see if it springs back smartly (note, the noise is just a big fan that was running):

You may have the problem where the distributor plate (that is rotated (ie pulled by the vacuum advance)) is so far out of adjustment that the spark is trying to jump between the rotor and the distributor cap electrodes when you open the throttle, because the rotor is too far away from the distributor electrode - thus the misfire as the spark is not able to jump the gap.

I suggest you unfreeze the vernier adjuster and try centre it between fully screwed in and fully out.

Dennis 69 OTS

Wouldn’t it have to be stuck at full advance to cause backfiring and bucking? And it would have other running issues (high idle/pinging). If spark stays at initial timing and never advances it will just have no performance. You know like a early S-2!

25-3000 is around torque peak. I think the spark is breaking down (bad wires, plugs, coil) or maybe it WAY lean.
Odeon, do you have to be driving it to feel the bucking or will it do it if you just rev it up in neutral?
When plug wires are cross firing you can sometimes see it at nigh/dark garage if you take the wire conduit/organizer apart. Try that tonight. Call us in the morning.

Another way to look for crossfire is to hook your timing light up to cylinders 2 thru 5. Aimed at the timing marks you should see nothing but if every once in awhile the timing flash shows the marks, that is crossfire.

Or you could grab the wires with your bare hand, hey George?
That’s probably how Wiggy’s Dad taught him. Toughen the kid up.
So why not use the light on cyl’s 1&6 as well as the rest?

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What wires are you using? That should be suspect number one in a pertronix conversion if it was running fine before. I used their wires and it runs great.

My reading was that he had the same problem with the points and was trying Pertronix hoping to resolve it.

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Ah, missed that post!

If you think it’s timing then you need to measure it and see what’s going on.

The vernier adjuster is not part of the vacuum advance; it simply allows you to make small corrective movements of the distributor without undoing the base plate.

If it is stuck then maybe other things inside your dizzy are too. I suggest you take it out, strip it and clean it and make sure that the advance plate turns and the weights move freely.

Now with the dizzy held in your vice measure the total advance available by turning the shaft with the rotor arm on it. I made up a 360 degree protractor to do this but you should be able to measure it well enough. It should be around 12 degrees depending on car and distributor. Correct numbers are in the Manual. Total advance = distributor advance x 2 + static advance. = 12x2+10 = about 34.

To measure the advance curve at speed you will need to buy a dial back timing light. Google them. Cheap ones are about $50 and you’ll wonder how you ever lived without one.

Simply get an assistant to rev the engine at say idle, 1000, 1500, 2000, 2500, 3000 and 4000 and measure the crank advance using the dial back light. You can then plot your curve, and compare it to original. Then you will know if your advance is correct.

Here’s one I did for my 3.8.


As an aside, I have fitted just about every available type of electronic ignition to one or other of my cars. I have gone back to points on all of my cars because they are simple and work. I know this isn’t everyone’s cup of tea but it works well for me.

I was always a ‘points guy’ but decided to try a simple electronic (Hot Spark, <40 bucks) on my spare distributor. I installed that distributor just to be sure the engine would run well with it. That was about 10,000 miles ago, never got around to switching back.

The main advantage for me is that on a long trip I use to check the points gap every few thousand miles, now of course that is not necessary. Not a big deal, just one less thing to think about.

Sticking with carburetors too, Andrew?
All this technology is a slippery slope. My buddy set of on a 4 day trip on his Harley. Day two it started running erratic. 2 days & $500 later of troubleshooting at a dealer, no joy. Just info from the tech that said there might be a continuity problem with a particular FI sensor wire. 14 hours of driving the bike arrived back home. One (of four) wire on the throttle position sensor had sheared. No strain on the wires, the break was 20-30mm upstream of the nicely crimped pin in the connector. 55k miles on the beast. No real failure explanation other than perhaps something happened when the harness was made. Another $250 to get a different HD dealer to put new pins on the harness. So $750us for a broken wire!
Can’t wait for my Toyota hybrid to start its electrical decline.

How’d ya know?? :grimacing: plus 100,000 volts…

Thanks to everyone who responded.

Followed all your tips and I discovered that the advance mechanism was frozen … that explains it.

I will next clean off the area where the distributor shaft enters the block, withdraw the distributor and do I detailed cleaning and inspection on the bench.

Will note the location of the dizzy and reinstall it.

Did this quite a few years ago and if I remember, it was not that difficult.

Also noticed that one of the alternator connections was not tight so I fixed that too. That could be one source of the bucking (like losing an electrical connection).

Once again thanks to all … will update when the unit is back in the car.


One of he first tasks upon getting a new car is to pull the distributor and clean it thoroughly. And… there is always a problem, frozen advance plate or a bad vacuum module. And Of course dirt and grease…


Wherever space and time interact, there is information, and wherever information can be ordered into knowledge, and knowledge can be applied, there is intelligence.
Pavel Mirsky, mid 21st Century Russian General

Right on.

Will start today with penetrating oil on the clamping unit to make life easier.

I have spare parts and if required I’ll purchase new parts.