Hello all. Have got the PAS up and running and have taken it on a little test drive and this has exposed the next issue. The car is back firing through the carbies. It happens on hard acceleration (eg foot pushed to the floor suddenly) or when under load eg driving along and try to accelerate. It seems to be worse when engine is not at operating temp.
This is a right hand drive car and it is possible i have bumped or disconnected something when fiddling with the lower steering column. Any suggestions or ideas please?cheers
Sounds like a timing problem Tim. Sounds like the timing is slightly out and firing when the inlet valves are open.
Possibly a problem with your advance and retard system on the dizzy.
Check that the vacuum pipe is connect to the dizzy and to the carb.
The advance and retard can get stuck up if left for a long time so pull the dizzy give it a good clean, free up the mechanism and a light oil then try again.
Was it ok before you carried out the recent work on it? If so then I would check:
That the distributor is tight and hasn't accidently been rotated.
That the starter carb is connected (electrically) and you haven't knocked the lead off the switch on the inlet manifold (if its still a problem when the engine is warm then this wouldn't be it as the starter carb should only work when the engine is cold).
As BSM states make sure there is correct amount of oil in the dampers ~ SAE 20W. If the pistons bang up to wide open too quickly on hard acceleration you will go lean & suffer engine stumble & backfiring.
Update. Checked the damper oil - seems to be OK. again checked the vacuum advance and that is ok. So took another approach. Logic is spark is getting to the wrong plug at the right time or, alternatively, spark is getting to the right plug at the wrong time. Following this logic through I wondered if there was somer sort of shorting going on with the spark plug cables. Lo and behold when I move the leads about and separate them a little NO backfiring.
Looks like I need new leads.
I have no idea Jeff. How do i tell? They have the bakelite plug fittings and they are black and the radio gets interference from the electrical system.
I used the genuine Jaguar lead set with copper wiring. I've taken a good peak under the bonnet at night & zero crossfiring between leads. No misbehavior. And I'm running an uprated, debranded by yours truly, Flamethrower coil. Now has correct Lucas sticker on it. I'm running the PerTronix Ignitor pointless ignition system contained within the distributor cap for POSITIVE earth.
Used these plug caps that were supplied with the kit.
I have no idea Jeff. How do i tell? They have the bakelite plug fittings and they are black and the radio gets interference from the electrical system.
If you have the Bakelite plugs, then most likely they are solid copper, even more so if you have the brass washers in the distributor where the wires are spread out.
I think the Bakelite Champion caps are resister at 5000 ohms as they should be with solid copper wires, but if they are, then running resistor plugs pushes should not be done if you're running points.
Glyn is running a Pertronix ignition with a hotter coil so he can get away with both, but I don't know if he is running resister plugs.
Do what he said and check the wires when the car is running and totally dark.
Some will take a plant mister and spray water on the wires while the car is running, this shows up any defects in the wiring if it creates a miniature lightening storm.
Someone I don't like anymore told me once that another way is to lick your fingers and run them up and down the HT leads when the engine is running. I only did it once and now only recommend it to people I don't like.lol.
Hey Glyn, does that black sleave come as part of the spark plug kit? Mione has pretty much disintegrated so the leads lie loosely along the valley in the cylinder head between the two cam shaft covers. I cant see any sparking but there's no doubt that the backfiring is less (much less) when I pick the leads up and spread them out. I would like to keep using the original bakelite plug caps if at all possible so I might just buy the correct length of lead and use the old fittings. Is the lead 7mm, 8.5mm or some other diameter?
Thanks for all you advice everyone
The conduit came as part of the kit when I bought mine in 2013.
Or you can buy separately. I presume you are going to make up your own new lead set? No need to buy a kit if you don't need one. It was not cheap. Conduit available in dark brick red or black.
I can't find my bloody vernier to check lead size. Friends have been at my tools again. I despair!
I have now taken all the cables out of the round guides so they can be separated. It is night here and just started the old girl and revved her a bit. Lots of spluttering when cold and a few little sparkes flying around. Once warm though I cant make the thing backfire - which is good. Nevertheless it looks like the leads do need replacing. The lead wires is about $3.50 (AUD) per metre. I will reuse the bakelit caps as they are original and would prefer to do what I can to keep them. Just need to source the little brass do-dads that are soldered to the distributor cap end of the leads - will use copper/brass washers if I need to improvise.
My vernier is MIA. Just take an acorn nut/plug cap/round spacer with you when you buy new cable for sizing.
The spread wires are not soldered to the brass washers. Any old school auto electrician should have the split brass washers. I'm sure you don't want to go to Barratts for them unless you are ordering a conduit. Shannons in Aus might be able to help you. Otherwise you will have to make your own.
Well, I'm stuffed - dont really know what to do next.. I guess I need to explainwhere I am up to at the moment:-
The "backfiring" actually comes back up through the starter carby - not through the other two - with a cloud of fuel being blown back - no flames.
There is a smell associated with it that smells like a mixture od rubber and fuel
The backfiring is worse when it is cold.
The backfiring can be caused by pushing the accelerator flat to the floor suddenly
The car is now MUCH harder to start when cold than before this issue started
I have replaced the leads and it makes no huge difference to the amount of backfiring.
The distributor is very tightly secured and cannot have been moved out of timing
The vacuum adv pipe looks OK and doesnt appear to have any holes or kinks..
I have got the car running then removed 1 spark plug lead at a time to see if the backfiring stops when a specific plug is disconnected - it doesnt
I interpret this to mean that it isnt crook leads or a damaged distributor cap.
--- and thats where I am at the moment.
Any ideas at all? Thanks
Recently I had a problem of a miss fire on cylinder number one at the back of the engine and I was getting a blow back through the starter carb normally when I was starting the car. Not the symptoms exactly that you are getting but it puzzled me for months until I took it to a Jaguar/Aston Martin specialist who straight away told me it was the vacuum pipe to the brake servo that was leaking.
I was like "What".
Turns out the take off vacuum pipe to the servo is on the inlet manifold close to cylinder number one. Because I had a leak in the pipe it was running weak on cylinder one which had the miss fire and that was putting everything else out. Once I had replaced the pipe the miss fire had gone and I do not get blowback from the starter carb anymore.
Not saying it is this but something else to check!
Question. Does it only backfire when the engine is under load? Or will it backfire with the vehicle standing idling if you floor the throttle? Bare with me on this because I had a similar incident which I will explain once I have an answer. It all relates to fuel pressure/flow to the carbs.
