Series 3 backfiring under load

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DanB257

New Member
Posts
3
Hi guys,

1968 series 2a with a 2.25L petrol engine. It starts and idles absolutely fine, and when warming up (~first 5 minutes running) it pulls really well and accelerates. After that when under load, going up hill or pulling away from lights, it fraps and bangs and misfires, making it kangaroo down the road.

My first thought was ignition, I replaced points, condensor, HT leads, spark plugs, air filter all to no avail. I have noticed that the vacuum advance doesn't appear to work. Sucking the vacuum pipe that attaches to the carb doesn't move the baseplate in the dizzy. Although my knowledge of how the vacuum advance works is limited, I believe that it only works at idle/small throtle openings, is this right?

Could this be the reason behind it or is there something else?

Thanks Dan
 
If the vacuum isn't working then there's a fair chance the centrifugal advance isn't working which would cause the problems you describe - timing not advancing. Broken vacuum advance usually just causes bother on cruise/overrun.

You need to get a timing gun and check that the dissy advances as you go up through the revs. It's not that difficult to strip down the distributor and lube it up. They're quite often stuck solid with old grease and get stuck or not advance smoothly but instead get stuck at certain points. I had an old dissy that used to do that and caused all manner of weirdness.
 
Thanks for all the help guys.

I've pulled the distributor apart and found what appears to be part of a broken rotor arm stuck in the mechanical advance holding it shut.

So the problem was within the vacuum advance or mechanical advance. Time for a new distributor I think.
 
I've had mixed results with new dissys - many of them look right but the weights are wrong and give crappy advance curves. In the end I bought a NOS Lucas one from the 80's to get something approaching quality (I know it was Lucas!)

Anyway a strip down and rebuild might be a better option. There's not much to them and if the mean bearing bush is ok it should be just a case of greasing everthing lightly and reassembling.

You should just need to knock the pin out at the bottom and undo a couple of screws to get the whole thing apart.
 
It appears to be an old rotor arm as the current one is complete and in good working order.

I have removed the distributor and dismantled it but it appears to have strecthed one of the springs in the bottom.

Ah, I may take your advice then as there is very little play in the main shaft (~5thou up/down, ~ 1or2 thou sideways). I'll have to find a replacement spring but as I work in an electricians it shouldn't be to hard.
 
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