Unusual engine fault

[RobertM]

Following on from my post on SU HIF6 carbs (weak running at around 3000rpm and then possible a worn camshaft) as a test on the running engine I removed each spark plug lead individually, then replaced and noted on the first two cylinders I tried that this created a slight misfire but the engine revs remained the same. However when I removed the plug lead on the third cylinder (actually No 6) the engine revs shot up by 500 rpm. When the plug lead was replaced the engine revs remained high. Can anybody suggest what might be going here? Thanks.

 

[rockdemon]

are the leads in the correct order?

 

[RobertM]

I will re-check, but I'm sure that the leads are in the correct order.

 

[RobertM]

I've now checked the plug leads and they are in the correct order.

 

[ghce]

worn cam lobes?

 

[Neilr]

Rob just got to the bottom of mine. It was the carbs. I have swapped for another set and she runs again.

 

[machman767]

Nice one, Neil, persistence pays off. Bet you're glad you didn't through the towel in!

Mick

 

[Neilr]

I was beginning to think I was doomed. But I'm chuffed she runs again.

Neil

 

[RobertM]

That's great news Neil.

Rob

 

[RobertM]

I have now sorted out my engine problems by carrying out the following:

• New 3.9 camshaft, hydraulic lifters, timing gears, distributor drive and timing chain.
• Fitted later SD1 cylinder heads ERC 0216 (bought used off eBay)
• Replaced distributor points with electronic module

Whilst I had the front timing cover off I replaced the original rope seal with a lip seal.

Following a recent rolling road tune-up it's now running great with good performance and better fuel economy too!

Thanks for all your advice everyone.

Rob.