Odd discovery that might be of interest to others too.
Posted: Wed Jan 30, 2013 5:04 pmDespite having gone to great lengths over the years to optimise the running of my Elan, including such things as fitting electronic ignition, having the carbs professionally analysed and set up correctly, taking great care setting the timing etc it has nevertheless always had a very slight misfire/stutter when accelerating off from idle and an occasional backfire when on the overrun. This I have come to accept as a characteristic of the twincam, maybe something to do with the cam profile and/or the Dell 'Ortos that are fitted (that aspect of matters has always been a bit akin to black magic as far as my limited engineering knowledge is concerned).
Recently however matters have deteriorated, insofar as a definite misfire developed at low revs/small throttle openings (although it's still been running fine when giving it a bit of welly) and backfiring violently when coming off the throttle at fairly high speeds. I checked, cleaned and gapped the plugs (they weren't far out anyway) then found myself wondering if a valve might be sticking slightly, freeing up whenever I gave it a booting, so I did a compression test which showed that everything is still OK, with good, near-book pressures and all pots within a spit of each other.
Having now decided that the next move would have to be to call in the cavalry and get a pro to have a look, I happened to glance under the front of the car and noticed a pipe hanging down. A further, quick inspection revealed that the plastic T-junction that connects the vacuum pipes to the front of the reservoir had hardened over its 40 odd years and eventually broken away. When I took the broken pieces off the pipes and the vacuum reservoir stub pipe, it was apparent that there must have been a long-standing failure crack or hole in it as there was actually a bit of it missing altogether.
I've now fitted a replacement T-pipe (from Susan Miller - off the shelf) and the car is running better than at any time during my twelve years of ownership. There's no longer any misfire at low revs (or at any revs for that matter), acceleration is clean throughout and there's no longer any tendency to backfire on the overrun. Best six quid I've ever spent.
Recently however matters have deteriorated, insofar as a definite misfire developed at low revs/small throttle openings (although it's still been running fine when giving it a bit of welly) and backfiring violently when coming off the throttle at fairly high speeds. I checked, cleaned and gapped the plugs (they weren't far out anyway) then found myself wondering if a valve might be sticking slightly, freeing up whenever I gave it a booting, so I did a compression test which showed that everything is still OK, with good, near-book pressures and all pots within a spit of each other.
Having now decided that the next move would have to be to call in the cavalry and get a pro to have a look, I happened to glance under the front of the car and noticed a pipe hanging down. A further, quick inspection revealed that the plastic T-junction that connects the vacuum pipes to the front of the reservoir had hardened over its 40 odd years and eventually broken away. When I took the broken pieces off the pipes and the vacuum reservoir stub pipe, it was apparent that there must have been a long-standing failure crack or hole in it as there was actually a bit of it missing altogether.
I've now fitted a replacement T-pipe (from Susan Miller - off the shelf) and the car is running better than at any time during my twelve years of ownership. There's no longer any misfire at low revs (or at any revs for that matter), acceleration is clean throughout and there's no longer any tendency to backfire on the overrun. Best six quid I've ever spent.
These cars form a continuous learning curve it seems. 