Lotus Elan

Odd discovery that might be of interest to others too.

PostPost by: hatman » Wed Jan 30, 2013 5:04 pm

Despite 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.
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PostPost by: cal44 » Wed Jan 30, 2013 9:40 pm

Thank you hatman. Funny how something like that can cause such a ruckus. I can't tell you how many vacuum leaks I have come across over the years with different cars. Now I just replace all the hoses as soon as I get a new one in.
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PostPost by: CLAY » Thu Jan 31, 2013 2:21 am

That's some good information. Especially how it progressed.
Hope to keep this filed away and remember when (not if) this happens to me.

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PostPost by: pereirac » Sun Feb 03, 2013 10:15 pm

It's amazing how quickly my headlights pop up now that I replaced my T piece (Sue Miller as well) ... And yes less 'popping' from the exhaust :)

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PostPost by: hatman » Mon Feb 04, 2013 9:34 am

It's just one of those daft little items that you'd never normally think to check - if it's still there, not hanging loose like mine was, you naturally assume that all's well and move on to check other things like plugs, leads etc. :evil: These cars form a continuous learning curve it seems. :mrgreen:
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