Lotus Elan and Lotus Elan Plus 2 Forums

HI all, after 32 years my 1968 +2 is back on the road but as you pull away it really back fires. I have done all the usual plugs, leads, cap, coil, timing. Carbs rebuilt still the same, I have a new luminition optronic which I have sent back to be tested, I have also checked all the earths. It starts well and ticks over perfect. as you can see Im a newby here, Ive been reading this site for a few weeks now and I must say how helpfull eveyone is.
ROY.

Roy,

I'd check for vacuum leaks, likely candidates are the "O" rings in the carb mountings or probably very likely cracked or leaking plumbing on the headlamp vacuum system.

Hi Roy, i did all the same as you ...then found the carbs were not balanced - not opening together (in fact the man at the rolling road found it).

ran fine at tickover and full throttle.

...could be that

Carb balancing and vacuum leaks would a good place to start
Check also
compression
valve timing (you got the two little notches in the sprockets pointing nicely to eachother at TDC)
coil- an overheating coil will fail you under load
quality of fuel - if it has been off the road for that long......
charge voltage- the electronic ignition can throw some gremlins in your joy if it does not get high enough voltage

good luck, you will find out what is wrong I am sure.

You left out ignition timing

ISTR that that can cause backfiring too.

If stromberg: check mounting height of jet and needle.Jet at 2.1-2.2 mm below deck and needle shoulder flush with air valve piston works for me.

Check the fuel supply - restriction on fuel hose (collapsed?), float height (if Webers), fuel pump pressure etc. My +2 had similar symptoms - fine at tickover, but started to misfire & backfire as revs increased or you put any load on the engine, such as pulling away). I traced the problem to a kink in the fuel hose, restricting the flow rate to the carbs. If you have Webers, keep a screwdriver in the car ready to whip off the carb tops and see how much fuel is in the bowls after the car mis-behaves.

Worth finding a quiet stretch or road to conduct a test, where you can stop and carry out the examination as above without being flattened..

Jeremy