Smokey puff from airbox on starting

[RichardS]

As reported on the Elan thread I'm just back on the road after 20 years.

Have had the engine fired up a few times over the last couple of weeks and seems to be running nicely. Did a couple of miles on the road this morning for an MOT and again running fine.

But - on several occasions when restarting the Twin Cam after switched off for a few minutes - if it doesnt start first time there can be quite a puff of exhausty smoke which wafts out of the airbox and out from under he bonnet for 5 or 10 seconds which looks a little alarming! No sound of a back fire. The engine has then fired ok the next time.

I don't ever remember this happening in the old days. Is it normal/wrong throttle technique/dangerous??!!

Would appreciate advice/reassurance/warnings

Richard

[oldelanman]

Could it be oil fumes ? After switch off the fumes in the crankcase take a while to disperse and if your breather still goes to the airbox the fumes will be drawn up when cranking. If the engine doesn't fire the airbox will be full of fumes which could be what you're seeing.

Regards,

[RichardS]

Could it be oil fumes ? After switch off the fumes in the crankcase take a while to disperse and if your breather still goes to the airbox the fumes will be drawn up when cranking. If the engine doesn't fire the airbox will be full of fumes which could be what you're seeing.

Regards,

Roger - no, my breather doesn't go into the airbox now so this wouldn't be he cause. It did happen once before I had fitted the airbox and the smoke "cloud" definitely eminated from the carb trumpets.

Richard

[richardcox_lotus]

Are you sure it's actually coming from the airbox ? I used to get a similar waft of smoke on start up which was from holes in the Y-piece of the exhaust near the bellhousing - the direction the vapour took was past both sides of the engine at the firewall/bulkead area.

Richard
'72 Sprint

[RichardS]

Hi Richard

I will double check next time it happens.

Richard

[rgh0]

I get something similar in my Esprit when starting from cold but never on the Elan or plus 2. No real backfire but a puff of smoke from the airbox seals. If i remove the airbox you see a puff come out of one of the carb trumpets.

sometimes it happens once, sometimes 2 or 3 occurences in first 30 seconds of running then it goes away.

I have always put it down to somehow the mixture in the inlet igniting due to a slow burn in the cylinder leaving residual hot gases when the inlet valve opens that ignite the incoming charge early. It only happens on starting as the slow burn is due to poor fuel vaporisation when first starting.

Maybe something similar going on in your Elan

cheers
Rohan