No oil cap = no idle. Why?

Have a look at where the breather pipe from the rocker cover goes. If the plumbing is anything like that on my Vitesse, it enters the inlet manifold after passing through a circular flame trap (?). Leaving the oil filler cap off buggers up the vacuum.

Because you probably have a crankcase breather connected to the carburetter. When the cap is removed there is nothing to stop the air getting in and giving you weak mixture, which is why pulling the choke out helps. An alternative quick fix would be to block up the breather pipe. Normally only a trickle of air gets in through the filter in the cap.

Driving like this for a short distance won't have done any harm, though you do risk burning pistons if you drive hard on weak mixture.

Had a similar thing in my ...... '78 Spit 1500.

However I had driven off with the Oil cap sitting on the top of the bulkhead ......

Doug

Do a compression check and clean the breather pipes -- it sounds like the crakcase pressure blew the cap off.

In article , Willy Eckerslyke writes

If it's a 1500 Spitfire it doesn't have that circular thing[1]. The breather passes directly from the rocker cover to the carbs, straight into the CD chamber. There may be a slight restriction in the pipes, but there's no flow limiting devices.

With the oil cap missing you get an air bleed right into the business part of the carbs, and your fuel metering goes to pot.

If the breather pipe was blocked then not having a filler cap wouldn't affect the mixture and idle speed. When I lost my filler cap the reason was that I had topped up the oil and forgotten to replace it.

When I was working in engine development / testing, not so long ago, we were once working with a modern diesel engine made by a reputable(?) european motor manufacturer which had a known problem with excessive oil carry over through the crankcase breather system. One day a technician inadvertantly left off the oil filler cap, and after only a few hours running, the whole heap siezed, with two burnt pistons and exhaust valves, and no oil left in the sump, as it had all been sucked through the breather into the intake! A proposal to help conteract this risk by connencting the filler cap to the rocker cover by a short link was rejected on cost grounds! I've not heard what the warranty costs turned out to be in production.

So beware losing the oil filler cap on your euro-box too!

Paul C Lewis (PCL snipped-for-privacy@pcls.freeserve.co.uk) gurgled happily, sounding much like they were saying :

Oooh! Twenty Questions! Remember - you can only answer Yes or No.

Was the manufacturer french?

I managed to have this happen with Dad's VW van. If you didn't nail the oil cap down it could vibrate loose and fall off. Then the oil pumped out through the hole and eventually it ran a big end (probably over-heating more than loss of pressure).

Didn't Minis do something similar ? I've certainly seen some horribly oily ones under the bonnet, where they'd lost the cap.

I forgot to replace the cap after topping my Merc up. 20 motorway miles later the oil was _everywhere_ - even running up the outside of the bonnet! Took me ages to get it clean, even with Gunk & the pressure washer.

That would be telling ;-), but I did say 'reputable'!

To be honest, I'd normally heve expected better from the outfit concerned, but everyone seems to be tightening their belts these days.

: I forgot to replace the cap after topping my Merc up. 20 motorway miles : later the oil was _everywhere_ - even running up the outside of the : bonnet!

I had the main high pressure delivery pipe on my DS fracture at 70 on the motorway. I lost a gallon of LHM hydraulic fluid - which ain't cheap - in about a minute. Best chassis and engine bay rustproofing ever!

Ian

Likewise with a 1.9 BX I once owned. Only mine decided to dump it's LHM in the Dartford Tunnel ;-(

Simon H

In article , Simon H writes

Likewise my old bx gti in the outside lane of the M3 at rather illegal speeds. Riding on the bumpstops at speed is, errmmm, exciting!

Ian Johnston ( snipped-for-privacy@talk21.com) gurgled happily, sounding much like they were saying :

Be thankful it was a later, LHM, D. If it was an early brake-fluid car..... - Best paintstripper you can get.

No. If you leave the filler cap off the rocker shaft oil feed isn't sufficient to throw out the oil. The breathers should have oil separators on them. There is a problem with A+ engines blowing out their dipsticks with the filler cap on. Most transverse A series engines leak oil from various places so keep the engine bay well rustproofed.

Oh, I have the rustproofing sorted anyway - leaking crankshaft rear oil seal! Only really noticeable at motorway speeds, of which I do 50-100 miles a week, but the whole front underbody is liberally coated. It also has the "advantage" of constant oil change - it leaks out so fast it doesn'y have time to get dirty! Just have to spin on a new filter and flush the sump now and then!

It's the loss of steering abd brakes as well that makes the whole experience so, um, "character forming". In the sense of "buttock clenching".

Ian