Intermittent Blue Smoke Air cooled Engine - help!

[InventEd]

I have a CU engine in my van that is only 1.5 years old and worked very well until last week. While driving back from MOT repair after two miles I suddenly got a huge cloud of (I think blue) smoke out that back, engulfing the poor driver behind. I pulled over in panic and turned the engine off. Look around I could see nothing strange so started the engine (which ran fine). Reved it etc and no smoke. So I drive off and it went fine for another 1 mile and then suddenly the same again. This time I pulled over but did not stop the engine. Round the back no more blue smoke even when reving the engine.

At the weekend I started it on my drive and after 15 minutes ticking over I got a couple of pops and some blue smoke. Looking at the air filter it seamed to have some oil in it, so I cleaned it up and changed the air filter (single, twin choke Weber). Fan belt checked, breather hose all attached correctly (and I could blow back through it from the carb). Started it again and left ticking over for 25 minutes. A couple of runs up and down my lane (as I did not have an MOT) and I could not get anything but normal running.

Yesterday I took it for the MOT retest and the same thing happened again. 2 miles out, big blue smoke out the back. I had to stop every 1/2 mile for a couple of minutes. Another driver pulled over one time and told me 'get out she is about to blow up!' because of the smoke.


Any ideas as I cant work it out and dont have enough knowledge of the oil system.

Ed

PS On the way to the retest I took the engine cover off and there were no fumes from there or anything.
PPS I had just done an oil and filter change about 6 miles before the problems in case that effects it (and checked the dip stick that I did not over fill)

[bigherb]

Check the engine oil level if it is too high. If has increased then possibly the fuel pump diaphragm is leaking fuel into the engine. Then check the crankcase breather pipe from the engine to the air cleaner is not blocked/collapsed.

[InventEd]

Thanks BigHerb,

The oil breather goes straight into the air filter housing above the carb, so I dont think the fuel can get in that way (is that what you meant?). The breather pipe does not look collapsed and I can blow through it. I have to admit I have not sucked through it so it could have de-laminated and collapsed internally. I will check.

Engine oil is only half way between low and high marks. When I did the oil change I only put in 3 litres (500ml less then the capacity) so I don't think I have over filled.

[InventEd]

OK, maybe this is my eyesight. My friend tried following me and he thinks the smoke is white not blue. Is there a way to generate a lot of white smoke once the engine has heated up? I am assuming that could be a stuck needle valve or something poring too much fuel in?

Spark plug on cyclinder 4 is covered in oil but all 4 cylinders get 4-6 bar pressure.

Single twin choke Webber so I guess I will try and take the top off it tonight and see how the float chamber looks.

[marlinowner]

I had intermittent white smoke on an old Reliant Scimitar due to brake fluid being sucked into the engine from the brake servo.
Diesel in the fuel gives white smoke as well.