Smokey on start up

chrisb · Post by **chrisb** » Sun May 06, 2012 10:04 am

Hi All,
My AJS 1949 18 500cc, blows a lot of smoke after 1st start it goes away after running for a few minutes. It runs quite well after warming up. I have done around 500 miles since replacing piston,rings,valve guides and valves, also 20 thou bore. Any ideas would be appreciated. I removed exhaust pipe when it cooled down and noticed slight oil on bottom of valve stem, is this normal? Any help appreciated. Regards Chris

TommoT · Post by **TommoT** » Sun May 06, 2012 1:27 pm

Hi Chris,
excellent bike you've got there! First of all your fresh rebore, piston and rings have not yet bedded in. So there could be a little oil left on the cylinder wall, which clears after warming up. Also if several days go by between start ups, a small amount of oil could accumulate in the sump, better known as the dreaded wet sumping phenomenon. The return side of the pump will clear this pool of oil in a few seconds/minutes, but until this has happened some of it will be burnt/blown out.

So let the mileage go up and observe the situation, and the ride the bike as frequently as possible. But not too many short runs without letting the engine warm up properly.

chrisb · Post by **chrisb** » Tue May 08, 2012 3:44 am

Thanks for your reply, I'll take it on a longer ride this weekend
Regards Chris

Ian5913 · Post by **Ian5913** » Tue May 08, 2012 9:15 am

I have a lightweight 350 and mine does this on occasion. I think I am right in saying mine cannot be wet sumping due to its design. Anyway it appears to do it when the engine stops in a set position. I assume one valve is open and oil must get down the stem from the head into the cylinder. I have lived with it for many start ups and as you say it clears after a while. I assume in my case its valve guide wear. But as it says above it could well be new parts bedding in. Hope this helps Ian

bigwol · Post by **bigwol** » Tue May 08, 2012 9:42 am

I remember a similar post a while back, the concesus then was the engine stopping in a certain position if stopped on the valve lifter. I have this problem with my 16ms if stood for a while so fitted a cut out button fopr the mag to try to cure it. No idea if it's any better as it's currently in bits!

wilko · Post by **wilko** » Wed May 09, 2012 12:37 am

Huh? What difference would that make?It's still going to stop on any random position!

bigwol · Post by **bigwol** » Wed May 09, 2012 9:48 am

No idea to be honest Douglas but the older post seemed to lean toward the engine stopping with the exhaust valve open when stopped on the valve lifter. I was always going to fit a kill button anyway and as and when i get the old girl back together i'll let you know if it improves the smoking on start up issue.

dave16mct · Post by **dave16mct** » Wed May 09, 2012 9:58 am

Stop with the valve lifter, then bring it onto compression with the kickstart. Thats the best place to leave the singles.

TommoT · Post by **TommoT** » Wed May 09, 2012 4:06 pm

If prevention of wet sumping is the issue, it has long been established that it is best prevented with a pump plunger and bore in first class condition and frequent use of the bike. My G80 will stand for months with only negligible seepage.

Next, if the pump plunger is positioned in its most rearward position in its bore, the smallest area of oilways will be left open for seepage.

All this has been extensively discussed and adressed in this forum if you search through old posts. A solution has even been suggested to establish pump plunger position without dismantling it.