My 77 green mini with the 1275 mosquito fogger. :-[ The compression is 182/187 across the board. Valve guides look good so do the seals, spring type not o-ring. Plugs are not oil fouled. The block has a timing breather, fuel pump breather block, and transfer case breather. So it should have very little crankcase pressure to cause blow by. Yet this thing still smokes like a coal fired steel mill.
The carbs are 1 1/4 HS2s with out breather port for crankcase venting. None on manifold either.
If the oil control ring or ring land between it a second compression ring was bad would it cause this and still have good compression? The pistons are slipper style 21253/std 9.75/1 ratio 3 ring pistons, 2 comp, 1 oil.
Got any ideas? I hate pulling this lump out and apart to guess at it without a second opinion.
Yes it needs Hi-Test fuel and likes to have additive to handle the compression without spark knock or ping.
Do the breathers go to a catch tank or back into the induction system somewhere ? Does it smoke all the time, under acceleration or on the over-run ?
The fuel pump hole requires a special adaptor to use it as a breather or you end up with a pile of oil coming out... I'm guessing you're running an electric fuel pump.
Do a leak-down test, it may indicate where the trouble lies.
At the minimum you will probably need to pull the head off and have a good look - I've chucked a gudgeon pin clip on the 1150 lump, and while it still has decent compression, there is a groove up and down the bore which I know will cause grief eventually. No harm in checking the guides and changing the seals while it is off.
Alex, The breathers go to the atomosphere, not to the intake system. The fuel pump breather is the adapter with oil seperator gauze in the port, and vent line running thru left inner fender. All breather lines have small filters on the ends. It can idle all day with very little if any smoke. Put it under hard acceleration, smoke. Back off, no smoke until you hit the throttle again. Then James Bond would be proud of the smoke screen it lays out. 1275 uses press fitted pins with no clips. The unit has about 5000 miles since rebuild. Smoke started in the last 200 to 300 miles. Guess it has to come out for exploritory surgery.