6 replies to this topic

[Keith Grendahl]

1275 A with dual HS2's. 1962 Morris mini, Austin America engine (1968).

When I bought the car it had an open breather system. The oil filler cap had a large bore pipe with a hose trailing behind the engine. The crankcase breather was also trailing behind the engine. Road draught system. Rocker cover was non-original alloy without a breather.

Oil would accumulate on rocker cover from oil filler gasket. Fitted a new cap without the hose but had several large breather holes. Engine runs fine but oil still accumulates on rocker cover. Tried fitting crankcase breather to carbs but too much air coming in the oil filler cap so it acted like it had a huge vacuum leak.

Fitted a new rocker cover with the proper vented filler cap, connected breather to the carbs via a y-piece. Did not change any settings on the dual HS2's other than increased the idle because it now idled low.

Lost a lot of power. Used to accelerate like crazy from 2500 rpm and up. Now it stutters on any attempt to accelerate and continues to stutter while accelerating. Cruises okay but it is not smooth, engine makes very slight rev changes on its own.

I did change a couple of other things while at the same time. I opened the spark plug gaps from about .035 to .039 (electronic ignition) and had both carbs off in to replace the heat shield. I don't think there is a vacuum leak I think it is related to what I did with the breather system.

Do I need to retune the carbs to account for the added gases piped to them? Or could it be that the engine is worn and there is so much blow by into the crankcase that it is forcing air into the carbs? Pretty confident that the engine has not had a rebuild since 1971 but also low mileage. Show/concourse car, maybe some type of racing here in the U.S. and then stood for nearly 20 years. Compression is 130 on all cylinders.

Keith

[jaydee]

Compression is low..anyway:
Sounds to me you're running too rich under load, check:
- Timing advance first
- Oil in the dashpot (probably too thick -flooding the engine- or too thin -but it will cause backfiring-)
- Air/fuel ratio, probably you need the needles to be reprifiled.
- Carbs balance.

[freshairmini]

Adding the breathers to a carb will affect the how it runs because of the extra airflow, same as if i was to disconnect the breathers from mine (these where connect since factory), it would then run rough.
You will need to re-tune your carbs.

[Keith Grendahl]

Thanks, I'll re-tune carbs and check timing. Needed confirmation that I should be able to get it to run better or if I should disconnect the breather.

[Keith Grendahl]

Reset mixture and balance. Same result, juddering on acceleration but would cruise fine when desired speed was reached. I just knew it had to be something I had changed so I disconnected the breather from the carbs, changed mixture to lean and richened a little at a time, reset spark plug gap to .035. No change in the condition.

Finally decided to take it for a run at 60 mph and check spark plug color. One cylinder was wet and fouled. It was receiving spark so I changed plugs between two cylinders and went for another run. Same plug was fouled in a different cylinder. Replaced bad spark plug and all is well again. Just need to readjust the carbs to run on four cylinders vice three.

I have never seen a spark plug go bad before. Must have happened when I initially opened the gap up. You would think that I would have noticed it when re-setting the gaps but they were all black and sooted from short runs at low speed that I just didn't see it.

I know better than to change more than one thing at a time so that it is easier to figure out where the fault might lie but sometimes I get in a hurry.

[Ethel]

How is it all plumbed together?

If the breathers are hooked up to the manifold, like the twin carb Coopers you could do with some sort of restrictor (Cooper's had the diaphragm valve) because they'll be lots of suction when the throttles are shut. If the carbs have a connection, like a single SU does, then one carb could be drawing off the other through the breather pipes.

[Keith Grendahl]

Single breather from crankcase to the carbs via a Y piece. Runs fine after I replaced the faulty spark plug. Carbs are balanced. With the engine at idle if I remove hose from breather the revs fall. With hoses connected if I remove the oil filler cap there is no change in revs. I feel a slight vacuum at the oil filler and it increases with revs.

Is there a problem with this setup? I think it is better than the open/unfiltered system I had.