Morris Minor Owners Club

I was investigating a noisy engine yesterday and discovered that I could block the air intake trumpet without stalling the engine.
Clearly I have an air leak somewhere.
I'm not happy with the way the engine behaves. It's in good physical order with no signs of age. It idles evenly has plenty of power at speed but feels rough, tight and noisy when revved - almost as if it's trying to cope with too small an exhaust pipe (spec: 1275 A+, water heated inlet, HIF44. Large bore twin box exhaust.). The car behaves like it's running lean but the plugs suggest the mixture is rich. Would this be indicative of an air leak? Also there is a smell of fuel at anything other than high speed but no visible leak up front. Timing and mixture have been set at idle and tickover is quiet and stable although there is a tendancy for idle to drop further when the engine is really warmed through. Carb is clean and dashpot free moving. I have a non-standard SU/Minor aircan arrangement which I have had a good look at and can't see any gaps but the airleak must be significant cos blocking the intake trumpet has NO effect whatsoever on idle revs. I'm wondering if the leak might be somewhere further up the intake system?

If its a non standard arrangement a picture might help.
I think some of the HIF carbs have an air balance pipe between the body and above the dash pot as well as connections for crankcase breathers etc.
If these have been plumbed in wrong you could get some odd symptoms.

What is non-standard is the arrangement to get the standard 1098 air filter can onto the HIF44. I have fabricated a spacer plate and gaskets to mate the two.

If you have some brake cleaner spray it at the manifold gasket joints if there is an airleak the engine note will change or stall if its bad
also what does it run like without the filter as the 1098 one could be a bit restricive on a 1275

The 1098 filter can has been modified by cutting off the inlet pipe and widening the hole that is left.

I seem to remember that the HIF series can suffer from strange fuel leak problems caused by the float needle valve (if I remember correctly) and that was why minispares brought out an updated version, it could be worth a look.
http://www.minispares.com/Product.aspx?pid=34063

Hmm, interesting. In the recent past I may have contaminated the float with dirty fuel (tiny rust particles). Would this be linked maybe?
When I looked at the carb although the venturi was clean I didn't check the float bowl. Could poor fuel atomisation be causing the running issues?

Hmm, interesting. In the recent past I may have contaminated the float with dirty fuel (tiny rust particles). Would this be linked maybe?
When I looked at the carb although the venturi was clean I didn't check the float bowl. Could poor fuel atomisation be causing the running issues?

Was that the structural rust of your fuel tank before you decided to flush it Pete?

No. I had flushed it very thorougly. But petrol, being a solvent, was finishing the job than drain cleaner and gravel had started. Then when I spotted the problem I had to remove the inline filter, drive 15 miles home and then replaced the tank.

Ahh very likely the floatchamber & jet will need cleaning out
if your still using a sandard SU pump the internal gause filter may also need cleaning out as well

Got a couple of HIF needle valves and gauzes here with O rings you can have one if you want pete?

The standard 1098 air filter assembly is FAR too restrictive to use with a 1275 engine - that's why it's struggling/rough etc. Try the car with NO air cleaner fitted for a check. Blocking the inlet at idle just means the pressurised fumes from the crankcase are sufficient to run the engine at idle !

The standard 1098 air filter assembly is FAR too restrictive to use with a 1275 engine - that's why it's struggling/rough etc

As previously mentioned:

The 1098 filter can has been modified by cutting off the inlet pipe and widening the hole that is left.

- with a 45mm holesaw.

Blocking the inlet at idle just means the pressurised fumes from the crankcase are sufficient to run the engine at idle !

A-ha! Thanks BMC.

OK all, I'll get under the bonnet and clean out the floatbowl and fule pump etc and report back.

Even modified standard air cleaner is hopeless - I tried it! It just doesn't flow the air - even with no paper filter in there. I tried the 'Mini' trick of cutting extra holes in the can - still useless. My car was pretty much as yours - unless NO filter casing fitted when it ran fine. It's now fine with a K&N 'replica' filter.

I'm not really short of power BMC. At 60mph you can put your foot down and he really does go as well as can be expected. It's the way the engine sounds - as if it's half worn. None of the sweet revvyness you can hear in minis for example. there's plenty of torque to get up hills with go to spare but it really does sound like it's running rough and stuff is fighting to get out of the exhaust. Actually now i remember that on the journey home from Stanford Hall it was worth travelling at 60mph because the engine sounded so much smoother than it did at any speed above 40.

Should I be looking to replace the needle?

Try it with NO filter or casing - then decide. Plug test by running flat out up a long hill - then switch off and coast to a halt - and inspect the plugs will tell you if there is enough fuel. White will be dangerously weak! Could be fuel pump - so check by pumping fuel into a pint bottle and measuring how long that takes. Your engine when flat out will be ~ 20 mpg - so at say 60 mph that means 3 gallons (24 pints) per hour - ie 1 pint in less than 2 minutes. If the pump can't do that then there's the problem. Check/clean pump filter and try again.