Morris Minor Owners Club

My moggy has been having problems with many things lately!
The first one is that the spark plugs are overheating and/or pre-igniting, i'm worried about the cause, cure and possible damage to the pistons. Another is that it won't stop pinking, no matter how much i tune it. What could the cause be and how do i fix it? please help!!!

Sounds like you are running VERY lean, and/or have your ignition FAR too advanced.

Which engine is it, and is it standard, also what year?

Has it just started doing this?

Have you tried running it with the choke pulled out to see if the pinking stops?

when you say:

no matter how much i tune it

What have you been trying?

Another is that it won't stop pinking, no matter how much i tune it

As Cam says what have you been doing, have you recently serviced it changed petrol type etc

i haven't changed anything in the engine recently, it is a 1971 standard engine, 1098cc. I changed to unleaded about 2 years ago, if that makes a difference.

No, it should not make a difference at all.

Right. First, check the timing to make sure that's set ok.

Then have a check to see that all the mounting bolts/nuts are tight around the carb/inlet manifold.

Take the carb dashpot off and have a look at the jet, it should be a few mm below the 'bridge' of the carb where the dashpot piston rests. If it is flush with the bridge, then adjust the mixture nut underneath the jet until the jet lowers.

If this is all OK, then you must have an air leak somewhere. Check the vacuum advance pipe for leaks and where the carb mounts to the inlet manifold and where the inlet manifold mounts to the head.

Let us know what you find.

Just a couple of additions to Cam and Kevin's thoughts -

What spark plugs are you using and what type of use is typical (e.g. long motoerway high speed - pottering around town?). The "normal" plugs are a compromise between the types of use - it's possible that you may need to move to a slightly different grade (usually one up/down).

Based on my experience, is it actually pinking you're hearing? Could it be a tappet type noise rather that the pinking?

Colin

I have look into the problem more closely. The engine starts fine and runs fine with seemingly full power until the engine reaches maximum water temp and oil temp power goes down slightly, less responsive at the throttle, it idles unevenly and pinks lightly at acceleration. The sparkies indicate overheating as they are whitish and blistering. Last night i had the carb off and used instant gasket to try and stop any air leaks. The car does run on a SU HIF38 carb. mu0u207b,

The car does run on a SU HIF38 carb.

Is anything else not standard as I assumed you had a standard engine.

What is the carb breather connection (close to the fuel inlet/overflow but sticking up slightly) connected to?

Sorry, my girlfriend initially posted the help message- shes better at this than me but not so technically minded!! The engine not all standard except for the HIF carb with water heated inlet manifold and electronic ignition. I did notice the other week that the coil was getting very hot to touch, could this be a possible cause. The carb breather is connected to the crankcase breather pipe and is assumed to be air tight as it is only 6 months old.

Have you done the above checks? If so, what have you found?

It's very difficult to diagnose a problem accurately without seeing the car, so we have to start somewhere!

Ive had the carb off along with the inlet manifold and made sure the surfaces were flat and clean and reassembled with instant gasket. That changed nothing at all- no better or no worse. Ive used colour tune to check the mixture on the plugs at idle and the mixture then seems to be ok. I have played around with the timing, varying it to optumise power but this has no effect on the pinking problem. The vacuum advance is brand new as the other one was punchered and initially i thought that this was the fault.

If this problem is only occuring when the engine gets up to temperature then I wonder if your bi-metallic mixture compensator is faulty in the carb base? Have you tried using the colourtune when the engine is hot? Have you got the correct needle in the carb and have you tried a different carb?

I havent tried using the colour tune when the engine is up to problematic temp. The carb uses the correct needle as specified by an article inminor matters, i think its an AAU needle. I certainly think it is worthwhile looking at the compensator and whether it is faulty, although i have retuned the engine when it runs badly, including enriching the fuel mixture with no improvement. I assume that if the compensator was faulty that this would have made a difference.

I would suspect the carb and try a different one. Then at least you can narrow down your search.

I assume that if the compensator was faulty that this would have made a difference.

It should have, but I had a carb once (HIF44) that would not adjust the fuel mixture beyond a certain value due to the screw/jet adjust section being damaged. Maybe this is the case here?

I would definately recommend changing the carb and trying again.

I have noticed that when trying to adjust the mixture that i can weaken it to such a point that the engine almost stalls but cannot over enrich the mixture so that the engine also almost stalls.

I have had that situation twice. Once when I had the faulty mixture screw and once when I had a massive air leak due to the breather being open to atmosphere.

Have you tried undoing the breather connection and physically blocking it at the carb then trying to richen the mixture, just in case there is a leak?

Also have you tried looking at the jet (with the dashpot & piston removed) to see if it actually IS lowering when you turn the mixture adjusting screw?

Ive just had a quick fiddle with the car, to try and get to the bottom of the problem. When the engine reached problematic stage and started to idle unevenly I disconnected the vacuum advance pipe at the distributer end whilst the engine was running, the engine revs picked up and the running was alot smoother, yet if i put my finger back over the pipe, still connected to the carb, the revs dropped and it idled unevenly. Is this a normal situation. I had tried to fiddle with the mixture strength and the timing but this did not increase the engine revs but only worsened the problem. Any suggestions, could what ever causes this increase in revs be the cause of the pinking??

Odd. if you open the pipe to atmosphere you effectively are leaning the mixture out. If the idle increases then it sounds like it was set too rich! Which is not the problem you say you have.

It sounds like you have set the mixture rich and it's leaning out later on for some reason.

Is the engine 'hunting' (revs sounding like - drum drum drum..... ) if so then you are running rich.

TRY A DIFFERENT CARB OR TRY THE SUGGESTIONS MADE ABOVE!!

disconnecting the vac advance at tickover will remove the timing advance and make a small air leak.
However if the biggest change comes from closing off the air leak which made it chug again, it sounds like the mixture is too rich.