Runing rich?

Post by **ani** » Sat Jul 11, 2009 7:56 pm

Following the great work by the boys at the National who cleaned all the rubbish out of the carb and petrol pump the car is running really well:D ....... However I've noticed that when starting it required no choke at all

Prior to the clean out it needed choke for about 6 miles

Can I assume the mixture is a bit rich - it does smell a bit of petrol after a few minutes on idle.

Post by **d_harris** » Sat Jul 11, 2009 8:01 pm

Best, and most reliable way to tell is to whip out number 1 plug and see its colour.

If its a light tan colour its correct, black too rich, white too lean.

http://www.dansmc.com/Spark_Plugs/Spark ... talog.html

Post by **ani** » Sat Jul 11, 2009 8:22 pm

Of course - forgot about that. The plugs were all a good colour prior to doing this work but of course it might have changed since then. I'll have a look tomorrow. Are you going to Ringwood?

Post by **LouiseM** » Sat Jul 11, 2009 8:58 pm

Moved to 'mechanical' as not really 'general discussion'

Post by **bmcecosse** » Sat Jul 11, 2009 11:02 pm

But it really should need some choke for a cold start -even in this 'warm' weather - so it does seem to be a bit on the rich side - at least at idle position. Does the fuel pump 'tick' steadily when the ignition is on - but engine not yet started ?

Post by **ani** » Sat Jul 11, 2009 11:19 pm

When you first turn the key there is a brief spell of very rapid ticking (which it didn't do before) then settles into a normal sort of tick!

Post by **bmcecosse** » Sat Jul 11, 2009 11:23 pm

It should settle into nothing! No more ticking - or just very occasional tick. I suggest the float level is too high - or the needle valve is leaking, thus allowing fuel to flood over the jet - hence plenty fuel there for cold start. When idling/running - it 'may' use up the slightly leaking fuel, and so be fine !
To check - remove the bell - switch in ignition - look down at the bridge. Fuel should be ~ 1/4" below the bridge and NOT flooding over.

Post by **ani** » Sun Jul 12, 2009 8:59 am

OK and thanks - best to check this out prior to making any changes to the mixture. I'll also have a quick look at the plugs again. I do know that before cleaning everything out the plugs were good so it will be interesting to see if that's changed.

Post by **8009STEVE** » Sun Jul 12, 2009 5:39 pm

When we did the work at the national, we told you that we had found the pump to be sucking a bit of air.

Post by **ani** » Sun Jul 12, 2009 6:48 pm

Ah - I thought that bit got fixed. How do I fix that or do I need to??

Post by **bmcecosse** » Sun Jul 12, 2009 8:52 pm

Where can it suck air from ?? If the tank has enough fuel to cover the inlet pipe - it should not be able to access any air! If it was sucking air - it would chatter away nineteen to the dozen. Pump some fuel into a glass bottle - and see if there is any air coming through.

Post by **8009STEVE** » Mon Jul 13, 2009 7:51 am

We did a flow test and noticed air when the pipe was inder the fuel in the can!!!!!!!!!!!!!!!!!!!!!!!
Dont tell me to suck eggs!!!!!!!!!!!!!!!!!!

Post by **bmcecosse** » Mon Jul 13, 2009 8:28 am

So - where does this air come from ?

Post by **8009STEVE** » Mon Jul 13, 2009 8:42 am

We were in a field, working under the bonnet. We suggested the fuel line from the tank to the pump, the connection at the tank or the tank itself. We were not doing a full strip down and rebuild, we were helping out a fellow (Sorry Ani, I know you are not a fella) moggie owner who had a problem with her car.
Considering where we were, what tools we had the tempreture and all the other things going on, I do not think that we did a bad job.

Post by **ani** » Mon Jul 13, 2009 8:53 am

Good morning - and a great job it was. I just didn't realise this was anything significant! Once the carb and petrol pump has been cleaned out it drove a million times better on the way home

So what I really need to know is how to fix this air leak. Is there a good way to approach it? How important is it to get fixed. I imagine there isn't much point playing around with the mixture till this little problem is out of the way. Many thanks in advance.

Post by **LouiseM** » Mon Jul 13, 2009 9:20 am

We did a flow test and noticed air when the pipe was inder the fuel in the can!!!!!!!!!!!!!!!!!!!!!!!
Dont tell me to suck eggs!!!!!!!!!!!!!!!!!!

Calm down Steve. Too many exclamation marks are bad for the blood pressure

Post by **ani** » Mon Jul 13, 2009 9:32 am

Going back to the original question .................. although the car is running well it doesn't require choke anymore which made me wonder if it was running too rich and also the smell of petrol is more evident once first started. I'm going to warm up the engine and check the plugs anyway just to see what they look like. Sorry to be a pain:D

Post by **autolycus** » Mon Jul 13, 2009 9:42 am

Even if there is an air leak (and it would be one that allowed air to be sucked in but didn't let petrol pour out when the pump wasn't sucking), I can't see how this would affect the mixture. If a bubble of air is entrained in the fuel as far as the float chamber, it will immediately burst and a bit more fuel will be pumped in to compensate. An SU pump can pump, say 8 gallons/h, but an engine might only use a a gallon or so per hour pootling along, so there's plenty of capacity to include the odd air bubble.

Look for a fuel leak, by all means - at a penny for every two teaspoonsful, you know it makes sense, but to sort out rich running, do as Roy says and check the fuel level before faffing around with the adjusting nut. Then you can look at the subtle stuff - appearance of plugs, effect of lifting the carburettor piston, and that general "feel" of whether an engine's running rich or lean, which only experience will bring. Some will never achieve that feel - the world divides into those who can use a choke, and those who can't.

Kevin

Post by **ani** » Mon Jul 13, 2009 9:50 am

Many thanks - that now makes perfect sense

Can I assume I can check the fuel level whilst the engine is cold? I know what you mean about the "feel" and having driven the old Minis for many years and now Moggies its pretty similar. I'm not yet the expert in adjusting these things but I'm usually correct in knowing when an engine is running a bit rich. Another telltale sign is a slight run on once engine is switched off. Thanks Kevin for your input

Post by **bmcecosse** » Mon Jul 13, 2009 10:21 am

" and it would be one that allowed air to be sucked in but didn't let petrol pour out when the pump wasn't sucking " Well spotted Kevin. I was waiting for that to come up!
Check the 'bridge' with engine cold - just take the bell off - switch on and let the pump tick away. the bridge is the little hump in the base of the carb - with the jet sitting in the middle and slightly below the surface. Don't pull the choke - just watch to see what happens to the fuel. Car should be on reasonably level ground of course!