Power Loss at higher speeds

Post by **AndrewSkinner** » Tue Jan 23, 2007 10:19 pm

Hi I am new to this forum and have only just purchased my 1959 original Morris Minor 948cc.

It has been driving fine for a few weeks but problems with power have started to arise!

About two weeks ago I weakened off the mixture as it was way too rich then about a week ago I noticed that at about 3/4 revs (Of what the engine could do) all of a sudden it would loose all power and slightly slow down.
This problem got worse until the other day it was miss-firing and spluttering. got it home and plugs 3+4 were fairly black, cleaned them all up and it ran fine BUT still with the power loss problem at 3/4 revs.

this problem seems to slowly be getting worse. the engine has only done 55,000 - and has been verified, and doesn't get through a stupid amount of oil. also i cannot see any oil leaks from head gaskets etc??

What could be the problem. I am a student and use the car daily and am worried that it may be serous or I am damaging it further?

please help!!

Thanks Andy[/b]

Post by **ben739** » Wed Jan 24, 2007 6:00 am

it sounds like the head gasket is going.

Post by **bmcecosse** » Wed Jan 24, 2007 7:44 am

Could well be petrol starvation - you need to check the pump can deliver a constant stream of fuel - take hose off carb and direct it into a can - switch on ignition. Should be steady tick-tick and steady spirts of fuel. There can sometimes be a vacuum in the petrol tank - next time it does this - take the filler cap off and listen for a sharp inrush of air. But most likely it's ignition related - and since it all costs very little it's best to just renew the points/condenser/rotor arm/distributer cap and maybe also the HT leads. If the spark plugs are by their best - new ones too. But why did you 'weaken off the mixture' - what guided you to this conclusion ? If now of this works - check the valve gap settings and get an engine compression check to gauge general engine condition. It's unlikely (but just possible) to be head gasket problems!!

Post by **picky** » Wed Jan 24, 2007 11:54 am

the first thing I would do is adjust the mixture to back where it was before, as your problems only seem to have occoured after you weakened the mixture. do you have a colortune? they are a transparent spark plug that lets you set the mixture very accurately. Get one!

Post by **AndrewSkinner** » Wed Jan 24, 2007 1:11 pm

Thanks for all of your replies.

I weakened off the mixture because it was really to rich, i was getting bad mpg and there was always a lot of black mess over the floor behind the exhaust!

After i weakened off the mixture it seemed to pull away better and mpg shot up.

QUESTION: If the ignition was at fault and every now and then a spark plug would not fire or had a very weak spark, would this cause the spark plug to turn black??? I am worried that in cylinders 3+4 there is a problem with burning oil??

Would fuel starvation cause the engine to miss-fire???

Post by **Willie** » Thu Jan 25, 2007 4:06 pm

It is common to have spitting back from the carb if the mixture is weak so
this could be a clue. Did you use the lifting pin to readjust the mixture?
You could also check the free movement of the carb piston by removing the air filter and lifting the piston with a finger. It should lift right to the top and fall with a soft plop. If it is sticking on the way up then you need to clean the piston and its housing. Do NOT use abrasives on these items.

Post by **eastona** » Thu Jan 25, 2007 7:19 pm

I'd start with a good tune up as bmcecosse suggests. points, plugs, tappets etc, etc, then start checking the ignition timing, and only then the mixture. There's no point in starting with the mixture if you've got dirty or pitted or badly adjusted points, bad timing or any other dodgy ignition type thing. So give the engine a good check over for the basics.

I've tried these shortcuts

and I always end up going back to the basics after ending up thoroughly frustrated

the other thing to check is a worn jet or needle (usually the jet) in the carb. I found with my MG that I could never set the idle and then get the engine performing well at WOT settings because when it ran well at WOT, at idle it was rich. When the idle was adjusted right, it was lean at WOT. new jets cured that.

where are you?

Post by **bmcecosse** » Thu Jan 25, 2007 8:18 pm

One reason for a 'rich' mixture - is a completely blocked air filter! The Minor design doesn't help here - nasty oil ridden fumes from the rocker cover are drawn into the filter and plaster over the outside - sealing it off. To correct this richness - the mixture gets weakened off - which is fine at idle (for a while!) - but the air filter is almost completely blocking the flow of air - engine can't breathe - car loses power. Take the air filter out and have a look at it. Try the car with NO filter to see how it goes - although it's likely you will need to re-adjust the mixture back up to where it should be.

Post by **AndrewSkinner** » Thu Jan 25, 2007 9:52 pm

Today I replaced the Needle/seat kit in the carb as the old valve was worn an allowing to much fuel into the float chamber. This has fixed allot of problems e.g. fuel leaking out of the breather hole on the float chamber and there was a blockage in the valve that COULD have lead to fuel starvation at higher revs. after replacing this part this morning it ran like a dream! Everything was smooth, responsive and had plenty of power. I was chuffed and thought that i had fixed the problem,

BUT............

After driving the car to work, it again wouldn't pull away at all when cold and then when it warmed up it was sluggish, wouldn't go faster than 20mph in 2nd gear and was starting to miss-fire again

I ordered new:
1) Distributer cap
2) Rotor Arm
3) Condenser
4) points

I will fit these all tomorrow.

I am only 18, and do have a fair bit of experience from working on my dads Sunbeam Alpine but I have never done ANY work on the ignition. How do you 'set up' the points?? ANY help on replacing all these parts would be helpful

Post by **Peetee** » Fri Jan 26, 2007 6:44 am

Is the carb freezing?
Make sure the air inlet pipe is close to the manifold.

Post by **bmcecosse** » Fri Jan 26, 2007 7:40 am

Ahh - you didn't mention fuel overflowing from the float chamber!! Fit all thes parts - dead easy although you may find it easier (I do) to take the dizzy out fit the points and condenser on the bench - then refit dizzy - it's only two bolts and if you don't move the clamp then the timing will not be totally lost. Check the vacuum advance is working when it's out - suck the pipe (be ready to spit!) and you should see the base plate move round and there should be a good vacuum. If no vacuum (and obviously no baseplate movement) then it needs a new vacuum unit. Also put a little oil down inside the dizzy - on the bob-weights mechanism - and check it's all free to move when you twist the rotor arm. But DO check the air filter - and try without.