Moss Motors, Ltd

998 engine.  Accelerates smoothly to 50/60 miles an hour and cruises there with no issues - as long as the road is flat.  As soon as you hit a hill and place more load on the engine it starts to "misfire".  I place it in inverted commas as I am not sure this is what it is doing - but that's how it feels.  The following has been checked/adjusted/replaced - valve clearances, float, dashpot oil, points and condensor replaced with magnetronic, dizzy cap, rotor, spark plugs, carb mixture, timing (not sure if I got this right, hence previous post).

The problem occured before all these changes and persists.  Someone has suggested that the petrol/gas tank may not be breathing adequately?  Can anyone help?

Wow, you've covered all the possibilities that come to MY mind.

Testing the tank breather is easy, go for a high speed drive with no gas cap. If your car still "misses", it's NOT the breather.

Hey...one more thought.

Have you checked to see that your vacuum advance is working correctly? It may be hanging up somehow. Make sure that your vacuum line is intact and that the mechanism in the dizzy moves freely.

Good luck!

The more I think about this as I keep this thread in the back of my head, I must agree with Barneymg. Actually, I had the same thing happen to me with my Sprite! 

I too had a stuck valve. Initially it was only while on the highway. When this happened, I took my foot off the gas then hit it hard, and the valve freed-up. Eventually, it stuck solid and I had to re-do the guides.  

Seeing as how you seem to have done just about everything on the ignition side of things, have you thought about an air leak in the suction side of the fuel system?

According to the book of words, if you have an electric pump you can check for an air leak by disconnecting the fuel line at the carburettor and immersing it in a half filled jar of fuel. With the ignition on and pump running, if you get air bubbles you have a leak on the suction side of the pump somewhere.

This problem disappeared for a while - but reappeared about 2 days ago.  An interesting development was that with winter approaching my trip home was in the dark - so had the headlights on.  When I felt the drag/hesitation the head and dash lights went dim.  When the problem went away - the head and dash lights were bright again.  Interestingly too - the problem occured intermittently all the time - so irrepsective of whether I was climbing a hill or not - was just more noticeable climbing the hill as you need all that the 998 can give you at times :)

I did some basic checks when I got home, like the tension on the fan/v-belt, checked all earth points for tightness and cleanliness - all seemed ok.  Any other suggestions??  I am running an alternator - replaced the gennie about a year ago.

Just give you spark plugs another check over! I had a misfire recently and it was one of the plugs I had just replaced a week earlier...I had a crack across the porcelain right at the bottom...just a thought? I can't think of any thing else pal?? what was actually replace? and what was just checked?

Took out the whole system and took it to a distributor specialist.  They bench tested it for me.  I have recently converted to Lumention Magnetronic ignition system.  With the ballast on the spark is poor.  With the ballast off the spark is good.

Question:  Can I run this Lumenition system without the ballast?  Or will it damage the module?

Darrel,

You haven't been running the module itself from a ballasted source, have you? I don't think it was meant for that. Only the coil itself may, or may not, need a ballast. Do you have the instructions for the Luminition? Check them over carefully. If the spark is lousy with a ballast and good without, I think you have an answer to that part of it, at least!

Thanks motorbill.

The lead from the ignition is attached to one side of the ballast.  That side has the red lead from the module too.  The other side of the ballast goes to the coil.  And the black lead from the module to the other side of the coil.  We thought the ballast may be faulty - but two other ballasts gave us the same result.  So it seems to me that the module is picking up it juice directly from the ignition?  Car electrics not my strong suite :)

Darrel what year is your car again? If you are ballast I personally would bypass it and replace the coil with a 12volt one! usually the ballast on a Mini is the wire itself and only one or two were fitted with an acual ballast risistor. To swop over to 12v is easy find a swiched 12v feed on the ignition side (so it goes off when the key is out) and swop the coil...thats it. I wasn't aware Luminition did a 6v unit?

Oz

Thanks for all your help on this one.  I removed the ballast and put in a new set of ignition leads (2 had a higher than should be resistance), connected it all up.  Started her - on the first twist of the key she purred into life - having stood for over a week.  A quick adjustment of the timing and I was up and running.  No starting issues since.

Just waiting to see if the problem that originated this post re-occurs.  So far, so good.

It is a 1968 Mini Estate/Wagon/Traveller.  Not running 6V, running 12V.

I've been having the same problem with missing at speed (or uphill)  on my '61 mini 998. I just got it a week ago and haven't had time to get into the engine, but the symptoms sound the same. After cutting out at speed, could you clutch it and ease back in without the car missing or bogging down? Mine will run fine for just a few more seconds after I clutch it or downshift, then continues to bog down when I try to accelerate. Runs fine around town though.

Anyway, I just noticed form your other posts that you've been fighting the problem for a while, and I wondered which of your adjustments have been the most effective?, and are there any false diagnostics that I should I avoid?