Symptoms in need of a diagnosis

[MGNoir]

I've got a stock '74 MG Midget with an ongoing problem I hope you all can shed some light on.

Let me just list the symptoms and what I've tried...

<ul>[*]Can sometimes run weak and rough under load. Hit the gas to accelerate and not a lot of zip. Put in clutch and no problem pushing up the RPMs[*]Bad gas mileage - about 15 mpg last time I filled it[*]Front plug consistently gets fouled. Black and wet. Replace the plug and the car runs a lot better until it gets fouled again.[*]Replacing distributor points has at times made it better for a while. Had to replace badly worn points after just 1 year. Actually not the points, but that plastic thing that pushes up against the square shaft - that plastic part got very worn down. See image below that shows where the wear was. [*]Have retuned the carbs several times to ensure it wasn't one of them running rich making the front plug be more fouled.[*]Have done a compression test and that looks good[/list]

So right now my intuition is telling me to just get a whole new distributor, that there is something wrong with mine that just replacing points doesn't fix - that something is making the points wear out and that's leading to inconsistent spark esp. in the front plug, which leads to that plug being wet/black + bad gas mileage + weak running. Something like the whole shaft is wobbly and making for bad wear and action from the points?

And if it was a case of replacing the distributor, any suggestions what to get? For cost and maintenance simplicity i've been eyeing something like the Pertronix flame-thrower

Thoughts?

Wear spots on distributor points...

 

[Trevor Jessie]

Certainly a good electrical system is important. Jeff at Advanced Distributors is a good source of help.

When was the last time you adjusted your valve clearance. The power problem you describe could also be caused by a sticking valve.

 

[Billm]

Did you grease the rub-block, change the condenser and spark wires?
Bill

 

[MGNoir]

Did you grease the rub-block, change the condenser and spark wires?
Bill

No yes and no.

 

[MGNoir]

When was the last time you adjusted your valve clearance. The power problem you describe could also be caused by a sticking valve.

Hmm haven't done this at all.

 

[jlaird]

May I suggest a bad dizzy cap. Of course that does not solve the bad wear on the points block but that may have just been a bad set of points.

A cap will give bad connection to one or more plugs causing just the symptons you describe.

 

[Trevor Jessie]

First order of business (if it were my car). New cap, rotor, points, condenser, plug wires, plugs, and adjust valves. This is all routine maintenance. Make sure dash pots have oil in them. Then check the timing, then sync the carbs, and set the mixture. Then resync the carbs and set the final idle speed as close to 850 as you can get it.

 

[Bruce_B]

I's also check that the pistons in the carbs are rising at the same rate. You could be having one piston running richer than the other, causing the plug to foul.

 

[jlaird]

Trevers got it, a thirtyfive dollar bill will give you a lot of peice of mind here.

However, that said I would think is a bad cap.

 

[MGNoir]

Forgot to mention i've replaced all the spark plugs and the distributor cap, plus points, rotors, condenser, plus repeated carb tuning and always check my dashpots every week. The only thing I haven't done so far would be the plug wires and valves.

 

[jlaird]

Oh God, tonite, after dark, start it up and look at number one wire, see a bit of fire on it? If not get ahold of it with one hand and ground your self see if it is leaking. Or better yet just change em all.

 

[bugimike]

If you are considering a dizzy replacement, I replaced mine a few years ago, and not wanting to go electronic, I got a Mallory dual point dizzy and have been happy with it ever since!

 

[Atrus]

For $200 or less, Jeff at advanced can rebuild your dizzy to better than new and put in a pertronix unit /bcforum/images/%%GRAEMLIN_URL%%/wink.gif I am just (anxiously) waiting for mine to arrive!

 

[MGNoir]

Spark plug wires all replaced - let's see what that does...

 

[Billm]

Be sure to put a small spot of grease between the distributer and the rub-block, just enough to make it stop "singing" when you spin the distributer by hand. Will make the points stay in adjustment a lot longer.
Bill

 

[jlaird]

A small dab usually comes with new points in a pill caseing.

Also a drop of oil in the top center of the Dizzy, should be a pit of cotton stuff in there so it does not leak back. This keeps the dizzy bearing lubed.

 

[MGNoir]

Bumping an old thread with the probable solution.

Jeff at Advanced Distributors has rebuilt my distributor for me, and reports that there was a lot of wobble in the shaft, which caused amongst other problems the rotor to contact the terminal associated with the plug that was always wet/fouled. Bad contact, weak spark, intermittent firing of that plug etc. Can't wait to get that sucker back and installed!

 

[jlaird]

Ahh, should be quite a difference.

Let us know please.

 

[racingenglishcars]

The drop of oil in the top middle is to keep the centrifugal advance unit lubed.

The grease in the tube that comes with the points is fine, axle grease is fine also. Either way listen to Bill, the rubbing block wearing is a sure indication that it hasn't been lubed. Just a little grease on the points cam will last a long long time. And even new distributors need a little grease on the points cam.

I guess since you replaced your plug wires already, it's useless to start it at night and look for the fireworks that come from bad wires. But that can definately cause a dark and fouled spark plug.

Another major cause can be oil leaking past the valve guide or rings. Fuel usually wont foul the plug, rather just make it black if it is firing (that is if you don't see clouds of black smoke behind the car). That is until it gets way too much fuel and stops firing. But then it will only be wet with gas, which dries off when exposed to the outside air. If it stays wet after taken out and allowed to dry, it's oil. And that comes from valve guides or rings.