Engine Sputtering Heavliy, help!

[4BritishEyesOnly]

I'm having issues with my Mini's engine. There is heavy sputtering under load/acceleration.

Tuned it up a month ago, checked compression and it was low in cyl #3.

Drove it every other day or so since then, about 100 miles total.

Took it for a drive last thursday and it started to sputter under heavier acceleration, it's worse at lower engine speeds. This gradually got worse over the course of my drive (half an hour total). Took it out again the next day and barely got home. The sputtering seems to happen whenever the engine is accelerating/under heavy load. At a constant RPM it seems fine. It will sputter even when revved in neutral.

My mini is an '89 998cc A+ engine - non-electronic distributor.

I have checked the following:

Reverted to old plugs, no change. When I removed the current plugs they were heavily fouled. Running on the old plugs for a few minutes fouled them too.

Checked my points and gap. They seem fine.

My distributor seems tight, won't turn (so i'm assuming timing is good). I don't have a timing light.

The 3rd cylinder seems to be detonating poorly. At idle you can hear a weak detonation. If I remove the spark plug wire from this cylinder the bad detonation drops out, but it keeps on idling without much change. If I remove any other wire, the engine stalls.

Tried switching wires between 2nd and 3rd plugs, no change.

Did another compression test. 3rd cylinder builds compression slowly and to a lower threshold than the other 3 cylinders. A teaspoon of oil in the cylinder remedies the problem temporarily. Assuming it's the rings/cylinder wall. I doubt this is the cause of my poor engine performance since it was low a month ago and the engine ran fine.

Choke doesn't appear stuck.

Coil is relatively new, connections seem good.

Distributor is relatively new.

Tonight I'm going to try putting the old points/condenser/distributor cap on.

Outside of that I'm stumped. Any thoughts/suggestions?

[mascher]

Number one is to check the oil in the carb damper. Although that doesn't explain the fouling. It's possible that you have a sinking float or a leaking float bowl valve that is causing the car to run rich.

While it is possible for a weak ignition to cause spark plug fouling I would have expected a different set of plugs to fix the problem for a little while. I restore fouled plugs by cleaning them with a fine wire brush and then burning off the old fuel from the electrode end with a propane torch. Don't overheat them, just burn off the old fuel.

Kelley

[GreenThumb]

Don't overlook your coil sometimes they go bad.

Steve-

[4BritishEyesOnly]

Looks like it was my points after all. I didn't see they were burned until I pulled them. Thanks for the help.

[4BritishEyesOnly]

My mini is running bad again...
After changing the points it ran really good for 20 miles or so. Now it's experiencing the same problem again.


Checked the timing, it's spot on.
Checked the gap with a dwell meter.
Tried my old coil which works - no change.
Put in old distributor cap, rotor, another set of new points, condenser - no change.
Checked the vacuum advance, seems good.
Took apart the carb, nothing seems unusual there, plenty of gas in the float chamber.

It seems to sputter throughout the rpm range, the more gas you give it, the worse it gets.

[skip]

Another trick that you might try is to take one of your now spare plugs. Ground it out with a pair of insulated pliers while someone cranks over the engine. If you have properly functioning ignition system you should see a blue spark and hear a crisp snap the crisper sound the better. Weak spark, look at condenser, coil, plug gap, points gap. If they are good get an ohm meter and check your ignition wires including the coil. Any carbon arcing inside the cap?

Do you have an auto parts store who can put a load test on the coil you mentioned that it was new, while they are at it have them check the condenser. (Those are getting harder to find, they just want to sell parts anymore rather than help you get a motor running right with what you already have.)

Then move on to the fuel system, do you have a stock fuel pump or some sort of larger aftermarket electric pump? Have you or anyone else changed anything in the fuel system? How does the air cleaner look? Kelly pretty much covered fuel system, (and very well I might add.)

Systematically go through each system, changing and checking one element at a time. Run the car around the block, check all four plugs, keep looking until you find the culprit. Usually it is something really basic, then again sometimes it isn't!!!!
It sounds like you are looking at all the usual suspects, you just might have to eliminate them one at time.

You mention no timing light. Back in the day, we used to use an AM/FM transistor radio to time a motor pretty accurately. If you have a portable AM radio it might work not sure, haven't tried it in years. What we used to do is get No. 1 cylinder on TDC, loosen the distributor hold down, have a buddy switch the ignition switch on. Next move the distributor back and forth slightly until you hear interference on the radio's speaker, which is the points opening and closing. Turn the distributor until you just hear the interference. You should have it close enough that the engine should run pretty decently.

[4BritishEyesOnly]

Hmm,

Spark seems good.
I have 2 working coils and swapping them makes no difference.
It's the stock mechanical fuel pump. Doesn't look like anyone has changed anything. There's plenty of fuel in the float chamber.
Runs the same without the air filter.
Got a Timing light and timed it.

Anyone know of anyplace I could take it where someone could look at it? I'd call Chuck but he's gone for another month.

[Mark]

Hi!
Sorry it's being a bugger for you. I haven't read everything written already really carefully, but, just in case, could it be vacuum line related? Can you have it running and monkey around with vacuum lines, perhaps even spraying some wd 40 or starting fluid ( very carefully ) on the vac lines, carb and inlet manifold, and their connections?
Finally, I realize you've eliminated that set of points, but could it be that the new set just put in are failing (intermittently) again? Do you have a spare set you can put in to try and see if (per skips recommendation) you can eliminate that from your "equation".
As for a good fresh set of experienced eyes, I would recommend James Thompson. He's South, but he's good. I believe he's JamesT.
Please let us know what you come up with.
Best of luck, and,
Best regards,
MSH

[4BritishEyesOnly]

Thanks Skip and Mark (and everyone else). I tried another set of points and checked the vaccum, no luck. I sent a PM to JamesT so hopefully he can help me get it running right.

[Mark]

I had a thought, could it possibly be the 12 v wire to the coil being intermittently "breaking" or opening with movement?
Best of luck, and,
Best regards,
MSH

[4BritishEyesOnly]

Thanks for all the help everyone, I finally figured it out! It was my plug wires all along. They appear quite new and I tested the only good one the first time I ran through everything. Just installed new ones and it makes such a huge difference. I have roughly 50% more power at lower RPMs than when I bought the car.

Thanks again, Time for me to go for a cruise!