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Discussion Starter · #1 ·
Hey friends,

My old 65 mustang (V8 289 with a new holley carb) is in trouble.

It was driving great for a year or so. A few days ago it had trouble starting. When it did start, it had a very rough and uneven idle, and very low power when driving - like it wasn't running on all 8 cylinders, felt like.

When i revved it in idle, it backfired and a lot of black gunk shot out of the exhaust (picture of the gunk on my driveway included).

It then idled OK, but there was A LOT of think white smoke and a strong gas smell - I might have flooded it with all the starting attempts, though.

I pulled a spark plug and it's very black, and oily (picture of the spark plug included).

I took an oil sample, you can see new oil in the shot glass on the left, and my dark-looking oil on the right.

Anyone have any advice on:
1) what could be the cause/problem of this?
2) how to proceed? How to i fix it?

Thanks so much to you all in advance!

Some more information to try and be as complete as possible*
  • as far as I know, the egnine was never rebuilt
  • the odometer says 25.000 miles, seller said 125.000 miles. No knowing how many times it really rolled around, though.
  • the carb was changed about 1.5 years ago from the original autolite 2100 to a holley 500 cfm street avenger
  • I had driven the car quite recently, most recently was a week before the issue. 3-hour drive and it drove like a charm
  • the oil is abouit a year old. I've driven about 1000 miles since the oil change.
  • i don't think the oil smells like gasoline, but i'm terrible at smelling things so not 100 siue :)
I'm pulling the rest of the spark plugs today to see how they all look individually. New ones have been ordered and are in the mail. I've also got a new set of spark plug wires sitting around, so I will take this opportunity to switch them out as well.

Once the plugs/wires have been replaced, I'm gonna try to start it, just to see what happens.

Basically my next actions next actions will be:
  • pull/inspect all plugs
  • put in new plugs
  • put in new wires
  • check float level (there's a little glass window on the side of the holley carb
  • If all the spark plugs look equally black/oily, was thinking about making the mixture a bot leaner too

After this i'll try to start her up, see what happens.

Any advice greatly appreciated! Thanks so much to you all in advance!
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1,823 Posts
Work on your timing before you ever start to monkey with your carburetor. Typically, "lean" or "rich" plugs always start with timing - not with carb problems.

Verify your damper hasn't slipped, check your timing marks, and make sure that your cap and rotor are in good shape! Then inspect your plug wires. If most of the plugs are okay, but a couple of them aren't, that may help you narrow the problems down. Only after you're certain your ignition's all perfect should you move on to fine tuning your carburetor.

Carbs are rather 'tolerant', and work within a fairly broad range. That is to say, even if it's not 'perfect' it'll probably run all right. Ignition is not nearly as forgiving! If you're off by a few degrees either way, your car will be well down on power, and potentially do things like foul plugs - or worse, burn things up. So start there.

Best wishes!

42,166 Posts
The oil on the upper part of the spark plug is from a seeping valve cover gasket. I'll bet you "dollars to doughnuts" that your camshaft sprocket has shed its "silent" coating of nylon and the timing chain has slipped a tooth or two.

Premium Member
9,509 Posts
Also, verify the choke plate is opening all the way within a few minutes of idling.
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1966 289 3-speed
2,354 Posts
Blown out holley power valve?
That's the first thing I thought of. Sounds like it was getting flooded based on your description of white smoke and strong gas smell. Did you let it sit and try again?

As woodchuck said, the oil on the threads of your plug is from the valve covers not inside. That plug does have some carbon build up though.
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