big block ken

I just added a full bottle of Gunk Motor Medic Lead Substitute to the tank of my '66. It's to be mixed with 20 gallons of gas. But I probably had a half tank..

The car ran great at first, but later on, it wanted to stall and had an irregular idle that I could not tune out at the carb. Has anyone had a problem using this stuff?














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Nowhere Man

Why did you need it in the first place??? Sounds lik you need to fill the tank up and go for a long long drive

Frankie the Fink

Yup -- get that Snake Oil 'venom' out of your gas tank...and get a 'do over'...

big block ken

I think I'll drain what fuel is left in the tank to do it right.

warrenmj

I don't think I would drain the tank. Just fill up using quality gas, drive it and fill it up again at half a tank or even a quarter tank so you keep thinning it out. Do that a few times and it will pretty much be gone and it gives you a reason to drive the car!

Powershift

Then change the spark plugs and install a clean set. The additive you used will likely have severely fouled them.

Larry

GTOguy

What Powershift said. Likely the cause of your ragged running. The only lead additive to run is TEL 130, which is actual tetraethyl lead, and it is used for raising the octane of the fuel. No need to add ANY lead substitute or snake oil to today's poor quality fuel. That said, a small amount of ATF or Marvel Mystery oil added to gas will indeed help leather accelerator pump seals from drying out and will also counter the corrosion to zinc and aluminum carburetor bodies caused by the absorption of water with our alcohol-laced fuels. Where I live, you can not buy non-alcohol-contaminated fuel, so MMO is a good idea. It doesn't take much, though.

big block ken

I didn't drain the tank, but added 5 gallons of premium with octane booster instead. The plug from #1 cylinder looked fine, so I put it back in and figured the other 7 plugs are okay too. But it still runs like a cylinder isn't firing and stalls. Hmmm.

The only other change I made was I installed a new set of offroad N11 mufflers from Corvette Central, which fit fine. Until I get them welded to the original tail pipes I used collar type clamps which are leaking slightly. So I can't image a restriction and a lot of pressure was coming out of both tail pipes when I had it running (like sh*t) last night, before limping it home.

The distributor is tight, so I can't imagine the timing changing suddenly. I wonder if I have a defective plug wire? I'm thinking ignition problem now instead of fuel.

GTOguy

Pulling only one plug won't give you any real useful information. You need to have a game plan for diagnosis. If the car ran fine before the additive, likely you have a fuel issue. If it has a dead miss, you need a vacuum gauge to verify.....and then you need to walk the cap to determine which cylinder isn't contributing. My advice is to use rubber gloves and insulated pliers when you pull each wire from the cap with the engine running. If you have no idea what I am talking about, you should take your car in to a competent mechanic.

Vettrocious

How long had the 1/2 tank of gas been sitting in the car since you last drove it?

bb62

Actually, today's fuel is anything but poor quality. The quality is typically top notch pretty much anywhere you go (driven in large part by federal regulations). Now complaining about today's gasoline formulas is a different matter.

Mossy66

What made you add the lead substitute? It really should not be necessary.


Gerry

big block ken

The fuel is always fresh, since I take it out every weekend and to shows constantly. I do all of my own work, and have been restoring Corvettes (on #14 now) for 35 years.

It's just odd because I finished installing the new N11 off road mufflers and put in the lead additive (which I've used many times before without a problem) at the same time. Then I drove it to work about 5 miles away and it ran perfect. It sat in my parking lot for 4 hours, then after work I drove it straight to a local cruise. And that's when it immediately ran lousy. No warning. From great to crap.

Being the suspicious type, I can only suspect some spiteful activity by guys who were cutting the company lawn nearby. But I see no sign of sugar or anything discolored in the fuel tank. The primaries on the carb (vacuum secondaries) are pumping out fine also. I do have a spare identical carb that I can throw on. And I also thought about installing temporary (non factory braided) plug wires when replacing the plugs. I can't get it to run, so checking vacuum is out.

phil2302

Wait till dark and run the engine (hood open of course) and look to see if any ign wires are creating a visible arc to the engine or nearby components.
PS stop adding miracles in a bottle to your fuel. ☺

Mossy66

It's probably unrelated to the fuel additive then. You know the drill... check for fuel, air and spark.


Gerry

big block ken

That fear of not having hardened valve seats. The engine at 89k miles has never been out or apart.

Mossy66

OK. But that only applies if you run the engine under a hard load for a long time. Think boats at wot with a load for a long time, or a truck pulling a heavy load. Your car may be under a heavy load for a few seconds. No need for hardened seats or lead substitute for our cars.


Gerry

phil2302

If you are doing 10-15K mile per year then maybe consider adding actual TEL
The additive you put in is not lead. It probably isnt related to the missfire you describe and I doubt it has any benefit in providing valve seat protection.

Mossy66

I wouldn't. Some folks like to add it as an octane booster, i think. And you are right, it wont provide benefits to valve seat protection.

Do the current engines with aluminum heads have hardened valve seats?
I don't know... just askin'.

Gerry

phil2302

I dont add TEL but know people that do. Logic would make you think if the original engine heads were engineered to need TEL in the fuel adding some to non leaded fuel would be ok. Probably needless but ok.
One step further. Couple of folks I know have taken the heads off their engines and had the valve seats modified to supposedly run without issues on unleaded gas and they had horrible results. I would never recommend having heads reworked for that purpose.
Back to OPs original problem.
I would drain the tank and stop using additives unless it is a stabilizer for long periods of non usage.
Next I would change any fuel filters. After ruling out any fuel related issues I think it is time for a compression test and if it passes start chasing down the apparent ign problem maybe even getting rid of of the points and installing an electronic system.