I have a 67 standard model with a 289 4v with the original 4300 Motorcraft carburetor. I only got it running after a 15 year storage a few weeks back. It was running pretty good, but recently started idling real rough after the engine gets warmed up.
I did replace the lower carb gasket when I discovered a slight vacuum leak there. It didn’t seem to help. So I removed the top of the carberator and cleaned out the sediment in the float bowl, as well as blowing it out with compressed air.
The car runs worse now… Any helpful advice is greatly appreciated.
One thing I found out the hard way that the base gasket has to be for a 4300, if it is on original manifold, I bought a base gasket from a parts store thinking all were alike, wrong, the gasket didn’t cover all of the manifold and caused a huge vac. leak and caused it to run like crap. The gasket fits a Holley but was not wide enough for the Autolite.
You really need to know if you have correct vacuum (at least 18 inches of mercury) and, if not, figure out where the leak is. Do you have a vacuum gauge? Owning a Cougar almost requires owning a vacuum gauge in my opinion. It’s very hard to get good idle without decent vacuum and the Cougar has more potential vacuum leaks than most cars. And, fixing one may not have fully corrected the problem.
If vacuum is good then other areas to consider are timing and fuel.
A good way to find out if you have a vaccume leak is to, while the engine is running use a rag to completly cover the top of the carb. If you can not stall the engine there is a leak.
Check the bottom of the carb for sediment. If you find very fine brown power, you have found your first major clue. The fuel lines rust from the inside out. One thing the alcohol in the new gas does is dissolve all of the accumulated shellac that build up inside the tank. That shellac doesn’t atomize so it is like spray adhesive when it get to the carb and intake. It builds up all over the place. Experience has taught us that after the gas has sat for several years in an old tank it is cheaper to put in a new tank and fule line than to constantly try to fix what all gets gummed up when you try to run the car. Fuel filters are not effective at catching the really fine stuff.
I am assuming that you did all the usual stuff like new points rotor cap condensor wires and plugs. And you kitted the carb to replace all of the rubber parts and in particular the power valve and accelerator pump? After 15 years the old tank was empty? You did replace the rubber hoses in the fuel line at the tank, and where the front and rear lines meet, and from the end of the line to the fuel pump? New air filter fuel filter and a change of oil and filter?
Good advice on the vacuum leak. Check for those first. What Bill stated about the modern fuels is correct as well. I had almost the same issue with my 68 convertible conversion project and it turned out to be some vacuum leaks.
Steven
I removed the carburetor and found the gaskets on both sides of the spacer to be soaked with fuel. They should be relatively dry, correct?
The carb was rebuilt about 17 years ago when I had to move the car from Dads storage. I’ve replaced points, condensor, oil, and all filters. It runs good on startup, but as I kick it down off of fast idle, it runs terrible.
Well, thanks everyone for chiming in. You all have some good advice. Tonight I blew out all of the idle circuit passage ways. Sure enough, it runs great now. I think I need to play with the idle mixture a bit, but it’s running better than it has since I pulled it out of storage this Summer.