Just got nice Stang but fouling plugs

[Red65Coupe]

Hello all! Im new to Classic Mustangs but consider myself a pretty good mechanic. Ive only worked on new cars though and am not used to distributors and adjusting timing.....and these carbuerator thingies.
I just bought this absolutely beautiful 65 coupe that looks awesome and has a recently rebuilt engine in it that is really clean. But it keeps fouling the plug in hole #6. It gets a nice carbon build up on it until it actually bridges the gap. Then the car runs like poo on 5 cyls obviously. The other plugs look ok. The car doesnt smoke. It fires right up but seems to idle rough. The lady I got if from very rarely drove it. I dont think shes driven at all in several months. She did tell me however that before she put it up for sale she had a complete tune up done to it including a new distributor. So I guess I just need to know what to look at first. I was thinking that maybe its doing this from lack of driving it and the rings are a little gunked up. But like I said... Im new to these engines. Funny how I would feel more comfortable on a late model car than these relatively simple older engines. Any help would greatly appreciated.

 

[mustang_65]

Assuming you've already checked the plug and plug wire for spark or just replaced them, I'd replace the valve stem seals. I had that prob. in three of my six cyls, and $11 worth of seals fixed the problem immediately.

 

[Red65Coupe]

Thanks for the info. Yeah I just replaced the wires and plugs to start. Is there a way to make sure valve stem seals are the prob? Ive never had to replace valve stem seals... how involved is the install? Thanks for any help!

Assuming you've already checked the plug and plug wire for spark or just replaced them, I'd replace the valve stem seals. I had that prob. in three of my six cyls, and $11 worth of seals fixed the problem immediately.

 

[PoliceInterceptor]

I would say run a compression test, wet and dry. If it is good and they are oil fouled, replacing the valve seals might help.

It is not hard.

Just remove the valve cover.

Remove Rocker arms (sorry forgot that)

Apply air to the cylinder you are working on (compression tester hose with the Schrader valve removed works well.) to hold the valves in place.

Remove valve spring.

Remove old seal

Install new seal,

Replace valve spring,

Move on to the next valve.

Course I ran my old truck around for weeks with no valve seals at all, and it didn't foul plugs.

 

[mustang_65]

On at least MY stang, changing the valve stem seals made a difference like night and day. As above, remove valve cover. Remove rocker arm assy (just a few bolts). I didn't have compressed air or a plug fitting, so I turned the engine by hand (plug removed) til the piston was near the top, then I crammed some clean rope into the cylinder to keep the valves from dropping when you unclip them. The biggest problem for me was that I had to buy a spring compressor. Compress a spring, pry out the hemispherical valve clips, pull the spring off, pull the old seal off (my old ones were hard as a rock) slide on a new seal, replace the spring, replace the clips, then do the other spring for that cylinder.

 

[PoliceInterceptor]

Oh one other thing,

Try to make sure you get all the old pieces of valve seals out. They can clog the drainback holes. In fact if the drainback holes are clogged, that could contribute to your problem.

Valve seals will generally smoke on initial start up in the morning as well.

 

[65shlbycln]

congrats on the new car. and welcome

 

[Red65Coupe]

Thanks for all the help guys. Im going to take on this project next week sometime. Ill let ya know how it goes. A couple more details I wanted to share though are.... the plug is only getting fouled up on one side. One side clean....other side thick with junk. I dont know if that means anything but thought it was worth mentioning. And since its seems to only be number 6 cyl with the problem should I just replace those 2 seals or would it be foolish to get in there and not replace them all? Thanks again!

congrats on the new car. and welcome

 

[mustang_65]

I'd replace them all, if you've got the time. The seals come in a set anyway, and then you only have to deal w/ the valve cover gasket once. My plugs also tended to be more crudded out on one side than the other. Whether it has to do with oil oozing down only one of the valves and not the other, I don't know.
I found a magnet useful to pick up the retainer clips when they're loose, to avoid clumsy, oily hands dropping them in bad places. And you need to know that the springs have to be compressed as far as possible to get the clips loose easily. It takes a little practice. I compress the spring, then work around the clip with a fine flalthead screwdriver, but you also need to "break the clips loose" a little with a good whack from a hammer/screwdriver. The clips go down about 1/4 inch; something I didn't know the first time I tried it.

 

[RGS0907]

I would say run a compression test, wet and dry. If it is good and they are oil fouled, replacing the valve seals might help.

Also, get yourself a vacuum guage tester & follow the directions. Between a compression test & the vacuum guage test, you may be able to pinpoint your problem for sure before you start changing seals.

Does the carbon build-up look oily or is it fairly dry?

 

[Red65Coupe]

I just wanted to send out a BIG THANKS to you guys for helping me out with this. I decided to go ahead and change those valve seals about a week ago now and my plugs still look great! The job wasnt hard at all. Just a little tedious. I was sort of worried when I pulled the old seals off since they really didnt feel to bad. They were still quite pliable. I guess they need to be pretty precise though cause the car is running great since I put the new ones in. Before it would foul the plugs in under 50 miles. So far ive got 300 miles and the plugs look great. Thanks again! It would have prbably taken me a while to figure this out on my own.

Also, get yourself a vacuum guage tester & follow the directions. Between a compression test & the vacuum guage test, you may be able to pinpoint your problem for sure before you start changing seals.

Does the carbon build-up look oily or is it fairly dry?

 

[RGS0907]

I just wanted to send out a BIG THANKS to you guys for helping me out with this. I decided to go ahead and change those valve seals about a week ago now and my plugs still look great! The job wasnt hard at all. Just a little tedious. I was sort of worried when I pulled the old seals off since they really didnt feel to bad. They were still quite pliable. I guess they need to be pretty precise though cause the car is running great since I put the new ones in. Before it would foul the plugs in under 50 miles. So far ive got 300 miles and the plugs look great. Thanks again! It would have prbably taken me a while to figure this out on my own.

It's always great to read that the problems posted here actually get resolved!