All Small Six 65 Mustang 200 Need Help

[Dshak65]

Hi All,
Having an issue with my 200 L6 on my 65 mustang. Have had this car for about 2 years now and replaced almost everything on the 200 (Too much to list but includes new bearings, piston & rings). Although pretty stable vacuum, still had a bit of a rough idle so I decided to take the head off and have it redone by my local race engine shop. They Cleaned, Tested, reground the valve seats / valves, new guides and seals. Put the car back together and it was running ok but smoking. After further investigation they installed the short Valve guide umbrella seals on the exhaust valves with in turn was allowing too much oil to run down into the combustion chamber. I removed and replaced with the larger original seals and the car was running ok and no more smoke but still a little rough. The car now has developed a misfire. It is intermittent at idle but if you step on it, it pops and stumbles and cant seem to figure out why. I ran compression test and all cylinders were 176-181. I performed a leak down and all in the 96% range. The distributor is new, as well as plugs, wires, cap. The timing chain and gears are new with everything lined up correctly. The carb is new and was dialed. I can get the pop to minimize a bit by advancing the timing but wont totally go away. This is a Load-o-matic and the SCV and advance are working as they should. Fuel pump was replaced....... Yesterday I decided to take it for a drive to work some gas through it. I went to accelerate hard, couple of pops later then bang.. Got it back home through it up on the lift and there was a big hole through the muffler. I pulled the plugs, they looked like it was running a bit lean. I cant figure out what is going on....... Is it starving for fuel? I think the only way a hole in the muffler blows through is if gas has accumulated (Would that suggest it was running rich). I am at a loss....... Any thoughts??

 

[drag-200stang]

Could be a bad ignition switch. Mine went bad when the car was 5 years old.

 

[Dshak65]

Could be a bad ignition switch. Mine went bad when the car was 5 years old.

Thanks!

 

[B RON CO]

Hi, pull one plug wire at a time and see which cylinder is misfiring. Good luck

 

[Dshak65]

Hi, pull one plug wire at a time and see which cylinder is misfiring. Good luck

Thanks. I did try that but too intermittent at idle and under load with acceleration to get that to work. Every plug pulled impacted the way it was running. It’s Driving me nuts. Thinking maybe the coil is starting to go bad although I am sure the engine would completely stall. It’s bucking under acceleration and popping. Like it is cutting out.

 

[DON]

The coil might be a good idea. I’ve had two coils go bad within 6 months several years ago and from what I remember, symptoms were similar, didn’t fail completely, but drivability problems

 

[B RON CO]

Hi, put a vacuum gauge on it. Look up a vacuum test chart and see if it helps diagnose the problem. Good luck.

 

[Dshak65]

Hi, put a vacuum gauge on it. Look up a vacuum test chart and see if it helps diagnose the problem. Good luck.

That’s where my frustration starts to kick in. I tried Al most everything. Vacuum steady at ~20 but when the intermittent misfire happens it does drop for a split second then back to normal.

 

[mustang6]

In the old days this is when I think they would take one of those analog engine analyzers and connect to your engine. With those they could look at the quality of the spark to each cylinder and tell you if the misfire is happening on one cylinder (cap, wire, plug) or moving around (distributor, coil, switch, wiring). Don’t know if anyone can do that for the old cars these days. I’m also leaning to an ignition problem because of the muffler explosion- only time I ever had that happen was when I had a Duraspark 1 distributor that had an intermittent short in one of the wires in the distributor. It wasn’t so much that the engine was running rich as when the distributor shorted it would go a stroke or two without combustion and then the combustion starts up again- bang! Coil is a possibility in your case but don’t overlook a possible bad condenser capacitor in the distributor, even though new. Towards the end of when I ran points, condenser quality was getting really bad, I have no idea what it’s like today.

 

[B RON CO]

Hi, what ignition are you running? What plugs? Sometimes an engine just doesn't run well with certain spark plugs, and sometimes new parts are worse than the old ones. Good luck

 

[DON]

Thanks!

You could temporarily by pass the switch. That might save buying a switch. Do you have the old ignition parts you took off? Maybe try putting one at a time back on? For 30 bucks and having replaced everything else on the ignition system, a coil might be a good idea. If you do have points, it might be good to go with Petronixs. I would still try the old capacitor first. Coils can do weird things. I had a 70’s vintage John Deere garden tractor that didn’t like to start when hot, put an old mustang coil on it and problem went away.
One more thing, was it doing this before you started doing your restorations? If it wasn’t, it is probably one of the new parts. I have learned that if you have a problem after repairs have been done, go over what was done with a fine tooth comb
You might try calling around to old shops and see if anyone still has an old Sun scope machine?

 

[Dshak65]

You could temporarily by pass the switch. That might save buying a switch. Do you have the old ignition parts you took off? Maybe try putting one at a time back on? For 30 bucks and having replaced everything else on the ignition system, a coil might be a good idea. If you do have points, it might be good to go with Petronixs. I would still try the old capacitor first. Coils can do weird things. I had a 70’s vintage John Deere garden tractor that didn’t like to start when hot, put an old mustang coil on it and problem went away.
One more thing, was it doing this before you started doing your restorations? If it wasn’t, it is probably one of the new parts. I have learned that if you have a problem after repairs have been done, go over what was done with a fine tooth comb
You might try calling around to old shops and see if anyone still has an old Sun scope machine?

Thanks will try to swap out and see what happens. I did pull the head again just to check everything make sure no valves are sticking. Not really a big job. Things look ok new head gasket coming them will get back at it. Wonder is it possible that the cam bent.

 

[Dshak65]

Hi, what ignition are you running? What plugs? Sometimes an engine just doesn't run well with certain spark plugs, and sometimes new parts are worse than the old ones. Good luck

It was running ok prior with same plugs they are the ngk v plugs. Wondering. What’s the possibility that the cam bent? Is there an easy way to check without pulling it? I have the head off again wanted to check for sticking valves and make sure one of the guides didn’t slip. Just don’t want to have to pull the pan and timing cover again. Have that all sealed up nicely.

 

[frozenrabbit]

Zero percent chance you have a bent cam without catastrophic failure, it's the carb or distributor. Do you have a ground strap from the block to the body? Trace back the coil wire for burns or shorting.

 

[Dshak65]

Zero percent chance you have a bent cam without catastrophic failure, it's the carb or distributor. Do you have a ground strap from the block to the body? Trace back the coil wire for burns or shorting.

Thanks. That makes me feel better. Was thinking maybe it ended up with a mild bend somewhere but with good compression and leak down figured it was highly unlikely. Once I get the head back on and new muffler, I will work backwards and see if I can figure it out. Seemed like last time it actually fire up and idled pretty well then after about 10-15 minutes of running at idle you started to hear the miss from the exhaust. Even when it was cold without the misfire as soon and you went to step on it it would buck and pop.

 

[DON]

Sounds like it could be in ignition. The more you open the throttle, the more resistance there is at the spark plug, that make the spark go to the next point with lesser resistance. Check for white tracks inside cap, on plug wire, could be coil, condenser. As it heats up, resistance builds with heat causing same problem.

 

[Frank]

Thanks. That makes me feel better. Was thinking maybe it ended up with a mild bend somewhere but with good compression and leak down figured it was highly unlikely. Once I get the head back on and new muffler, I will work backwards and see if I can figure it out. Seemed like last time it actually fire up and idled pretty well then after about 10-15 minutes of running at idle you started to hear the miss from the exhaust. Even when it was cold without the misfire as soon and you went to step on it it would buck and pop.

It really does sound like weak spark. More spark energy is required as combustion pressure rises.

 

[Dshak65]

Thank you everyone for the guidance. Quick update: Finally got back to it last night and turns out the coil was the culprit. The resistance readings were within specs but once it ran for 30 seconds it would start to misfire (coil was breaking down with heat I guess). Put the old one back on and boom problem solved. Took the coil back and they are getting me a new replacement. Again appreciate all the responses and help.