I've had my '87 250 with a 351 for about 4 years. I know this is the 1980-86 forum but I think you guys have more in common with my carbed truck rather than the FI brethren. Anyway, I got the truck for next to nothing and is in good shape except fot a small rust issue (easy fix) and ongoing issues with the engine in terms of idling, rough idling, pollution crap. I installed a cat to get past the emissions test. If I have it bone stock I can get "collector" inssurance at about 1/4-1/3 the yearly rates. However, the pollution (Thermactor?) system is driving me nuts!!! It has been disabled but there is a problem with a particular piece; there is a set of 4 tubes that are connected to the exhaust manifold on each bank. These connect to a larger single tube and from there the left side connects with the right side and then onto somewhere. Yesterday one of the valves (?) above the single tubes broke off letting the exhaust escape into the engine compartment and making it sound like I had no muffler. I know my description may be a little sketchy but should I just get a new valve(?), block off both valve inlets, try to get back to orig., or what???? In additional the bugger is running quite rough, stalls out even after it's up to operating temp (which takes a long time). I need advice PLEASE!!!

 

That's the system that pumps air into the exhaust to help emissions. It can usually be taken off with no ill effects EXCEPT if you have smog inspections and they lift the hood. This system is very large and it's very obvious when you take it off.

If you do not have inspections, I would get new or used exhaust manifolds, and get rid of the whole thing. You can take the pipes out of your manifolds and put plugs in them, but they usually are very difficult to get out.

This system won't have anything to do with running problems.

 

Thanks for the reply. What if I replace that valve thingy and then just tie the left and right banks together? Any bad side effects? What about just plugging the holes where these valve thingys fit?

 

Amen to that! Those fitting rust in there something awful! I've been working on one and we've had no end of head-aches trying to get them out. We had to cut the pipes, and put an impact gun on them. Two came out (after about half an hour) and the other two broke off. We didn't even touch the other side. My suggestion would be to cut the pipes, fold them over and pinch them off.

Sam

 

Decided to remove those valves that regulate air flow from the Thermactor system just before it goes into the distribution log and the 4 lines into the exhaust manifold. Had to heat the bases where the valves screw into 4 times to maintain heat so the valves would back out; they were in there TIGHT! Plugged the with a 3/4 pipe thread plug. Also found a rubber cap on one of the carb tubes had rotted away. Replaced that and now engine is happier. Choke seems to work but stumbles a little from a standing stop even when the engine is up to operating temp for the first little while. Could the timing or idle setting be causing this? My dad once told the Carburator was latin for "Keep your hands off!".

 

Sounds like your idle air/fuel ratio is slightly lean and the shot of gas the accelerator pump gives when you blip the throttle doesn't quite suffice. If that is the case, and if your idle air screws are adjustable, turn them out slightly while listening to the engine's speed. What you are looking for is max RPM, and the best way to find that is either with a hand-held tach or a vacuum gauge.

Also, the tube/manifold that connects to the back of the heads can be removed if need be. The heads are taped 5/8 - 11 and you can put short bolts in there to seal them. I use bolts that are threaded all the way to the underside of the head and cut them off to about .4". Use some high-temp gasket sealer on the threads and underside of the heads and put them in after cleaning the head as the bolt seals to the head.

 

Good tip re: the short bolts. I'll make a mental note: "Shoulderless Bolts". Don't have to do that yet. Waiting for the verdict re: keeping it bone stock so I can qualify for "Collector Plates" with my insurance company. They said on the phone that if parts are obsolete from the manufacturer and it passes emissions then I could take off the non-functioning parts. Apparently the valves I removed are obsolete from Ford!