rough running 250 straight six

How are you timing it? The worst way to time an old engine is with a light, as the vibration damper on the crank often moves on the rubber over time.

Vacuum guage. Essentially, adjust to high vacuum. If you get a ping, back off in small increments until it stops.

Alternatively, you can either change the vibration damper, or pull a plug, turn the engine to TDC, and make a new mark on the damper to allow you to use the light.

I would just use the vacuum guage.

Vacuum gauge can get it close. short of replacing the balancer there is no way I know of to get it dead on the money. there is no timing chain, its gear to gear so that rules that out. I would imagine the carb is in pretty nasty shape internally, and minimum drain gas tank and replace fuel filter. There are lots of parts out there for that 250 performance wise if you know where to look. And even in stock form it will go just as fast as a 350, just takes a bit longer to get it wound up. Something else came to mind, the grease under the ignition module may have dried out, and your not getting a good ground. make sure the vacuum line to the advance is hooked to the correct port on the carb, and disconnected and plugged when setting timing (not trying to be insulting here, just not making any assumptions) Whitelightning

Don't assume anything. Check the entire ignition system, part by part. Make sure the distributor is installed with proper gear timing, or by dry timing. Check plug wires not crossed. Could be cracks or carbon in distr cap. Flush the entire fuel system and make sure gas is fresh.

Sounds like the timing chain is stretched way out severely retarding the valve timing which screws up the ignition timing cause the distributor is run off the cam. Remove the dist.cap and observe the rotor button while rotating the crankshaft back and forth....this will indicate how much slack is in the chain. Any slack is too much.........!

Key words "250 straight six" translation, no timing chain, gear to gear.

Whitelightning

Oops.....my bad

Thanks for all the help. I have been able to get the timing adjusted. I found several things wrong after going back a double checking everything. The #5 spark plug was broken where the porcelain mates to the metal. So needless to say no fire to #5. I also found several vacuum leaks, mainly ones going to the emissions canister. I've replaced the manual tranny, installed a TH 350, cleaned the carb, installed a rebuild kit, and upgraded the manual brakes to power. I should have the old truck on the road real soon. Thanks again for everyone's inputs.

Chris