87 half ton truck

[Kevcules]

I posted here before for my fathers truck (150 slant 6) on adjusting the carb and got a good response and worked good for a few months.
Now his truck is choking itself out when driving or idleing with the air filter in. When he takes the breather cap off , and filter out, it works fine.I think this was the original problem. He now drives with no filter or breather cap.!!! It seems like the exaust is plugged some how and the back pressure wants to escape through the top. There is alot of black soot on the carb and breather. We've never seen this before. There is a butterfly on the manifold but it's not seized and the engine sounds the same in either direction.Does this sound familiar to anyone??

[praisethelowered]

To check for an exhaust restriction, hook up a vacume gauge to the manifold and rev the engine up, the vacuum will gradually drop if this is the problem. If so, it's probably your catalytic converter. My truck (87 150le) could barely get up to 40 mph, I ended up removing the cat and it ran much better.

[Kevcules]

Originally Posted by praisethelowered

To check for an exhaust restriction, hook up a vacume gauge to the manifold and rev the engine up, the vacuum will gradually drop if this is the problem. If so, it's probably your catalytic converter. My truck (87 150le) could barely get up to 40 mph, I ended up removing the cat and it ran much better.

Thanks for the reply. I'll let my father know and we'll give it a try sometime soon I hope.
Kevin