351 carb

kenbob · Jul 21, 2019

Took my 351 on a 53 mile tractor ride yesterday. THe carb we had so much trouble with being lean is fixed. Have good power and smooth the tractor really goes. It runs smoothly at idle and under load, but when coasting or idling down there is lots of snap crackle and pop out the exhaust. Tried several adjustments on the carb but it hasn't seemed to help. Any advice?

Joe (Wa) · Jul 21, 2019

(quoted from post at 20:15:33 07/21/19) Took my 351 on a 53 mile tractor ride yesterday. THe carb we had so much trouble with being lean is fixed. Have good power and smooth the tractor really goes. It runs smoothly at idle and under load, but when coasting or idling down there is lots of snap crackle and pop out the exhaust. Tried several adjustments on the carb but it hasn't seemed to help. Any advice?

After fire in the exhaust is usually lean mixture.

kenbob · Jul 21, 2019

Thanks, At least I know which direction to go with the carb.

kenbob · Jul 21, 2019

joe, would you know which needle is too lean--Power or Idle?

kevinthefixer · Jul 21, 2019

If it's happening with the throttle butterfly closed, it's idle mix. A leaky exhaust manifold or gasket or headpipe can also cause that.

kenbob · Jul 21, 2019

Thanks, I need to recheck the manifold. I switched it from up flow to down flow and used new gaskets but i am a chicken when it comes to tightening old stuff...especially manifold nuts or bolts. Really don't want to twist one of those off. I may need to feel for leaks and retighten.

kevinthefixer · Jul 22, 2019

Hold a rag in the tailpipe while it's idling, or have someone else do that while you feel and listen.

kenbob · Jul 22, 2019

You probably nailed it. When I got the tractor last year I took it on a ride. It was lean then and had to run with the choke out. Since then we got the carb working by taking out the economizer valve and I did the change on the manifold from up to down. It ran great on short trips. I am guessing that is where the problem is. It probaby loosened up a little after some run time.

chuck machinist · Jul 23, 2019

I feel your pain when it comes to torqueing intake and exhaust manifolds. Stay within the specs, and if it continues to leak , you resurface ,and or replace with a gasket. CM. Gremlins no longer live in my shop! But they live just outside the door.

Joe (Wa) · Jul 23, 2019

(quoted from post at 21:55:43 07/23/19) I feel your pain when it comes to torqueing intake and exhaust manifolds. Stay within the specs, and if it continues to leak , you resurface ,and or replace with a gasket. CM. Gremlins no longer live in my shop! But they live just outside the door.

Manifolds usually have brass nuts so not common to strip the threads on the ferrous stud but they tend to thermal flex at a different rate than the stud and require retorque. Torque is 30 ft lbs on 300 G148 engine, about normal for a small Case engines.

Joe

351 carb

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