hooked up smog pump...backfires (1 Viewer)

[hooter]

august '77 40 California spec with all smog equipment in place. PO let the belt break on the air pump and never fixed it. pump seized. In an effort to stay original and smogged, I've obtained a refurbished pump and attached a new belt. All systems are functioning on visual inspection.


First run out of the garage and I've got a new backfire on decel and on gear changes through the tailpipe.

Timing is good (arrow and BB line up perfectly).
currently running Aisan carb stamped august 1982....I have the original august 77 carb rebuilt and ready to go.
420 mmhg vac steady at the booster with no detectable leaks

Best i can tell, I have now introduced air into the exhaust system and 2 things are possible...
1) with the timing being good, i'm running too rich. Air, fuel,heat = kaboom out the tailpipe.
2) valve lash is off and i'm sending unburnt fuel out. or at the wrong time.

Other than rip the smog stuff off, where would one go from here?

hOOter

 

[1911]

All else being good, backfire through the exhaust indicates either the carb mixture being too rich, or a leak in the exhaust manifold/header.

If you're determined to keep it smogged, then download the 2F Emission Control Repair Manual and have at it - diagnostics for every system are in there. If you can't find it easily here on Mud, then PM me with an email address and I will send it to you.

I'm sure you know it's not required in Texas (for any vehicle 25 years old or older). You're not saving the planet by driving one of these old tractors anyway, fully smogged or not.

 

[hooter]

All else being good, backfire through the exhaust indicates either the carb mixture being too rich, or a leak in the exhaust manifold/header.

If you're determined to keep it smogged, then download the 2F Emission Control Repair Manual and have at it - diagnostics for every system are in there. If you can't find it easily here on Mud, then PM me with an email address and I will send it to you.

I'm sure you know it's not required in Texas (for any vehicle 25 years old or older). You're not saving the planet by driving one of these old tractors anyway, fully smogged or not.

Appreciate the reply.
I've had a suspicion of 'rich' since owner ship. (Starts way to easily, etc.) I've run about 500 miles on the current carb setup with new plugs. Will pull the plugs today and check how black and sooty they are.

I had the manifolds off and put fresh gaskets due to a hole the EGR cooler. I spent quite a bit of time inspecting headers and no evidence of a crack. They were flat with no gaps at the joining surface.


No interest in being a greenie hero. I'm more into the nostalgia of 'original'.

If I'm running rich under full power, no mixture screw in the world is going to adjust that out. Assuming the carb is clean, how does one lean out the mixture? Rejet the carb?

hOOter

 

[1911]

I had the manifolds off and put fresh gaskets due to a hole the EGR cooler. I spent quite a bit of time inspecting headers and no evidence of a crack. They were flat with no gaps at the joining surface.

Headers are very susceptible to pinhole leaks in the tubing; they always end up rusting out in my experience.

If I'm running rich under full power, no mixture screw in the world is going to adjust that out. Assuming the carb is clean, how does one lean out the mixture? Rejet the carb?

hOOter

Yep, changing the jets is the only way.

 

[Cat Scan]

Good advice from 1911 regarding the 2F Emission Control Repair Manual. It has been years since I ran a smogged 2F but I suspect there is an anti-backfire valve in the system. Just a guess on my part as I had the same issue running a SBC pump engine and suddenly picking up a backfire. New valve and the problem went away. Just a guess, might be worth looking into. Good luck.

 

[hooter]

Good advice from 1911 regarding the 2F Emission Control Repair Manual. It has been years since I ran a smogged 2F but I suspect there is an anti-backfire valve in the system. Just a guess on my part as I had the same issue running a SBC pump engine and suddenly picking up a backfire. New valve and the problem went away. Just a guess, might be worth looking into. Good luck.

I had yet to consider the ABV.....
one more thing to check and probably replace.