walbro hd-12 epa vs. hd-6

[InTheNorth]

Looking into the differences between these carbs and wondering if anyone has experienced a noticeable performance change between the two. Seems like whenever EPA is attached to something there will be a compromise of some sort. After viewing the parts diagram of both models it seems like there are a few things not the same. The high/low screws on the hd-12 are different with what appears to be a provision to work with the limiting caps although I cannot tell if the dimensions are the same between the hd-12 and hd-6 screws. More concerning is the two jets. First is an air jet( hd12-503943601/ hd6-503800401) and second is another jet( hd12-537003301/ hd6-503688201). Would it be worth changing these two jets on a hd-12 carb if this is possible. The carb will be used on a woodsported and decked 372 OE. Thanks in advance and all the best

 

[Funky sawman]

Looking into the differences between these carbs and wondering if anyone has experienced a noticeable performance change between the two. Seems like whenever EPA is attached to something there will be a compromise of some sort. After viewing the parts diagram of both models it seems like there are a few things not the same. The high/low screws on the hd-12 are different with what appears to be a provision to work with the limiting caps although I cannot tell if the dimensions are the same between the hd-12 and hd-6 screws. More concerning is the two jets. First is an air jet( hd12-503943601/ hd6-503800401) and second is another jet( hd12-537003301/ hd6-503688201). Would it be worth changing these two jets on a hd-12 carb if this is possible. The carb will be used on a woodsported and decked 372 OE. Thanks in advance and all the best

Hd12b works just fine in 98 percent of stock and ported 372,375, 365 whatever. I have seen some changes in top rpm power when using a 385/390 boot and carb conversion

 

[John235]

I believe the venturi is bigger on the hd12. I bought a used 372 with an hd6 and I replaced it with a brand new hd12 and it ran better/stronger. But also I’m comparing old, used to brand new.
But I would guess the bigger Venturi would help make more power.

 

[huskyboy]

The HD12 makes a bit more top end power vs the HD6 on a 372xp. At least in my experience. The venturi is larger.

 

[InTheNorth]

Thanks guys I appreciate the help!!!