Cmb 80 with mac carb

Drew St. Amant · Oct 6, 2024

I have some cmb 80s and I need a carb that can be flipped etheir direction and still open forward. I've contacted a couple carb manufacturers and all that I have been able to get in contact with have been out of stock and are not sure if when or if they will be again. My question is other than obvious problem of getting them to fit can a mac 84 carb run well on a cmb80 hr or has someone tried this before? It would seem that more people might be willing to let a few of these go where as a speedmaster or kre carb are much harder to get my hands on

timothy johnson · Oct 6, 2024

As you may already know the CMB 67/80 is the same block. The Mac 84 carb will fit with a little work. If I remember the bore for the MAC is larger. Hang in there for a bit, there should be lots of replies to your request.

Danny King · Oct 6, 2024

If you have the stock Cmb 80 carbs Mark Bullard Does a mod to them so the are More like a Mac. Price is good and they work.

Drew St. Amant · Oct 6, 2024

I did think of modifying the stock carbs to basically eliminate the cam feature for the low speed needle. It could be done in my lathe relatively simply, the main reason I was wondering about the mac carbs or any of the other aftermarket options is what Timothy mentioned with the bore being bigger.

Danny King · Oct 6, 2024

Drew St. Amant said:
I did think of modifying the stock carbs to basically eliminate the cam feature for the low speed needle. It could be done in my lathe relatively simply, the main reason I was wondering about the mac carbs or any of the other aftermarket options is what Timothy mentioned with the bore being bigger.

Make a new barrel and you can make the vote yourself.

Timbo Whalen · Oct 20, 2024

Danny King said:
If you have the stock Cmb 80 carbs Mark Bullard Does a mod to them so the are More like a Mac. Price is good and they work.

Think Mark refers to that as his 'barndoor' job.

Timbo Whalen · Oct 20, 2024

Drew St. Amant said:
I did think of modifying the stock carbs to basically eliminate the cam feature for the low speed needle. It could be done in my lathe relatively simply, the main reason I was wondering about the mac carbs or any of the other aftermarket options is what Timothy mentioned with the bore being bigger.

I think you'll find the stock bore adequate enough. Larger bore tuning becomes more difficult, and they don't like hotter weather.
You'll also get better response and more torque with std bore vs large bore.
Pushing the blowdown to high via raising exhaust port you'll wind up with a toggle switch powerband, and that'll kill a hydro setup, for the most part.

Cmb 80 with mac carb

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