Amal premier jetting for 4000' elevation?

Hello, I recently purchased a 75 MK3 and I am new to Nortons and Amal premier carburetors. The bike came from a sea level location, and I am located in Billings MT. We are at 3,500' with riding close by that exceeds 10,000k. I am hoping to gain some knowledge on jetting for these carbs at elevation. It currently has 220 main jets and definitely is running rich and bogs on higher in the revs. I intend to drop the needles and read the plugs when the weather allows, but I am hoping that someone on here can give me some ideas on jetting for a similar elevation.
Thank you in advance!

Kind regards,
Scott

Wireman said:

Hello, I recently purchased a 75 MK3 and I am new to Nortons and Amal carburetors. The bike came from a sea level location, and I am located in Billings MT. We are at 3,500' with riding close by that exceeds 10,000k. I am hoping to gain some knowledge on jetting for these carbs at elevation. It currently has 220 main jets and definitely is running rich and bogs on higher in the revs. I intend to drop the needles and read the plugs when the weather allows, but I am hoping that someone on here can give me some ideas on jetting for a similar elevation.
Thank you in advance!

Kind regards,
Scott

Click to expand...

Hi Scott, welcome to the forum.

"Reading plugs" went away with leaded fuel. The only time plugs color with unleaded gas is when it's OFF the map rich.
Sacred cows abound.

You'll need to lean it all across the range, take the main jets down a size (two sizes if your not scared and know when it feels lean)

Yes, drop the needles, all the way.
There are different cutaway slides to lean it more beyond that.

I like to go too far, then work back toward optimum.

Certainly, there are some mountain men who will come along soon with some empirical data.

I lived in Lake Tahoe for 5 years, lake level was 4500 feet. My final solution, because of the constant elevation change up and down, was to leave the carburetion as is and just run hotter plugs. At 3500 feet use the correct plugs. While riding up Kingsbury Grade to the lake I could feel the power dropping off as I climbed the grade. Hotter plugs would allow the plugs to stay clean for awhile longer. Much easier to change plugs than change jetting. Always carry a couple sets of plugs. When below 4000 feet use the correct plugs.

concours said:

Hi Scott, welcome to the forum.

"Reading plugs" went away with leaded fuel. The only time plugs color with unleaded gas is when it's OFF the map rich.
Sacred cows abound.

You'll need to lean it all across the range, take the main jets down a size (two sizes if your not scared and know when it feels lean)

Yes, drop the needles, all the way.
There are different cutaway slides to lean it more beyond that.

I like to go too far, then work back toward optimum.

Certainly, there are some mountain men who will come along soon with some empirical data.

Click to expand...

Thanks for the welcome and the quick reply. I appreciate the advice on the leaning and the slides. Ironically, the last bike i tuned for this elevation had mikunis and needed shallower slides to run happy. I don't think this one is that far off.
Cheers

seattle##gs said:

I lived in Lake Tahoe for 5 years, lake level was 4500 feet. My final solution, because of the constant elevation change up and down, was to leave the carburetion as is and just run hotter plugs. At 3500 feet use the correct plugs. While riding up Kingsbury Grade to the lake I could feel the power dropping off as I climbed the grade. Hotter plugs would allow the plugs to stay clean for awhile longer. Much easier to change plugs than change jetting. Always carry a couple sets of plugs. When below 4000 feet use the correct plugs.

Click to expand...

Great info, thank you. I never considered running hotter plugs up higher, I am going to look into that. Thanks for the help.