Main Jet

[moore020]

How much should I decrease my main if I would like to put my airbox lid back on? I have a 416, that runs great with a 172 main. I am thinking a 168 with the lid back on, any suggestions?

[Scro]

It would need to be less than that. I would say in the 150ish range.

[moore020]

I had seen a lot of people with similar setup running a 155, that just seemed like a big jump from the 172 to the 155, but maybe the addition of the lid requires that big of a difference in jetting.

[Scro]

Yeah, a lid really restricts the amount of airflow in the motor.

[honda400ex2003]

my guess would be to go down 6 sizes so a 165 may be close imo but i have never actually tried it. usually when i recommend i go 4 sizes with the lid off. let us know what you have when you are finished. I am interested. steve

[moore020]

Follow-up: I went from a 172, tried the 170, 165, and eventually settled on a 160. Running good now.

[honda400ex2003]

good to know! thanks for the follow up :D steve

[clemsonteg]

Whats your elevation? Just curious, I know generally a 150-155 is good for a stock bore with a slip on/filter, lid on or off is within that range as well. I know you are running a larger bore.

Steve-I know you have some general rules of thumb like above going from one size to another with different mods, what is yours on changing bore size?

[moore020]

I ride at about 700 ft.

[honda400ex2003]

usually i got around 12 for a bore size it seems. But on the other hand, all factors come into play along with the lid and such. I try to look at all of that before I make a judgement on it. I take 12 or so and go up or down from there with elev and temps. it could be as much as 20 and as little as 6 or 8 depending on where you are at. steve