Topic: 1975 cb400f main jet sizes

[plug1]

Why do these main jets run from size 80 to 98 w/ nothing in between. I'm currently running 80's but I'm a little lean and wanted to try the next size up. I'm sure 98's are way to big. Am I missing something?

[DarcyCB400F]

A stock air box perhaps?    You must be running pods to need 80's and it's still lean??

Stock jets are 75's.

[plug1]

Correct. Stock mains are 75. The 80's were fine w/ pods but adding a new exhaust w/ less restriction caused a bit of a lean condition. I was just wondering if I was missing something w/ these jet sizes.

[DarcyCB400F]

I am not a pod man or pretend to know anything about them BUT if you want more richness, have you tried raising your needle clip position?

[camelman]

plug1,

Where in your throttle position does the bike get lean?  Darcy had a post that TwoTired listed a graph showing which components of the carb are responsible for which ratio of throttle twist.  Once you know that, then you'll know which part of the carb to address.

Carb sizes in the range you are looking at come in steps of "5".  I have 85 mains in a 400f I'm tuning right now.  I might have to go up to 90s though.  If so, then I'll send you the 85s for what I paid for them.  Alternatively, you could just order a set through siriusconinc either on eBay or through their online store.

Camelman

[DarcyCB400F]

Here's the post Camelman refers to- Credit goes to TwoTired (aka TT)!!!

http://forums.sohc4.net/index.php?topic=87727.msg991728#msg991728

[plug1]

Darcy. not a pod man? You must not like tearing your carbs apart twice a week to try to tune them properly . Needle position is my next option but to answer camels question, there is hesitation/cutting out at higher rpm's starting at about 5500 - 6000. It's not much but I can certainly feel it. I'm also getting some backfire on deceleration which wasn't present before the new exhaust was installed. I actually referred to that chart before I posted this and thought mains were my best bet for the higher rpm but the backfiring I'm not sure about. i have to try that site you posted. I've been dealing w/ pjmotorsports.com but they don't seem to have 85's. Thanks for the posts.

[DarcyCB400F]

Darcy. not a pod man? You must not like tearing your carbs apart twice a week to try to tune them properly .

Are you kidding?  I had my damn carbs out three times in the last week trying to get them figured out! Holy crap am I gald that's all done now that it runs like a banshee!!! 

Your needle clip position is integral at mid throttle position so this may be your solution as main jets are mostly effective at WOT...

TT is the real carb guy here in this forum so I am sure he will chime in ( hopefully)! I would wait to see what he has to offer for sure. He has pointed out lots to me, so I may not have it right... TT  help??

[camelman]

Plug, you are off track by considering rpm. Throttle position will tell you what part of your carb needs adjustment. Check out the chart again.