Topic: Carb tune/ jetting questions

[Psychonaut]

CB400f. Stock needle height, 21mm floats. Carbs are perfectly clean.

I have been trying to get my AFR perfect. AFR was high 12.8-13.5 at cruise. Wack it and it would go lean for a second then go. Once going good around 7000+  it would bounce around high 13's before settling around 13.3-13.5 to redline. I wanted to get it around 12.8 at WOT so I went from a 75 main to an 80. Now I am 11.7-12.3 at cruise and right about 13-13.2 at WOT. There is no stumble and it just goes when wacked at any RPM now and the WOT is better but the problem is going larger on the main richened up my cruise to 12.0. The bike runs perfect but I know that cruising at 12:1 is going to foul plugs, waste gas and make my buddy's eyes water.

Here is my question. I was under the impression that increasing the main would mostly effect WOT. In my case it effected cruise more.  I could try lowering the needles and see what that gives but I was hoping someone could give a little insight as to the rich cruise and only slightly richer WOT before I pull the carbs.

[bjbuchanan]

The mainjet has most of its effect towards WOT but the effect is noticed all around, just less important. I'm sure someone will pull out the cute little chart to dispute me but put a set of 140's in a stock 750 and watch your eyes burn at idle from super richness

With that being said, if you are using stock carbs you have just about nailed it really. To perfect it more you would probably need a more tunable carb setup. Using the stock stuff you are seemingly doing a good job. the original setup seems about right because it would of course go lean when you whack it, you don't have accelerator pumps. If you had accel pumps it would go richer when whacked then fix up.

IDK if your pilot jets are easily replaced on those carbs but that may be what you would like to work on

[Psychonaut]

LOL, I looked at those charts a hundred times.  That's why I went to change the mains. I agree, the charts are wrong. I will see what the pilots cost. I could go from 40 down to a 38. Do you know how far up does the pilots effect fueling?

[crazypj]

CB400f. Stock needle height, 21mm floats. Carbs are perfectly clean.

I have been trying to get my AFR perfect. AFR was high 12.8-13.5 at cruise. Wack it and it would go lean for a second then go. Once going good around 7000+  it would bounce around high 13's before settling around 13.3-13.5 to redline. I wanted to get it around 12.8 at WOT so I went from a 75 main to an 80. Now I am 11.7-12.3 at cruise and right about 13-13.2 at WOT. There is no stumble and it just goes when wacked at any RPM now and the WOT is better but the problem is going larger on the main richened up my cruise to 12.0. The bike runs perfect but I know that cruising at 12:1 is going to foul plugs, waste gas and make my buddy's eyes water.

Here is my question. I was under the impression that increasing the main would mostly effect WOT. In my case it effected cruise more.  I could try lowering the needles and see what that gives but I was hoping someone could give a little insight as to the rich cruise and only slightly richer WOT before I pull the carbs.

 Drop needles and raise float height

[bjbuchanan]

I dont have first hand knowledge but i would try one set down and one set up of pilot jets and then play with the mains. You already have a good approach to the work so keep at it

[crazypj]

Pilot's ain't going to do anything for mid-range problem, it's on the needle