Jetting 101 help for CB400F

[neevo]

First up I am pretty confident jetting a modern dirtbike so know the principles. Do these translate to my 400F or am I over thinking it?

Will be running a 466cc kit with stacks, a 4-1 header and short cone muffler at the end. What do I need to replace in the carbs to get it running right (excluding suggestions of lager carbs/boring them out at this stage)?

Anyone got a good guess at a baseline for me to start with?

Jetsrus.com seem to have a good selection of mains, I was hoping they might have everything I needed.

 

[Legionnaire]

If I am not mistaken you will need to replace your main jet, pilot jet, and adjust your mixture screws till everything is nice and even. Do tons of spark plug chops after riding the bike around hard to see where you stand as far as "rich" or "lean". Here is a neat chart I made combining lots of peoples images...

 

[neevo]

That's what I though, main and pilot. However I was confused why the needle and needle jet wouldn't need touching too.

Going to whack it on a Dyno at the end to dial it in properly. Only about $150 in Sydney.

 

[neevo]

Just found a great rebuild guide:

http://www.cb400f.btinternet.co.uk/carbv02.doc

 

[Legionnaire]

I remember someone saying a Dyno doesn't really do shit for tuning carbs, I remember hearing that. Let me try and find some facts to back that up. Nothing can take the spot of a good ear and a really perfectionist attitude plus a lot of time tuning it.

 

[Big R]

Good article Neevo - thanks for posting it!

Legion: I've never heard that before. Is it because there is no load on the motor? I would think the actual numbers and charts would be far more helpful than a "butt dyno ".

 

[Legionnaire]

That carb rebuild thread is amazing, it's pretty cool that someone out there with your exact parts did a total tear down with pictures and instructions. I luckily found one as well! Sheesh... four carbs does not sound like fun!

@Big Rich... makes sense, but I swear I will find the article and show you guys!

 

[Legionnaire]

I am not sure if the Keihen carbs are CV's or not, but here is the article I was talking about with tons of goodies: http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

"There is no dyno that "tells" one how to assemble or modify the carb to deliver proper power and response.
Perfect Carb Kit TUNING requires patience and perseverance and "reasonable" feel to feel the changes - of which - most motorcycle riders have a good ability to do.
When a dyno "operator" says he/she has to ride the bike after dyno tuning to do the final tune for cruise smoothness - that's what they are doing. Avoid any dyno operator who says that they don't have to do that!!!"

That is at the very very bottom! I guess for last adjustments and ultimate fine tuning it makes sense, but the large majority of it is patience and trial and error.

 

[neevo]

My understanding of Dyno tuning was it used fuel burn/exhaust gasses to gauge how efficient each stage was.

Pretty sure it's the best way of tuning, but may be talking out of my arse

 

[neevo]

Good article, maybe the results many are getting is the Dyno operators skills rather than the Dyno. Seems I was talking out of my arse.