TOPIC:

Yo everyone!

So i got a 79 kz400 which the previous owner switched the carbs to a single mikuni vm34 with a big ass K&N podfilter. I got a 25 pilot jet for now and 150 main, Needle jet is P6-159 (the previous owner had really small jets on i learned after getting deeper into this stuff. like a 12,5 pilot a P2 needle jet and a big(?) 170 main for some reason). He also installed an electrical ignition system from boyer bransden. (keep in mind this was my first bike some years ago and i've kinda been struggling with it trying to get it to run right which i now know isn't weird after actually educating myself how hard it can be with a single carb etc, etc) i got the parts to change the ignition system to stock don't know if that will make anything better though (got good spark). The petcock is also changed to gravity instead of vacuum (i have the original).

So the things i really need input on (please .) is:
The new petcock is a little smaller than the stock will this make a big difference? Fuel line from petcock to filter is 6mm and filter to carb is 8mm.
I've played around with the size of the jets and the position of the needle but it doesn't feel like it makes any obviously clear difference.
The Spark plugs almost always eventually get really dark even when the jets are smaller to make it leaner)
Its been kinda difficult to start even after riding and engine is hot
i've been thinking of changing the K&N podfilter to a uni instead do you think this will make a major difference?

As always thanks in advance and i would really love (and need) some solid advice on this from y'all who know this stuff so well!

Love from Sweden

www.mikunipower.com/Manuals/VM_Manual.pdf

Courtesy of Craig on the accessnorton.com forum.
www.accessnorton.com/NortonCommando/tuni...e-vm34-mikuni.19925/

Yes i've seen this before and i understand it and understand how to tune the carb but it feels like whatever i do doesn't make a major difference. especially getting a smooth start and a smooth first gear acceleration. Made the topic to see if anyone had something out of the box or had a similiar experience. Thanks for the reply though! Definitely gonna read through i again to see if i missed anything! (i get i'm asking a bombardment of questions at once)

You may try running a hotter spark plug as well. If your plug fouls at idle, it won't allow you take off smoothly. It will run smoother once the carbon burns off.
You want to plug to run 500C-800C. This will keep the firing end clean.

Ideally, you should do spark plug chops to see what your mixture looks like at different throttle plate openings.
Your mixture could be all over the place at different throttle openings.
If you run a hot plug in a lean cylinder(plug firing end over 800C), you could run into pre-ignition.

Cycle World article circa 1983 re: tuning carbs for pods.

magazine.cycleworld.com/article/1983/1/1...ch-of-the-free-lunch

This is the web version.  Long-ish read, but time saved chasing jetting could be considerable.  We have a good original copy in .pdf we'll post in the carbs subforum shortly.  It's in seven files & includes the charts & graphs the web version lacks.  We searched the carbs subforum, but it returned over 100 pages of post & thread results.  The original article may be on KZR somewhere if one chooses to wade through massive search results.

EDIT: Full 7-part.Cycle World pdf article w/ charts & graphs posted here.  Same long-ish read:
www.kzrider.com/forum/3-carburetor/62013...ch-of-the-free-lunch

Good Ridin'
slmjim & Z1BEBE
 

That is something i hadn't even considered! Thanks! Gonna look into it. Excuse the late response btw been a hectic month