Hi folks!
I just finished a bike project where I also replaced the old YX140 with a 155ZS and a OKO28mm carb.
I did some test riding but wasn't able to do some serious riding yet, however I'm not satisfied with it's setup so far, although the new engine/carb combo seems to be pretty impressive.
From what I read so far in this thread seems like I should approach setting the carb up like that:
1)Find correct main valve by spark plug checks at full throttle
2)Find correct pilot valve by checking mixture screw setting at fastest idling (the more the screw is in the higher the likeliness I'll need a bigger valve (or by checking spark plug at "zero throttle" /idle?)
3)Find correct needle height by checking response and behaviour when opening throttle from 25 to 75%
Correct?
As far I did 2 test runs... First one was pretty impressive, however it was kinda hard to start and it bogged sometimes and also... how do you call it?... "backfired" a lot... when unburnt fuel ignites inside the exhaust and causes little explosions. It even blew out a piece of grill inside the exhaust thats supposed to dampen that effect haha
On second test run it was hard to start too (choke wouldn't make much of a difference if at all) but I might heaven't given the engine a proper warm up period. It backfired a lot and seemed to have a lot of failed ignitions since it ran very.... unpredictable... sometimes it was near dieing and then were also these sudden "power thrusts" that sometimes where close to kick me off the bike ^^
I was able to ride about 200m or more at full throttle to check for spark plug color and found it to be on the lean side. It's not that white it would make me feel the electrode would turn to dust by touching it but it's got a white tint.
Also it's still quite cold outside. -1°C when I did the 2nd test run, maybe about 4-5°C when I did the first.
Edit: did a testrun again today and also checked carb setup. I did carb chops at near idle, 25%open, 50% open, 75% open and 100%open (while riding!). I started at idle and worked up. Tendency was rich (dark spark plug) at low trottle and the higher opened the leaner (grey to white tinting).
Behaviour of bike was overall pretty good, maybe a bit hesitating and backfiring a little. Unfortunately I can't compare to other carbs running well on this engine but the increase in power compared to the old YX140Z40 is notable.
Carb setup is as follows:
Pilot: K48
Needle: 1notch up (richer), JJH type
Main: 130 (!?)
Well, if I heaven't read through that thread I'd no doubt get a one step bigger size main, but from what I read here I'd better start with needle center notch and a Keihin 97,5 main.
Again, engine is a untuned Zongshen 155 used for dirttracks.
I guess that K48 means it's a Keihin valve, right?
Does anybody know which one is the main? it only says 130 and is lettered in a small bow on one side of the hexagon towards the end that sticks out at the bottom. (is that clearly? ^^)
Martin
