extremeodd
Active Member
- Local time
- 4:04 PM
- Joined
- Mar 30, 2019
- Messages
- 284
So I picked up a new KTM50SX carb aka the PHBG along with a handful of jets. Finally got around to installing it today and of course it's off to a terrible start.
It fired up on the second try, and seemed to rev much harder but it quickly started stumbling like it was over fueled then died. I kick started it for about 5 mins, trying both the choke on and off (mostly on) and moving the idle mixture screw from all the way in to all the way out. With it at the default setting the only time the motor would fire was when pedaling at about 10-13mph and only at full throttle. The moment you dropped from 100% throttle it would die. So I've gone ahead and put my 2nd smallest jet in (80) as the factory one wasn't marked but looked to be near the size of my up 90s jets.
At this point I've put the NT carb back on as I'm sick of working on the bike today, so I figured I'd do some research and ask some questions in the meantime.
Before anyone suggests, I've found the moped army guides on these carbs and so far it's been helpful. Honestly, these questions could be pointless as I haven't tested the jet change yet. Installing a new/used rim + tire/tube + hub adapter (which has already slipped a tiny bit after the bike fell of its kickstand in the middle of the hardest kickstart I've ever done, bending the f***ing spokes a bit....) and getting it all mounted with a derailleur that won't stay in place has my back hurting and my patience short.
Do I need to connect the 2 brass barbs that point down to anything? Or are they just vents that require a short length of tube?
Do I need any jets other than the main? I have the 5x8mm set from here
https://www.amazon.com/gp/product/B077BWHCLC
As I'm typing this I realized that I never adjusted the needle from the stock '2nd from the bottom' setting. I'm willing to bet with the smaller jet and the needle moved I could probably get this thing to run.
Anything I should know about these that might make life easier?
EDIT: I should mention that after putting the NT back on, it took a bit of revving to clear out the excess fuel/oil from the motor. Probably was just the rich af jet.
It fired up on the second try, and seemed to rev much harder but it quickly started stumbling like it was over fueled then died. I kick started it for about 5 mins, trying both the choke on and off (mostly on) and moving the idle mixture screw from all the way in to all the way out. With it at the default setting the only time the motor would fire was when pedaling at about 10-13mph and only at full throttle. The moment you dropped from 100% throttle it would die. So I've gone ahead and put my 2nd smallest jet in (80) as the factory one wasn't marked but looked to be near the size of my up 90s jets.
At this point I've put the NT carb back on as I'm sick of working on the bike today, so I figured I'd do some research and ask some questions in the meantime.
Before anyone suggests, I've found the moped army guides on these carbs and so far it's been helpful. Honestly, these questions could be pointless as I haven't tested the jet change yet. Installing a new/used rim + tire/tube + hub adapter (which has already slipped a tiny bit after the bike fell of its kickstand in the middle of the hardest kickstart I've ever done, bending the f***ing spokes a bit....) and getting it all mounted with a derailleur that won't stay in place has my back hurting and my patience short.
Do I need to connect the 2 brass barbs that point down to anything? Or are they just vents that require a short length of tube?
Do I need any jets other than the main? I have the 5x8mm set from here
https://www.amazon.com/gp/product/B077BWHCLC
As I'm typing this I realized that I never adjusted the needle from the stock '2nd from the bottom' setting. I'm willing to bet with the smaller jet and the needle moved I could probably get this thing to run.
Anything I should know about these that might make life easier?
EDIT: I should mention that after putting the NT back on, it took a bit of revving to clear out the excess fuel/oil from the motor. Probably was just the rich af jet.
Last edited:
Links to Amazon may include affiliate code. If you click on an Amazon link and make a purchase, this forum may earn a small commission.