- Location
- utah
Hey guys, I was wondering if any of you pros might have some tips for me. I had Group K machine some parts for me to build a sleeper JS550. It’s ported, has a milled head, SBN 44 carb, aftermarket flame arrestor, and a West Coast pipe. I ride at about 4500 ft.
Currently, it has issues where the way it likes to be started once it’s warm is with no primer, no throttle—you just crank for a while and then it will finally catch. It starts as a low rumble that barely seems alive, then it eventually stabilizes. Once it’s started, you can’t jam on the throttle; you have to ease into acceleration. But once you’re past 1/2 throttle, it shoots like a bat out of hell and is crazy fast.
What’s strange is I asked Group K what jets they put in since I paid them to jet it for me, and they told me they used a 100L and 120H. I just found out that’s completely false. I took the carb apart and it actually has a 152.5 high jet and a 120 low jet. Pop-off was at 12 psi with a 65 g spring.
I purchased all four springs and also a 90 jet and a 105 jet (because I assumed I had a 100 low and wanted to jet above or below this).
Can anyone give me some tips on where I should actually be targeting? 12 psi pop-off seems off. From what I’ve seen on forums, most people say around 18–23. I can get 17 pop-off with an 80 g spring. Are my jets too far off that I need to change them, or can I make these work by adjusting pop-off and the adjuster screws?
Currently, it has issues where the way it likes to be started once it’s warm is with no primer, no throttle—you just crank for a while and then it will finally catch. It starts as a low rumble that barely seems alive, then it eventually stabilizes. Once it’s started, you can’t jam on the throttle; you have to ease into acceleration. But once you’re past 1/2 throttle, it shoots like a bat out of hell and is crazy fast.
What’s strange is I asked Group K what jets they put in since I paid them to jet it for me, and they told me they used a 100L and 120H. I just found out that’s completely false. I took the carb apart and it actually has a 152.5 high jet and a 120 low jet. Pop-off was at 12 psi with a 65 g spring.
I purchased all four springs and also a 90 jet and a 105 jet (because I assumed I had a 100 low and wanted to jet above or below this).
Can anyone give me some tips on where I should actually be targeting? 12 psi pop-off seems off. From what I’ve seen on forums, most people say around 18–23. I can get 17 pop-off with an 80 g spring. Are my jets too far off that I need to change them, or can I make these work by adjusting pop-off and the adjuster screws?
