Super Jet 61x sbn46 on group k motor tuning

[mjkammes]

i have my 61x group k ported 82.5mm with a factory limited pipe and carbon reeds. 180 both cyl. i have tried lots of jetting combos and cant seem to make it too rich which makes me wonder if its lean. harry recommends a 170 main on my set up.
currently i have a 2.3 n/s with 95 spring 135 low 200 high. this is the best combo i have found and feels extremely strong. from idle to wide open. tach hits 7000. plugs have a light tan color not much but are not to hot after a long run. no air leaks on the engine. tried 2 different 46s with the same results. when i started with a 170 the bigger jet i used it would increase midrange power. screws are at 1.25 low and 2.5 high could my ski need more jetting. have done any wot runs for more than 2 sec. to hit 7k rpm.
any input appreciated.

 

[kevbo]

i have my 61x group k ported 82.5mm with a factory limited pipe and carbon reeds. 180 both cyl. i have tried lots of jetting combos and cant seem to make it too rich which makes me wonder if its lean. harry recommends a 170 main on my set up.
currently i have a 2.3 n/s with 95 spring 135 low 200 high. this is the best combo i have found and feels extremely strong. from idle to wide open. tach hits 7000. plugs have a light tan color not much but are not to hot after a long run. no air leaks on the engine. tried 2 different 46s with the same results. when i started with a 170 the bigger jet i used it would increase midrange power. screws are at 1.25 low and 2.5 high could my ski need more jetting. have done any wot runs for more than 2 sec. to hit 7k rpm.
any input appreciated.

Your tach makes tuning the main circuit much easier. Start with the 200 and open the top screw until peak rpm drops. If it happens with less than 1 turn out then use the smaller main jet. It is actually safer to open the top screw 3 turns and lean to peak or until accelleration declines. That big single will probably need to be tuned a little rich of peak rpm for best acceleration unless the pilot and popoff are also plenty rich. A stock flame arrestor will help fuel draw if you cant get it rich enough.

 

[mjkammes]

thanks kevbo. i have tried the 3 turns out on high with no change. it does have a a/m flame arrestor on it wish i had a stock one to throw on. is there a big difference in power if i bought a 44 to put on it instead?

 

[jd91t]

Ur eng is moving some AIR.
Thought my ported 83mm 61x ran strong..
I've got an sbn46, 155main at 1.5turns.
You with a 200 at 2.5.. Dayum