Gx390

B

Bobby l

Member
Gx390 .I have a gx390 on a mini late running on a small tight dirt track built a torque motor ported head 50lb blue stripe springs 280-411 nr racing torque cam stock piston timming set at 28 deg long 2 stage header motor turns 52 to 5300 rpm changed gears 2 teeth didn't seem to help much from 51 to 5300 even put lighter drive in car no change checked tach pulls good just cant get rpms up .would like to at least get to 5800 unloaded rear wheels and it will turn 64 easily???
 
The specs say 6000 max . What carb size ? Short header for higher rpm .
28* seems low . Did you add gear or remove gear ? Is the chassis tight .
 
flattop1 said:
The specs say 6000 max . What carb size ? Short header for higher rpm .
28* seems low . Did you add gear or remove gear ? Is the chassis tight .
Click to expand...
Stock carb 28 low jet 38 high yes went from 80 to 82 gear little to no difference from 5100 to 5300 after Chassis was adjusted .checked plug looks to be running on the ritch side maybe bad o ring on low jet?
 
Me , i would say change 5 teeth less to rule out gear selection .
Carb too rich maybe 38 is to big .
28* still seems low .
 
Think I found problem bad o ring on low jet installed new one and now can set air screew to about 2 turns out .revs faster and idles better now will know for sure this weekend
 
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