Past the power curve ?

GoldenMotor.com

rob king

New Member
Oct 13, 2009
8
0
0
wilmington nc
I've got a stinger sd"80cc" motor on my board tracker. Have run about a gallon of gas through it @16 to 1.I just swithched to synthetic motorcycle racing oil @ 50 to 1. Engine makes real good power under load but when bike is atwide open throttle and cruising ti kind of fallsoff and surges . throttleback and put load on it pulls hard again. I have 44 tooth sprocket. Should I goto a smaller rearsprocket to keep it in the power band better. My friends bike with 80cc slanthead motor and I think36 tooth rear sprocket seems to pull all the time even at cruise wide/open. Plug is fresh ngk and nicegrey/tan color after hard run. Anythoughts
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
7,266
1,797
113
Los Angeles, CA.
Just go to a hardware store that sells tiny 'jewlers' bits; find the one that fits in your jet perfectly, & then buy the next two smaller sizes!! I think #70 is what the stock jet is??
 

BarelyAWake

New Member
Jul 21, 2009
7,194
21
0
Maine
Another thing to check/try is bending the float tabs up a hair - could be just a starvation issue... It was with mine anyway ;)
 

rob king

New Member
Oct 13, 2009
8
0
0
wilmington nc
Ive tried your suggestions about going to smaller jet size . my original was in between #70 and # 71. TI have a metal lathe and can make my own jets ,wanted to save the original intacked. went down .004" problem seems a slight bit better but much. I'm not sure this thing is fukky broken in yet, I'm going to run it more and see what happens. even after going down in jet size plug still looks just a touch rich. How long does it take to fully break in one of theses motors? thanks for all the help. I'm stuborn and wont quit until it runs right!
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
7,266
1,797
113
Los Angeles, CA.
Ive tried your suggestions about going to smaller jet size . my original was in between #70 and # 71. TI have a metal lathe and can make my own jets ,wanted to save the original intacked. went down .004" problem seems a slight bit better but much. I'm not sure this thing is fukky broken in yet, I'm going to run it more and see what happens. even after going down in jet size plug still looks just a touch rich. How long does it take to fully break in one of theses motors? thanks for all the help. I'm stuborn and wont quit until it runs right!

Don't try to re-jet your carb until you've fully broken in the engine!!! (about 4 gallons!)
It will start running different as it breaks in! (& you'll have to re-jet again)
 

rob king

New Member
Oct 13, 2009
8
0
0
wilmington nc
First let me apologize for my spelling errors. hard enough to get your thoughts across without all the mispelled words! I found a problem that may not be that unusual but caught me. Even after trying rejetting with no noticeable change, I got to thinking about what else could be at falt. New motor and all I new it probably won"t run as well as a well broke in engine, but I knew something was definately wrong. Still surging at cruise speed. Pulled bike into the shop and sat there just reving it a few times when I saw the carb moving! Intake bolts were loose. Funny cause they were tighten with wrench yesterday. Come to find out, factory installed acorn nuts were bottomed out on studs. felt tight but no pressure on intake manifold.so it was wiggling and allowing intake to leak.any one seen this one before? for such a simple engine, look for the simple problem! got rid of acorn nuts and put regular nuts with lock washers. anyway it runs much better now and i'm sure will run better as it breaks in more. I put original jet back in and will run it like this for awhile .thanks again for all help
 

sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
1,839
471
83
california
I have seen the bottomed out acorn nut issue and changed mine out as well. I also suffered from high rpm fuel starvation. Drilled out the lower fuel petcock and put in a larger fuel filter. The guy at the lawn mower shop told me to always use the metal screen type filters for gravity feed applications. Paper type filters will not flow enough fuel. Problems solved and I now have plenty of fuel at WOT.
 

spit_fire

New Member
Aug 28, 2009
207
0
0
Brampton
i have a question to all the have rejetted with the almost pubic hair size drill bits, do you do it by hand with a hand drill, dremel, or some sort of drill press?