Hi there can anyone give me some advice on carb jetting.My 1000 triple has hi comp pistons full flow collector box ,the big valve head ,but standard A11 cams .My carbs have 145 main jets fitted but the book states 120 jets for the standard triple,which way would be best to go?thanks paul.
carb jetting question.
- Thread starter bakerslav
- Start date
Mines a standard 81 Jota which is still purring like a kitten after 32 years. They dont make em like this anymore ... still good enough to outpace many modern sports bikes and unburstable highway cruising. Anyway ... I digress. Standard Jota mains are 145. I'm currently running 132 which has crispened the response.. howls like a banshee. Search this site you'll find lots on carb jetting.
R
Reggie3cl
Guest
145 is way too big- 118 or 120 maybe closer to the mark. Mine (79.5bhp at the back wheel on the dyno, wouldn't outrun a well tuned 350LC) might have even been running some smaller. Best thing is to get a selection of mains and spend an hour or two on a dyno.
mauricejota7604
Hero member
- Location
- Victoria Australia
Probably depends a bit on the fuel you have available, I have an 81 Jota and she is vey happy with 125 mains.
- Location
- Calgary, Alberta, Canada
ok, I'll bite.....
mark your twist grip with a baseline;
then mark your throttle housing with throttle closed, 1/3, 2/3's, and wide open
starting circuit and initial idle is choke jets, pilot (idle) jet, and idle mixture screw. Make sure your choke plunger rubber tips are in good shape, and close FULLY when shut off, otherwise all your other jetting efforts will be wasted. Pilot jet start around 60, if rich, go 57.5 or 55's. Idle mixture screw, you will know you have the correct pilot jet when it idles best at about 1 and one half turns out
1/3 to 2/3's throttle, the biggest changeable item to affect mid range is needle and needle jet. Needle jets AB 265, needle K 1, start in middle notch.
Main jet depends on properly getting everything else right, but essentially by he time the bike is on wide open throttle is when the main jet size is the real issue. You are going to have to do some wide open throttle runs. Start at maybe about 128 main jets, run wide open throttle, see what happens, bike runs well, big bogs?
best easiest ad quickest to get this right is with a wideband exhaust sniffer on a dyno, make sure you check closed throttle, 1/4 to 1/3 throttle. 2/3 throttle, and wide open throttle, a lot of dyno operators just want big wide open numbers, useless to you for daily riding and tractability.
If you don't have access to a dyno, at wide open throttle, back off to about 2/3's throttle, if the bike doesn't accelerate harder when you back off and the needle lowers partially obstructing the main jet, you have it about right. Too big main jets will make the bike bog at full throttle, if backing off to 2/3's throttle (into the needle and needle jet) will result in the bike accelerating, go smaller on the main jet.
for your initial testing, leave the 145 mains in, run the bike at wide open throttle, observe whether it is puling hard and cleanly, or not, then back off to about 2/3's throttle and observe what happens, if the bike accelerates harder at 2/3's throttle your 145's are too big.
When you go smaller on the main jet, be careful to take occasional plug readings to make sure you don't wind up too lean, you want a nice tan coloured electrode, not black for too rich, or white for too lean.
Paul LeClair
ps also remember, 90 % of carb problems are something other than carbs....... before you start on the carbs, make sure ignition and ignition timing are spot on, adjust the valve clearances precisely, check for intake leaks, all BEFORE even touching the carbs....
mark your twist grip with a baseline;
then mark your throttle housing with throttle closed, 1/3, 2/3's, and wide open
starting circuit and initial idle is choke jets, pilot (idle) jet, and idle mixture screw. Make sure your choke plunger rubber tips are in good shape, and close FULLY when shut off, otherwise all your other jetting efforts will be wasted. Pilot jet start around 60, if rich, go 57.5 or 55's. Idle mixture screw, you will know you have the correct pilot jet when it idles best at about 1 and one half turns out
1/3 to 2/3's throttle, the biggest changeable item to affect mid range is needle and needle jet. Needle jets AB 265, needle K 1, start in middle notch.
Main jet depends on properly getting everything else right, but essentially by he time the bike is on wide open throttle is when the main jet size is the real issue. You are going to have to do some wide open throttle runs. Start at maybe about 128 main jets, run wide open throttle, see what happens, bike runs well, big bogs?
best easiest ad quickest to get this right is with a wideband exhaust sniffer on a dyno, make sure you check closed throttle, 1/4 to 1/3 throttle. 2/3 throttle, and wide open throttle, a lot of dyno operators just want big wide open numbers, useless to you for daily riding and tractability.
If you don't have access to a dyno, at wide open throttle, back off to about 2/3's throttle, if the bike doesn't accelerate harder when you back off and the needle lowers partially obstructing the main jet, you have it about right. Too big main jets will make the bike bog at full throttle, if backing off to 2/3's throttle (into the needle and needle jet) will result in the bike accelerating, go smaller on the main jet.
for your initial testing, leave the 145 mains in, run the bike at wide open throttle, observe whether it is puling hard and cleanly, or not, then back off to about 2/3's throttle and observe what happens, if the bike accelerates harder at 2/3's throttle your 145's are too big.
When you go smaller on the main jet, be careful to take occasional plug readings to make sure you don't wind up too lean, you want a nice tan coloured electrode, not black for too rich, or white for too lean.
Paul LeClair
ps also remember, 90 % of carb problems are something other than carbs....... before you start on the carbs, make sure ignition and ignition timing are spot on, adjust the valve clearances precisely, check for intake leaks, all BEFORE even touching the carbs....