anyone have tried changing the MAIN JET of carb?
- Thread starter traxxas-modifier
- Start date
docgabby
Super Veteran
my sniper135 has the following modifications: endurance pipe, hispeed high comp piston 54.05mm, hispeed 330 degrees camshaft, kitti xbox, kitti transmission, ported and polished head, ngk iridium sparkplug, hi tension sparkplug wire, magnum ignition coil. i changed my carb to a 28mm nsr oval carb. i am having difficulty tuning the carb in trying to eliminate the backfire by changing pilot jets, main jets, needle clip positions but to no avail, the backfire would lessen but did not totally disappear. so i decided to disconnect the air induction system. the backfire totally disappeared!!! the bike is running fine with good throttle response and speed. my carb setting was 40 pilot jet, 132 main jet, clip at the 3rd needle position. when i decide to reconnect the air induction system with this carb setting, backfire came back. so i decided to leave the air induction system disconnected. i need your/pthers opinion? :?: 
:roll:
:roll:
docgabby said:my sniper135 has the following modifications: endurance pipe, hispeed high comp piston 54.05mm, hispeed 330 degrees camshaft, kitti xbox, kitti transmission, ported and polished head, ngk iridium sparkplug, hi tension sparkplug wire, magnum ignition coil. i changed my carb to a 28mm nsr oval carb. i am having difficulty tuning the carb in trying to eliminate the backfire by changing pilot jets, main jets, needle clip positions but to no avail, the backfire would lessen but did not totally disappear. so i decided to disconnect the air induction system. the backfire totally disappeared!!! the bike is running fine with good throttle response and speed. my carb setting was 40 pilot jet, 132 main jet, clip at the 3rd needle position. when i decide to reconnect the air induction system with this carb setting, backfire came back. so i decided to leave the air induction system disconnected. i need your/pthers opinion? :?:
from the service manual:
AIR INDUCTION SYSTEM
AIR INJECTION
The air induction system burns unburned
exhaust gases by injecting fresh air (secondary
air) into the exhaust port, reducing the
emission of hydrocarbons.
When there is negative pressure at the exhaust
port, the reed valve opens, allowing secondary
air to flow into the exhaust port. The required
temperature for burning the unburned exhaust
gases is approximately 600 to 700 °C.
AIR CUT-OFF VALVE
The air cutoff valve is operated by the intake gas
pressure through the piston valve diaphragm.
Normally, the air cut-off valve is open to allow
fresh air to flow into the exhaust port (å to ∫).
During sudden deceleration (the throttle valve
suddenly closes), negative pressure (ç) is generated
and the air cutoff valve is closed in order
to prevent after-burning. Additionally, at high
engine speeds and when the pressure decreases,
the air cut-off valve automatically closes to
guard against a loss of performance.
from the diagram below, which part (number) did you removed?
AIR INDUCTION SYSTEM DIAGRAMS
1 Bend hose (air filter case to air cut-off valve)
2 Air cut-off valve
3 AIS resonator
4 Vacuum sensing hose
Attachments
docgabby
Super Veteran
i disconnected the vaccum sensing hose (tube 4) from the cut off valve (number 2) and plugged it up with a screw, so the cut off valve is left open, the tube to the carb manifold is closed. i used a manifold from a raider 150 for the nsr carb. i plugged also tube number 1 (tube from the airbox), so no fresh air now is drawn to the exhaust port. this is just backyard remedy to eliminate the backfire. i also tried plugging tube number 1 and left the vaccum sensing hose attached. this eliminated the backfire but i end up with a high idle during cold starts which eventually normalized after a few seconds. i wanted to make the air induction system work again but couldnt eliminate the backfire. help!!!! :cry: :?:
:cry: :?:
bro can you show picture of NSR carbs?