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 Yamaha bwa 125 engine problems 
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Joined: Sat Jun 23, 2018 8:13 am
Posts: 4
Post Yamaha bwa 125 engine problems
Dear all
I have a yamaha bws 125 having the following upgrades
Cylinder malossi 155 cc
Variators malossi front and rear
Rollers malossi 12g
Belt malossi
Fuel injector 180 cc taida
Body throttle koso 30mm
Camshaft 180cc taida
Oxygen sensor bypass by mosmotor

The problem started with engine pressure keeps on getting high and low specially in early morning if the bike is still cold. First for the first ride turning it will be normal as soon as i go for a ride ans leave the fuel it starts getting high and low pressure and the rpm starts jumping from 1 to 4 and back to 1 for 5 minutes. i have to turn it off and turn i back on and everything comes back to normal condition.
I am suffering from this issue.

Help please

Sat Jun 23, 2018 11:20 am
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Joined: Sun Sep 06, 2009 3:45 pm
Posts: 2085
Location: San Antonio, TX
scooters and mods: 2009 Yellow Zuma 125, RC Scooters 168cc Stroker BBK
Post Re: Yamaha bwa 125 engine problems
The explaination is difficult to interpret, but it sounds like you are having an issue with the idle speed control (ISC) valve.

This valve gets dirty after several thousand miles depending on how often you maintain or replace your air filter. The ISC valve is located on your throttle body and can be carefully removed and cleaned with WD-40.

Make sure to avoid getting any cleaners/solvents on the small circuit board or any wiring pins and connectors. Spray a rag or small cleaning brush and clean the part with the rag/brush. You will need to carefully unscrew the black cone until it is completely separated from the brass base. You may need to carefully and firmly hold the shaft that goes into the black cone so that you can fully unscrew the black cone. I suggest using small needle nose pliers and a rubber band wrapped around the shaft to hold the shaft and protect it from getting scratched/marred or damaged from the pliers. Then just unscrew the black cone to remove it. Clean the brass parts & shaft and also the black cone with WD-40. Reverse the disassembly process to assemble the black cone. Thread/position the cone at the approximate position where it was before you disassembled it.

To take the throttle body apart and remove the ISC valve refer to the thread: You might as well clean the throttle body and the air temperature sensor while you have everything apart.

After you finish cleaning and reinstalling the parts, you must perform an ECU reset to have the ECU recalibrate the ISC valve. NOTE: The ISC valve and air temp sensor cannot be purchased new without buying the entire OEM throttle body assembly. Be very cautious when you disassemble, clean and assemble these parts.

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Thu Sep 20, 2018 5:55 pm
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