RaWarrior
Well-Known Member
Figured I'd toss this here and see if any of the smart fellers here have any ideas on what's going on.
It's a 2012 Yamaha Zuma 125. Fuel injected single cylinder scooter. Been modified with a 155cc big bore kit, cam, and Bazzaz fuel tuner with wideband O2 self-tune module. After all the mods were installed at the same time at around 5000 miles, it ran perfectly for probably 12-1300 miles. Got the mapping dialed in and it ran flawless.
Around 6500 miles, it started developing an issue where sustained WOT (say more than 15-20 seconds) would result in it slightly bogging and losing power, getting worse if you stayed on the throttle. Had the trademark lean "bwahhhhh" sound, if you rolled off the gas it would run fine. Stay off the gas for a few seconds, back to WOT, and it'd pull strong for another 15-20 seconds before doing it again. Nothing had changed with the fuel tuner, and the self-tune was disabled and had been for some time.
Over the past 4-500 miles, the problem steadily got worse. It can't sustain more than maybe 60% throttle indefinitely, and WOT craps out after only a couple seconds. It still runs great for a bit, but then falls on it's face. Lower speed driving it runs perfectly fine- if you never ask it to go more than 50-55, you'd never notice the issue. Occasionally it was a little difficult to start, and the fuel pump would make a warbling, unsteady tone now and then when priming.
OK, fuel pump is going bad. Pulled the tank and pump cartridge, and swapped in an aftermarket pump with new filter. Not OEM, but a Kendon brand Japanese made one, that had a lot of good reviews. Sounds strong and steady as you'd expect. The occasional starting problem is gone, but the high throttle/RPM bog is not. Exactly the same as before.
~60% throttle- runs fine indefinitely
~70% throttle- no change in power/speed from 60%, but slight bog sound noticeable
~80% throttle- still no additional power, some popping starts coming from the exhaust
~90-100% throttle- actually starts losing power/speed, vigorous popping/flames out the exhaust
I checked the TPS, which was perfectly in spec. Plug looks fine, a bit sooty as if maybe a tad rich, but not wet or ghost white or anything. Battery voltage and charging is fine- 14v just off idle, no issue there upsetting the ECU. Pulled the injector, looked perfectly clean, but powered it open and blasted it with carb cleaner to make sure. No change. I hooked up a tablet to the Bazzaz to read the o2 sensor in real time, while it was misbehaving just to see if it was going rich or lean- I suspected lean from the bog and popping, but if that's the case, the o2 sensor doesn't pick up on it- indicates it's more or less hitting it's WOT target of 13:1.
What else could be bad here? I'm really at a loss as to what else to try and diagnose this.
It's a 2012 Yamaha Zuma 125. Fuel injected single cylinder scooter. Been modified with a 155cc big bore kit, cam, and Bazzaz fuel tuner with wideband O2 self-tune module. After all the mods were installed at the same time at around 5000 miles, it ran perfectly for probably 12-1300 miles. Got the mapping dialed in and it ran flawless.
Around 6500 miles, it started developing an issue where sustained WOT (say more than 15-20 seconds) would result in it slightly bogging and losing power, getting worse if you stayed on the throttle. Had the trademark lean "bwahhhhh" sound, if you rolled off the gas it would run fine. Stay off the gas for a few seconds, back to WOT, and it'd pull strong for another 15-20 seconds before doing it again. Nothing had changed with the fuel tuner, and the self-tune was disabled and had been for some time.
Over the past 4-500 miles, the problem steadily got worse. It can't sustain more than maybe 60% throttle indefinitely, and WOT craps out after only a couple seconds. It still runs great for a bit, but then falls on it's face. Lower speed driving it runs perfectly fine- if you never ask it to go more than 50-55, you'd never notice the issue. Occasionally it was a little difficult to start, and the fuel pump would make a warbling, unsteady tone now and then when priming.
OK, fuel pump is going bad. Pulled the tank and pump cartridge, and swapped in an aftermarket pump with new filter. Not OEM, but a Kendon brand Japanese made one, that had a lot of good reviews. Sounds strong and steady as you'd expect. The occasional starting problem is gone, but the high throttle/RPM bog is not. Exactly the same as before.
~60% throttle- runs fine indefinitely
~70% throttle- no change in power/speed from 60%, but slight bog sound noticeable
~80% throttle- still no additional power, some popping starts coming from the exhaust
~90-100% throttle- actually starts losing power/speed, vigorous popping/flames out the exhaust
I checked the TPS, which was perfectly in spec. Plug looks fine, a bit sooty as if maybe a tad rich, but not wet or ghost white or anything. Battery voltage and charging is fine- 14v just off idle, no issue there upsetting the ECU. Pulled the injector, looked perfectly clean, but powered it open and blasted it with carb cleaner to make sure. No change. I hooked up a tablet to the Bazzaz to read the o2 sensor in real time, while it was misbehaving just to see if it was going rich or lean- I suspected lean from the bog and popping, but if that's the case, the o2 sensor doesn't pick up on it- indicates it's more or less hitting it's WOT target of 13:1.
What else could be bad here? I'm really at a loss as to what else to try and diagnose this.
