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Post by scooter on Nov 4, 2014 3:57:54 GMT -5
"Scooter" did some pressure measurements on his vacuum (OEM) pump and found the psi to be from 1.5psi to 4psi. So, anything in that range is fine since it simply duplicates what the OEM vacuum pump provides. His reading was of fuel vacuum pressure, not the pressure of the fuel pump outlet.... I guess I didn't realize they would be the same...However, the vacuum pump's psi drops off as engine RPM increases, while the electric pump is constant at all engine speeds (a plus). I did both vacuum and fuel pressure. Vacuum to operate the pump is measured in inches of mercury. Fuel pressure output is listed in psig. As RPM goes up, vacuum drops.
vac hg rpm
11.0 @ 4,500 1.5 @ 7,500
As RPM goes up, fuel pressure rises.
fuel psig rpm
1.5 @ 1,500 4.0 @ 7,000 Pump performance dropped off at 8,000 RPM. Vacuum drops as RPMs increase because the open throttle plate is letting in more air. Pressure rises as RPMs increase because the pump is receiving more pulses per minute. |
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Post by dmartin95 on Nov 4, 2014 10:54:00 GMT -5
These pumps we have on our scoots operate on pulses. Every time your intake sucks in air, the pump's diaphragm is pulled and afterwards released, thousands of times per minute. As you saw in my gauge testing results, a smaller 3 inches of vacuum at 7,000 RPM produces much more fuel pressure than a much larger 11 inches of vacuum at only 4,500 RPM. More small pulses is better than fewer big pulses. I wonder why these scooters are cutting out at WOT....!?! If it's getting the best fuel pressure at higher RPMs, then what do you think is the cause of these scooters cutting out at WOT? I really want to get to the root cause of why all these scooters "cut out at WOT"... It seem to be the case that these particular scoots (turtle shells as shannen calls 'em  ) with the tank in the bottom have this particular issue.... Xyshannen, Katastroff, Me, rcq and the list just goes on.... But, like Alleyoop said, thousands of these scoots with the same design operate just fine.... Perhaps it's the case that some of the fuel pumps had a bad batch of diaphragms or something odd like that.... As to the root cause of the scoots cutting out at WOT, your post has confused me more than helped.... |
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Post by scooter on Nov 5, 2014 6:58:15 GMT -5
These pumps we have on our scoots operate on pulses. Every time your intake sucks in air, the pump's diaphragm is pulled and afterwards released, thousands of times per minute. As you saw in my gauge testing results, a smaller 3 inches of vacuum at 7,000 RPM produces much more fuel pressure than a much larger 11 inches of vacuum at only 4,500 RPM. More small pulses is better than fewer big pulses. I wonder why these scooters are cutting out at WOT....!?! If it's getting the best fuel pressure at higher RPMs, then what do you think is the cause of these scooters cutting out at WOT? I really want to get to the root cause of why all these scooters "cut out at WOT"... It seem to be the case that these particular scoots (turtle shells as shannen calls 'em ) with the tank in the bottom have this particular issue.... Xyshannen, Katastroff, Me, rcq and the list just goes on.... But, like Alleyoop said, thousands of these scoots with the same design operate just fine.... Perhaps it's the case that some of the fuel pumps had a bad batch of diaphragms or something odd like that.... As to the root cause of the scoots cutting out at WOT, your post has confused me more than helped.... Sorry for the confusion. The RPM and vacuum are two separate issues. The faster the RPM, the more the fuel pressure rises. BUT At WOT, more air is being allowed into the intake, reducing the vacuum. If that vacuum drops too low, the diaphragm won't be actuated properly. This is why using a bigger carb can be a problem. It increases the amount of air that can get into the intake, thus reducing vacuum at WOT more than a smaller carb would. Also, any vacuum leaks are going to have a similar effect on the pump. This whole thing is a system, and a system needs balance. Too much or too little of any component in the system will cause imbalance and this failure. And, even if the system is in balance, at some point, the pump will be outside of it's working range. That might be at 10,000 pulses per minute, or 15,000, or 200,000. What we DO know is that on these GY6 engines, with no vacuum leaks, and with a stock carb, you can run at WOT and the system works. By using an electric pump, you can just bypass that system of vacuum output and consumption via the intake, and replace it with a new system based on electrical current output and consumption via the stator. |
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