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Discussion Starter · #1 ·
So here's the backstory... Someone listed the scooter for sale locally and was transparent with the fuel pump problem. According the the owner, he said the scooter didn't start so he started tearing it down to see if he could fix it. He stripped most of the bodywork off to gain access to the fuel pump assembly. At some point, he decided to just haul it to his local Yamaha dealership to have to diagnose it. Dealer tore more stuff apart like unbolting the fuel tank and removing the six bolts that fastens the fuel pump assembly to the fuel tank. Unbolting the fuel tank leads me to believe they weren't 100% sure what they were doing and was trying to figure out how to remove the fuel pump assembly from the fuel tank. According to the owner, the dealer told him they were able to get the scooter running with starting fluid and diagnosed it with a bad fuel pump. After getting a quote for the fuel pump assembly at $300+ for parts only, he decided that getting rid of it was his best option. After some back and forth, we strike a deal and I tow the scooter home.

After some research and digging through this forum, I message minimac and he jumps in to the rescue. After a few message exchanges, I felt that I was armed with enough info to tackle the fuel pump repair. With the help of a neighbor, I was able to lower the subframe and get enough space to wiggle out the fuel pump assembly. I opted to replace just the pump with a Kemso pump off eBay and a new fuel pump seal from my local dealer. Pump replacement was pretty straight forward and getting the assembly back in resulted in some head scratching but got it back in w/o bending or breaking anything. I connect the battery, turn the key on and my neighbor alerts me that fuel is leaking everywhere. I immediately turn the key to the "Off" position and check around the fuel pump assembly and it's dry. I switch the key back on and discover fuel is spraying out of the injector area. I check the bolt that fastens down the fuel injector and it is completely loose (I'm guessing more dealer "exploration?"). I tighten it down, turn the key and fuel still sprays out from where the injector seats against the motor (or throttle body?). So I loosen the bolt and tried to pull the injector out. I get it unseated but there is a bracket that keeps the fuel line in place preventing me from completely removing the injector. There is a small fastener holding the bracket in place (I think it's an Allen head) but it's on there pretty tight and I'm scared to death about stripping it. I decided to push the injector back in but had a tough time getting it back in. At this point, I started losing daylight and decided to call it a day. Good news is that I was able to remove and replace the fuel pump. Bad news is that I can't figure out how to properly reinstall the fuel injector. Gonna spray some WD40 on the Allen head fastener and let it sit overnight and give it another go tomorrow. Plan is to hopefully remove the bracket that's holding the fuel line and pull the injector all the way out to inspect the condition of the o-rings. Reinstall injector and torque the fastener to spec and hope there are no fuel leaks. If anyone has been down this path and has any advice, it would be greatly appreciate it!

Sorry for the lengthy post, but I wanted to provide as much info as possible in hopes of getting the right help in getting the scooter back on the road. BTW, the scooter seemed to be well taken care of and kept in a garage most of its life with just under 12K miles on the odometer.

Thanks!
 

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Discussion Starter · #4 ·
Yes and no. I ended up stripping the the fastener that holds the bracket that supports the fuel line. I had a T15 Torx bit and it didn't help. I ended up unclipping the fuel injector from the fuel line and there is a gasket and an o-ring (they both look like o-rings but that's how the Yamaha microfiche lists them). Dealer did not have them in stock so I had to order them. Hoping to get them this week. Seems really odd that the fuel injector only has a rubber gasket and o-ring to keep it from leaking with a fastening bolt torqued at 9.7 ft lbs. I'm reeeeeally hoping this will solve my problem. The only other thing I can think of is that the Kemso pump is pumping higher PSI than the factory pump but I don't have a pressure gauge to test.

Here is a pic of the fuel injector. The top one is what Yamaha calls a gasket and the bottom one is an o-ring. The top one definitely looks skinnier in circumference and the bottom one looks thicker. They have different part numbers so I'll be careful to make sure I put the correct ones in each slot.

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Discussion Starter · #5 ·
So I got a new gasket and o-ring for the fuel injector. Installed them and torque down the fastening bolt to 9.7 ft lbs per the manual and it still sprays out fuel. I've looked at all the different diagrams in the manual and parts microfiche and don't think I'm missing any pieces. Any idea why I have fuel spraying all over the place? I shot a short VIDEO showing where the fuel is spraying out from. Any help will be much appreciated.
 

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Possibly a crack in the injector plastic body. You need to find exactly where the fuel is coming out of to be able to correct it. Otherwise, it's just throwing guess parts at it. The O-rings on the injector look fine and I did not think that was your problem from seeing the picture. The "gasket" terminology is because it is the sealing area for the outside. The O-ring terminology is because that is the sealing seal from the inside.
Correct - most of us would just call them "O-rings". But being an aerospace engineer that terminology is what I am used to in diagrams.
 

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Discussion Starter · #7 ·
Thanks, BHR! Do you know if there is supposed to be any type of o-ring or gasket in between the black plastic piece that the fuel hose is connected to and the top of the fuel injector (silver part)? Unfortunately, I don't have any equipment to do any type of pressure testing but I'll go pick them up if it's not too expensive. The only things I can think of are a cracked injector as you've suggested, missing gasket/o-ring for the top of the injector or the fuel pump is pushing more psi than the gasket/o-ring are rated for. I'm going to stop by the service department and show them the video to see if they have any ideas.
 

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You might be able to use the tool checkout at Autozone or one other parts stores for an injector pressure checker - Not sure. it's just an idea for you to look into.

I doubt the pump is over-pressurizing. Far too much liability on a fuel related part to not have at least some decent quality control. As for the seal - It looks like it has the seals in the picture that are normally on an injector.
 

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Discussion Starter · #10 ·
Not a bad idea to check with Autozone to see if they have a loaner pressure gauge. Thanks for the suggestion! The way the fuel is spraying out looks like something is missing or completely clogged. I would think a cracked injector would result is a fast seepage with everything sealed unless it is a huge crack.
 
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