Fuel coming out of a muffler

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Giuan
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Motorcycles Owned Currently: 1993 Yamaha XJ600

Fuel coming out of a muffler

Post by Giuan » Sat Jun 17, 2017 4:07 am

Hello everyone!
As I was trying to resolve a fuel supplyissue, consisting in the engine running rich, I bought a cheap fuel pump to see if I could notice any improvement.
After being done installing it, I set the fuel screw to 2 turns out as stated in the manual and I started the engine; I felt like it was idling slower than usual and It could barely tick over. As soon as I took a look at the ground I saw a puddle. It didn't smell like gasoline but it was very liquid.
I was in the street so I didn't know if it was already there: I started the engine again and I noticed that it was coming out of my right muffler! Each muffler has a tiny hole at the bottom: that's where the fuel is coming from :cry:
I immediately put the old fuel pump back, thinking that the new was causing too much pressure, but even with the old one is the same story now.
I used the bike yesterday and I didn't notice anything like this.
What could possibly be causing an issue to bad?

Crimson
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Re: Fuel coming out of a muffler

Post by Crimson » Sat Jun 17, 2017 6:08 am

Most standard exhausts have a small hole in the silencer somewhere to allow water (condensation/rain/flood) to drain. I would first confirm that it really is unburnt fuel. It could be water.
When your bike was running rich, did you check the carbs first? If my bike was running rich, I would first identify the rev range where the richness is worst, then work from there, setting the mixture screws, making sure the air filter is clean, then going to look at what jets are installed.
You say you set the fuel screw to two turns out. Did you set the pilot mixture screws (there are 4 of them) to 2 turns out? I wonder which screw you turned out. You set the idle speed screw (a different screw) globally by ear and eye, to make it idle at around 1200-1300 rpm.

Giuan
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Joined: Tue Jun 07, 2016 2:00 pm
Region or State: France
Motorcycles Owned Currently: 1993 Yamaha XJ600

Re: Fuel coming out of a muffler

Post by Giuan » Sat Jun 17, 2017 7:49 am

Hi Crimson, thank you for your reply!
For starters, I gotta tell that I solved this: I inadvertently swapped the outlet of the pump with its inlet of the vacuum pulses :o
Basically, I was skipping the carbs and sending fuel straight to the second cylinder, which overflowed. I really don't know how could the engine start (lucky me, I let is run just for seconds). I hope you guys admire my honesty for telling this :oops:
Answering to your question, I meant the mixture screws which more precisely should be fuel screws (you scew in you let less fuel pass; you screw out, you let more fuel pass): do you confirm this? I am talking about the Mikuni BDST28, those with the oil-based heating system.
The carbs seem unresponsive to the setting of those screws, I don't know what's the jet she has, as it is kinda old and I took it just one year ago! I'm still discovering her, in my spare time. The air filter is pretty ok, I clean the carbs many times. The richness appears to be in the low RPMs range, so the pilot jet is the first to look at; however, I cleaned them to perfection and nothing changed. I am suspecting that the POs might have messed with the jet settings, so I am waiting for a #15 pilot jet to arrive and I will see if that cylinder leans out.
By the way, even with this new fuel pump nothing changed at all!

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