My Yamaha 1982 xj550j keeps flooding everytime it idles.

My friend had the bike for a long time and he never winterized it, and you can guess what happened. After rebuilding the carb and cleaning it out with carb cleaner the bike would start, and then just choke it self from the fuel. I had taken apart the carb 4 times and it looks like the float needles and move freely and the float height is correct. I even synced my carbs with a home made manometer, even tho I didn't have the YICS tool. I honestly have no idea why it's flooding!!! I even changed the fuel filter I litterly tried everything. Please help!

The Petcock isn't on prime!!
and the carbs are Mikuni BS34.

 

Update:

Took the carb out again and removed the float bowls, I did a little test to see if it's the float needles are leaking. I plugged up the fuel tank took off the floats and just put the needles in the seats by then selfs, turned on gas nothing, took the them out and surly there is gas squirting out. So that rules out if the needles and the little brass thing the needles goes it are bad.

I also measured the float when it's upright as I push it with my finger which is 18 mm, isn't it supposed to be 20-21 mm?


I also saw a video of this guy saying that the float drop might cause an issue if its hanging too low so I'm going to try that now.

 

Another update:

So I thought if that the reason to why this was happening is because the floats were being held by the rubber gasket so before putting the carbs back I violently shook it till I could hear all the floats move freely and then to make sure I bench synced the carbs and raised the idle speed by about a full turn up.

And boom! the bike started and the idle sounded really good, I got about quarter of a mile on it! I got into 4th gear and then started to down shift to first and then the bike just starter revving uncontrollably like crazy when I was at the stop sign. So I had to kill switch it and bring all the way home.

I took the carb out and set the idle full turn back because I thought that's the reason it was reving like crazy and guess what! it started leaking again!!!!

Mind that to adjust the idle speed I have to take off the whole carb because some genius decided to put the screw in the bottom.

 

It's a tight fit for the hand to get to the idle screw. You should be able to reach it with fingertips.

 

It's impossible to turn the idle with your hand, anyways I turned up the idle half way in the screw and nothing changed still flooding

 

turned the screw up by a half still flood, then turned it up by a fourth and it started to do the mega acceleration in neutral, im guessing I put on and took off the carb so much I damaged the rubber gasket seals and now it's a vacuum leak problem.

 

Not sure what you are doing here. You should never take any measurements while putting any pressure on the floats. You also should be performing a wet set of the float levels. That is the ONLY way to determine how high your fuel level will be in the bowl.
Are you sure you have the right carbs?
Mikuni BS28 (all XJ550 except 1984 XJ550L):

-Fuel level measured via the clear-tube gauge: 2mm +/- 1mm (.08 +/- .039 inches)

-Float height: 21.5 +/- 1.0mm

As you can see the fuel level is supposed to be 2mm +/- 1mm with the BS-28 Mikuni carbs.

Here is some forum info on the BS-28's:
https://www.xjbikes.com/forums/threads/mikuni-carbs-part-1-exploded-view-with-pics.31061/

 

Ah, I see! hmmm I always thought I had BS34 because the BS28 had some weird tubes coming out of them and my carbs don't have that.

I'll check the float height again when I get home, also what do you mean by "perform a wet set" is there a guide on how to perform it?

 

https://www.xjbikes.com/forums/threads/hanging-float.58701/#post-449657

 

Update again:

The floats are all correct height of 21-22 mm and the fuel level is correct aswell.

I discovered that the fuel also leaks when the engine is off! So maybe somehow the fuel tank is just forcing fuel into the carb and pushing out the needle? I have no idea how to test this or what to do next

Also the mega rev was because the idle was up too high but the carb is still leaking specifically out of the 4th carb the right most. and the engine overflow tube.

 

Final update!

Holy shit! I found out why all of this was happening!!!! So there is this rubber gasket on the float bowl and when you screw in the float bowl it expands! and guess what! the float was getting stuck on it . I just took all of them out and stretched them, so far no leaks and no mega rpm problems!

 

So ummmmm

I hoped on the bike and went crazy on it, when I came back home there was smoke/vapor and a smell of sunflower oil. it wasn't like black smoke burning it was like water boiling vapor smoke, then I saw that there was oil splattering out of the air box, my whole air filter is now coffee brown color!

Tomorrow I'll check the engine oil level on the stand leveled and see if the there is some issue with the crankshaft (preying to god it's not)

This has never happened before and I'm guessing this is caused by me going 80 mph for the first time in like 10 years.

 

The oil level looks fine, I'm honestly stumbled at what could cause this. Has anyone had this issue before? maybe some line is clogged in the crankshaft and caused alot of pressure when the bike was going 80 mph?

 

Maybe when your bowls were overflowing, the gas went into the oil and overfilled the crankcase. The while riding the extra fluid flowed into your airbox. Better check your oil for contamination.

 

That's probably what it is. I'm gonna change the oil see if that fixes the issue. the oil is black anyways

 

Try to never ride with gas mixed in the oil, it should go without saying.

 

Yeah, I lowkey didn't know that it was even connected to the airbox like that. I thought the oil was coming out from the carbs until some research

 

Just changed the oil, it's really dark and smells like fuel. it was also sparkly I think because of metal bits. I'll take it for a ride right now see how it feels.

 

Alright, the first drive after the oil change seemed magnificent! The next ride the bike seemed to be a little sputurly under load. there was a little bit of vapor coming out of the air box every time it's running.

Currently no filter because it's soaked in oil

 

Update: Bad luck,

The engine was always running with a dead cylinder and had random misfires and had what sounded like lifter tick i believe was due to a broken spark plug cap which i thought i fixed with electrical tape. Today i found out what prolonged misfires do, i was driving on a low rpm when the engine cries and came to hault with a loud screech. Back home I took off the cylinder I found out this bike never had lifters and as i came to the cylinder i discovered it broke. The exhaust valve snapped clean off right into the piston and i know you know what happened. See videos and a photo below.

Rip Yamaha Xj550j 1982

1982- October 21 2024


Trigger Warning!!!!





Im gonna get a new cylinder head, pistons and a piston ring. Hopefully it will come back to life.