'77 XS360 flooding on left side at wide open

[74Torino]

My 1977 xs360 hasn't been wanting to rev past 7-8000 rpm without sputtering out, you can hear the left cylinder start to crap out. I tracked the issue down to that side flooding with gas, but only at wide open. I ran it around just cruising, pulled the plugs and they both look healthy. A couple minutes of trying to rev it up high and the left plug goes black. I can even pull back the air filter boot and see the carb spitting out fuel when I rev it. I can also shut off fuel flow and it'll start to rev up like normal.

I've been through the carbs numerous times, haven't found any clogged ports, ripped rubbers, anything. I did replace the needles and seats and confirmed the floats are air tight. Floats are set to 26mm off the base. Checked timing, recently replaced coils, carb holders, set valves, fixed a low voltage issue, replaced plugs. Nothing changed the issue. I haven't checked compression, but it feels strong with my finger over the plug hole. And reaching over the carb while revving, it starts to suck my hand forward.

For the life of me I can't figure it out. I can only think to lower the float height a bunch, but if it's in spec I can't see how it would be the issue. And everything on the bike is pretty much stock by the way.

 

[Jim]

Don't recall a bunch about your bike... had a few XS400's back in the day.... so take this as a generic answer... and a grain of salt.

Sounds like the main jet is too big. If you put too big a main in, you can compensate (to a degree) by moving the needle down a few notches. Then the bike will run fine in the mid range... but will run rich when it's wide open and the needle no longer has an affect.

 

[Raymond]

But why just on one side? Couldn't be a leaky float valve? Just clutching at straws . . .

 

[Bruno_c]

It is not clear whether the problem is related with high revs or with wide throttle opening.

 

[Jan_P]

Dont know anything about that bike but I would consider shift ignition parts left to right and right to left
Cleaning and use contact grease or so
I dont know if this is a points bike or electronic ignition
It says points there
https://www.motorcyclespecs.co.za/model/yamaha/yamaha_xs360.htm

Thinking that if out of spec not giving time enough for strong spark at High rpm
I would probably consider new points unless tip top --ans set the gap exactly to spec since they are giving problems on XS 650
Problems That can be difficult to find

 

[74Torino]

Thanks for everyone's responses, I do believe I resolved the issue. I pulled off the carbs again and stared at them until I noticed that on the side running rich, one of the holes holding the float pin is quite "wallered out", giving the pin & float a lot of wiggle room. I figure that's throwing off the measurement of the float. I eyeballed the float a few millimeters lower than spec and put it back together. I did a couple of runs up and down the street and it happily pulls throughout the power band. I'll check the plugs again after more riding, but I feel pretty good about it being fixed.

I noticed too that before I put the air filter boots on, I revved it up and saw both carburetors misting out gas. Is that normal then, considering it's running fine now?