Running rich

[DiverRay]

Then you do have an '80 carb. Follow the setting for the 80, but also make SURE the "O" ring and washer are under the adjustment screw. If they are missing/bad you will not be able to tune the carbs correctly. The other thing is the '80 carb does NOT have an adjustment for the needle, and uses a different slide. If someone tried to put early slides in the carbs, that could be part of the problem.

[BLOWCLVL]

Then you do have an '80 carb. Follow the setting for the 80, but also make SURE the "O" ring and washer are under the adjustment screw. If they are missing/bad you will not be able to tune the carbs correctly. The other thing is the '80 carb does NOT have an adjustment for the needle, and uses a different slide. If someone tried to put early slides in the carbs, that could be part of the problem.

Previous owner was original owner and he did not ever touch the slides. only thing he did was put in new stock size 142.5 pilot jets. O-rings and washers are in.

[BLOWCLVL]

Here is a pic of what the mixture screw looks like on my carb. The o-ring is new and at the bottom, then the washer then the screw.

[DiverRay]

OK, for the adjustment on them, set the idle to about 1000 rpm, and starting with #3, adjust the mixture until the idle gets as high as it can, turn back 1/8th turn, and go on to 4, then 2, then 1. After that, re-sync, then check the adjustments once again and re-sync. Seems like a lot of work, but it's the only way to get it to run properly. This is assuming you have the correct jet sizes in, and all vents are open.
One thing I would do is squirt some carb cleaner into each vent on the intake bell and make sure it flows through to the bowl. If you have an obstructed vent it WILL cause flooding and high fuel levels at low speed, and fuel starving at high speed.

[skids]

The mixture screw is on the outside of the carb recessed in a small stack and is at 1 turn out. I had the floats set to 26mm already and someone here said that was incorrect and to set them at 23mm. The clip adjusting metering rods were in there when I got the bike. According to Yamaha they are the correct ones. I haven't received my 100 mains yet or my 140 pilots

I guess you meant #40 pilots. Keep in mind that the mixture screws that you talked about are only to compensate for fuel feed in the idle circuit. That is less than about 2500 rpms. You need to figure out what rpms/throttle positions is causing fuel fouling. Like I said before, (which is what I think you are doing) is get is as close to stock as possible, then color the plugs at wide open throttle, adjust mains, then color the plugs for the idle circuit and adjust that. Adjusting all over the board at the same time can drive you nuts!

[BLOWCLVL]

I guess you meant #40 pilots. Keep in mind that the mixture screws that you talked about are only to compensate for fuel feed in the idle circuit. That is less than about 2500 rpms. You need to figure out what rpms/throttle positions is causing fuel fouling. Like I said before, (which is what I think you are doing) is get is as close to stock as possible, then color the plugs at wide open throttle, adjust mains, then color the plugs for the idle circuit and adjust that. Adjusting all over the board at the same time can drive you nuts!

Hahaha yes #40 pilots. I do know the mixture screw is for the low RPMS and those are also an issue. With the carbs synced and idle set the bike fires up instantly with no choke when cold. It will run at about 2500 RPM until it warms up then drops to about 1200. It will idle nicely at 1200 for a few min then just die. It doesn't just sputter either just up and quits. It requires choke or some throttle to restart after that until its cold again.

[Bonz]

Are you feeding the bike fuel from an alternate fuel source like a funnel when it dies (like when doing a sync)? Or is the tank feeding the bike when it dies?

Has anyone suggested an issue with the vent on the fuel tank?

[BLOWCLVL]

Are you feeding the bike fuel from an alternate fuel source like a funnel when it dies (like when doing a sync)? Or is the tank feeding the bike when it dies?

Has anyone suggested an issue with the vent on the fuel tank?

Feeding from the tank. What vent on the tank?

[Bonz]

The fuel tank needs the vent in the filler cap to be clear. It's like chugging a beer. If you only suck from one end you can't get it out because the vacuum builds. If you have a vent on top everything flows smoothly. That may help figure out why it dies. Don't know that it helps on the running rich.

[BLOWCLVL]

The fuel tank needs the vent in the filler cap to be clear. It's like chugging a beer. If you only suck from one end you can't get it out because the vacuum builds. If you have a vent on top everything flows smoothly. That may help figure out why it dies. Don't know that it helps on the running rich.

Ahhh ok well it does the same thing with the gas filler lid open. so im thinking the vent isn't the issue.

[Bonz]

Gotcha. Sounds like that is out of the picture.

[skids]

Well, if it starts with no choke, and all head pipes get hot within a reasonable amount of time when it seems to run right, I would say it might be fuel fouling. As you probably agree, a cold engine needs to have a richer fuel mixture and then as the head heats up, the fuel is better atomized (or at least that is my take on it, but I am pretty sure Brant will chime-in ). The only way to tell for sure is to color a set of plugs. If it were me, I would first get the engine warmed-up and then install the new plugs, run it for 5 minutes using a box fan and holding the throttle at about 1200 rpms, then examine the plugs. I assume you already made the changes to the carbs for a starting point.

[BLOWCLVL]

Well, if it starts with no choke, and all head pipes get hot within a reasonable amount of time when it seems to run right, I would say it might be fuel fouling. As you probably agree, a cold engine needs to have a richer fuel mixture and then as the head heats up, the fuel is better atomized (or at least that is my take on it, but I am pretty sure Brant will chime-in ). The only way to tell for sure is to color a set of plugs. If it were me, I would first get the engine warmed-up and then install the new plugs, run it for 5 minutes using a box fan and holding the throttle at about 1200 rpms, then examine the plugs. I assume you already made the changes to the carbs for a starting point.

I have taken it out for a god 20 min ride, come home and put bran new plugs into it then restarted and let idle for about 5 min resulting in black sooty plugs.

[motoman]

I have taken it out for a god 20 min ride, come home and put bran new plugs into it then restarted and let idle for about 5 min resulting in black sooty plugs.

Having even too lean of pilots, shouldn't happen. From some of your previous input, I highly recommend you pull that carb bank, remove float bowls and make dern sure those floats(all eight) are all IDENTICAL setting of 23mm. 'Close' doesn't cut it. IMO, that definitely would be a good start........then can help with attacking a highly possible secondary ignition issue. BTW, float level setting IS very critical pertaining to the later model 80-82 Mikuni carbs!

[BLOWCLVL]

Having even too lean of pilots, shouldn't happen. From some of your previous input, I highly recommend you pull that carb bank, remove float bowls and make dern sure those floats(all eight) are all IDENTICAL setting of 23mm. 'Close' doesn't cut it. IMO, that definitely would be a good start........then can help with attacking a highly possible secondary ignition issue. BTW, float level setting IS very critical pertaining to the later model 80-82 Mikuni carbs!

I will remove and re set them again but I know they are exactly 23mm