1980 xs11 special dies with throttle

[darylcaribou69]

Yes, very odd indeed. It's got me beat. The spark stays strong through the stall of the bike. Idles good (rough to start). Runs awesome up top. Moving the floats to 25mm helped the issue a bit. When it's about to die the exhaust will pop (A high pitched noise) then go back to normal over that "transition range". Maybe I have the wrong needles installed? They might have used some from a kit. Would the too big main jets cause this? Possibly adding to the issue. But it seems like it would be lean during the transition because with more air it wants to die. Like the diaphragms aren't opening fast enough? Or the needle taper is wrong. Maybe there's something in the ignition system that isn't moving the way it should, maybe not enough vacuum to move the advance thing at lower engine speeds. I really have no idea. I'm all over the place here. If anyone takes the time to read this you're awesome.

Thanks for the help, advice, and knowledge.

[Schming]

Some things to ponder . . .

What liquid did you boil your carbs in ?

I see you've stated your going to replace the mains with genuine mikuni.

Actually all jets and float needles and seats should be genuine mikuni.

Are you sure the enrichener shafts are sealing properly ?

Have you changed the butterfly shaft seals ?

[TopCatGr58]

Hey again Daryl,

Okay, not sure why but you changed the float height from 23 to 25. The 80-81's use the 23mm height, not the 25. The 25 would make things a bit leaner.

DiverRay may have mixed up your year, and was possibly thinking you had an earlier model that uses the ~25.7mm =/-1.0 spec??

Okay Genuine Mikuni pilots 42.5, and possibly getting 110's mains, running 120's now, and strong rpm/throttle to redline once past the transition.

You didn't say how many turns OUT on the pilot screws you have?? Beginning setting is 1.5 turns out from "GENTLY" seated. This controls fuel/air mixture for the PILOT circuit which involves idle. However, there are 3 little holes in the top throat of the carbs just behind the butterfly when it's mostly closed, and they are what get involved and contribute with the increasing of the throttle/opening of the butterfly, but are metered just by the pilot jet size alone. So we are back to your float height setting, you put them at 23 which makes it a bit more rich, and this seemed to help things a bit, which does clue that it's a bit lean=popping.

You're running 4-2 pipes, they do flow a bit more, and therefore could need more fuel, so you may also need to get the next size up pilot jet. With the engine running ok with WOT, the 120's may already be adequate and not necessarily too rich.

Greg/BA80 has reported a hesistation in that transition zone on a bike that he had one brand of 4-2 pipes on and could NEVER get completely smooth. But he eventually put on a different set of pipes, and the problem was fixed.

Keep in mind, you want to make just 1 change at a time, and then see how it affects performance, and then change another 1 thing, retest. IT's time consuming, but otherwise you can't tell what change might help and which might not when you make too many at one time.

T.C.

[motoman]

This is the part I'm hung up on. If it idles fine and runs fine on wide-open throttle, then it would seem to me like fuel level in carbs isn't the thing that's most out-of-whack, since that would affect the entire RPM range.

Well, associated with fuel bowl levels, does NOT affect all of rpm range.

[skids]

Fyi i had to go with 3.5 turns on the idle screws with proper orings and washers using 81 carbs (similar).

[motoman]

Fyi i had to go with 3.5 turns on the idle screws with proper orings and washers using 81 carbs (similar).

Wow skids! that far out with the idle mixture screws on the later model carbs tells me one of two things. First being those teeny sealing O-rings on the mixture screws are not sealing properly. Or secondly, that setting not using the lean-drop method for setting the mixtures wasn't used. My Venturer setting those mixture screws using the lean-drop method ended up 2 1/4 to 2 3/8 turns out. Each carb/cyl. did come out set just slightly different, but 3.5 turns out tells me one of those two things previously mentioned is an issue.

[skids]

Wow skids! that far out with the idle mixture screws on the later model carbs tells me one of two things. First being those teeny sealing O-rings on the mixture screws are not sealing properly. Or secondly, that setting not using the lean-drop method for setting the mixtures wasn't used. My Venturer setting those mixture screws using the lean-drop method ended up 2 1/4 to 2 3/8 turns out. Each carb/cyl. did come out set just slightly different, but 3.5 turns out tells me one of those two things previously mentioned is an issue.

My point is that 1.5 turns might not be enough. Also, my bike is running quite well.
42.5 pilots
pilot screws to 3.5 turns
Adjusted floats[.925 (lean) to .886 (rich), middle is .906]
No.1 No.2 No.3 No.4
.905 .902 .904 .904
185 air, 300X2 nozzles, 110 mains

8500 feet elevation, stock airbox with K&N, 4 into 2 81H pipes.

[darylcaribou69]

When I was messing with the carburetors last night I played with the idles screws a bit.

It would only change when I completely closed them. I was able to open them a lot like 5 turns. Almost so they were completely out. Nothing changed. It still ran exactly the same at half a turn out and 5 turns out. I didn't just jump to 5 turns I went in 1/4 turn incrimates. I'd turn the screw. Try to rev it. It acted exactly the same every time.

[skids]

When I was messing with the carburetors last night I played with the idles screws a bit.

It would only change when I completely closed them. I was able to open them a lot like 5 turns. Almost so they were completely out. Nothing changed. It still ran exactly the same at half a turn out and 5 turns out. I didn't just jump to 5 turns I went in 1/4 turn incrimates. I'd turn the screw. Try to rev it. It acted exactly the same every time.

Do your pilot screws have tiny o-rings with washers above those? It does make a difference with the adjustment. What you might also want to do is warm the engine, turn off the choke, throw in some clean plugs, and try to keep the bike running 5 minutes where there is the onset of trouble. Then quickly shut off the bike and examine the plugs to see if they are white (lean) or sooty (rich) or wet (no spark or no burn due to way rich).

[darylcaribou69]

There are o rings and washers on them. I'm gonna do that with the plugs. I never thought of that.

My thoughts as of now. Pilot jets are too small. It's hard to start and I can unscrew the idle screws all the way to the moon and dump gas directly down the carb and it still runs lean. Haha!

If for just a short period of time is it an issue to test if it's running lean? I know lean is hot and hot is bad.

[motoman]

When I was messing with the carburetors last night I played with the idles screws a bit.

It would only change when I completely closed them. I was able to open them a lot like 5 turns. Almost so they were completely out. Nothing changed. It still ran exactly the same at half a turn out and 5 turns out. I didn't just jump to 5 turns I went in 1/4 turn incrimates. I'd turn the screw. Try to rev it. It acted exactly the same every time.

With no changed cept when a mixture is all the way in, which in fact should kill the motor, definitely says there is a vacuum leak. Most likely the o-ring on mixture screw is NOT sealing properly,(BTDT). I suggest replacing those mixture screw teeny O-rings first off. Then with motor warmed up, let it idle and back out first mixture screw several turns(5-6), then start in slowly till a sound change that stays constant occurs. Then back screw out 1/8 to NO MORE than a quarter turn. Do next three same way, adjusting idle down each time to 900rpm range. You have just used the 'lean-drop' method. Now, go back and set sync using 4 vacuum gauges or manometer(my preference is manometer). I also go back and re-set idle mixtures one more time for precision and re-check and set sync.....ride and enjoy the new smoothness of these motors.

[darylcaribou69]

I did replace the o rings with 3mm inside diameter by 1mm cross section o rings. I read somewhere that those are the ones it needs. Probably not though.

[motoman]

I did replace the o rings with 3mm inside diameter by 1mm cross section o rings. I read somewhere that those are the ones it needs. Probably not though.

Obviously have previously replaced mine with similar issue, but they were sent to me IIRC from Yamaholic. So consequently, have no knowledge of their actual size, but highly suspect based on my own experience that is the first suspect issue. After putting new 0rings on those mixture screws, smear just a shiny coating of dielectic grease on them. This keeps them from being pinched or distorted when screwing them back in carb.

[darylcaribou69]

Will do when I can get back at the bike.

Thank You!

[motoman]

My point is that 1.5 turns might not be enough. Also, my bike is running quite well.
42.5 pilots
pilot screws to 3.5 turns
Adjusted floats[.925 (lean) to .886 (rich), middle is .906]
No.1 No.2 No.3 No.4
.905 .902 .904 .904
185 air, 300X2 nozzles, 110 mains

8500 feet elevation, stock airbox with K&N, 4 into 2 81H pipes.

Between your elevation location and mixture screws 3.5 turns out.....definitely too rich.....unless vacuum leak getting by those mixture screw O-rings. Also, at your elevation, I'd lower those fuel bowl levels another 1/4mm. That factory float setting of 23mm IS sea-level settings, as is the 'check while idleing' hosed 3mm fuel levels. Based on my many decades of automotive re-building and setting up of carbs, better results can be had with bike carbs also by dropping that fuel level a smidgen from stock sea level settings.