Need Carburetor Advice

[Petersg_99]

Yesterday I tried to get through emissions and failed, previous post here:
http://www.xs11.com/forum/showpost.p...postcount=1474

So this morning:
1) Ran bike to temp. with new timing and original carb settings, it was backfiring on deceleration and the idle was too low.
2) Discovered that the throttle cable was too tight and that was overriding the idle adjust knob on the carbs.
3) Adjusted throttle cable so to fix #2.
4) Rechecked carb sync (They were pretty much dead on)

Now comes the funny part, when I tried to set the idle adjustment the carbs just acted goofy, and I've got to admit they've always been this way:

1) set idle set screws on all carbs about 1.5 turns out from lightly seated, initial RPM around 1000
a) turn idle set screws on carbs 2 or 3 in and the RPM goes up all the way to lightly seated.
b) turn idle set screw on carb 4 and RPM goes down, lightly seated, bike dies
c) idle screw on carb 1 doesn't seem to have much impact.

2) I tweaked all the carbs to about 3/4 turns out and got the RPM set around 1000 and attempted to drive down to the emission place. I never got out of the neighborhood, the bike was running so badly I was lucky go get back home.

I cleaned/replaced the float valves on the carbs when I first got the bike, but ever since I got the bike I've been suspicious of the carbs because the set screw on the #2 carb was ground down (see pic), and the needle valve is shaped a little differently in #2 than it is in the other 3 carbs.



I just got another set of 81 carbs (my bikes an 80) from ebay that don't have the ground idle set screw on the #2 carb, but they're pretty dirty and even though the seller said they came off of a running bike, they're leaking gas all over the place when I tried them out.

At this point in time I'm inclined to abandon trying to get my 80 carbs working and shift my attention to the 81 carbs.

Do you guys think I'm on the right track now, or should keep slugging away at the 80 carbs???

[motoman]

Yesterday I tried to get through emissions and failed, previous post here:
http://www.xs11.com/forum/showpost.p...postcount=1474

So this morning:
1) Ran bike to temp. with new timing and original carb settings, it was backfiring on deceleration and the idle was too low.
2) Discovered that the throttle cable was too tight and that was overriding the idle adjust knob on the carbs.
3) Adjusted throttle cable so to fix #2.
4) Rechecked carb sync (They were pretty much dead on)

Now comes the funny part, when I tried to set the idle adjustment the carbs just acted goofy, and I've got to admit they've always been this way:

1) set idle set screws on all carbs about 1.5 turns out from lightly seated, initial RPM around 1000
a) turn idle set screws on carbs 2 or 3 in and the RPM goes up all the way to lightly seated.
b) turn idle set screw on carb 4 and RPM goes down, lightly seated, bike dies
c) idle screw on carb 1 doesn't seem to have much impact.

2) I tweaked all the carbs to about 3/4 turns out and got the RPM set around 1000 and attempted to drive down to the emission place. I never got out of the neighborhood, the bike was running so badly I was lucky go get back home.

I cleaned/replaced the float valves on the carbs when I first got the bike, but ever since I got the bike I've been suspicious of the carbs because the set screw on the #2 carb was ground down (see pic), and the needle valve is shaped a little differently in #2 than it is in the other 3 carbs.



I just got another set of 81 carbs (my bikes an 80) from ebay that don't have the ground idle set screw on the #2 carb, but they're pretty dirty and even though the seller said they came off of a running bike, they're leaking gas all over the place when I tried them out.

At this point in time I'm inclined to abandon trying to get my 80 carbs working and shift my attention to the 81 carbs.

Do you guys think I'm on the right track now, or should keep slugging away at the 80 carbs???

............either or, your choice............but, if you've changed that static timing, it needs to go back to stock position first, or your gonna chase your tail. This for what it's worth changes ALOT more than just timing. Changes vacuum in the different rpm ranges which changes vacuum on diaphrams which changes needle position at a given rpm....and on an on. So, as you can see, that little tweak of the timing changs a whole array of functions......and now a change may be made in carbs........your headed down a dark frustrating path, but guess your gonna do do whatever in spite of experienced advice here. BTW, know your area and Tuscon very well.

[natemoen]

Little confused by your post so I am just going to explain a few things on the carbs first and then we can go on from there later. I do agree that you need to put the timing back to where is was originally first.

There is on 1 idle set screw and that is the big knob pointing down in-between carbs 2 and 3. That is the ONLY thing you should be using to set the idle RPMS.

The other 3 screws that are up in-between the carbs are the sync screws. Those are to change the position of the butterfly's to set the carb sync.

The 4 screws set down in the tunnel on top of the front of the carb is the idle mix screw. As you tun that screw in you lean out the idle mix, and as you turn that screw out you richen the idle mix.

[TopCatGr58]

Hey Nate,

I agree that I think there is some confusion about the different screws on the carbs and what they do. He did say that he was able to check the "carb" synch...and that it was dead on....but he didn't say VACUUM synch, so I'm wondering if he means the Bench Synch??? After adjusting/turning the large spring/exposed screws between the carbs, he should have gotten the VAC synch all out wack...which partly sounds like what happened=why it's running like crap now!!!

The ground down "idle/Pilot" screw he called a SET screw....well..the screw isn't ground down, just the TOWER that it sits in! These appear to be the later series carbs...80's...so their pilot screws are not as prone to getting broken off in the carbs.....but I can't see the top of the #1 carb pilot screw tower very well but it looks like the factory seal is still in place. I think he's only been able to see the #2 screw and that's why he calls it a set screw...but he will need to drill thru the caps and remove them from the other 3 carbs IF they are not open/exposed.

Then he'll need to take the carbs off, at least take the pilot screws out, and spritz thru the pilot circuit to ensure that it's open and flowing freely, and THEN he'll be able to properly adjust the idle/pilot circuit tuning.

Would also suggest a search for emission test for some threads... remember reading one about being able to use a special fuel additive that can help bring down the emissions...at least temporarily so he can pass the test!

T.C.

[motoman]

Not intended to be a thread hi-jack, but as for the emmissin testing in Phoenix or Tuscon, called my son in Tuscon and this is what I got....."until the EPA takes action on a submitial from Phoenix, motorcycles are continued to be tested. Nothing is exempt unless it's under 90cc's OR it's a vehicle older than 1970"........BTW T.C. SeaFoam is what your lookin' for......

[Petersg_99]

Ok, so the consensus is to change the timing back to the original setting which is set to the "T" not the "F". I'm OK with that, it's not like I can't change it again if needed.

I synced the carbs with vacuum gauges, and they're pretty much dead on.

I set the rpm with the single knob on the bottom

I adjusted the idle air screws (the 4 brass ones - one per carb) 3/4 turns off lightly seated. The funny thing is that turning the idle air screws in on carbs 2 and 3 - lean the mix - the RPM goes up and the highest RPM is when these screws are lightly seated (leanest mix possible).

The thing that worries me is the differences in carb #2 between the other 3, and the fact that the carbs don't behave like other carbs described here on XS11.com...

[natemoen]

put the idle mix screws at 2.5 turns out. 3/4 of a turn is going to be too lean.

As odd as it sounds, the rpms will increase as you lean the engine out. Those screws control fuel NOT air.

[Petersg_99]

It's not super obvious, but the idle mixture screw on the left is from carb #3 and the one on the right is from carb #2. The mix screw from #2 is shorter than the one from #3. It's real obvious when you run your finger on the inside of the throat of the carb with the mix screws lightly seated.

This along with the ground down tower makes me wonder why did the PO do this? The bike ran like a scalded ape even though it failed emissions with these carbs (a little flat up to 1500-2000 rpm, but took off like a rocket after that), but it still spits and burps at idle and I think that's one of the things causing the emissions failures. With the different needle valves and the ground down "tower" is it even possible to get everything dialed in enough to pass emissions?

[Petersg_99]

Ok, I'll put the timing back to factory and try the original carbs one more time starting with 2.5 turns out. If that goes all pear shaped I'll turn my attention to the new carbs...

put the idle mix screws at 2.5 turns out. 3/4 of a turn is going to be too lean.

As odd as it sounds, the rpms will increase as you lean the engine out. Those screws control fuel NOT air.

[bikerphil]

If you hook your vacuum gauges back up, then turn the idle mixture screw until the highest vacuum reading is achieved. Watch the gauge closely, it won't be much of a change. If you do this with each carb and then re-sink, the screws should be then correct. I also suggest if you haven't resealed the carb boots to the head, to do so. A vacuum leak up there will make things impossible to tune. No response from one of the idle mixture screws could mean a clog in the pilot circuit or a vacuum leak. HTH, GL

[natemoen]

The tower being ground down makes no difference. The mix screws were "sealed" from the factory by a plug at the top of the tower. As long as the threads for the mix screws are all still there then the rest of the tower is not needed.

[BA80]

If you hook your vacuum gauges back up, then turn the idle mixture screw until the highest vacuum reading is achieved. Watch the gauge closely, it won't be much of a change. If you do this with each carb and then re-sink, the screws should be then correct. I also suggest if you haven't resealed the carb boots to the head, to do so. A vacuum leak up there will make things impossible to tune. No response from one of the idle mixture screws could mean a clog in the pilot circuit or a vacuum leak. HTH, GL

+1....time consuming and repetetive but that's how it's done.
You should do this over and over until there is no change.

[LoHo]

I imagine the PO tore the seized brass needle so badly that he couldn't get it out, so he cut down to where he could use more persuasive methods, then put in another needle he had handy. The fact that it fits and has the same geometry is a good sign. I may be wrong, but if it lightly seats and has the same threading as an original, then two turns out is two turns out and it should work fine.

[Petersg_99]

Unfortunately I didn't get to try anything today. I'm back to work Monday, and I'll be layed up from surgery next weekend, so I'm betting it will be a couple of weeks until I get a chance to put the timing back to factory and re-install the carbs for round 3, or 4, or whatever of tuning.

I ordered a colortune too, so next time I'll have another data point to confuse myself with (yes, I know some people say they're a piece of poo...).

Thanks for the suggestions

[Petersg_99]

The Bike is running...

So, surgery is over, and I'm starting to get a cold, what else to do but work on the bike .

I took everyone's advise and changed the timing back to the factory original setting.

Then I took the original carbs and replaced the funky needle in the #2 carb with one from the new set of carbs that matches the other 3 needles.

I set the initial needle valves at 2.5 turns off lightly seated and set the butterflys so they were just in the middle of the little idle circuit hole in the top of the throat (per the carb how to postings here on XS11.com).

I fired up the old gal and let her warm up, she was a little finicky, but not too hard to keep running. I then ran a colortune across all 4 cylinders and adjusted the needle valves for a consistent blue across the cylinders.

I took the bike out for a quick run up and down the street, and I'm pretty sure the bike is running better than before. I'll run it through emission testing on my way to work on Monday and see if it passes.

A side note on the colortune. The one I got tended to jump the spark across the top of the sight glass which is really funny since the electrode gap in the combustion chamber is pretty small compared (like 10 to 20X smaller) to the gap it was jumping outside. I'm not sure if I got Bunsen burner blue, it seemed more of a whitish blue, but I did notice a yellowish blue when the mix was too rich, and it seemed like I was getting excessive sparking outside the chamber when the mix was too lean. All in all, not exactly what I was hoping for with the colortune, but at the same time, it seemed to provide some additional feedback along with the idle speed for setting the needle valves.