Carb Riddle...

[Shuriken]

~5700ft Elev
Stock 79sf except for 4-1 exhaust.
Can't remember jetting, but will have to go back through my notes to find out.

Bike does not start without a full choke. After about 10 seconds, I back it off to middle choke, then about 30 seconds later, I turn off choke altogether.

After it is thoroughly warm, it runs pretty good and idles pretty good. The carbs are in synch according to my Carbtune guages.

Haven't checked compression in awhile, but last time I did, all were around 130 I think.

I will check plug color again, but before I get into that, I wanted to ask for opinions.

I've been riding other modern bikes lately that have made the old XS feel pretty slow. Most times I swap rides. Well, when I ride behind my XS on another bike, I can smell a very rich exhaust smell, like the bike is running way too rich. Gas mileage isn't very hot. I think around town it is only 25.

The question is, why does it require choke to start and yet smell rich all the time when running? Keep in mind that I have a 4-1 as well. Something doesn't add up. Although I'm pretty happy with the way my XS runs, I still don't think it is dialed in just right.

Ben

[xschop]

heres the problem

you're probly higher than member Skids ( elevation wise)~5700ft Elev. and you need less gas/ vol. air. IMHO I wouldn't have a 4-1 pipe above 3k elevation. The newer fuel inj. bikes take care of this problem that all carbed vehicles run into. Jet down

[skids]

Re: heres the problem

Theoretically 4-1's will run lean, but using 4-1 Jardines, I have experienced the need for lower mains on one set and higher mains on another. If it smells rich, it is rich. I don't know what rpms/speed your is running rich, but try the adjustments one or maybe two at a time to assess the affect of any changes. PS, you have a pretty good memory Chop. 5400 ft elev. here. Examine those pilots and make sure they are pinholes near the outllets rather than the K&N types...unless you know how to deal with that! (I don't).

Originally posted by xschop
you're probly higher than member Skids ( elevation wise)~5700ft Elev. and you need less gas/ vol. air. IMHO I wouldn't have a 4-1 pipe above 3k elevation. The newer fuel inj. bikes take care of this problem that all carbed vehicles run into. Jet down

[79XS11F]

You can't really compare your running fuel mix to your idling mix. At idle the main and needle jets will not have come into play yet. This is why an engine can be ether rich or lean on idle and the opposite when in use and the other jets come into play. Richen up your idle to fix the cold blooded part of your issue and adjust your needle and or main jets as necessary to correct what sounds like or smells like a rich condition.
Richening up your idle will automatically make the midrange and top end a tad richer but it does not go the other way. Idle setting will affect all others settings. Also keep in mind that these older bikes did run richer then modern bikes.
Also .. In my opinion the jaridne 4 in 1 or 4 into 2 pipes are not true proformance pipes so re-jetting is often not needed and when needed the change needed is usully minimal. Perhaps even less then the next jet size which sort of makes it difficult to get it perfect.
Rob

[Shuriken]

I haven't had any time to get to this problem yet.

I did yank the air filter out and the bottom-housing. I ran the bike that way for a couple of blocks to see how this condition would affect overall performance.

The bike did not have nearly as much power under acceleration as when the filter is installed. I expected this, since this condition leans out all circuits.

In talking out loud about these replies, it seems that idle is lean and mid/WOT might be rich. If I remember correctly, I have fiddled with the needle position before and the results did not improve. Perhaps I have the wrong main.

Also, I've synched the carbs, but if you get the synch off, you can also get that "rich" smell.
Ben

[DiverRay]

Ben,
Don't forget the float level!!! On these old bikes, it has a LOT to do with the way it runs. If you are high by 2 mm, you will be running way rich at mid and full throttle. I would drop the float 1mm at a time, once you KNOW all 4 are THE SAME.
By drop, it should be if the setting is 25mm, go to 26mm. That will DROP the level of fuel in the bowel.

[Shuriken]

Originally posted by DiverRay
By drop, it should be if the setting is 25mm, go to 26mm. That will DROP the level of fuel in the bowel.

Ex-Lax will drop the fuel level in the bowel!

No, I agree. I need to check the levels while the carbs are installed. This entails connecting bleeder screws to plastic tubing that is carefully marked. There has been discussion on this before, but I haven't done it yet.

Measuring float bowl height is very tricky. Makes me wonder how it is possible to get all 4 exact when 1mm is so small.

Thanks for the reply.

Ben

[randy]

Ben, you have a '79 Special. Stock carbs don't have bleeder screws, you flip the carbs over and manually set the floats.

Unless you have a later set of carbs, in which case, your mains may be wrong-sized to begin with?

[Shuriken]

Yeah. I meant adapter bleeder screws.

A certain size of brake bleeder screws work on these float bowls. I don't remember the mm right now....

Ben

[egsols]

Ben,

I found it easier on the 79 just to pull the carbs and make a quick guage to set all floats the same, and at what level you want and then reinstall. I set mine to factory specs, currently have a 4 into 1 Jardine and it seems to run good. Maybe a tad rich by smell but plugs look good. Rarely have to go to full choke to start, half works most times.

[Jeremy_Sells]

http://www.xs11.com/forum/showthread.php?s=&postid=31944#post31944

Here is the link to using a brake bleeder screw to set the float height on the 78-79 carbs. I think the pitch is 8x1.25. With these early carbs with brass floats, I have found that after I set them up with the clear tubing method and then went back in and checked them with a caliper - they all vary. The reason the factory started adding the bleed nipple and stop screw to the bottom of the later carbs is because it allows for a much more accurate calibration and setting. Depending on how delicate the previous owner/mechanic was when they worked on your carbs, the chance that all the little bends and shapes of each individual float are still the same is very slim! I have mine set so that the fuel level in the clear tubing is in line with the base of the screw head that holds the float bowl on. I get the bike on the center stand and shim under the front wheel so that the carbs are level and then do the testing. You will have the carbs on and off at least 4 times so it makes sense that you will also want to have the airbox out while you are making the adjustments. Good luck! P.S. If you have a spare cylinder head and remote fuel tank, this can be done on a bench and it is A LOT easier!

As far as mixture/jet settings go, even a perfectly dialed in carbureted bike will seem weak at your elevation. CV carbs rely on air density and velocity to move the diaphram/piston up into the carb body so with less air density (higher elevation) the piston will rise less at any given throttle position. You're never going to make the power that you can at lower elevations because piston rise controls both airflow and fuel delivery. You could alway add a turbo! If your floats are set, valves adjusted, colortuned idle mix, clean air intake and you smell rich above 3K, decrease the size of the mains. A rich running bike will perform like a lazy dog while an overly lean bike will surge and hesitiate - two ends of the mixture spectrum with very different "feels". Good luck!

[gareth]

FWIW...

I just set the float heights on my '79SF. I found that the 3/16" thick wall clear tubing bought at a local hardware store threaded tightly into the float bowl drains. YMMV.

Gareth.

[randy]

Gareth,

I see you're in NYC. My Brother and I are doing a Montauk run on Sat Sept 1. You up for it?

For that matter, anyone else in the NY metro area is welcome.

Voice your interest and i'll post details.

[gareth]

I do wish that my bike was thisclose to being ready to play Dodge-the- Truck on the L.I.E..but float height is just task #12 on a list of, say, ten XS-ential Tweaks for this bike. No way to be ready for test drives by Sept 1. Keep me updated on other outings, though. Sounds like fun on a working, reliable Special.

Gareth

[egsols]

Hi Randy,

I'm thinking off swapping out my 4 into 1 Jardine for a 4 into 2 Macs. I see that's what you have. How do like them, are they close to stock?

Ernie