Another carb tuning question

[Hobbit]

79 Yamaha xs11 Special

Rebuilt the carbs with new jets (numbers are the same as previous jets), new floats, new float needle and seats and new venture needles (came with the rebuilt kit).

The bike start fine using the choke, the choke can be shut off almost immediately and the bike will idle just fine.

Transition from idle to mild or aggressive acceleration is good and the bike runs strong when pulling. The problem is at a 45 to 55 mph cruise, the bike loads up and surges. When I pull the plugs they are black and sooty. Obviously rich.

Now the question is: Do I try lowering the float level a little more, or should I lower the needles?

[Snow]

After you put in the new float needle seats, do you test to make sure they are all seated correctly by flipping the carbs upsidedown and blowing in through the gas lines? If those leaked, you could definately run a little rich. When you check the plugs, are you doing a plug chop with new plugs or are you just simply pulling the plugs out at home?

Did you reset the float to stock height?

It does sound like a rich condition, but better to doublecheck the easy things first.

[pgg]

Heaps of combinations to try mate. You'll have removing and installing your carbs down to a fine art. he-he.

[Hobbit]

The floats are not leaking. I checked the new plugs by running the bike about 8 miles between 45 and 55 mph. Then I disengaged the clutch at the same time that I hit the kill switch. I coasted to the side of the road and pulled the plugs. As I said, very blackand sooty.

Full throttle seems to clear it out, so I'm thinking that the main jetting is okay, and the idle is good. When you twist the throttle from idle, there is a quick puff of black smoke.

[Snow]

You should try doing a main jet plug chop -

First, warm up on the plugs you have now and bring along new plug(s) and a spark plug socket and socket wrench. After she is completley warmed up, then pull over to the side of the road, put in the new plug(s), and shift up a couple gears as soon as you can (like 3rd or fourth I believe it goes). Then, go WOT, preferably uphill, but where you have a long distance you can go without running into the man

Then cut the motor via killswitch, pull in the clutch, and pull over and pull the plug(s) and take a gander.

If you run 8 miles 45-55 about the only thing you will be checking is your midrange.

If the plug chop I describe comes up as a nice tan color, then you are good on Mains and need to lower your needle (move clip up) to lean up the midrange.

If the plug chop shows that the mains are too rich, then go down one main size and do the plug chop again.

To the gurus: please correct me if any of that info is off.

Btw, are you planning on going to XS East in October?

[Snow]

Doh! Another thing to try, try spraying some good carb cleaner in through the main air jets to make sure they are all clear and maybe even pull out the emulsion tubes and spray compressed air through them.

[Hobbit]

Thanks for all of the info.

First, The carbs have been at least triple cleaned, with new jets installed, the tubes pulled and cleaned, fuel filters added and so on.
Second, I don't think that I can find a hill in this part of Florida.
Also, this is the first time in about 10 years that this bike has run. I'm just now in the process of resurrecting it. (Brakes, forks, seat, fuse box, paint and carbs, etc.)

The ride at TWO? You bet! My wife, son and I are planning to be there with either both of my xs11s or one 11 and my son's 650 Maxim. (That's why I'm trying to get it running right.)

I have some pics posted at:
http://www.imagestation.com/album/?id=4289368357

[Snow]

Kewl, hope to see you all up there if I can get my gremlins sorted out. Yeah, I'm in the mountains of Florida I actually do my test up the tallest hill in the Capital City of Florida

Nice lookin' XS - is that color changing paint?

[Hobbit]

Thanks for the help and the kind words Snow.
Yes it is "Mirage" paint (even the stripes and cross are Mirage.).
I painted it myself and also made the back rest and redid the seat along with all of the mechanical stuff.

We have reserved te trailer at TWO, stop by when you get a chance.

[TopCatGr58]

First, The carbs have been at least triple cleaned, with new jets installed, the tubes pulled and cleaned, fuel filters added and so on.

Hey there Hobbit,

After reading the above, it sounds like it might not be the carbs so much as the rings, and excessive amounts of carbon buildup!? You may want to try to MMoil in the topend and in the oil to free up possibly stuck rings. Where was this engine stored? Was it properly setup before storing....ie. oil in cylinders, etc.?

Also, you will want to get it out on the highway in 4th gear, not 5th, at about 65-70mph, and run it for at least a half hour or so that way, to really clean up the insides, burn off all that old carbon, and heat the engine up good, possibly help in unsticking rings, or at least to reseat them.....?mild rust in the cylinders?

How many miles on the engine, what grade of oil, have you done a compression test? If it's got a lot of miles, you could have worn cylinders/rings, and getting some mild oil past them into the combustion chamber?

Finally, cruising at 45-55mph, if you are in 5th gear, and then trying to accelerate from 45......you're close to the lugging rpm if it's at or below 3k in that high a gear, IMHO. I always try to keep my RPM's near 4k or above, try using a lower gear and run that same transition speed and see if you notice the surging, my guess is you won't!!

Looking forward to meeting a lot of the southeastern XSives at TWO also. An ex-Floridian...(Orlando '58-'73).

[Hobbit]

The engine seems mechanically good. I soaked the rings with Marvel Mystery oil before I cranked it up, changed all of the fluids etc. Vacuum and compression are both good.

The bike had been stored inside and had been maintained before they gave up on it.

Apperently the pick-up wires broke and nobody could figure it out, so they just let it set. It went through at least 3 different owners before I got it. (They had no clue what was wrong and didn't try to find out.)

I'll try keeping the revs up and see what happens.
Thanks.

[pgg]

Your pilot circuits are definitely way too rich. If your new jets weren't mikunis then they will almost certainly be a different size even if they have the same number. Mikunis are rated by flow rate eg - 150 equals 150 mls of fuel per minute. Whereas dynajets are rated by diameter eg - 150 equals 1.5 mm. If you lower the needles 1 notch it will probably run cleaner at low revs but I'd be inclined to rejet to the standard needle position rather than the other way round. The main jets also affect your low down circuit as well. On an xs11 around 4800 revs and below. Just looking at your message , you say you have new venture? needles - then I'd say the needles are different than the originals and you'll probably get things right by lowering them alone.

[Hobbit]

Thanks a lot for the information. I think the first thing that I'll do is compare the jets using the numbered drill bits to see how much different they are.
I'll also inspect the needles and see what looks to be the best route to try.

Thanks again.