Yet ANOTHER carb question

[Grimace]

I have a 79standard, 4-1 exhaust, pod filters, jetted for the filters and exhaust. I have been fighting this 3500 rpm bog, and a wide open throttle stutter for a long time. I can ride my bike with no problems, (reset the float levels using a clear plastic tube like in the tech tips) until I reach 3500 rpms. Then I get a bog. Upshift to 5th, and I can putt around town with no issues turning about 3k rpms. Or I can downshift to third and turn 4k and be fine.

Then, get on the highway, and if I gradually roll into the throttle, I can sustain wot to over 100 mph. If I just twist the throttle really quick, it stutters and bucks.

1,2,3 plugs are really clean, and 4 has a little black soot on it. I turned the idle mixture screws on 1,2,3 out a quarter of a turn, and 4 in a quarter. Seems to run ok, but now I have a very slight pop through the exhaust at idle. I also have a very noticable popping through the exhaust at throttle closed deceleration (engine braking).

Another thing I noticed, is when I get a strong sidewind, my bike bogs really badly (slow in town riding) and I have to twist the throttle to get it to clean out again. This is from the open filters, but does anyone have a fix other than put an airbox back on? would the velocity stacks and custom side plates be an option?


Any help is always appreciated, and I am ordering all new coils, wires, and plug caps tomorrow.


Justin.

[egsols]

reset the float levels using a clear plastic tube like in the tech tips

How did you attach the tubes to the bowls? If the bowls are made for the tubes then I don't you have '79 carbs on there and that could be part of the issue.

[boyat68]

Grimace:

In the Yamaha Manual, page 4-5, it shows that your carbs have a Jet needle clip that can be used to set a lean or rich mixture by moving the clip. I quote from the manual, "The mid-range air/fuel supply is affected by the position of the needle in the needle jet. Check to see that the needle clip position is correct." There has been a lot written on this site about positioning the clip on the 79 set of carbs as that will cause rich/lean problems in the mid range of the carb cycle. Also some contributors have suggested that leaving the clips in the middle and changing jet sizes does the same thing.

Also note that the 80 carbs do not have the adjustable jet needle. It is suggested that putting a small washer under the jet needle head will raise the needle a slight bit allowing more fuel to reach the venturi, thus enriching the mixture in the middle range.

[DiverRay]

With the adjustments you have done, did you use a carbstix or vacuum gauge to sync the carbs?? If not, THAT is your "Starting Line".

[mason79]

get rid of the pods

[planedick]

What Mason says

He knows that stock is best.....

[79XS11F]

When I owned my first 1978 11 and put a Kerker 4 -1 pipe on it I was instructed to increase the main jets as usual but there was no adjustment of the clip position on the needle. The needle was REPLACED with a different size richer needle. I clearly remember waiting for them to arrive. Sorry ... I don't remember what size the replacement needles were. You may notice that dyno-flow carb kits come with replacement needles in many cases.
The bike run very well with that setup.
Rob

[Grimace]

To attach the tube to the carb bowl, I cut the plastic tube off of an old fix-a-flat can. It threaded perfectly in the drain plug hole. I have original 79 carbs, and I checked the needle position, all 4 are in the middle groove.

Ray, I used a motion-pro mercury stick, and adjusted all four carbs to 18 inches of vacuum.

Would a shroud around the air filters get rid of my problem with side winds? I don't have the original airbox, and really no desire to change back. I know there are tons of people running pod filters, and they are not having the problems I am. I just need to keep plugging away at it and I will find the solution.

Thanks for the help guys, and I ordered replacement coils today from mikesxs. Why do I keep hearing that it is bad to tell him the parts are for an xs11?



Oh yeah, my pilot jets are 45 and the mains are 147.5

[DiverRay]

It sounds as if the float height is off. If all 4 are the same, try going up or down 1mm. As I don't know what you have them set to now, I can't say what way to go. I have mine set off just a little from the stock height setting. The bog is just as you go into the mains, and the stumble may be running lean, or very rich. I would do a "plug read" and go from there. Put in NEW plugs, go for a ride at the high RPM stumble stage, cut the engine, coast to a stop and pull the spark plugs. Look at the color and write it down in a book. If they are white, you are probably running lean. If they are dark brown to black, you are running rich.
If lean, lower the float height by 1mm. If rich, raise the float height by 1mm. If you are at 26mm now, and running lean, set ALL the floats to 25mm. If you are running rich, set them to 27mm.

[81xsproject]

You don't need a shroud and you CERTAINLY don't need the darn airbox. Big help guys... Anyway, they cross wind thing makes me wonder where and what you have done with the bowl vent tubes. Here on the coast we get some pretty viscous winds. I have ridden in crosswinds that despite my leaning were still making the bike go sides. Never once has the wind caused my bike to fault. Also, what type of pods are you using? If they are the EMGO ones, some restrict flow throw the airjets and cause issues.

[Grimace]

I have the float height set like the tech tips said, but I will try to reset them. I did a wot blast and killed the engine. I coasted into my shop and pulled the plugs. 1,2,3 were mostly white, with one little tiny spot of light tan on them. 4 was all dark tan.


The pods are the little cone shaped ones, not sure of the brand. I did trim the inside of the rubber part of the filter so it wouldn't restrict the air to the jets or the diaphram.


Thanks for the help guys, I am still plugging away at it. Can't do any riding/testing right now. I have the wheels off and am re-doing the wheels.

[Nate Dogg]

Detonation on 1, 2, and 3? Need to increase rich on those cylinders if you see brown spots/flecks.

[prometheus578]

"Just an oddity..."

81xsproject...
I recall reading a technical bulletin on one of the Kawasaki MULE utility vehicles.
If towing the MULE on an open trailer with the MULE facing backwards... the airflow past the carb vent line causes the carbs to flood.
(wonder how long it took them to figger out that one?)

[egsols]

As noted by 81XS, what did you do with your carb vents? On the 79 they ran back to the airbox but with pods you have to find a different route and method to keep junk out of the lines.

[Grimace]

Carb vents are run up near the battery tray.