emulsion tube/slide needle/slide/body wear

[Hawkins]

Has anyone had any experience with wear of any or all of the above causing mixture problems? I have seen some websites (e.g. www.factorypro.com) that describe my symptoms as being a result of this kind of wear.

My carbs are pouring a lot of gas through them. The floats and seats are fine - no leakage. Last night, as a test, I put the carbs on with no airbox. I didn't use any throttle or choke and cranked it over a few times. Took the carbs off and there is a puddle of gas in the intake rubbers. The only thing I can see is that the vacuum is pulling too much gas past the slide needle.

Tonight I will lower the needles (raise clip) and try the above test again.

Any day now we'll get pseudo-summer here in New-fog-land and I want to be riding for the 2 or 3 weeks it's here. 10 deg C here now at mid-day.

Any help / advice / black magic appreciated.

[mro]

lower the needles (raise clip)

Should not effect starting.

I'd check/lower float height while you got em off.



mro

[John]

Have you checked the O rings that seal the float needle seat to the carb body? They can leak and flood the carb even if the needle and seat are sealing well. I myself don't think that the wear on the parts you mentioned would cause the problem you described. I know you said that the float needles are in good shape, but being rubber tipped, they may have some wear on them allowing fuel to seep by, but I don't think it would be enough to cause a flooding problem while the engine is running. Do you have the correct carbs on the bike? How many hoses are there attached to the carbs? How many holes ring the air inlet side of the carbs? What are the float heights set at? Because the throttle plates are closed at idle, then vacuum should not be applied to the main jet circuit, so something else is causing the leak.

[Hawkins]

The seats, valves and o-rings are new. No gas leaks past regardless how much head I put on them by lifting the bench gas tank higher, or how long I leave them there.

The carbs and bike are 80SG, but the engine is '79F. The bowl vents are in the air inlet horn (1 on either side, + air screw, + main air jet).

Floats are set to have fuel level at the 1st edge of the bowl, about ~4mm below the mating surface.

The butterflies are open slightly at idle. I always had the understanding that the slide needles prevented the mains from supplying any gas until ~3000 rpm, but with air moving past the emulsion tube and a gap between the needle and the tube, I can't see how some gas won't leak past.

Anyway, more trials tonight. I'll try to pinpoint the source of the gas, but from what I've seen so far it doesn't seem to be getting in through the idle or enrichment circuits - it seems to be coming from the main, unless there is some other passageway there I'm not aware of.

Thanks for the input!

[mro]

Might want to read down to motoman's post
describes your problem, though cause could be something else

http://www.xs11.com/forum/showthread...t=float+height

then on left in tech tips describes how to set float height.

_______________
just my opinion
I'm sure whatever choice, upside down or slighty past horizontal seems to be working for eveyone. That was just a bit of info, as a Yamaha service tech, who had been factory trained for all the bikes of that era held my carb assembly in both positions and showed me what takes place when assembly goes towards totally upside down, rather than tilting assembly till floats fall till needle just seats. There is quite a noticable difference to the eye. Anyway, that's kinda why I also added that the difference between 23 and 27 mm is minimal for the specs. on the different years. That procedure as per Yamaha was for those that may be experiencing some over-fuel or flooding situations, and my 81H is liking the 27mm at the 5,000 ft. elev. where I live. For the most part, everything goes up from there, unless I travel more than 400 miles in any direction. Just something I learned this past week from someone who especially knows and likes these old XS's, and had been schooled in them.

motoman
________________________________

just edit post and added his comment

mro

[Hawkins]

getting closer

...but not there yet. Last night I closed the butterflies completely and tried cranking the engine - lots of gas in the boots. I then screwed the idle mixture screws all the way in and cranked again - no gas.

I have it idling well now at about 1/4 of a turn out. Skids said in a previous post that I would need really small mixture settings with 45 pilots. I had went as low as 1/2 a turn - crazy low I thought, but not low enough it seems. Where those 45's came from I don't know. I seem to recall checking once before and thinking they were all factory spec jets, with the exception that the mains are 110's for all 4 cylinders.

Anyway, idles great but has no power and sputters/backfires under load, unless I pull out the choke, which lights her up nice.

Wondering now what the best adjustment is to make next - raise the floats, raise the slide needles a hair or two, or wait until I can get a set of 42.5 pilots and 115 mains delivered and adjust around that. I like to have a margin of error on the float level to help prevent leaks, so I'd rather not mess with that.

FAnyway, just thinking via writing about it. I'll post the final solution when I find it - hopefully save someone else some headache at some point.

BTW, I found out last night that an oil change makes a big difference after spending time running way rich. The oil didn't smell gassy and wouldn't burn, but there was enough gas in there to cause problems.

[Hawkins]

had a ride yesterday, running good with 1/4 turn on idle mixture and half a notch (washer under c-clip, not over) richer on the slide needle. Still cold blooded and doesn't idle perfectly - seems too rich on idle and slightly lean above that. Need a day to do some plug chopping. Think 42.5 pilot jets are a no-brainer though.

Thanks to all who helped. Workng carb and electrical issues simultaneously is challenging at best.