Anyone ran an XS on a 5 gas analyzer? Normal readings at idle?

[Jaymichael]

One of the spiffs of working at an automotive school is access to fun toys. I had set up my carbs using normal methods in the fall. I suspected my idle mixture was a tad rich as my most stable idle was found with my idle mixture screw pretty much all the way in running a 45 pilot jet. I ordered up a smaller pair of jets but to be sure where I was starting from I ran her on our exhaust sniffer last night. I confirmed she is running quite rich, started about 10% CO which is about 10.7:1, I closed the pilot screws completely and she dropped to 8% C0, which correlates to 11.5:1 fuel ratio.

I just swapped in some 42.5's this morning and will try running it again the next couple nights. If anyone has done this before, what specific fuel ratio did you dial it into? The tune up guys here are telling me in the range of 3-5% CO is what I should shoot for, that would put me around 13.3-12.6:1. Personally I don't mind keeping it slightly on the rich side to avoid higher temps, and a smooth idle is paramount of course. Any one gone this route? Care to share your results?

 

[gggGary]

 

[5twins]

From what I see, you have an older model ('74) so it may very well show as richer, even if jetted correctly, than what's considered normal for a modern engine.

 

[Jaymichael]

Hard for me to say what it ran like stock, never did hear it run. Slight head work and 750 kit has prob changed demands a bit. I def need to drop a pilot jet for sure, having the pilot screws all the way in allows me no room for fine tuning. Ill tune it as per our regular procedures and then put it back on the sniffer to confirm a perfect balance side to side. Ill keep this thread informed what the numbers are as I go, always good for reference I guess. Been reading a bunch of articles on appropriate idle air fuel mixtures for air cooled engine, 13:1 keeps coming up, which would be right around 4% CO. Modern cars would land quite a bit leaner than that.

 

[lakeview]

Looking forward to the results of your research.

 

[Jaymichael]

Still a work in progress... I have run out of free time for this week, hope to dive deeper next week. I was able to spend about an hour playing around last night and after dropping from a 45 to a 42.5 pilot jet I have been able to drop my CO content from 8% to 5%, resulting in a fuel ratio of 12.6:1. Idle is still super tidy and smooth and off idle acceleration is nice and snappy. This is still considered to be quite rich even for an old air cooled engine. On an interesting side note my hydrocarbon numbers dropped huge, from around 1200 ppm to 350 ppm, meaning I have much less un burnt fuel exiting the exhaust. Will continue to update

 

[TwoManyXS1Bs]

Hey, Jay. I reviewed your last year's thread on your mix screw issue:

http://www.xs650.com/forum/showthread.php?t=43516

And, I'm curious to know if your carb throats may be non-round, squashed, like mine.
The thinking here is that, if they are, then your idle stop positions may have too much of the transfer (bypass) ports exposed, reducing the effectiveness of the mix screws, and putting more reliance on the pilot jet sizes to control the idle air/fuel ratios.

Have a look at this album pic, and proceed backwards another 8 pics, to see if this applies to you.

 

[gggGary]

I really am interested in this discussion, 2 wide band O2 sensor/gauges are in my future.

 

[Jaymichael]

twomany.... Yikes! That's pretty weird. Let me see if I can get a caliper on mine today and I'll let you know. I had rationalized that I needed to go down a jet size due to increased air volume created by the 750 kit, but perhaps this could be contributing as well

Gggary, I also have a wideband kit that I plan to use to see where I land in my mid and main circuit operation. I've built a pair of pipe extensions that slip over my headers with bungs welded in to house the sensors. Keep me posted on how you make out, information rules

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