EGT range

[chaklid]

to the advanced xssers. i have a '79 xsSF. the engine runs nice; good power through out RPM range. however, took an infra red thermometer and observed upto 100++F of temp difference on the pipes at the engine outlet.

HOW SO????? when it idles steady at 1050, powers up great, and starts anytime, anywhere, hot or cold. plugs are all even, slightly on the dark side; fuel consumption on the high side, probably because i ride lots of stop and go.

SO, tell me, what should i check for??????

thank you all

chakli

[TopCatGr58]

Hey Chakli,

Which pipe(s) are hotter?? You may have a vacuum leak causing the hotter one to be running leaner compared to the others!

Have you pulled the plugs and checked their condition?

Several sources for vacuum leaks, as well as EXHAUST leaks, which can also cause overheating of cylinder! Try carb cleaner sprayed around intakes, check manifolds for leaks, also check the rubber vacuum port caps....can age, get brittle and also leak.
T.C.

[prometheus578]

Recheck all carb settings: mixture screw, float height, synch, etc.
These things will idle fairly smoothly, while only "fully" running on three, and even two cylinders.
Harbor Freight sells a infrared thermometer for $39 which, in my opinion, is every bit a good as the $200 one from MAC Tools.
And for the cash challenged... you can always just splash water on the header pipes and compare the sizzles... which is what I do 90% of the time anyway, for a quick diagnosis.

[Goin Commando]

Won't the cylinders in the middle run hotter than the ones on the outside?

[prometheus578]

Yes, they will. What the actual temp. readings should be because of that difference, who knows. In a perfect world, cylinders #1 and #4 should be the same, as should Cylinders #2 and #3. (But again, also in "perfect world", the richer jets in the middle carbs in later models would perfectly even the heating out)
Either way... I wouldn't sing to much about unequal heating. It's when one pipe, or two, are vastly different that I get concerned.
In our applications... a digital infrared reading is too accurate, and to try to adjust things to get all pipes the same would be futile due to all the variables of the engine.
Now... using a spray bottle of water on the pipes will show a less "exacting" tempurature difference. And if you can detect a difference between sizzles with your eyeballs, then you have something wrong that you can tune out by simple carb adjustments. (provided everything else is ok)

[skids]

If you tue it exactly at idle, it may be a bit off just above idle. I wouldn't sweat it too much as long as the performance is where you need it (not necessarily at idle).