Peak EGT Temperatures

[Adam_Winstone]

^... but I don't like the common approach of reducing main jet size to clean up lower stages of throttle progression as it can then lead to a situation where the main cannot supply what the engine is demanding at full WOT. IMO a carb should be set so that each of the progression steps is correct, rather than adjusting the adjacent stage too much to influence a problem stage.

Recently, I've been finding that I have to modify needles to give me exactly what I'm looking for. Indeed, even this bike of mine is running a reduced shaft diameter to give me a slightly richer lower progression, whilst keeping it correct at higher stages, which would become too rich if I simply fitted a richer atomiser. This practice of reworking needles is something that I know is very common with dyno centres but it does mean that you are in danger or thinking that a modified needle can still be thought of as the value marked on it, i.e. a modified X7 needles may then be much closer to X13 or X2 values, and would cause issue if a standard X7 was used as a replacement (or the atomiser and needle values quoted to a pal who might be looking for set-up ideas).

Adam

[nelson pk]

We all seem to agree that 1/4 throttle to half throttle is where the engine runs leanest/hottest. My point is that most people put too much emphasis on the main jet and loads and loads of people have over rich main jets in. In fact if you run a larger atomiser needle combo you will find you can run a slightly leaner main jet than if you were running a leaner needle /atomiser. That is pretty factual and i am not advocating leaning out your main so much that it goes pop on long stretches of full throttle but you both have said it gets hottest at 1/4 to 1/2 throttle and much cooler at over 1/2 throttle and this is where the main jet comes into play so what does that tell you? It would tell me that the bleed hole between the atomiser and needle may not be big enough at low throttle openings when cruising at higher revs. This is especially apparent on low revving expansions like the JL3 from what i have seen and been told and from my own experience.
A power jet will also allow you to richen up the mid range with minimal splutter and supply enough fuel at top end as well so it is a good solution.
With all the different set ups, pipes etc that are used sometimes its impossible to set the carb up to deliver enough fuel at high revs when fast cruising at 1/4 to 1/2 throttle and balance that with enough fuel at w.o.t and get this with splutter free running at low revs!
Thats my opinion and i'm sticking to it............for now!

I have heard about altering the needles but i can imagine this to be a very tricky process but if you can do it i think its certainly a good solution!

On the EGT. I think its definitely got to be a sensor issue.

[coaster]

I phoned Skydrive the other week as my CHT probe had failed within a few weeks. I was really only after some reassurance that it was worth my while buying another one. He told be that they were known to fail but should last longer than that. He also explained how the probes work. The technollogy is simple, to dissimilar metal wires are twisted together, the metal in the wire is chosen specifically as when they are in contact and heated, an electrical cureent is produced which is proportional to the heat applied. On a CHT the wires are simply crimped into the spark plug ring but on an EHT the wires are encapsulated in the thin cylinder. I reckon the water spray is sufficient to cool the encapsulating cylinder and stop the current being generated.

As an aside, he told me that my CHT had probably snapped a wire or that the crimp might need squeezing with some mole grips. I had a close look at mine through a magnifying glass and could see that one of the wires had broken. So I stripped the insulation back and twisted the wires together again. Wasn't sure how many twists were necessary so just went for 2 twists and manageged to re-crimp it onto the ring. Bingo, it worked and the gauge reads dead on 100 degrees if emersed in boiling water. Unfortunately, re-sealing an EHT probe would be nigh on impossible.

[sideout]

During the euro my EGT was reading 480 at 60-65 mph (true speed not lambretta speedo) and the highest it read was 580 when giving it some.

one problem however was that every time it rained the EGT would read 0, then once the roads dried it would start working again the digital gauge stayed on but read 0

Any idea why that would be????????????

Eden, do you have a splash plate fitted? (The standard fitment attached by the stand brackets.)

[mnpes]

When installing the egt thermocouple I apply A sealer ( welseal ) before tightening up ~ Plus use rubber boots (Koso ) on the male ~ female plugs ~ No water issues then

The cht sensor when wet reads zero ~ But soon as the head is warmed up ~ Works fine