Pilot with CR500 conversion EGT Temps

[Odyknuck]

I am having an odd issue with my jetting and EGT. No matter what I do with my jetting the EGT runs on the high side between 1200 to 1400 degrees in the mid range to WOT. I have jetted the main from a 165 to a 190 (Kehin Carb) and the temps remain about the same. I have also change the clip position for mid range jetting. I know the jetting is making a difference because of the way it runs. It runs the best with the 165 and the worst with the 190 (too rich) and clip position runs best in the middle. The odd thing is that the when doing the plug chop routine the color is allways a shade of Charcol gray to brown. My question is can the EGT be bad and still read, just not correctly. This is an analog EGT. Also why is the plug Grey? I use 80/20 Synthetic oil. I have done jetting many times and have not seen thisa yet.

[bdkw1]

What kind of air filter are you using?

Which carb?

[Odyknuck]

I am running a Kehin PWK 38 carb. I am running the stock air box with a uni-filter along with external Uni-filter as a pre filter. I have been running this set up for years with out these odd findings. After my initial post I realized that I had replaced the EGT with the one from my other Pilot. In order to test it I used my Berns-O-matic (could not find a BIC). I may have over heated the Thermalcouple. This still does not explane the Grey plug.

[bdkw1]

Hmmm, have you pulled the emulsion tube and checked it out?

[Odyknuck]

No I did not check the Emulsion tube however I did blow all the passages out on the carb. [i] did a search on plug color and a lot of them say gray is ok:
Spark Plug Colors Reading Instructions - ATV Technical Articles

[IronSpade]

Is it simply a CR500 grafted to the existing CVT or a complete shifter setup? I would think by the temp of 12-1400 degrees at WOT you would be running way lean! I have a similar setup on a roadrace 350 twostroke that even after going to 320 mains I still get that magical number of 1350 F. at WOT and I have to be conservative cause I know what will happen if I stay at that temp for longer than a few seconds at a time. Kabboom!

Most all analog gauges are set for an ambiant temp of 75-80 degrees so if its 100 F when your out driving you have to add that extra 20-25 degrees on top of your readings. I know that 25 degrees doesn't sound like much but it could be the difference between burning up your cylinder and having a great day driving.

If your having a delema between running it rich to keep the EGT readings down and fowling plugs remember it will always run better at the leanest settings but it's also on the ragged edge of destuction when running lean. A solution that I've found is a Mikuni Power Jet carb kit which uses an extra jetting circuit for highspeed operation. So you jet your carb for idle through 2/3 throttle just like before but then you have an additional tuneable spraybar at the bell mouth of the carb that helps control lean conditions at WOT. It realy works well and I've used this setup on several race bikes. Problem is these carbs aren't very cheap at nearly $600 each.

As far as the grey plug, are you looking down into the plug at the base with a plug reader for a reading or simply looking at the color of the exterior? If you have a manual clutched motor and you can disengage the drivetrain and then do a plug chop/kill switch at the same time the motor will not run on possible contaminating the plug with fresh fuel charge.

If you also get a CHT (Cylinder Head Temp) gauge along with the EGT you could more accurately jet for all conditions without relieing on plug color as the tell tale. Remember 1350 is your safe max temp, anything over 1400 for more than a 3-5 second burst pistons start melting. Exhaust Gas Temps can be a tricky way to tune as I've been doing it this way for many years with road racers and laydown enduro karts but they really are designed for guys doing very fine tuning to get that last 10th of a second and running on that ragged edge can be very expensive. My suggestion, set it up rich and have fun! So you end up changing a few plugs, last I checked a new top end can run upwards of $500, plugs are $10 each. You do the math. Hope this helps. Later Travis

[Glamisman]

Not to claim the I am an expert in any way on jetting but what you are experiencing is not out of the realm of possibility. If you look at the needle shaft you will see 3 letters i.e. DGJ or other combination's of letters. Do a Google search in Keihin needle chart and you will see that they relate to taper, length and diameter. It sounds like you have a needle that requires more fuel in the midrange. By changing the clip position all that you are doing is moving the effective range of the needle in the throttle opening range. Like Travis suggests set it up rich and save a meltdown. BTW, needles are not too expensive and can make a great improvement in opperation.

[maustin]

How far from the piston skirt do you have your egt probe? This is very important. If it is too far you could be reading the unburnt fuel temp.

[Odyknuck]

Guys these are all good points that I am allready aware of and do practice. My point of contension is that the plug color and EGT readings do not change all that much regardless of jetting. Weather I use a 165 or 195 main or bottom or top needle jet clip position. The motor definatly runs different depending on jetting as it should. The motor was running fine for 2 seasons and it started to get tired and running spratic like the rings were starting to bind in the glands. Sure enough this was the case and I did a top end job on it.
As a recent update I have changed the the fuel pump (this is the second one since this thread) and was able to get the plug color in the brown range. It appears it was leaning out on extended runs from the pump not being able to keep up with demmand. However the EGT temps remain the same. I will say that the EGT probe may have been damaged during the probe heat testing and that may be why it reads high. I have come to this conclusion and deem the EGT defective and I am going by plug color only like I normally do and will replace the EGT when I get the oppertunity.
I also was testing the pulse port on the motor and this is what I found. At idle the gauge bouces like I would expect. As you increase the throttle it stableizes in a vacumme except it will go past zero and into a positive pressure at higher RPM. This seems odd to me, any thoughts.

[turbotexas]

It is possible you are picking up some kind of interferance by your cables...
Send your egt back to Digitron for diagnosis and repair... If your sensor or cables are worn or tattered buy new ones...
Never "re-jet" a motor by using your digitron!!! Always use your plug color... and no, grey is not a good color on a plug chop. I have poofkapoomed several 2 stroke motors and never pulled a brown colored plug! Always grey to white!!!