This is a very complicated situation....I just recently picked up a 1999 Scrambler 400 2x4 from a friend and polaris dealer. It really runs well and has a lot of guts...well when i got it, it had a HPd Racing Pipe, HPd Cool Head with a 12:1 Compression Ratio, Wiseco Piston and Rings, Cylinder Porting, Girdle Kit, RacePak Avenger 1 Temperature Gauge from EGT, and V-Force Delta Reeds. After I got it I put on a 38mm TM Mikuni Carb. Then it ran really good, and had even more power....long story short it was running lean and really hot, I did re-jet...it helped a little, about two months later it burned up the piston and rings...this was last weekend. So this friend, also a polaris dealer found another motor for me and last week was the mad dash to get it into the bike so I could go riding this weekend. The new motor is stock as for as engine mods go...but it still has the pipe, temp. gauge, and reeds on it. We put the old carb. back on it, and it runs fine. the only problem is that it gets hot in the midrange and top-end still. It runs fine and stays cool on the low-end, so I figure the Pilot Jet is fine, I tried raising the needle, and it just ran crappy. So I put it back where it was, the the second highest position.

The temperature rises just as fast in the midrange as it does on the top-end,

This is the "Exhaust Gas Temperature" not the "Head Temperature"

It runs at about 600-750 degrees on the bottom-end depending on the load,

I've seen it hit 950 degrees in the midrange and continue to climb past that,

It does the same thing on the top-end,


I am trying to cool it down so that I do not have to replace the motor again....or at least the piston and rings.


Any Help would be GREATLY Appreciated


Wes (love2tinker)

 

hey,run engine ice in your radiator,that will cool it down..what are you doing with the old motor?

 

950 is about right on in mid range. SHouldn't go over 1250 on top end runs.

 

It's normal for exhaust temps to rise as throttle increases, 1100 in the mid range is fine and 1250 max on full throttle

 

Raising the clip lowers the needle.
What type of air filter does it have?

 

Were did you get the carb form adn what is in it for jetting? This is what we send out 38mm tmx out with: 310 main / 15 pilot / 4.0 slide / 6ej12-58 needle in the 4th clip from the top. This is for sea level summer time riding 70 dgrees or so.

 

speedwerx, i have got the old carb back in it...which is a 34mm. as far as that goes...

Pilot: 25
Clip: 4th from top
Main: 260
----------------------

drlang, i have lowered the clip...which in turn raises the needle, i already understand this. it has a k&n air filter though.

 

As long as the engine temp is in the acceptable range (radiator not plugged up?), then there are 2 only reasons why an EGT will show high. One is if the probe is too close to the piston exhaust side, or the engine is running lean. I personally like to see no more than 1150-1200 on top end. Keep in mind that the pilot jet feeds throughout the range of the carb and will affect main jetting too. The temp will raise in a 2 cycle under a hard load and even if the jetting is perfect to a hair rich it will raise the temp if the motor is run for a long extended run. As long as the motor responds good and is crisp then use the EGT only as a secondary measurement and also keep a close eye on plug readings. Read the lower base of the porcelain instead the tip as most people do. This is a common misunderstood point.

One more thing, the red primary spring is a little low for the race pipe on top rpm. I always used that for an aggressive spring for use with the trail pipe. You wont be getting full rpm for the race pipe with that spring. That could be putting you down on power a little and causing it to load the motor a little more. Just a thought to keep in mind. IMO the race pipe needs at least 275lbs top spring pressure to work the best. Bubba

 

i really doubt you got more power with the tmx 38 than the pwk 39,but if
there is you liked best that cool...
it run best in midrange at 1050 to 1100 and mine run 1175 in the top with
a 170 main.that engine always raise faster the egt's in the midrange cauze it is it's peak powerband rpm there,put the sensor at 5" inches from the pistons skirt to get accurate reading.
a 36 helix is bad choice with race pipe,you should get a little steeper
helix to keep the pipe in the meat of the clutch system.
i run over 305 lbs of spring pressure on mine primary spring.
so don't worry,it is not that hotter anymore for the setup you run.