Maintenance & Technical > KX250 / KX125
Best low end-mid pipe for 98 kx250
motopunk:
--- Quote from: zz3gmc on February 13, 2014, 09:37:24 AM ---Im building a big bore 04 KX250,290cc. In 250 form I ran a Enduro Engineering pipe which worked well across the board. Its a pretty rare pipe, seems like they only made them briefly. Ive also used a Gnarly, good low and mid but signed off a bit early. The stock pipe worked well also. What pipe would you recommend with the 290? I have a never used Pro Circuit Works pipe and have been thinking that it would work well. They seem to be a mid to top oriented pipe. Im not new here Im the Flyin Hawaiian. Ive been having trouble getting on the site so I made a new acct. up.
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welcome back flyin hawaiian ... :-) which piston size do you use for the 290 big bore?...
i have an 96 engine bored up to 353,8 ccm.thats the absolute maximum ,you can get out of the 250 engine ... 74 stroke and 78 bore(modified piston from suzuki rm370) ..at the moment big trouble with the handmade headgasket and have to find a better solution... so i use in the moment a 03 stock cylinder with 66,4 bore on it = 270 ccm ... real great bottom -mid and little bit less top end . i plan to go to 72 bore with an old worn 95 cylinder that i have laying around. i had a 2000 gasgas ec300 and i loved this added torque that the engine made...
for the 360 engine we needed a special pipe... no kx250 pipe was working well enough ... we tried next a modified ktm sx360/380-pipe .. better,but not the best result ... at least "van hasselt" in belgium made a pipe for us. with this pipe it felt very strong from bottom to top and in direct comparing 1,5 hp more than a stock ktm sx380 on the rear wheel. ;O)
dirk_411:
--- Quote from: zz3gmc on February 13, 2014, 04:56:54 PM ---Im not sure of the diameter of the T4 spring versus the 98/99 spring. I have some powervalve governor shims that I used in my 90 KX250 and they wouldnt fit my 04 gov. I cant remember if it was the diameter of the shaft or the spring itself. Im thinking that the spring from the 90/91 KX and your T4 might be comparable in size since the engines changed in 92 and went on to 04.
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I ordered an 98-99 and an 04 governor spring. We'll see if either fit
zz3gmc:
Let us know of your findings. I love tinkering with these engines. I shimmed the gov spring on my 07 KX250 with good results. The 07 has little in the low end with a monster hit in the midrange. Retarding the timing slightly and along with the shim helped noticeably smooth the delivery. Seemed to add a bit bottom also. Next step is having the head modded for more compression and add some more bottom. May try a APT Smart Carb too.
Foxx4Beaver:
--- Quote from: dirk_411 on February 15, 2014, 05:03:59 AM ---
--- Quote from: zz3gmc on February 13, 2014, 04:56:54 PM ---Im not sure of the diameter of the T4 spring versus the 98/99 spring. I have some powervalve governor shims that I used in my 90 KX250 and they wouldnt fit my 04 gov. I cant remember if it was the diameter of the shaft or the spring itself. Im thinking that the spring from the 90/91 KX and your T4 might be comparable in size since the engines changed in 92 and went on to 04.
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I ordered an 98-99 and an 04 governor spring. We'll see if either fit
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ok you two have caught my interest enough to try some different setups on my 250 as well.
dirk_411:
ok you two have caught my interest enough to try some different setups on my 250 as well.
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EDITED. March 13/14
I stand corrected. I for some reason had it in my head that the oem power valve mechanism balls were stainless steel. They are NOT stainless. Void my reference to stainless
I found a read by eric gorr. I am not an eric gorr fan because of the one and only time I spoke to him. However I like to root through his literature, largely impart because it's everywhere on the net. So check out this brief read regarding the power valve governor mechanism. It really sheds light on the possibility of combinations. I have tons of tecate 4 PV gov. mechanism spares. If anyone wants to exchange spares and do a little R&D let me know. I would have endless combinations of KX parts to try. Im kind of thinking if im running the "1851" jug I should start first with those parts. After all im am essentially running the KX jugs for there improved performance over the T4 jug, and parts availability. It could be entire mechanism swap or parts and pieces. I understood the centrifugal operating principle but never pondered changing springs, ramps and SS balls. Very interesting none the less. Im thinking of playing with combinations on my current motor and then build this into my new motor. I like the fact I sent the gov mechanisms shaft, ramp and cup for micro polish
The exhaust valves are opened and closed by a centrifugal governor mechanism. The governor is mounted under the right side cover and is gear-driven by the crankshaft. As the engine rpm increases, the governor spins, thereby increasing the angular momentum of the four steel balls encased in the governor. The steel balls fit into an angled ramp-and-cup arrangement. A spring is used to provide tension on the steel balls. When the momentum of the steel balls overcomes the spring’s tension, and the balls force their way up the angled ramp. A spool attached to the ramp, enabling it to change its linear position with changes in rpm, and the spool is attached to a linkage system that operates the exhaust valves in the cylinder. Factory race teams have different combinations of springs, ramps, and balls to tune the exhaust valve operation and enhance the powerband.
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