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Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Mon Jan 06, 2014 7:30 pm
by azwood80
Has anybody got any idear what jets a kr runs i have 1,45 mains but it feels like it may need to go bigger it seems like its leaning out at wot but nice up antill then
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Mon Jan 06, 2014 8:09 pm
by hybrid
My 500 shifts that way. Most race bikes also shift that way.
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Mon Jan 06, 2014 8:31 pm
by azwood80
hybrid wrote:My 500 shifts that way. Most race bikes also shift that way.
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Tue Jan 07, 2014 5:50 am
by EPApolice
The KR runs a 137.5 main jet but I would suggest your pipe is going to be a major problem. Just because it fits in the space on the bike doesn't mean its going to work right. I see a huge meltdown coming up.
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Tue Jan 07, 2014 8:35 am
by fred99999au
Wasn't that they way to define the perfect 2 stroke pipe? Once it is the right dimensions and size it cannot possibly fit the chassis or if it does, the bike wont move or lean?
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Tue Jan 07, 2014 9:24 am
by Jeram
its a bit hard to see in the video, but it seems that you've moved the stinger offtake from the end of the pipe, to the belly section.
This should work fine, but one thing you will need to do as a minimum is you will need to cut the end off the pipe where it has the blunt end, fabricate a cone section of the correct dimensions and weld it on
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Tue Jan 07, 2014 3:46 pm
by hybrid
I couldn't work out how the pipe was done.. my head was about to explode, so I gave up.
As you say Jeram - stinger out the belly is fine, but the end cone is still required.. otherwise you might as well have a straight through pipe really. I guess the belly and stinger will provide some back pressure, but no real return wave without the end cone.
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Tue Jan 07, 2014 5:17 pm
by azwood80
fred99999au wrote:Wasn't that they way to define the perfect 2 stroke pipe? Once it is the right dimensions and size it cannot possibly fit the chassis or if it does, the bike wont move or lean?
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Tue Jan 07, 2014 5:23 pm
by azwood80
The stingers were added later they were 24mm id and about 500mm each to the muffler whitch is a single unit with twinn pipes all the way threw. I dont think the shape is that bad realy ossa makes a 300cc enduro with the pipe the same way thats where i got the idear
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Tue Jan 07, 2014 5:25 pm
by azwood80
EPApolice wrote:The KR runs a 137.5 main jet but I would suggest your pipe is going to be a major problem. Just because it fits in the space on the bike doesn't mean its going to work right. I see a huge meltdown coming up.
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Tue Jan 07, 2014 5:50 pm
by azwood80
I undersatnd how a pipe works and i know that you cant just guess what size to make thats why i used a pipe calculator and studyd what sort of pipes worked on the kr,s but i still know that there is a lot of complex math behind a good pipe and dont say i am a exbert at this at all
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Tue Jan 07, 2014 6:59 pm
by hybrid
That sharp bend straight out of the exhaust port is not going to be great.
I think I remember lozza mentioning that a nice straight section out of the exhaust port is ideal. I applaud you for having a go though.. I'm all about it.
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Tue Jan 07, 2014 8:38 pm
by azwood80
hybrid wrote:That sharp bend straight out of the exhaust port is not going to be great.
I think I remember lozza mentioning that a nice straight section out of the exhaust port is ideal. I applaud you for having a go though.. I'm all about it.
i see what your saying with the straight section working best.but sometimes we need to compromise between funtion and form thanks for helping keep me motorvated with the project and advice
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Wed Jan 08, 2014 3:59 pm
by azwood80
Today i decided to have anouther look at the carbs the front one has still been flooding hwen i start the bike.here is what i found 1 old line had crap in it 2 float hights were set at 20mm not 23 and the float in the suspect carb was slightly bent so i fixed all that and will get some nice new lines tomorrow.also the low jets are 35,s and mains are 1.40 front and 1.45 rear carb i have heard of people makeing the back richer because it sees more heat i think it might be a little better after fixing all that.
Re: Crafting a kr250a1 motor into a dirtbike frame ???
Posted: Wed Jan 08, 2014 4:52 pm
by JonW
Interesting what you find in old engines, who knows the level of understanding any DPO ever had, but its usually close on zilch LOL!