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485 jetting issue at WOT


lt1bird

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Guys, im in need of some help. Ive got a 485 street bike...cheetah with block off plates, stock porting 39mm pwk carbs.... my jetting at WOT seems to be way off and I cannot seem to fix it.

 

I started at 152 mains, it ran lean 650c... I went up to 180 mains and its close at 610C but still a tad lean but runs hard, im getting very close. Here is the problem... the main is so large that when I go WOT and im not on the pipe it 4 strokes a lot....I can slowly work through it...or down shift and get the rpms over 6k and on the pipe and its happy. how the hell can I get rid of the 4 stroking when at WOT but not on the pipe?  Well I added some power jets, and it does run much nicer with them at WOT...tons of fuel added and 580C egt is prefect...but the power jets start adding fuel at like 1/2 throttle so the problem actually got worst... I cant seem to get a happy balance. I tried moving the power jets out of the carbs more to raise the activation point of the power jets but that did not seem to change much. Im sure I could cut them more, move them out more but it might not work any more if I go to far.

Thanks!

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yes, stock cyl...no porting...I just clean up the mold lines a bit...

 

the neddles are DGH I think im at now... second clip position... I don't think the needle will have any influence at WOT as its not really in the bore much.....

 

yes, gearing is very tall.... takes a bit to get to 6k rpms if in higher gears.... I can down shift a few gears and get through but I don't want to have to do that....

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yes, stock cyl...no porting...I just clean up the mold lines a bit...

 

the neddles are DGH I think im at now... second clip position... I don't think the needle will have any influence at WOT as its not really in the bore much.....

 

yes, gearing is very tall.... takes a bit to get to 6k rpms if in higher gears.... I can down shift a few gears and get through but I don't want to have to do that....

So wait, stock cyls or stock Un touched cheetah?

 

Also, don't depend on the pyrometer egt's to much until you know you have a good tune up from plugs then take readings. Your location can change temps drastically. So in a sense you have rouse it to look for melt down temps, but you can't really tune off it till you have the baseline.

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Yes....Ido lug I then go wot.".pulls for a bit fine...then seems to start loading up..then 4 stroking...then on the pipe and running clean....I wonder if the k&n filters are a litte restrictive ausing it to suck too much fuel.... I'm tuning by feel... Egt for reference...I run egts on all my 2 strokes. I've built a bunch of these motors...mostly for drag racing...

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It's a 155 psi motor...stock trinity porting..none.... Basic squish.positve unlik trinity domes lol...newer build....leak down was fine... It runs and drives just fine.....all in al you can drive around town etc...just fine... If you start in lower gears and go wot it will pull Caen right past the Souter, no issues...I really am luging it low..4th gear at 40 mph...3k rpms.....then go wot...I'm in that gear fora while before I hit 5-6k then it 4 strokes....then gets on th pipe and pulls hard. I wonder if I had the power valves in there if it would still do it...it lost a bunch of mid range power without the power valves...

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im sorry for the crapy last posts...did it on an ipad and it just stinks...

 

motor specs

 

485cc

stock ported trinity power valve cyl with port matched block off plates

wiseco 10018m07300 pistons

ring gap .012

custom domes 73.5-24-12 degree .054 squish positive to a .058

155 psi compression

.059 base gasket

268 gears

slingshot lockup

vforce reeds

k&n pod filters

ignitech cdi ignition running stock curve +4degrees

110 race gas to be safe

PWK 38mm carbs DGH needle 2nd clip, 178 mains, 48 pilots, stock slides, power jets

 

it is geared very tall as its a streetbike!  In the lower gears is will pull through fine with little issues...just loading it down in a high gear...and going WOT, without down shifting... it will load up off the pipe.... maybe I just need to adjust my driving style.....or put power valves back on.... I did not like the power valves as they pulsated real bad a cruise...maybe stiffer springs would have helped...I hated the oil dripping from them...etc...had one break... but the bike did have a ton of midrange power... almost 4 strokish power band which was a bit boring LOL.

 

 

 

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42 rear

268 gears

rz350 transmission

17 front

 

yes, way over geared but I really wanted to drive at 80 on the highway at low rpms etc....

 

I think I will just tune it more and live with it.... ill just down shift if I want to get into the power band quick... im pretty sure its just loading up while it waits to get on the pipe.... like you said...just not realistic to ask it to do that with the setup I have.... I could maybe lean the crap out of it in the midrange and make it work but its just not cool to do that either...

Edited by lt1bird
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