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rebuilt my engine then ran the same carb settings as previous carb settings are 180main 55 pilot neddle 2nd clip from top, slide 6.5mm cut ,39.5m carb riding at sealevel 10m to 300m ok well anyway went for a ride bike was splutering3/4 throttle like to rich then would clear out at full throttle.thought i would go for more octane and it then was fine for a ride then went back to the same thing.running 25;1 tts castrol,was running r30 caster but last piston .50 had the megga blow by but that to me was poor machining ,now im 1mm vertex . the exhaust bridge was releived but the guys that do my barrel now say they havent done that in 10 years.anyway the head has 65.5 engraved into it isquish . and the person who did this to my bike is a 4stroke rider wr450,i said when you hear it splutering back off he did not .he gave everything it had . the plug was leaned and the engine was not that hot at all.well well well i dont no this weekend im putting it back together and i do have pics just having trouble trying to send them.

I run 40:1 try it and see if it clears up your 3/4 throttal problem. a 55 slow is stock thats the 1st place to start jetting your motor then your neddle & main. what neddle are you running?

i got the exhaust bridge done ,try 40;1 sthill and no probs yet but i stuck the 190 main there hey .idle down the chock nobb go for a little ride then come to stop and idle is litlle higher again then i will adjust idle down again.why?

Not to affend you but do you speak good english?? I am having a hell of a time reading what you are typing.

Remember, when you ADD oil it LEANS the mix. And when you remove oil (40:1 is LESS oil then 25:1) you are RICHENING the mix.

ok thats alright . so even i ran 25 to 1 before now i run 40 to 1 with bigger main jet it shouldnt seize up top . my key board skills are not that good

So what size is the needle? and why would you richen the main when it sputters at 3/4?

Normally a 55 is pretty rich for a PWK 39.5?

i think it is r1368n . also with the bigger main i thought because it is 1mm over and ported qoute me if wrong?. well now thought about it and the bike was always ran arround 40 to1 my boss tells me.The 25 to 1 mix that ive been running has been the problem all along to rich leans at top end , well i will learn these things as i go along. I ride forestry breaks, enduro style riding and that;s it . Anymore help would be appriecated

oh the spluter was because to rich ,also put the original plug back in b8eg

kanecr50094 wrote:ok thats alright . so even i ran 25 to 1 before now i run 40 to 1 with bigger main jet it shouldnt seize up top . my key board skills are not that good

Going from 25:1 to 40:1 is ADDING a ton of fuel, while at the same time REMOVING OIL. So if you also put in a bigger main jet then you richened it up twice. But its not FUEL that lubes your motor, its OIL so if you went from 25:1 (wayyy too much oil BTW) to 40:1 and seized it, you are prolly too small on the main starving the motor of fuel and LUBE or you have a huge vacuum leak.

Dont forget theres other ways to sieze a motor no matter how much oil is in the mix. Engine breaking down a big hill (especially after running it hard UP the hill), vacuum leak (gasket or seal) etc.

seized it when my mate rode it and when it had the 180 with 25to1 and now it is fresh again with 40 to 1 190main, 1 and a bit turns on the mixture screw, going for a ride this arvo ,i will hold it flat and see if i can seize it.

kanecr50094 wrote:seized it when my mate rode it and when it had the 180 with 25to1 and now it is fresh again with 40 to 1 190main, 1 and a bit turns on the mixture screw, going for a ride this arvo ,i will hold it flat and see if i can seize it.

Well dont forget that most 2 strokes are rated for how much time WFO they can go before consuming all the oil pool in the case and siezing up. I think 250's are 15-30 seconds, not sure about the 500 though...

Most of the desert racers I know (prolly spend more time WFO then any other discipline) ride the kill switch for a few seconds at a time every so often while WFO for long periods of time...

I have for the last couple duning season gotten in the habbit of hitting the kill switch and pumping the throttle while engine breaking down a big hill after hitting it real hard. Cools the piston/cylinder and replenishes the oil...

M.F.D.B. wrote:
Remember, when you ADD oil it LEANS the mix. And when you remove oil (40:1 is LESS oil then 25:1) you are RICHENING the mix.

That is correct when refering to "mix" of fuel to OIL. But your confusing people by saying that when the people are talking about fuel to air ratio. You mention how it's hard to understand the original posters writing, but what you posted was so hard to decipher I had to read it 20 times to understand your point, it sounded backwards to me.

Ported&Polished wrote: talking about fuel to air ratio. You mention how it's hard to understand the original posters writing, but what you posted was so hard to decipher I had to read it 20 times to understand your point, it sounded backwards to me.

I never have talked fuel air ratios, I think you are confusing yourself...

Hey bro in aussie land - what brand of oil and what kind of fuel do you use ? that has a olot to do with your problem.

Tony

qld hervey bay, was using sheel vsx,then next piston used tts castrol,and have used castrol r30,now i run what my friend runs in his at the finke desert race alice springs,same mods to engine[power flow melbourne do the work and said to him what ever oil you have been runing keep using that.It is sthil chainsaw lube 40 to 1,made by castrol

The specific gravity of two stroke oil is different than gas, so it actually makes the engine run leaner when you have more oil in the mix.

Ported&Polished wrote:

M.F.D.B. wrote:
Remember, when you ADD oil it LEANS the mix. And when you remove oil (40:1 is LESS oil then 25:1) you are RICHENING the mix.

That is correct when refering to "mix" of fuel to OIL. But your confusing people by saying that when the people are talking about fuel to air ratio. You mention how it's hard to understand the original posters writing, but what you posted was so hard to decipher I had to read it 20 times to understand your point, it sounded backwards to me.

nmdesertrider wrote:The specific gravity of two stroke oil is different than gas, so it actually makes the engine run leaner when you have more oil in the mix.

Ported&Polished wrote:

M.F.D.B. wrote:
Remember, when you ADD oil it LEANS the mix. And when you remove oil (40:1 is LESS oil then 25:1) you are RICHENING the mix.

That is correct when refering to "mix" of fuel to OIL. But your confusing people by saying that when the people are talking about fuel to air ratio. You mention how it's hard to understand the original posters writing, but what you posted was so hard to decipher I had to read it 20 times to understand your point, it sounded backwards to me.

Uh, thats what I said (more oil means leaner mix)...

All this talk about mix ratios isn't leading him down the right path. Its good to know though.

Stick with a 40:1 ratio for now. If its going to seize jetting will play a bigger part in that.

Now he says its been ported, well that throws the jetting specs out the window.

You never said weither its a PWK/39.5 or the PJ carb.

In either case the needle may need to be 1468 or DGJ for a ported motor.

Just sell it and buy a thumper...

iggy amsoil thankyou bloke,it is a pj 39.5 and rode yesterday after checked the timing was out in the forword position and then the bolts were lose , so the timming is good now . all starts fine, no splutter yet, normal pump gas ,and will get back to you with some pictures of the old piston.40 too 1. roger that .

this is for you m.f.whatever ,you get a thumper dood

kanecr50094 wrote:it is a pj 39.5

It has to be one or the other. PJ's only came 38mm and 39.5 is the Kawi PWK...

Is the slide oval or "D" shaped?? Is there a seperate idle speed or do you turn the choke knob to change the idle??

kanecr50094 wrote:this is for you m.f.whatever ,you get a thumper dood