Calling jetting experts!

Todd5774 · #1 02-07-2012, 01:02 PM

I've just converted my 02 300ec to a 250, wanted to be riding on the pipe more, and where i ride thats not possible on a 300, as soon as you get on the pipe you need to haul it down again.

Ive gone the whole hog and got everything off a running bike with the cylinder, head, piston powervalve and cdi off a 03 ec250, and have everything buttoned up, runs smoothly.

But.....

Its so smooth that there dosent seem to be any hit at all, dosent even seem or sound like im riding on the pipe, feels more like an electric bike

car'nt even pull a wheelie!! dont get me wrong the bike is coming on the pipe, just dosent feel or sound like it, its too smooth. Ive also taken the LTR Big cover off the powervalve chamber.

jetting is

175main (was 178 when it was a 300)
40 slow
jd red needle
a/s 2 1/4 out
no 7 slide

elavation sea level to 500m/ at the moment 0 degrees celcius.

Not great at idling, but not to bothered about that can let the bike die whilst i wait for others!

So then jetting experts(Jakobi) what can i do to get the hit back? i want to feel like im riding a 2 stroke not a 4banger.

Or do you think i need to be playing with base gaskets? ive left the 2 i had on there with the 300 cylinder think they are a black one and a green one, if that makes a difference?

Jakobi · #2 02-07-2012, 02:28 PM

Hey mate,

I'm no expert when it comes to these things. Just been reporting my findings (through research and trial).

You didn't mention which clip pos the needle is in?
I assume the jetting specs you listed are the same you ran as when it was a 300. I'm not sure how much difference is required between the 250/300's. From what I've read not too much.

You could try other needles to change the power delivery characteristics. I think that JD's triple taper needle is designed to beef up the mid range and provide a somewhat smooth delivery. The yamaha needles N3Ex/N3Cx (C being half clip leaner) will without doubt give you a mid range hit if thats what you're looking for. Its a 2 taper needle which runs from rich to lean. The transition onto the lean taper is what gives it the big hit. This is one of my favourite needles. I would suggest the W diameter for a 250. N3EW is the stock needle for 2006+ YZ250. Shouldn't be hard to find one to try.

In relation to the gasket stack, you can't really just pick a number and say its right. Its all relative to the cylinder ports and the piston. I like have the top of the piston level with the bottom of the exhaust ports with the piston at BDC. This will give you a softer bottom end, with a nice transfer into the pipe and good over rev. Having the piston sit a bit higher than the ports (less gaskets) will beef up the bottom end but sacrifice the top (probably not something you want to do to a 250).

Also, may want to check the powervalve has the correct tension on it and is opening and closing as expected. May be some slight slop in the actuator arm depending on differences in the jug.

After you get the base gasket stack where you want it to time the ports you'll then want to measure the effective squish band before buttoning the head back up. Ideally you want to be between 1.2mm and 1.8mm (smaller = better power but may require more stable fuel loads)

Todd5774 · #3 02-07-2012, 03:16 PM

Sorry clip is in the middle, tried a clip leaner and it just felt like it was struggling abit, so went back to the middle.

Think there was abit of slop in the actuator arm, i left the 300 arm in, so il take it apart and put the 250 arm in and properly tension it.

Thanks for the tip on the yamaha needle, will try and track one down here in the uk.

Jakobi · #4 02-07-2012, 05:12 PM

Quote:

Originally Posted by Todd5774

Sorry clip is in the middle, tried a clip leaner and it just felt like it was struggling abit, so went back to the middle.

Think there was abit of slop in the actuator arm, i left the 300 arm in, so il take it apart and put the 250 arm in and properly tension it.

Thanks for the tip on the yamaha needle, will try and track one down here in the uk.

You should be able to simple adjust the tension on the actuator arm you have at the moment. You will have to remove the primary drive engine cover to access it though.

Innit all fun and games. The needle shouldn't be hard to find. Usually Yamaha dealers around every corner/online. I think KTM can order them too (certain years used N3CH as an added needle in the spares kit). I can't remember which brand could sell them cheaper off the top of my head.

Did the 300 have a hit to it? A sloppy power valve will affect your punch off the bottom end more than the top, which could make it harder to wheelie depending on your technique

Hope it all works out

Todd5774 · #5 02-07-2012, 05:20 PM

Only place I could get a n3ew needle was from the USA so ordered one!

Yes the 300 did have a hit, not a big one but it was there enough to power wheelie.

Thanks for the advice, want to get the bike right as I have a 3 day trip coming up in 2 weeks, and I'm leading so don't want to be faffing about on the side of the trail tuning my bike!

This is why I love this site! A fellow rider helping another from the other side of the globe..

lonetree · #6 02-07-2012, 07:08 PM

must say it doesnt sound quite right, my 250 is WAY snappier than my 300. doesnt pull quite as hard but really snaps on when you hit the pipe.
mines a 09 so a bit of difference there... but mine is running standard jetting and needle, N1EG and i think 38/178 but not 100% on the jets...

GMP · #7 02-07-2012, 08:02 PM

Sounds lean for a 250, all three of mine liked richer. JD Red was way too lean for me. Try this (0 - 1500', pump gas):
180 main
JD Blue #3, (DDK is OK too, but JD better)
45 - 48 pilot (45 in summer)
1.5 turns out
#7 slide

Remove the reed spacer that comes with the 300.

I had an '03, and from my experience, the CDI map was a dud. Bike was way too soft. If all else fails, find an older XC CDI or one from an MC or a 200. This will really wake it up.

VForce instead of the RAD Valve is good too.

Also, make sure that your PV is working properly, correct preload and no dislodged balls in the governor.

Todd5774 · #8 02-08-2012, 12:04 PM

NEVER NEVER EVER TRUST A SELLER ON EBAY!!!!!!!!!!!!!!!!!

Went to check that the powervalve was working ok and no bearings were displaced, and discovered that the pin which holds it all together is missing.....

That means that the guy i bought it off has dismantled the powervalve removed the pin and then put it all back together and then sold it on..

what a DICK.

well lesson learned never trust anything you havent put together yourself, no wonder i had no snap!

so i've taken the powervalve out of my 300 head and slotted it in the 250, but im unsure what way up it should be when the engine's not running, should the flapper be open so that you can see the piston through the exhaust port?

like this?

Have done all you suggested with the jetting Glenn and have reinstalled my 300 cdi, will that be ok? also removed the reed spacer.

wence · #9 02-08-2012, 12:47 PM

You may be able to check online through one of the ,(sticky), online manuals to see the correct installation. I would also check that the flapper is not protruding into the cylnder too much as it may jam on the piston.Easy to do just flick it open and closed and have a look from above.
I had to file mine back a touch on my last bike once I cleaned and replaced bearings just to be sure.
Cheers Mark

GasTimppa · #10 02-08-2012, 01:25 PM