Jetting a YZ 265cc

WFO · Dec 2, 2002

I'm having trouble jetting my '97 YZ 265. Eric Gorr set it up for pump gas and the bike is stock except for a PC pipe and a Boyenson reed. When I got this bike, the jetting was stock other than the main being one size leaner (I quess this was to compensate for the reed).
After the bore job, I assumed that the bike would probably be slightly rich. There was a slight gurgle (like it was loaded up) just past 1/8 throttle. Raising the needle clip helped, but didn't eliminate the gurgle. Adjusting the air screw doesn't seem to make much difference, plus the bike is hard to start.
I went from a 48 pilot to a 45. Starting was still hard and the bike "popped" when I chopped the throttle. I went back to the 48 and the popping stopped.
I gather from reading Canadian Dave's dissertation on carbs that my next bet would be the cut-away or the jet needle.

Question; does any of the preceeding make sense? Am I completely off base here? I don't want to just start buying parts and just quessing if I'm going in the right direction. What jetting changes have you other 265 owners made?
Secondly, if I am on track, where do you get jet needles and/or slides? I can find no source as of yet.

EricGorr · Dec 2, 2002

Try running the 45 pilot and fiddling with the air screw setting. Don't worry about the pop when you shut off the gas, just the response when you accelerate. Also try a projected nose plug like a NGK BP7ES, you can buy those at import auto parts stores. The Champion equivalent is ok too. The plug holds temperature better at low rpm. What is the condition of your reeds? If they're leaking a bit, meaning a free gap of .025inch or more, throttle response at low rpm will always be gurgly.
Good luck

WFO · Dec 3, 2002

The reeds had a small gap when I cleaned the carb, so I flipped them over and they looked OK (I didn't measure). Would this also cause the hard starting? I've also noticed that at idle it seems to surge slightly rather than run at a constant rpm.

cr25096er · Dec 3, 2002

my bike dosnt surge but after i run for a while it idles high but if i sit for a little the idle is low? could that be a sign of bad reeds?

WFO · Dec 6, 2002

Bingo! Eric scores again. Took the reeds out and sure enough, a visible gap! Big enough to not need to measure it. Got one on order.

bscottr · Dec 6, 2002

Originally posted by WFO
Would this also cause the hard starting?

WFO,
I know you have new ones on the way, but yes, reeds can cause hard starting.

WFO · Dec 8, 2002

The cartilege (or lack there-of) in my right knee says why didn't I know this sooner.

WFO · Dec 22, 2002

@$!%*#&@!
It's not the reed!
Just installled brand new Boyesen Power reeds and nothing changed. Same hard start, same gurgle. At wide open throttle, the plug (a new BP7ES) shows to be lean.
My next stupid question is......(drum roll please!!)
Can a crank seal leak give different symptoms at different rpms? Is it possible to suck crank oil (or air) at low rpms and not at high? If I do a pressure check on the case, will I need to remove the reeds to seal it, or will they seal well enough on their own?

Luft · Dec 25, 2002

What air screw settings do you use with the different pilot jets? I would go back to the 48 and set the air screw at 1-1/2 turns out. Test the bike in second gear by quickly opening the throttle to the position where you have the gurgle. Turing the air screw out 1/4 turn (leaning the pilot circuit) at each run and compare how the bike pulls. If you get to two or more turns out go to the next leaner pilot and repeat the process. When you get to the pilot that works best for you try turing the air screw back in 1/8 to 1/4 turn at a time and evaluate how the bike pulls. Put the needle back in the stock position for your testing. Once you dial in the pilot you can fine tune the needle.

WFO · Dec 25, 2002

Thanks. And since you brought it up about the needle, I noticed in another thread where someone made reference to an inherent problem in the jetting of an '96 YZ 250 where the stock factory needle was too rich. I gather this was some info from Eric's book. Is this a problem inherent to the '97's as well? Is there a known fix?

whyz · Dec 26, 2002

Originally posted by WFO

. At wide open throttle, the plug (a new BP7ES) shows to be lean.

From what I gather from Rich,
its best to tune with an ES plug (easier to read),then go to a better plug for ripping.
And I also found it hard to start if your PJ was too rich. (flooding)
(with our 133 anyway) And a dirty carb.Did you do all the other recommended testing before you start to jet?

For the needle,I would be looking for a .5 leaner one.
Have you tried putting the clip at the very top? Just to see? I dont lke going to the very top so I buy diff. needles instead.
Good luck man. I'd like to hear what you came up with. :silly:

Luft · Dec 26, 2002

I doubt that the needle is the problem for richness. The jet needle overlaps into the main jet circuit when you raise the clip the needle goes deeper into the bore and restricts fuel flow. What is the clip raised to when you got the lean reading for the full throttle chop? If you lower the clip what reading do you get on the full throttle chop? Compare the plug read to how the engine pulls. One rule is to find where the main pulls the best and go 1 size rich.

Rich Rohrich · Dec 26, 2002

Originally posted by WFO
[B At wide open throttle, the plug (a new BP7ES) shows to be lean.
[/B]

An extended reach BP7ES will run VERY HOT at WOT (probably TOO HOT) and will burn off all the deposits.
SOOOO all you are reading by looking at the nose of the plug and seeing it white is the running temperature of the plug NOT the mixture strength.

WFO · Dec 26, 2002

Once I saw the plug, I shut down any further attempts because I did not have a richer jet. Because I couldn't ride, and it was a typically ugly Texas winter (65 degrees and one or two clouds), I decided to re-jet my liver with a Corona.
SOOOO....Let me make sure I'm on the right page here.
Eric had recommended that plug for low rpm riding and I had assumed that it would be best to jet with the plug I was going to use. Would the stock BR8EG be OK for jetting? And when (YES WHEN...NOT IF!!!) I get the bike jetted correctly, it will be OK to go to the BP7ES without any detriment to the engine.
As to the other responses, raising the needle clip to the leanest position improved the rattle, bur did not eliminate it. Going to the leaner pilot jet did not improve starting, and frankly, I couldn't tell a whole lot of difference between the 48 and the 45 PJ (other than the popping) regardless of where the air screw was.

marcusgunby · Dec 26, 2002

If the airscrew doesnt make much difference you are way rich on the pilot-try dropping to a 40.

Rich Rohrich · Dec 26, 2002

If you jet the bike correctly you might not need a plug hotter than the stock 8. If you are going to be running it WOT to jet with I would suggest using a BR8ES or a similar 8. Once you have it jetted the plug will give you a good indication if it's the right temperature or if you need to go to a hotter plug.

bclapham · Dec 26, 2002

do the BP plugs have a resistor? i wonder if the EM signal is playing havoc with the ignition? or have we mixed up nomenclature of the BR vs BP plugs?

talking of electrics, how is the timing?

whatever, i would also try the BR8ES as suggested. there was agreat debate on this, i didnt like the idea of the 7 but others did. to see for myself, i went to the track and tried the 7 it pinged comming out of corners and still did this even with a richer pilot, the bike ran no better either...needless to say, the 8 went back in!

Luft · Dec 27, 2002

Try the 40 pilot at 1-1/2 turns out. Ride for 10 minutes to get the engine up to temperature and test in 2nd gear turning the throttle the way you usually do. Turn out the AS 1/4 turn at a time and test keep going until you observe the change you want. Also test the 40 AS by turning it in to find the sweet spot. You are almost there.

Jetting a YZ 265cc

WFO

EricGorr

Super Power AssClown

WFO

cr25096er

WFO

bscottr

WFO

WFO

Luft

WFO

whyz

Luft

Rich Rohrich

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WFO

marcusgunby

Rich Rohrich

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bclapham

Luft

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Jetting a YZ 265cc

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