2 Stroke Calling all 2t jetting guru's

Rivethead242

Rivethead242

Ok, so getting the bike ready for LPNF coming up in a few weeks.... particularly jetting issues as last time she was running a bit rough at such high elevation. Before I get started it would help if you knew the bike. 1995 CR250R with FMF Fatty Pipe, and FMF Turbine Exhaust. I was having jetting issues when I first picked up the bike (same pipe, different exhaust), she was running too lean (spark plug test, white) and dying in high RPM's. Unfortunately I do not recall what jetting I had in there.....I was still new to turning a wrench, and wasn't aware of the forum world. After picking up a handful of jets and testing em till the spark plug wasn't white anymore. She is currently running a 55slow jet and 185main jet, and doesn't seem to have any issues at sea level (non that I can recognize anyway). Needle is on the 3rd click (which corresponds with the manual as well) which is correct up till 7500ft. The manual calls for a 52slow and 175main for sea leavel. I find myself riding more in the 2500-5000ft range these days which calls for 52slow and 170main. However, knowing my numbers are currently off what do you guys suggest I do. Obviously I need to bump down both jets. FWIW I have checked the reed valves as well which have no "goop" on them, and no chips. Who wants to help save me some time and nail it right the first time!?

Also, I keep having a leaky carb. I've replaced float chamber gasket and reed valve gasket. Both the the air side and reed side rubber boots are snug. Nothing I have done has made any difference with my leak. Where else could it be leaking from!?

Please school this rookie!
 
Rivethead242

Rivethead242

bobkyle2:
Im not near good enough on jetting... But where is the carb leaking at?
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Wish I could tell you. I've cleaned it up MULTIPLE times to try and narrow it down. But it gets covered in dust too fast to tell exactly where the source of the leak is. It doesn't leak unless it's running (yes, I've left the gas on overnight just to check), no signs of a leak when idling either. The only thing I have not replaced is the "bolt" on the bottom of the float chamber which appears to have a gasket as well. Just noticed that in the manual....that will probably be my next step.
 
Rivethead242

Rivethead242

James:
https://www.dirtbikeaddicts.com/forum/content/214-pre-mix-ratio-101.html

Like Kyle said, where exactly are you seeing the leak? Is it coming out of the overflow hose?
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Oops, forgot to state that as well. I am running 50:1 amsoil race oil. Which I am pretty sure isn't the issue.....

It could be the hoses, but doubtfully seeing as how they all go bellow the case. It's probably about time to replace them as well, seeing as how they are getting hard and cracking at the ends.

My main concern isn't with the slight leak, as much as it is the jetting. Back to reading that jetting thread.:thumb:
 
Rivethead242

Rivethead242

"The only way to know what jetting changes you will need is by trial-and-error. No one can give you jetting specs, because every bike is different, every rider has a different style, and jetting is totally weather dependent. Unless the person telling you what jets to use is riding an identical bike, on the exact same track, at the same time, his recommendations are meaningless. Someone with a good understanding of jetting can get you in the ball park, but you need to do the testing to determine the correct jetting yourself if you want it right."

Well there goes my idea of time saving.....but I am sure there are engineers out there that would dispute that :lol::foul:
 
bobkyle2

bobkyle2

Take the over flow tubes off....And try to see where its leaking....You could have no issue at all.. Just the fuel leak is the problem.
 
Rivethead242

Rivethead242

James, thanks for posting that jetting link. I definitely know it is a jetting issue after reading that article. I've got my cheat sheet, testing will commence tomorrow, which should at least give me a base to work around with the current jets I have. Only thing it doesn't discuss is how much of a difference will each step up or down for jetting size make? Ill be sure to post up before I start ordering "test" jets.

Preliminary brain testing time. The 55 pilot I have in (manual states 52 for sea level->5k, 50 for 5k->10k). This would explain my "bogging" throttle response and rough idle (combined with air screw). My 185 currently in (manual states 175 sea->1k, 172 1k->2.5k, 170 2.5k->5k, 165 5k->10k) would explain the fouled plug last time at LPNF (however, I never get fouled plugs in lower elevation(1k-3k)) as well as the exhaust spooge. Now, how do pipes/exhaust affect jetting? Is there a general rule of thumb to follow in regards to jetting with certain pipes/exhaust ,requiring oversize jetting (or something along those lines...)?
 
jackson409

jackson409

Rivethead242:
James, thanks for posting that jetting link. I definitely know it is a jetting issue after reading that article. I've got my cheat sheet, testing will commence tomorrow, which should at least give me a base to work around with the current jets I have. Only thing it doesn't discuss is how much of a difference will each step up or down for jetting size make? Ill be sure to post up before I start ordering "test" jets.

Preliminary brain testing time. The 55 pilot I have in (manual states 52 for sea level->5k, 50 for 5k->10k). This would explain my "bogging" throttle response and rough idle (combined with air screw). My 185 currently in (manual states 175 sea->1k, 172 1k->2.5k, 170 2.5k->5k, 165 5k->10k) would explain the fouled plug last time at LPNF (however, I never get fouled plugs in lower elevation(1k-3k)) as well as the exhaust spooge. Now, how do pipes/exhaust affect jetting? Is there a general rule of thumb to follow in regards to jetting with certain pipes/exhaust ,requiring oversize jetting (or something along those lines...)?
Click to expand...

You can go to the pipe manufactures website and they can get you close on what changes should be made from factory settings. Also you should always start with a fresh packing and good compression before you can get spot on with your jetting. Here is what FMF says you should be at but they and I always use 32:1 thats what factory calls for thats what I would run. You can"t fix jetting issues by changing your premix ratio.

Tuned To Perfection
We know how difficult jetting can be sometimes, that's why when we test our exhausts we also adjust the jetting to see what works best. Sometimes stock jetting works fine, other times a slight adjustment is needed. Here is what we've come up for in our area and is a great starting point for you as well.
We developed these specs with a 32:1 fuel to oil mixing ratio of a 50/50 mix of race fuel and super unleaded, 0 - 1500 ft altitude at 70 degrees outside temperature.
Please note: There are way too many variables in jetting to give you a recommendation that works perfect. Use these specs for a reference to help aid you with your specific bike.
Make Your Selections
Make ----------- HONDA Model ----------- CR250R Year----------- 1995
Jetting Results
Main Jet172 Pilot Jet55 NeedleR1369N Needle Position 3RD Air Screw1.5
 
M

MikeinFresno

I think you are making this too complicated. Since it runs ok now I would just go one size smaller on the pilot, lower the needle one clip, and go down on the main a size or two. Get it close to what it is supposed to have in there and it will run, then fine tune it. I do not agree with the post that you copied above that no one else can tell you what jetting to use cuz its all different bike to bike---thats BS. With KTMs it is very common to just ask on line and get an exact and it works, so why would a Honda be any different? So to do this the easiest you can you need to find some on-line forum and find out what others are running---or just start off stock and work from there. I know that Hondas are very close to perfect as they come stock, so just going down a size or clip should do it for you.
 
James

James

Staff member
Rivethead242:
"The only way to know what jetting changes you will need is by trial-and-error.......

Well there goes my idea of time saving.....but I am sure there are engineers out there that would dispute that :lol::foul:
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I'd say that for the most part using the recommended settings will get you to the point that you can just go ride. However to fine tune it, it'll take some "trial-and-error" because like others mentioned there are a lot of variables.
 
Rivethead242

Rivethead242

Thanks for all the input guys.

Should have known to look at FMF's site for specs :banghead:

The needle I've got in doesn't match up to the manual, nor FMF's site. So I am going to at least give that a shot. Why I have my main at 182 is beyond me. Based off what FMF's site is telling me. The Main should be 3 units smaller than what is stated in the FSM. I am going to bump it back down to a 172, with the correct needle and see what that does for me.
 
Rivethead242

Rivethead242

Alright so I am having a hell of a time hunting down a R1369N needle (as per the FMF site, which appears to be a kawasaki needle but they use the same carb). Just got the email from ronayers that there site was not up to date, and it had been discontinued....after I placed my order for everything else as well. I've contacted numerous vendors with no luck in finding this exact needle. However, I am able to find a R1369MS needle (from multiple vendors) which is listed for my honda and not a kawasaki. Do you guys know what the end letters indicate?
 
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