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Help a 2 stroke noob...

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Hey, I'm having some probllems with a new bike, hoping to get a little help.

It's an 08 RM250 bone stock, no mods. I am riding between 800' and 2500' (most of which around the 2200' mark) at an average of about 70-85 deg F, and an average humidity (about 50-65%). I am a new rider who is even newer to 2 strokes, so I don't ride all that hard although I try. (I'm not the slowest rider in our group, but certainly not the fastest) The vast majority of what I do is trail, with a little track on the side.

My current Jetting is: (Mostly Stock)

Main: 172 (I have a 168 and 175)

Pilot: 50

Needle: NEDH 3rd postition (mod from stock which is 4th position) (I have a NECH)

Air Screw: 3 Turns out

Fuel Mixture: Has been changing between 32:1 and 40:1, but I'm now shooting to keep it at 36:1 ('Spooge' has stopped leaking out the exhaust since the needle clip change)

Spark Plug: NGK BR8EG

Here's my two problems:

1. Fouling plugs like crazy 👍 This doesn't seems to be any better no matter what I do.

2. At full throttle, tapped out in any gear power dies off and sputters (forgive my lack of knowledge of terminology). This seems to be worse at higher elevations (I think)

Now, I tried to do the pilot cicuit tonight by warming her up, turning the idle up, and turning the screw out until I get the fastest idle possible (guy at work told me to do it like this). It seems that the idle speed increases after 3 turns, which says to me that I am too rich.

So here's the thing... I've contemplated picking up a JD jet kit, but I'm not sure that it's going to have what I need (there's no pilot jet in there) so what I'm hoping for is to get a starting point, and a few suggested jet sizes that will put me in the ball park, and I can go from there.

BTW, I'm primarily concerned with the plug fouling, but it would certainly be nice to have her running like she should!!

Thanks in advance,

Johnny

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Johnny,

For your current temperature / elevation conditions I would start with a 165 main, 48 pilot, NECH needle with the clip in the #2 (from the top) position and the airscrew @ 1-1/2 turns out from fully seated. Make sure the motor is fully up to operating temp before adjusting the airscrew in 1/8-turn increments for the best throttle response. The bikes delivered in the US come jetted stock with a 168, 48, and NECJ needle in the 3rd position for 70 degrees and 0’ elevation. The jetting is very close stock. I will try to put together / post a jetting chart in the next couple of days.

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Thanks a lot, I sure apreciate the help!! That chart would be fantastic if you could post it.

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Johnny,

Here is a chart that you can refer to when jetting your bike. I think this should help illustrate how/why-jetting needs to be adjusted for different conditions. I used a 168 main, stock NECH needle with the clip in the 3rd clip position from the top, and a 48 pilot for 70 degrees and 0’ elevation. Start with you airscrew at 1-1/2 out from fully seated and you will be within 3/8 of a turn + or – from the ideal setting. All you need to do is find the temp and elevation combo for your current riding conditions and adjust your main, clip position, and pilot jet accordingly. I hope this helps you out. 👍

2008RM250Jetting.jpg

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This chart is great. Where do you get this kind of information? Do you have a chart for a 2005 YZ250?

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This chart is great. Where do you get this kind of information? Do you have a chart for a 2005 YZ250?

paccorti,

The chart below will work very well for your 05 YZ250. Start with the airscrew 1-1/8 turns out from completely seated and you will be within a ¼ turn + or – from the ideal setting. All of the settings listed below will work with your stock N3EJ needle or, you might want to try the N3EW that has been the stock needle for the last couple of years.

Let me know how this works out for you.

2003-08YZ250Jetting.jpg

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Vetmxrider,

This is so cool. I know that my bike likes the 48 pilot jet at higher temps but you're showing me that I should step down the main too. Now I just have to get a 175 main jet. I'll try getting the new needle too. You have saved me an enormous amount of time. I probably would have never tried a combo of leaning the main and pilot while richening the needle.

BTW I just got my 11 year old son a 2007 RM85. Out of the box it's way too rich. I read on one of these forums to step the pilot down to a 48 (or 45) and the main down to a 122. I've already raised clip up one. Do you have a chart for 07 RM85 (see what happens when you are helpful 👍 )?

Peter

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BTW I just printed your chart and added it to my manual. I feel like I'm in a Visa commercial. "A new YZ250 $6000. A properly jetted YZ250... priceless"

I can't help but wonder why manufactures don't include this type of chart in the manual. It's like having the lights on instead of fumbling around in the dark. In fact I might buy a bigger main jet for my cold riding.

I can't thank you enough.

Peter

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Peter,

I just finished the chart for your son’s bike. Start with the airscrew @ 2 turns out and you will be within 3/8 of a turn + or – of the optimum setting. The stock 50 pilot is rich for 70 degrees and sea level so I built the chart with a 48 for 0’ and 70 degrees. Please let me know how this works out. 👍

Ed

2002-08RM85Jetting.jpg

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Hi,

I am also having problems with spooge on my 08 RM 250 and splutter on constant light throttle openings (I do a lot of trail riding and technical slow stuff)

I have found that the 08 RM's come in 2 specs

I am in the UK and this is my Standard setting with what i'm using in brackets

Temp has been around 60 here recently

172 main (168)

50 pilot (45)

NEDH 4th from top (2nd)

Power jet 55

Air screw 1 turn out

This is the other standard setting the bike may have

168 main

48 pilot

NECJ 3rd clip from top

Power jet 45

air screw 1 turn out

Notice the difference in power jet size? Is there any reason for this to be so much different?

I like the bike to be jetted a quite lean so the silencer stays dry and keeps the noise down.

I am currently trying reducing powerjet size in an effort to cure the spooge although main, needle and pilot seem ok I may go up 1 on main and raise needle 1 clip during this process.

Does anyone have an explanation of how and when the powerjet circuit works and it's effects would be usefull.

Many thanks

George

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Ed,

I tried this combo tonight on the RM. The 07 RM85L comes with a 128 main (stock). The temp is around mid 80s. Per your chart, I put in the 122 main and the 48 pilot. Previously I had set the needle to the 2nd clip from the top (stock is 3rd); so I left that alone. I don't know my altitude but I think I'm basically sea level (or near).

Observations:

Less smoke for small to mid throttle. Pretty smokey for full throttle. When I snap the throttle open I think it kind of pauses before the power hits (of course it could be my 190 lbs)! I'm thinking that it is still too rich up high. I didn't have enough time to try many air screw setting although this combo did cause it to stall during idle (I had to boost idle).

What I have:

I have the stock NAAH needle

I have a 45, 48 and 50 pilot jet

I have a 122, 125 and 128 main jet

What do you think of the spanky's jetting guide methodology to test the pilot jet size (set fast idle, adjust air screw for max RPM, if airscrew less than 1 turn out then bigger pilot, out more than 2.5 then smaller pilot)?

Your help is much appreciated 👍.

Peter

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Peter,

After you have the motor completely warm and up to normal operating temp, try adjusting the airscrew 1/8 turn at a time to see if you can eliminate the “flat spot”. I agree with the method you posted for adjusting the airscrew. The only stipulation is that sometimes you will still have to adjust the airscrew slightly (1/8-3/16) to eliminate a flat spot just like the one you are describing. Do you live/ride along the coast in VA? I thought the avg. elevation was around 2900’? If this is the case, I would try a 120 main, 45 pilot, and move the clip to the #1 (Top) position on the needle. Then I would adjust the airscrew as described.

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Hi Ed,

I'm in Northern VA close to but not on any mountains (Westerners would call them small hills; town of Leesburg is nearby). My wife thinks elevation is 300 feet or so (BTW been trying to find a web site to check my elevation but not having much luck). I'd be really surprised if we were up near even 1000 feet. Temp mid 80s again.

I tried the airscrew test and it wants a leaner pilot so I went down to the 45. So my setup right now is: pilot 45, main 122, stock needle on the second clip, airscrew 2 turns (more testing necessary on that).

Observations:

Much less smokey even at high RPMs. No longer riding the Exxon Valdez! I think it feels much better now. The hesitation on quick throttle opening is still there but less pronounced. My plan was to fool around with the airscrew so more and if that doesn't get me anywhere then raise the needle clip one more. If necessary I'll buy the 120 main. I do want to be careful not to lean it out too much. It will never pull like my YZ250 (BTW bought the needle you suggested but it's on order and got a 175 main too).

In your professional opinion if there is a slight hesitation from say 1/4 - 1/3 throttle to full throttle (and you're in the appropriate gear for pulling a wheelie) how would you diagnose (assuming the pilot jet is correct)? My plan is: tweak the airscrew to remove as much of the hesitation as necessary and then try the needle clip (up first then possibly down). Could you ever imagine using the 45 pilot with a main larger then the 122 (should I even bother trying that)?

To be perfectly honest I'm kind of enjoying this exercise. Good excuse to fool around with the motorcycles and now my son's learning how a carb works. What could be better?

Thanks,

Peter

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Hi Ed,

My plan is: tweak the airscrew to remove as much of the hesitation as necessary and then try the needle clip (up first then possibly down). Could you ever imagine using the 45 pilot with a main larger then the 122 (should I even bother trying that)?

To be perfectly honest I'm kind of enjoying this exercise. Good excuse to fool around with the motorcycles and now my son's learning how a carb works. What could be better?

Thanks,

Peter

Your plan sounds solid to me. Stay with the 45 pilot and I bet you will be able to adjust the hesitation / flat spot out. How many hours did you run the bike with the overly rich jetting? I am wondering if the silencer packing is full of spooge? Before you go to a larger main I would get the carb dialed in (airscrew) with a clean air filter and good silencer packing and take a look at the plug. It’s not a problem to run a larger main with the 45 pilot if the plug looks lean.

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Vetmxrider,

The silencer has about 10 hours on it. I guess I should check how gummed up it is.

I think I'm getting pretty close to optimal jetting here. My set up: 45 pilot, 2 turns on airscrew, stock needle on 1st clip and 122 main.

Observations:

I've pretty much eliminated the big smoke so the bike at least looks close. From a hit standpoint I think it is still a little tentative from 1/4 throttle to full throttle. Moving the clip to 1st helped I think (dyno wouldn't hurt, judging by feel can be tricky). At this point I think I'll try the NAAJ needle (have to buy it). NAAJ is the next leaner needle (by diameter not 1/2 clip position).

I'll keep you posted if you are curious.

Peter

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Vetmxrider,

The silencer has about 10 hours on it. I guess I should check how gummed up it is.

I think I'm getting pretty close to optimal jetting here. My set up: 45 pilot, 2 turns on airscrew, stock needle on 1st clip and 122 main.

Observations:

I've pretty much eliminated the big smoke so the bike at least looks close. From a hit standpoint I think it is still a little tentative from 1/4 throttle to full throttle. Moving the clip to 1st helped I think (dyno wouldn't hurt, judging by feel can be tricky). At this point I think I'll try the NAAJ needle (have to buy it). NAAJ is the next leaner needle (by diameter not 1/2 clip position).

I'll keep you posted if you are curious.

Peter

I'm very interested in your findings.

I'm dialing in my sons rm85 for 600 ft and 80 degrees. with the 50 pilot and the NAAH needle at the leanest clip position (#1) I still have an off-throttle sputter (1/8 - 1/4 throttle).

I plan to go to the rocky's next summer, and have to know how to jet appropriately (7-10K ft, 60-80 degrees). I will have to buy a leaner needle - just don't know which one.

Thanks

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RayIn,

We can keep comparing notes if you like. Right now I'm mid 80's and sea level. We have a brand new 2007 RM85L. Have you tried testing the pilot jet with the airscrew? That's how I got to the 45 pilot jet. What main are you running? I've tried from 128 to 120. I've had 4 things that I'm trying to fix.

1. Initially lots of smoke

2. Initially lots of spooge out the pipe

3. Original plug appears very dark and on the verge of fouling

4. A power hesitation from 1/4 throttle on. Let me explain this more. From a 1/4 throttle until full it seems to take a while to get to the "hit" part of the powerband. It doesn't miss or stumble (a momentary loss of power) it just seems to take a while to get through these lower RPM's.

I'm not sure if #4 is a real problem or not. I have a YZ250 which is pretty fast and I can pull a wheelie at any time just by twisting the throttle. I shoudn't expect the RM to be the same. I bought an NAAJ needle which is leaner then the original NAAH. I'll probably swap it in soon just to see what it is like.

Perhaps you know this already but you can loosen the rear brake resevoir to get better access to the carb. In fact I can spin the carb around enough so that I can get to the top (needle) or bottom (remove float bowl) without removing the carb (from the left side of bike). Other than spilling some gas it is pretty quick.

Peter

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Thanks Peter - I haven't leaned out the pilot and the MJ yet, but will.

I'm interested how your needle works for you.

I ride KTM's and spend more time than I would like to admit time jetting for different altitudes, and have a big pile of brass. There's a lot of info on jetting KTMs around - especially needles, and that is pretty important for the 1/8 - 1/4 throttle range (of course the pilot circuit will affect it too). I'm looking for the same type of info on RM85 needle jets.

BTW, I bought a used 2003rm85, but I think the motor / carb is not very different from the new ones. It came with a NGK BR8 plug (stock is BR10) but was not comfortable running it that hot - it did not foul. I run a BR9ES as a compromise. Mine smokes and spooges, but I don't care much about that, just how it runs.

Thanks for the tip on the brake reservior

Regards,

RayIN

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