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Old 10-10-2016, 02:36 PM
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Default 2003 RM 250 Jetting question

     

Hi guys first post here.

Couple questions regarding jetting. I mostly ride motocross in denver. ALt=5280. I have been told kind of general rule for here is stock jetting minus 10%. Thats what my bike is at right now. I cant remember the numbers. I can get those soon though. I have read that stock jetting on the 03 is too rich from the start. So I think that im still too rich. It does ok on the motocross track here where I can wind the bike out. But This weekend I went up in the mountains at between 8-9k alt with the same jetting to ride single track trails. It got kinda loaded up warming the bike up and it took about 10 min of riding to get it cleaned out. I never felt it was at tip top shape the whole ride but was pretty good. It is hard to get it cleaned out on tight singletrack.

Anyways I am just wondering what some of you guys are running at sea level and what you would recommend for 5k and for 8k. I have read some guys on what they run at sealevel. Im just not sure how much more I should lean the bike out.

Also I am running amsoil dominator at 44:1. It says on the back of the bottle to run it at 50:1. Should I go with what it recommends? Im not really interested in really really tuning the bike. I just think pretty easily I should be able to make it run a bit better.

Dont want to run it too lean thats my main worry.
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Old 10-10-2016, 06:33 PM
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Try changing your fuel mix to about 32:1. At 44:1 you are creating a rich condition. Before I would change the jetting, I would change the fuel mix to see if it helps. If so then yes you should be able to go down on the pilot and min jet sizes and maybe even go back to your 44:1 mix. ( That is an odd mix as it would be 2.9 oz of oil to 1 gas of gas...Is that how you are mixing it?)

Paw Paw
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Old 10-10-2016, 09:51 PM
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Yeah my ratio right has 40 44 i think 48 and 50. I understand that less oil in the gas creates a richer fuel mixture. So more oil leans out the fuel mixture. But then I would burn more oil and it would smoke more. It does not smoke in denver at the motocross track except when its warming up. On the trial every time I stopped it would smoke when reving. I could not see when I was actually riding tho.

I will say when I first got the bike I mixed at 40:1 and it seemed to bog more. So I went to 44 at the track and it seemed good. My plugs are always black When I change them. I know to accurately do a test you need to go full throttle then cut the motor then check.

The bike is defiantly rideable and has lots of power still. But it does not seem quite as good as good. You can tell in the sound when you first get on it out of a corner it has a bit of a burble as its cleaning out.

I just dont think I should be running the same jets at 8500 as I am at 5000.

And amsoil recommends 50:1
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Old 10-11-2016, 10:03 AM
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Remember that the oil company is speaking only of the oil's ability to run that mixture, but your bike maker will show what is needed for your bikes mixture and does so with the jetting in the OEM setup. I would suggest going with what the bike maker calls for rather that the oil company. Your mixture is just too rich and with the elevation changes it will even be worst. As already stated, I would go down on both the pilot and the main jets one size and see where you are then.
Have you set your float height? It also effects your fuel mixture.
Are crank seals in good shape?

Paw Paw
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Old 10-11-2016, 10:15 AM
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I have not checked the float height. I have not checked crank seals. Like I said the bike has been running good at the track and also ran pretty good on the trail this weekend.

My question about the oil is coming from that my bike is a 2003 thats almost 15 years now. The oil I have now is from 2016. Thats 15 years newer technology than when my bike was giving what the manufacturer calls for. Now amsoil has oil you can mix 100:1. At 32:1 im sure it would smoke and run like crap.

I understand more oil means less fuel which means lean. But if the bike is smoking and loaded up I dont understand why putting more oil will help that.

Also dont take this as me telling you you are wrong. This is purely me trying to understand this concept. This is probably why no body can agree on what you should actually mix your bike at.
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Old 10-11-2016, 10:48 AM
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That is ok, I have only been doing this for about 52 years now...So what would I know...
Oil tech does change, but your bike has not nor have the original engine and jetting requirements. The OEM jetting at the OEM fuel mix ratio at your elevation will be rich and at your fuel mix it is very, very rich.
Do as you please, change, stay the same, ignor other possible issues or what ever.

Paw Paw
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Old 10-11-2016, 11:11 AM
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Thanks for the info. Ill do some checking. My dad is coming in this weekend to go ride with me. It may be best to leave everything the same until we get done with this ride. I dont get to ride with him almost ever.

I have an 04 rm 250 manual (ebay said it was an 03) its not. Ill look through that for mix recommendations. Im sure its probably the same between the two years. Im guessing the jetting is not tho.
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Old 10-11-2016, 11:53 AM
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I had an 04 and it too was rich right from the factory.

Paw Paw
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Old 10-11-2016, 12:16 PM
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So after doing some more reading on premix. I need to go down to 32:1. Then probably still drop main and idle jets down a size as well.

Its crazy what you learn on the internet. I did not know that gas is a coolant in the cylinder. So with more gas and less oil the cylinder is cooler therefore there is less burn causing more oil to not get burnt.

I dont have oil coming out of my pipe but I do get black spots on my fender.
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Old 10-11-2016, 04:29 PM
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Is there some kind of rule for elevation? I think my numbers right now are 162 and 45 for main and idle jets. I was thinking of trying to drop to high 150s like a 158 if thats a size and go to a 42 idle jet and lean out the clip one notch. Also go to 32:1. Is there a possibility of hurting the bike? I will be riding over 8k this weekend?

Thanks again Paw Paw for the time and info so far.
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Old 10-11-2016, 07:42 PM
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I would take it one step at a time.
Fuel mix and chop test
Jetting one step at a time with chop test at every change

Paw Paw
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Old 10-11-2016, 07:55 PM
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Quote:
Originally Posted by PawPaw View Post
I would take it one step at a time.
Fuel mix and chop test
Jetting one step at a time with chop test at every change

Paw Paw
Do you remember me saying chop tests are BS? Had to do some the other day .
New engine paranoia made me do it .



OP. Once you have your bike sorted. I have a brand new JD Racing Ignition with mapping switch for your bike if you're interested. It cost me $490.00 USD, I'd let it go for 200.00 USD.

http://www.ferracci.com/jd-electroni...-450-4116.html

http://www.jdracingignition.com/faq

I have an 06 engine, I got the wrong one.
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Old 10-11-2016, 10:33 PM
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Thanks guys for the info. I got into it tonight before I read the latest posts. I also dont really have time right now to do testing. Plus I live in the city. I pretty much know exactly how to get to everything now so when I have some time I need to spend a bit of time by myself at the trail and test some different setups and at the track with some set ups.

So decided to get into it tonight. Moved the carb to the side and took the jets out. Realized I had to take the carb out to get to the needle. So I got it all out. Also took the float cover (is that the bowl?) off just to look

What was in it
MJ 160
IJ 45
Needle is stock I think at the 2nd clip (1 leaner)

So I had a 158 and a 42 so I put those in.

Put the carb back in, tank on and seat on. Hooked up the fuel and started it.
It reved to the moon. So I played with the throttle cable by the carb thinking i pinched it or something. Started it again same thing. Played with some stuff and kept trying and it kept doing the same thing. I noticed when I put the choke on it would help.

So I took it all apart again and looked at everything. I also put the original Jets back in. I got it all back together and started it.

Same thing maybe a touch better. At this time im freaking out my dad is flying in to ride with me in 3 days and one of my two bikes is not working.

I realized I had played with the idle and the air screw. I re adjusted both and it was better. So I screwed the air screw all the way in and it finally idled really low. So I backed the air screw out 3/4 and it was pretty good. It was maybe a touch under 3/4 out. Is that ok?

Also this was still with 44:1 I am thinking about going to 40:1 this weekend. Im worried it may be too lean at 32:1 and lots of ppl run 40.

I will also bring an assortment of jets just incase something does not work right. It should tho because its the same set up.

Thanks again for all the help. I really appreciate it.

I would maybe be interested in the ignition but not right now. Next things to buy is a enduro tank and new chain and sprockets.

Oh and the bike was not warmed up. My bike always idles a touch high when cold. Im hoping is will mellow down a bit when warm and I can re adjust the air screw a bit.
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Old 10-12-2016, 09:43 AM
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Doing some reading this morning and some people have been able to use a 42. Should it really be having this problem with a 42. I know the bike was not warm but even with the 45 I was on the very lower in of the fuel air screw. This has kind of got me worried.
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Old 10-12-2016, 02:18 PM
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Jetting FAQs - Dirt Rider Magazine

This seems to be a really good explanation of how to do testing
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Old 10-12-2016, 03:00 PM
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Quote:
Originally Posted by lcgordon711 View Post
Thanks guys for the info. I got into it tonight before I read the latest posts. I also dont really have time right now to do testing. Plus I live in the city. I pretty much know exactly how to get to everything now so when I have some time I need to spend a bit of time by myself at the trail and test some different setups and at the track with some set ups.

So decided to get into it tonight. Moved the carb to the side and took the jets out. Realized I had to take the carb out to get to the needle. So I got it all out. Also took the float cover (is that the bowl?) off just to look

What was in it
MJ 160
IJ 45
Needle is stock I think at the 2nd clip (1 leaner)

So I had a 158 and a 42 so I put those in.

Put the carb back in, tank on and seat on. Hooked up the fuel and started it.
It reved to the moon. So I played with the throttle cable by the carb thinking i pinched it or something. Started it again same thing. Played with some stuff and kept trying and it kept doing the same thing. I noticed when I put the choke on it would help.

So I took it all apart again and looked at everything. I also put the original Jets back in. I got it all back together and started it.

Same thing maybe a touch better. At this time im freaking out my dad is flying in to ride with me in 3 days and one of my two bikes is not working.

I realized I had played with the idle and the air screw. I re adjusted both and it was better. So I screwed the air screw all the way in and it finally idled really low. So I backed the air screw out 3/4 and it was pretty good. It was maybe a touch under 3/4 out. Is that ok?

Also this was still with 44:1 I am thinking about going to 40:1 this weekend. Im worried it may be too lean at 32:1 and lots of ppl run 40.

I will also bring an assortment of jets just incase something does not work right. It should tho because its the same set up.

Thanks again for all the help. I really appreciate it.

I would maybe be interested in the ignition but not right now. Next things to buy is a enduro tank and new chain and sprockets.

Oh and the bike was not warmed up. My bike always idles a touch high when cold. Im hoping is will mellow down a bit when warm and I can re adjust the air screw a bit.

Forget the Over sized gas tank. They truly suck balls. For not a lot more money you can buy a Lectron carby. You'll get better economy from the Lectron and stock tank than you will with the OS tank and stock carby.
Plus it'll be really easy to tune. No Jets lol .
OS gas tank will just trash the ergos and make the bike "top heavy".

When you lean the bike out it's pretty normal for it to idle higher. 40:1 is all go. 32:1 is richer, not leaner. More oil= a richer mix. As long as you use good quality oil, 40:1 is fine.
I run 32:1 myself. If I were racing i'd run 40:1.
2nd clip from the top of the needle is pretty normal.

---------- Post added at 08:00 AM ---------- Previous post was at 07:45 AM ----------

Also. If you don't already havve a hot plug/Iridium spark plug, get one.
I'm not sure about the 250's. But with the 02/03 125 you Have to run a hot plug.

Last edited by 2 stroke bloke; 10-12-2016 at 02:54 PM.
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Old 10-12-2016, 03:18 PM
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I know how confusing this can be.. oil's coming out of the pipe, so you figure there's too much in the gas and decide to put less oil in (higher premix ratio), but no luck. It would only make sense that the less oil you put in the gas, the less comes out of the pipe, right?
I wish it were that easy..
What determines how much oil will come out of the pipe is how hot the conbustion temperature gets. You need a certain amount of heat to burn off the oil. When you run 32:1 premix, you basically have 97% gas and 3% oil. When you run 40:1 premix, you have 97.5 gas and 2.5% oil. So, in 40:1 you have more gas in each charge than in 32:1 - with me so far? OK - now more gas means richer mixture... the mixture is determined by a ratio of gas to air, and oil isn't factored into the equasion. 97.5% gas is more than 97% gas, right? Ok - so now we know that 40:1 ratio is actually richer than 32:1 (Air fuel ratio). The richer the mixture, the cooler the combustion temperature. Believe it or not - gas acts as a coolant in the cylinder! So - by going to less oil (40:1 or higher) then you're actually making the mixture richer, which in turn makes the combustion temperature lower, which means there is not enough heat to burn off the oil.
So what should you do? It sounds to me like you have a jetting problem. Go back to 32:1. Make sure you are running the proper temp plug for your bike, then lean out your jetting a little until the bike runs well, and doesn't drool oil excessively out the pipe.

From another forum. Good bit of info that really explains why more oil makes fuel/air leaner which is what you are jetting for.
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Old 10-12-2016, 03:43 PM
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Quote:
Originally Posted by 2 stroke bloke View Post
Forget the Over sized gas tank. They truly suck balls. For not a lot more money you can buy a Lectron carby. You'll get better economy from the Lectron and stock tank than you will with the OS tank and stock carby.
Plus it'll be really easy to tune. No Jets lol .
OS gas tank will just trash the ergos and make the bike "top heavy".

When you lean the bike out it's pretty normal for it to idle higher. 40:1 is all go. 32:1 is richer, not leaner. More oil= a richer mix. As long as you use good quality oil, 40:1 is fine.
I run 32:1 myself. If I were racing i'd run 40:1.
2nd clip from the top of the needle is pretty normal.

---------- Post added at 08:00 AM ---------- Previous post was at 07:45 AM ----------

Also. If you don't already havve a hot plug/Iridium spark plug, get one.
I'm not sure about the 250's. But with the 02/03 125 you Have to run a hot plug.
Your statement as it relates to fuel mix is wrong! The more oil in the fuel mix creates a leaner condition.

Paw Paw
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Old 10-12-2016, 04:00 PM
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Thanks Paw Paw for the all the info. I knew a little bit about carb tuning before this but listening to what you have to say really had made me curious. So with your info and the research I have been doing it has gave me a much better understanding about carb tuning and mix ratios and stuff. I am really excited to get out and try to get my bike really dialed in. Both of them actually im sure my 450 could used a bit of dialing as well. It is a real pain to get into the carb the frame just covers the carb pretty well.
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Old 10-12-2016, 04:57 PM
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Quote:
Originally Posted by PawPaw View Post
Your statement as it relates to fuel mix is wrong! The more oil in the fuel mix creates a leaner condition.

Paw Paw
More oil in the gas is still a richer mix though, as in, it's richer with oil. Isn't it?

Tuning isn't that hard, unless you want to make it hard .

32/40:1 oil mix. Get the engine "4 stroking", lean it until it stops 4 stroking and runs clean. That's the sweet spot.

2T engines don't like heat.
Fuel is cold.
More fuel = less heat and more power.

I get what you're saying. Hence why I'd run 40:1 if racing. But, I like the K.I.S.S theory myself (Keep It Simple Stupid). To most people when talking about a rich fuel mix, lean means less oil, rich means more oil. Don't blame me for that.
You need to remember. Common sense isn't all that common anymore. Hence K.I.S.S.
People aren't taught to think, they are taught to follow directions. I've found that when I go to Macca's (McDonalds), you have a much better chance of getting what you want by keeping it really simple. Don't confuse them or you don't know what you'll get.

Obviously in this instance the OP gets it, but, IMO, you got lucky this time. He obviously took some time to think about it, most wouldn't have. Try handing the same advice out on TT. It'd be a 100+ page thread.

If you're running Motul, go 50:1.

Last edited by 2 stroke bloke; 10-12-2016 at 05:22 PM.
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