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I don't know much about dirt bikes can you help

today i was riding and it was going well for about 1.5 hours then the bike started to bog down and died it's wants to start when you bump start it but it sounds really bogged down.

After in ride should i clean out the exhaust it looks kind of greasy inside and i don't know really what it should look like also what kind of after ride maintence should i be doing the bike is a 91 cr 125 and yes i am going to buy the book
 

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The CR's are race bikes, the 2 stroke bikes in particular.

The 2 stroke CR engine needs to maintain a fairly high level RPM... due to it's racing design.

After 1.5 hrs. of riding... your probably getting tired... and driving the bike more like an Enduro, Trail, or 4 stroke bike.

What happens is: the combustion chamber carbons-up which leads to fouling of the plug.

What you have to do then is: pull the head off the cylinder-case and clean all the carbon build-up off the bottom of head, piston top, spark plug, and ports... when running perfectly, these area's should be clean'ish and slightly grey'ish in color... when re-assembled, you can monitor by pulling the spark-plug and inspecting burn characteristics... if you pull the spark-plug now, the bottom is probably black'ish and oily'ish.

If you do that... you'll notice the bike runs better... but it'll still be prone to the same problem if it gets ridden like a trail bike for a long enough period of time.

You might want to check out a 4 stroke CR for race/trail riding if you also like to take it easy in the trails... you can ride a CR slow, but not for very long before you foul the spark-plug or get carbon build up in the combustion chamber.

When I use to ride my CR 250R on day long trail type rides... I use to take a fresh-spark plug with me... and I occasionally had to change them on the trail for peak performance.

And pulling off the head and cleaning the combustion chamber is fairly standard maintenance when racing 2 stroke bikes competitively.
 

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make sure you are mixing the right proportions of oil/gas. i usually run anything from 50/1 to 80/1. also used the expensive 2 cycle oil, it runs cleaner and will be less likely to carbon up your plug. (I like to use bel-ray H1R synthetic)
 
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i didn't know that you couldn't run thus like a trail bike thanks for the help and the new plug solved the problem but it still has an idle problem
 

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Be careful if you plan on just changing your fuel/oil ratio. Putting in less oil, going from say 32:1 to 50:1, will give you bike more fuel making it run richer. I suggest mixing your gas at 40:1 then jetting the bike properly. It sounds like your bike is loading up which is caused by overly rich jetting.

To jet a bike properly, start with the main jet. Find a fire road or something that is fairly long, straight and is on a slight incline. Put a new plug in the bike, cheap ones will work just as well. Run the bike wide open for at least 15 seconds then (this part is important) pull in the clutch and kill the engine. It is important that you don't let the bike idle down.

Pull out the plug and look down into the plug where the electrode comes from. It should be a nice medium gray color. I would be willing to bet that yours will look quite dark and black. This indicates that you are too rich and need to go down one size on the pilot. If it's really light grey or white then you are too lean and need to go up one size on the main.

From there just adjust you needle until the bike runs the best. With the pilot, adjust the air screw in and out until it runs the best. If the air screw is backed out too far then you are too lean and visa versa and need to change the pilot.
 

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lightning said:
i didn't know that you couldn't run thus like a trail bike thanks for the help and the new plug solved the problem but it still has an idle problem
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My version of trail riding is more like Enduro or Cross Country racing.

You've probaly still got a carbon build-up in your C.C.

Once you've cleaned your C.C. ... and you've got your fuel mixture dialed in, and it still idles poorly... dial in your carb (with help from the manual).
 
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Discussion Starter #7
I checked out the air screw and it was almost all the way in what does this mean and the previous owner mixed 40:1
 

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lightning said:
I checked out the air screw and it was almost all the way in what does this mean and the previous owner mixed 40:1
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You need to refer to the owners manual for positioning on the air screw... I can't remember what the spec's are from memory... and I no longer have my CR.

Check the spec's from the oil manufacturer for the correct mix ratio as it should vary from brand to brand... I use to use a Bel-Ray brand oil in my M.X. bikes.
 

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What years your bike, and what jet sizes do you have do you have now, and does it have the stock pipe and silencer, all these will have a big effect on your jetting? Allso what are you running for a plug, having the wrong plug can allso seem like it's the jetting and it may be the plug.

All the manufactures bikes (2 Strokes) bike come jetted WAY to rich and you have to rejet then to get them to run good. I have raced and ridden 2 strokes for over 25 years and allways had to lean out the stock jetting. You can run any 2 stroke slow if if it's jetted correctly with out fouling the plug. You can usually find the correct jetting for your bike by talking to racers who have had the same bike. But you need to tell them all the details about it, pipe, silencer, and fuel/oil ratio.
 

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gpgreg said:
What bike are you running? I personally would never ever ever go leaner than 40:1, that's on my modded 125...
ummm 2000 cr250 pretty much stock, but i've alway ran that on my motocross bikes problem free.
 
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The owners manual will only give you a base setting for your air screw. The normal operating range is between 1 and 1.5 turns out, so if you find the ideal setting is less that 0.75 turns out consider installing the next richer pilot jet (larger number ). If you find the ideal setting is more than 2 turns out consider installing the next leaner pilot jet (smaller number ).
 
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