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Discussion Starter #1
I recently picked up a Raptor 250 second hand, and after trying to reach top speed (in 5th gear on a downhill road for 20 seconds straight), and it only reached 44 mph tops even though they're supposed to go like 50-60.

The airbox lid is off and it has an FMF slip on exhaust. I'm riding in around 40 degree weather if that makes a difference.

Does anyone know what's going on? Thanks
 

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First check the plug. With the airbox lid off and a pipe it should have been re jetted. The plug should be coffee brown ideally. Then I'd do a compression and leakdown test. This will tell you about the health of the motor. These things should give you a direction to investigate.

Mad
 

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Discussion Starter #4
First check the plug. With the airbox lid off and a pipe it should have been re jetted. The plug should be coffee brown ideally. Then I'd do a compression and leakdown test. This will tell you about the health of the motor. These things should give you a direction to investigate.

Mad
I was told it's running lean, but I'll check the plug.
Here is a video of how it sounds and runs:
 

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Yeah, you want to check the plug. If it's bright white, you're running lean which can eventually destroy the motor. Check to see if your clutch is slipping too. Sounded kinda like it was in the lower gears. Engine sounds reasonably healthy. That misfire up top is no Bueno.

Mad
 

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Yeah, you want to check the plug. If it's bright white, you're running lean which can eventually destroy the motor. Check to see if your clutch is slipping too. Sounded kinda like it was in the lower gears. Engine sounds reasonably healthy. That misfire up top is no Bueno.

Mad
I was in 5th gear top speed. Everyone is saying that it sounds lean and I should get larger jets.

Would the misfiring top end be caused by a lean carb?
 

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Yes it could. If the fuel mixture is so lean that it's on the edge of being uburnable, it could cause your misfire. You really need to look at the spark plug. Because if you're running that lean there's a really good chance you can burn up the top end. Piston seizure or burned valves could result. If the plug is white, immediately go up maybe 2 sizes on the main jet and re check it. You want the plug porcelain to be coffee with creamer brown color.

Mad
 

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Yes it could. If the fuel mixture is so lean that it's on the edge of being uburnable, it could cause your misfire. You really need to look at the spark plug. Because if you're running that lean there's a really good chance you can burn up the top end. Piston seizure or burned valves could result. If the plug is white, immediately go up maybe 2 sizes on the main jet and re check it. You want the plug porcelain to be coffee with creamer brown color.

Mad
Okay
 

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Hmmm that actually looks pretty good. Ok, what you can do is things like
Check the valve clearances
Do a compression and Leak down test. ( these things will give you a baseline of the health of the motor. If you don't know the history of the machine, checking valve clearance is worth doing. Clearances can affect how much vacuum the cylinder pulls and therefore fuel use in the motor )
Make sure you have fresh gas and don't have any water in the fuel system. ( You can drain the float bowl into a glass jar. Water will sit on the bottom)
Check your chain and sprockets. That skipping sound could be the chain jumping teeth. Set the chain tension
Try to determine if your clutch is slipping. ( A crude way is to have the front wheels against a wall. Feed out the clutch. Engine should die pretty quick. If you can feed a lot of clutch engagement, the plates could be worn. However, you should be able to hear the revs rising without an increase in speed while riding. )
Sorry I can't be of more help. Hopefully, something I suggested will point you in the right direction.

Mad
 

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Discussion Starter #11
Hmmm that actually looks pretty good. Ok, what you can do is things like
Check the valve clearances
Do a compression and Leak down test. ( these things will give you a baseline of the health of the motor. If you don't know the history of the machine, checking valve clearance is worth doing. Clearances can affect how much vacuum the cylinder pulls and therefore fuel use in the motor )
Make sure you have fresh gas and don't have any water in the fuel system. ( You can drain the float bowl into a glass jar. Water will sit on the bottom)
Check your chain and sprockets. That skipping sound could be the chain jumping teeth. Set the chain tension
Try to determine if your clutch is slipping. ( A crude way is to have the front wheels against a wall. Feed out the clutch. Engine should die pretty quick. If you can feed a lot of clutch engagement, the plates could be worn. However, you should be able to hear the revs rising without an increase in speed while riding. )
Sorry I can't be of more help. Hopefully, something I suggested will point you in the right direction.

Mad
I actually got a reply saying it was too lean from the look of that picture, and I should go up 3 jet sizes.

Here's what he said:
"Lean is Hot.
Hot is what has melted that electrode unevenly, and given it and the ceramic insulator the high heat baked look.
The cruddy oily looking part is likely at or in the threads of the head, vs being out and deeper into the combustion chamber where it would get burnt off.
The rest of that plug probably looked oily and black too before the mods...but the extra air from their extra flow that has caused the Lean condition, burnt it off easier.
Buy the next 3 main jet sizes up, and it'll probably be the 2nd or 3rd.
Trial and error as to which of the 2 is best.
Mains control the upper 3rd of the rpm range.
You can try moving the needle down 1 groove now, or after, just do one thing at a time.
The needle controls the middle third of the rpm range.
It should run really well from that point, and you should try opening the air screw a quarter turn at a time, as you may or may not get some low end improvement.
The pilot should not need to go up a size, as it controls the lower 3rd of the rpm range.
There, that IS the answer, and what you need to do to fix it."
 

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I pretty much agree with him. On my Kindle the picture didn't come out too good. If it were mine, and I didn't know the history of the vehicle, I'd still do a compression test as well as a leakdown test. You may just be dealing with a tired motor. If you want guidance with these, just ask. Right now you need to build a base oh knowledge about this quad. Especially if you plan to keep it.

Mad
 
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