Man 4-strokes are pains... HELP

gregsterrkerr
Edited Date/Time 1/25/2012 5:11pm
So i just bought a 2008 kx250f. My first 4s. It has stage 1 hot cams, a PC high comp piston and some jets. The guy i bought it off of never told me what jets where in it. Well im trying to get it running, it starts perfect and has great compression. the problem is when i rev it, it boggs down at about 1/4 throttle. Any Ideas?

My dad said screw the air/fuel screw in all the way then back it out 2 whole turns, add some new gas and it should be fine...

ANY IDEAS?
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RNagy052
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RNagy052 2/17/2010 12:58pm
2/17/2010 12:58pm Edited Date/Time 4/17/2016 8:50pm
Has the bike been sitting (stored) for any period of time?

If so, drain your gas. Get a can of carb cleaner and clean the carb and jets. Put some new gas in the bike and see if that fixes the problem.

If the bike has been sitting for a period of time the carb may just need a good cleaning.

And why are you posting this in the Moto Section instead of the RACE SHOP section of the forum?

darn noobs.
miedosoracing1 2/17/2010 12:59pm
2/17/2010 12:59pm Edited Date/Time 2/17/2010 1:00pm
Sounds lean. Way too lean. I would look for air leaks. Clean the carb. If not, take your needle and move the clip down, so the needle is actually higher, thus lets more fuel in.
Tiki
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Tiki 2/17/2010 1:00pm
2/17/2010 1:00pm
Give the bike away. Two strokes will solve all your problems. TRUST ME! They have no jetting issues.

How about you take the jets out and READ what they say on the bottom. Then - go to the manual and READ what it says for temp, heat and elevation.

Sorry Greg - there is no magic dust for motorcycles.
gregsterrkerr 2/17/2010 1:04pm
2/17/2010 1:04pm
Rnagy it is about 15 degrees here so yea it has been sitting for 2-3 months.
Im going to try Some new gas and see what happens...hopfully i can figure this thing out.

The Shop

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RNagy052
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RNagy052 2/17/2010 1:09pm
2/17/2010 1:09pm Edited Date/Time 4/17/2016 8:50pm
gregsterrkerr wrote:
Rnagy it is about 15 degrees here so yea it has been sitting for 2-3 months. Im going to try Some new gas and see what...
Rnagy it is about 15 degrees here so yea it has been sitting for 2-3 months.
Im going to try Some new gas and see what happens...hopfully i can figure this thing out.
Ok, well temp changes will make a difference too. Like mideosracing said you may also need to re-jet. If the bike was running fine in the summer when it was 80 - 90 degrees out, then you try and running it at 15 degrees, then you will need to make some jetting changes.

More than likely you are going to have to do 2 things;

1. Clean the carb and get some new gas
2. Make some jetting adjustments.

If you have the owners manual it should tell you what jets are recommended for what temp ranges.

You can start there as a base. or just clean the carb and wait until spring when the temps warm back up. Smile
miedosoracing1 2/17/2010 1:13pm
2/17/2010 1:13pm Edited Date/Time 2/17/2010 1:14pm
The reason 4 strokes are different in jetting, is because they actually run super bad if jetted wrong. So in jetting terms, it's almost better how bad they run. If they are lean, you know it for sure. On a 2 stroke sometimes, people run them lean and don't know it, until, blaaa bllla bla bl.
2 strokes with direct or fuel injection. Now that will be very good. 2 strokes will not have to worry about something like that, and they will last much much longer for everyone.
gregsterrkerr 2/17/2010 1:14pm
2/17/2010 1:14pm
alright well it was ran about 70-90 degrees and it is usually that temp here in summer so i think im goin to clean the carb get new gas and i guess wait til it warms up... would that also fix the little bit of smoking its doing?
miedosoracing1 2/17/2010 1:15pm
2/17/2010 1:15pm Edited Date/Time 2/17/2010 1:16pm
Ok, well from experience, if you are trying to run the same jetting from 70-90 and now 15 degrees. Yeah, you have to rejet. Go lower on the clip and atleast 1 size bigger on the main. It will not just be the fuel cleaned and carb cleaned. It's too cold to run the same jetting.
gregsterrkerr 2/17/2010 1:17pm
2/17/2010 1:17pm
ok thanks alot guys
im gonna do the gas and cleaning first and wait til it warms up a little bit haha!
mx5471
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mx5471 2/17/2010 1:37pm
2/17/2010 1:37pm
If the guy you bought it from raced it,chances are he used some type of race gas in it. A lot of that race gas is notorious for gumming up the carb after sitting a while. Before you do anything,take that carb off and clean it (inside) good,then drain the tank and put in fresh gas. My money says it'll be just fine.
Bret
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Bret 2/17/2010 1:54pm
2/17/2010 1:54pm
Old gas = clogged jets. Clean the carb.
over the hill 2/17/2010 1:59pm
2/17/2010 1:59pm
Bret wrote:
Old gas = clogged jets. Clean the carb.
x2
damn ethanol in the gas is bad for carbs
DrSweden
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DrSweden 2/17/2010 3:36pm
2/17/2010 3:36pm
Changes in temperature change the bike, but not that dramatically? I have newer re-jetted a bike in my whole life, and I ride both winter (snow) and summer (30 c°).
Flatliner
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Flatliner 2/17/2010 4:34pm
2/17/2010 4:34pm
miedosoracing1 wrote:
The reason 4 strokes are different in jetting, is because they actually run super bad if jetted wrong. So in jetting terms, it's almost better how...
The reason 4 strokes are different in jetting, is because they actually run super bad if jetted wrong. So in jetting terms, it's almost better how bad they run. If they are lean, you know it for sure. On a 2 stroke sometimes, people run them lean and don't know it, until, blaaa bllla bla bl.
2 strokes with direct or fuel injection. Now that will be very good. 2 strokes will not have to worry about something like that, and they will last much much longer for everyone.
still waiting for a two stroke with fuel injection. Looked around plenty and not a peep about anything going into production anytime soon.
need love
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need love 2/17/2010 4:44pm
2/17/2010 4:44pm
ya before ya go and waste a bunch of time, take the carb off and clean out every passage. you'll know if ya find one that was clogged......Then find someone at your local track that can help you out with jetting. You can read up on it and do it yourdelf with a little time and patience.........
jmar
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jmar 2/17/2010 5:10pm
2/17/2010 5:10pm Edited Date/Time 4/17/2016 8:50pm
Sell it and buy a stocker.


If you are looking for advise here on a motoboard, you don't need to own a modified 250F.
gregsterrkerr 2/17/2010 7:52pm
2/17/2010 7:52pm
jmar wrote:
Sell it and buy a stocker.


If you are looking for advise here on a motoboard, you don't need to own a modified 250F.
not that i need advice ive just never owned a 4s be for..
chill out hoss

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rallendude
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rallendude 2/18/2010 1:40pm
2/18/2010 1:40pm
meidoso is right. The bike is WAY lean. Not riding while it's cold because you bike is jetted too lean is a sorry excuse. Buy a 180 main and stick it in and you'll be ready to go.

I'm waiting on warm weather too but my bike is a fuely.
89'cr dude
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89'cr dude 2/18/2010 3:34pm
2/18/2010 3:34pm
okay, drop into a napa near you, and they sell this kit that comes in what looks like a paint can for cleaning carbs. it has a built in strainer and you put your carb in there and it should clean it. if you dont feel like investing in the whole carb clean out kit, take the carb off, take the float bowl off, then clean the bowl, floats, hole, and make sure the floats operate smothely. then take a compresser and blow through every possibile hole in the carb, this is not quite as good as the kit, but that also costs money. after cleaning the carb buy fresh 93 octane gas, put a small amount in, and try starting it. if it runs like the piece of s**t i suspect it is, richen up the mixture by adjusting the air screw a little. just trying to help out, although i still like the switch to a two stroke idea because im a two stroke guy myself, keep on rock'n it oldschool with the two strokes!
project racer 2/18/2010 4:47pm
2/18/2010 4:47pm
If you use the Chem-Dip bucket or similar solutions with the soak basket, make sure to remove all rubber components from the carb. That stuff is not as strong as it used to be, but may swell the rubber parts/ O-rings of the carb.

For final clean up / rinsing of the carb, I use brake cleaner or contact cleaner. It dries clean with no residue.

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