Question about 2003 Yamaha YZ 450 F

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What should the adjustment be for the air fuel mix screw inside the bottom of the 2003 yz450f carburetor?

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Run it all the way in carefully then back out 2 full turns all are diff but that is where you should start once running go 1/8 turn at a time back and forth till it smooths out hope this helps

Posted on Sep 30, 2010

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Motor stops


Hi, Anonymous and the usual suspects are:
1. Severely discharged or a damaged battery, should have 12.5 volts or better and be able to pass a load test if necessary.
2. Failed alternator/generator and or voltage regulator.
3. Loose or corroded battery terminals and or cables especially the "NEGATIVE" cable, look for loose, corroded, or broken connectors inside the cable harness at "BOTH" ends.
4. Failed main circuit breaker or ignition switch, check for loose connections and continuity.
5. Failed system and or ignition relay, check for continuity.
6. Failed ignition coil, ignition/electronic module.
7. Failed CKP, CPS, CMP, MAP, TPS, or BAS sensor, corroded, loose or broken wire connector pins/sockets.
8. Throttle cables and or idle speed improperly adjusted hot idle speed should be 950 RPM to 1000 RPM.
9. Air/fuel mixture screw improperly adjusted.
10. Accelerator pump damaged or not working.
11. Water or dirt in the fuel system, carburetor or filter.
12. Restricted, blocked or kinked fuel line.
13. Fuel tank empty.
14. The gas cap is not venting properly or fuel tank venting system blocked.
15. A failed fuel pump, pressure regulator and or fuel injectors.
16. Vacuum line from intake manifold to petcock broken, cracked, or not attached, carburetor vent line plugged.
17. Needle and seat stuck closed in the float bowl.
For more information about your issue and valuable "FREE" downloads that you need please click on the links below. Good luck and have a nice day.
06 dies after engine is hot
2010 YZ450f starts but soon stops bike stalls FOUND ANSWER
YAMAHA YZ450F Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Jul 07, 2014 | 2006 Yamaha yZ 450 F

1 Answer

ADJUSTING CARB ON A YZ 450 F


Hi, Anonymous the carburetor throttle shaft wheel has two cables the cable closest to the right side of the bike is the throttle cable and the one closest to the left side is the idle cable. Right about the middle between the two is the idle adjustment bolt it faces out towards the air filter end of the carb . The engine should be at operating temperature with the enrichener off to set the idle between 950-1050 rpm. Turn the idle adjustment bolt clockwise to increases idle speed and counterclockwise to decrease idle speed. If you have access to your air fuel mixture bolt you may adjust it as well if not there is a video below on how to gain access, make sure you start with clean or new spark plugs. Gently turn the air fuel mixture bolt clockwise until it starts to bottom out "STOP" do not over tighten as it will damage the taper on the end, now back it out 2 full turns to establish a starting point start the engine and check the idle rpm's and adjust the idle adjustment bolt accordingly for 950-1050 rpm if necessary, adjust the air fuel mixture bolt 1/4 turn at a time and let the engine settle for about 10 seconds, clockwise for a leaner mixture and counterclockwise for a richer mixture you are seeking the highest rpm your air fuel mixture bolt can acquire without going past 3 full turns from bottom then readjusting the idle adjustment bolt back down to 950-1050 rpm If you can not detect any rpm change and can not stall the engine by turning the air-fuel mixture bolt all the way in then your pilot/low-speed jet is too big. Final adjustment should be made with a clean air filter mounted to the carburetor. For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have nice a day.
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Yamaha YZ450F Owner Service Manual
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Yamaha YZ450F Owner Manual

Apr 04, 2014 | 2003 Yamaha YZ 450 F

1 Answer

2003 yz450f too lean backfiring on deacceleration


clockwise is rich & cc is lean which way are you adjusting?
clean the small air port in carb with adjustment screw removed.
Screw should be set 1 1/2 turns fron light seated position.

Nov 21, 2013 | Yamaha 2003 Yz450f Yz450 Yz Wr 450 Stator...

1 Answer

Engine chugging


Hi, Anonymous and the usual suspects are:
1. Idle speed improperly adjusted.
2. Air fuel mixture screws not properly adjusted.
3. Inlet system air leak.
4. Leaking accelerator pump.
5. Loose low-speed jet.
6. Plugged low-speed jet.
7. Contaminated or plugged low-speed circuit.
8. Enrichner valve/choke not seated or leaking.
9. Multi carburetors out of sync and need to be balanced.
For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
2006 YZ450F Running Rough as Hell YZ 400 426 450
Dirt Rider Magazine
YAMAHA YZ450F Owner Service Manual
OEM parts for Yamaha
http://www.yamaha-motor.com/assets/service/manuals/2004/lit-11626-17-11_784.pdf

Nov 05, 2013 | 2005 Yamaha yZ 450 F

1 Answer

Will not idle without choke


Hi, Anonymous and the usual suspects are:
1. Fuel cap or fuel tank is not venting properly.
2. Fuel filter clogged.
3. Fuel line pinched or kinked.
4. Float needle and seat sticking.
5. Float level too low.
6. Carburetor bowl vent line clogged/blocked/pinched.
7. Idle adjusting screw set too low.
8. Air/fuel mixture screw set too lean.
9. Idle port, transfer ports, slow air jet clogged.
10. Slow fuel jet clogged.
11. Faulty fuel pump.
For more information about your issue and valuable "Free" downloads that you will need please Click on the links below. Good luck and have a nice day.
05 yz450f wont idle must run by friday YZ 400 426 450
Wont run without the choke yz450f 03
YAMAHA YZ450F Owner Service Manual
OEM parts for Yamaha
http://www.yamaha-motor.com/assets/service/manuals/2004/lit-11626-17-11_784.pdf

Jul 21, 2013 | Yamaha YZ 450 F Motorcycles

1 Answer

05 YZ450F wont idle just not sure how to adjust the idle?


Hi, Bryce and the usual suspects are:
1. Idle circuit and transfer ports clogged.
2. Air fuel mixture adjustment too lean.
3. Pilot jet clogged.
4. Faulty accelerator pump.
5. Float level too low.
6. Float bowl contaminated old fuel, water, dirt, rust, etc.
7. Float bowl vent or overflow tube clogged.
8. Fuel flow to carburetor restricted.
9. Intake manifold leak.
For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have nice a day.
04 yz450f wont idle NEED HELP
06 YZ450F Wont Idle
YAMAHA YZ450F Owner Service Manual
OEM parts for Yamaha
http://www.yamaha-motor.com/assets/service/manuals/2004/lit-11626-17-11_784.pdf

Jun 25, 2012 | 2004 Yamaha YZ 450 F

1 Answer

I have a 2008 yz450f , I was practicing at Glenhelen sat . After 2 practices without any problems. 3 laps into the 3rd. Moto it backfired and died. The motor.kicks over but wount fire. Carb. Is getting...


Hi, Ssfichter1 and the usual suspects are:
1. Severely discharged or a damaged battery, should have 12.5 volts or better and be able to pass a load test if necessary.
2. Failed alternator/generator and or voltage regulator.
3. Loose or corroded battery terminals and or cables especially the "NEGATIVE" cable, look for loose, corroded, or broken connectors inside the cable harness at "BOTH" ends.
4. Failed main circuit breaker or ignition switch, check for loose connections and continuity.
5. Failed system and or ignition relay, check for continuity.
6. Failed ignition coil, ignition/electronic module.
7. Failed CKP, CPS, CMP, MAP, TPS, or BAS sensor, corroded, loose or broken wire connector pins/sockets.
8. Throttle cables and or idle speed improperly adjusted hot idle speed should be 950 RPM to 1000 RPM.
9. Air/fuel mixture screw improperly adjusted.
10. Accelerator pump damaged or not working.
11. Water or dirt in the fuel system, carburetor or filter.
12. Restricted, blocked or kinked fuel line.
13. Fuel tank empty.
14. The gas cap is not venting properly or fuel tank venting system blocked.
15. A failed fuel pump, pressure regulator and or fuel injectors.
16. Vacuum line from intake manifold to petcock broken, cracked, or not attached, carburetor vent line plugged.
17. Needle and seat stuck closed in the float bowl.
For more information about your issue and valuable "FREE" downloads that you need please click on the links below. Good luck and have a nice day.
2006 YZ450f backfires then dies YZ 400 426 450
2010 YZ450f starts but soon stops bike stalls FOUND ANSWER
YAMAHA YZ450F Owner Service Manual
OEM parts for Yamaha
http://www.yamaha-motor.com/assets/service/manuals/2004/lit-11626-17-11_784.pdf

Feb 26, 2012 | 2007 Yamaha yZ 450 F

3 Answers

Trimmer will only run for a few secs then dies out


Sounds like you will need to clean your carburetor.
Sometimes you can get by with priming it a few times, and letting it
run a few times like that and it will flush the gunk out of the jets,
but most of the time you will need to rebuild the carburetor.
If the mower is over a couple years old, then I also recommend that you
buy and install a new carburetor repair kit, because the diaphragm will
get hard and that will cause it to be hard to crank.
When you clean your carburetor and remove the jet screws, count the
number of turns it takes to seat the jets from their original position.
That way when you go to put the jets back in, you know how many turns
they were in/out.
Please do not forget to rate me, Thanks
Good Luck, I hope this helped

May 17, 2010 | Craftsman Convertible 25cc. Gas Line...

2 Answers

Engine speed surges


Surging engines in lawn mowers are usually related to a lean fuel/air mixture. With today's environmental concerns, the carburetors on these engines are set with a very lean mixture (to reduce air pollution). Furthermore, they usually put limiter caps on the carburetors where you cannot easily adjust the mix to get the engine to run better.

If there are adjustment screws on the carburetor, try turning the high speed adjustment screw a bit counter-clockwise (if the limiter cap will allow it). This will enrich the fuel/air mix a bit and might help the engine run a bit better.

Oct 11, 2009 | Garden

2 Answers

Yamaha 125 grizzly starts and idles when choked but dies when acc


check that reed valves not sticking and check the pilot jet its prob. half blocked. have to stick a very thin wire through it.

Aug 12, 2009 | 2003 Yamaha YZ 125

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