Question about 2003 Yamaha YZ 450 F

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My 2003 yamaha yz450f will back fire the whole time when i stop giving gas, with choke on or off and if i put choke off it dies

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How work hot start lever of my yz450f
2004

Posted on Oct 03, 2015

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  • Yamaha Master
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There may be a problem with the exhaust valves first check and adjust the clearances,

another reason can be leaking inlet or exhaust gaskets

Posted on Mar 16, 2011

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1 Answer

Engine stops when giving it gas and then it's hard to start


Hi, Anonymous 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.
10. The gas cap is not venting properly or fuel tank venting system blocked.
11. Vacuum line from intake manifold to petcock broken, cracked, or not attached, carburetor vent line plugged.
12. Needle and seat stuck closed in the float bowl.
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.
Bike dies when you give it throttle
DOWNLOAD NOW Yamaha YZ450F YZ450 2003 2008 Service Repair Workshop Manual...
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Mar 01, 2015 | 2004 Yamaha YZ 450 F

1 Answer

I have an 07 YZ450F, it runs great until it warms up then it starts back firing, bogs and doesn't want to stay running. I checked the vavle clearance, timing and both are good. What else could c


Carburation! If the air/ fuel mixture is not carefully adjusted by the choke system after warmup it will do just what you describe...check it out!

Jan 12, 2013 | Yamaha YZ 450 F Motorcycles

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
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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

1 Answer

I have a 2003 ttr225 I can get the bike to start with the choke on ihave to let it warm up for an extremly long time before I can push in the choke . once the bike is warm and I hit the throttle hard ,...


Sounds like the idle circuit in the carb is restricted. The engine is running on the choke only. When the engine reaches a certain temp the fuelthat does get is more readily burned allowing you to back off the choke. The choke probsbly can't be completely opened? right? Fuel quality is also something to consider Oil content in fuel affects combustion temps and volatility. _good luck_Ned_



Nov 16, 2010 | 2003 Yamaha TT-R 225

1 Answer

Hi there guys i have a yz450f 2005 was running like a dream no moke started real easy, then it just stopped. no bangs or noises but now it seems harder to kick and it will back fire then can hardly kick it...


Hi, Kurtn420 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. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
3. Faulty main circuit breaker and or connections.
4. Faulty ignition coil and or connections.
5. Faulty spark plug, oil or gas fouled, wrong heat range or service type, wrong gap, loose in the cylinder head, broken electrode or insulator.
6. Faulty spark plug cables, leaking or broken, internal damage.
7. Faulty ignition module, switch, CKP, MAP, CMP, sensor and or any connector in the ignition circuit could have corroded, loose, or broken pins/sockets
8. Burnt exhaust valve or air leak in the exhaust system.
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.
07 yz450f backfires when kick starting
yz450f popping backfiring
YAMAHA YZ450F Owner Service Manual
OEM parts for Yamaha
http://www.yamaha-motor.com/assets/service/manuals/2004/lit-11626-17-11_784.pdf

Sep 25, 2010 | 2003 Yamaha YZ 450 F

1 Answer

Engine back fires


It may still have some water in the tank/system or the spark plug is no good.With a full tank of fuel,add 200ml of methilated spirits.It breaks up any moisture and lets it burn away.Also,with the motor out of gear,run the bike at higher revs and close the choke fully on and give full throttle at the same time.When the motor starts to die,flick the choke off.This can sometimes unclog a carby jet that may be slightly blocked because with the air choked,it gives a sudden **** off fuel.This may/maynot fix the bike but it the 1st thing to try before paying a dealer and it can't hurt anything.Hope this helps you

May 29, 2010 | 2003 Honda CRF 230 F

2 Answers

How many kicks should it take to start a 2003 yamaha yz450f?


One, That thing should fire up in a second, if not, you got to get it so it will. Try not touching the gas, just pull on the choke, and give it a try. If that doesn't do it, try something else next time. I had a KLR 250, kick only, and that thing would start first kick every time, no matter what. I loved that little bike. Hope this helps.

May 13, 2010 | 2004 Yamaha YZ 250 F

1 Answer

Engine dies


Does it respond better with the choke on? Has the bike sat for an extended period of time (a year or more)? If either answer is 'yes', then you need to have the carburetors disassembled, cleand and put back together (overhauled).

Nov 04, 2009 | 2004 Yamaha V Star Classic

1 Answer

My 01 yz 125 is running really strange


your problem sounds common. i would also try a rejet!

Apr 07, 2009 | 2003 Yamaha YZ 125

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