Question about 1998 Yamaha YZF-R1

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I need to alter the fuel/air mixture

My bike will not tick over and only runs well with the throtle fully open, it is using loads of fuel with a lot of black soot in the end of the exhauast. I need to know how to alter the fuel/air mixture and how to balance the carbs

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Posted on Mar 04, 2009

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Why doesn't it idle unless choke is on?

Maybe you are running too lean. When the choke is on it reduces (chokes) the air being drawn in meaning higher fuel to air mixture (richer because of more fuel and less air). Turn the choke off and more air is drawn in and the fuel to air mixture is reduced. There should be a mixture screw where you can alter the mixture to the required setting for normal running.

Feb 16, 2016 | 2004 KTM SX 450 racing

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Air intake problem or carburater problem?

Check there are no air leaks around where the air intake rubbers are at your carburetor. It sounds like your bike is running too lean or weak which means your air/fuel mixture is running on too much air and not enough fuel. This would explain it running smoothly when you put the choke on as the choke "chokes" the majority of the air from the carburetor and allows more fuel to flow through the carburetor creating a richer mixture. There will be a mixture screw somewhere on the carburetor which will allow you to either richen (more fuel and less air) or weaken (more air and less fuel) by turning the screw either in or out. Only adjust this by a small amount (about a quarter turn at most) at a time and try the bike to see how it rides each time. After adjusting the screw each time let the engine idle for about 30 seconds or so to let it settle to the new mixture setting before riding. There will be another screw on the carburetor which is your "idle" or "tick over"speed adjustment screw which adjusts how high your engine revs while the engine is "ticking over". Turn it in to increase idling speed and out to lower the idling speed. This will probably need adjusting as you change the fuel/air mixture. I hope this helps you and good luck :o)

Jul 17, 2013 | Motorcycles

1 Answer

Bike ticks over on choke but won't run if a touch

Hi, Gerard 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.
Yamaha XV535 runs only on idle choke
Yamaha XV 535 DX Virago Service Manual
OEM parts for Yamaha

Oct 08, 2011 | 1994 Yamaha XV 535 Virago DX

2 Answers

Bike wwould not run today without choke pulled all the way out. yesterday much colder choke only half out then pushed in when did sit for 5 yrs. added seafoam and 92 octane fuel yesterday...

You are correct, the mixture needs altering.

Start up with the choke in position were it will start, run a few minutes to warm up engine.

Turn mixture screw all the way in, don't screw hard in (Gentle) could damage screw seating, listen to engine when it starts to faulter gradually turn screw out, listening to the engine sound till she is running smooth on tickover. Reve up quick shut down on throttle, and if setup correctly should return to tick over without stopping. Lucky person.

May 26, 2011 | 2005 Triumph Triumph Bonneville

1 Answer

I have had the bike since 2006 and it ran great love the bike. i bought it used with vance and hines sstraight pipes sounds great! never had a power issue is any gear at any speed i took it in for...

If they replaced the jets, did they replace them with the correct size? First off, the metering jets do not wear. Ethanol does not wear jets. If they replaced them, they replaced them to change the mixture. I would have them replace the jets with the original jets. Now, if something is going to wear, it the "needle jet" which isn't really a metering jet. It's the jet that the needle slides in when the slide in the carb goes up and down. It will wear due to the rubbing of the needle against the inside of the jet towards the engine side of the jet. Again, someone it telling you a story. Ethanol will not wear a brass jet. They changed the jet to change the fuel air mixture and now it's not right.

To find out which way it's wrong, try taking the air filter out of the air box and ride the bike at the speeds you have the problem. If the problem gets worse, you are jetted too lean. If he problem gets less severe, you're jetted too rich. By removing the air filter, you're allowing more air to get into the carb leaning the mixture. Now, since at this speed you are not a Wide Open Throttle, you're still running on the needle in the mid-range of the RPM range. You can lean the mixture by lowering the needle and richen the mixture by raising the needle.

What you need to do is take the bike to someone with an Exhaust Gas Analyzer and a Dyno. They should be able to put the load on the bike exactly like it's on the road and check your fuel air mixture at any given RPM. This will tell them if you're too rich or too lean and the RPM range will tell them which jet to change or the needle position to change.

Ethanol does not wear brass jets. The shop screwed up the mixture on your bike, that plain and simple.

Good Luck

Aug 25, 2010 | Yamaha Road Star Silverado Motorcycles

1 Answer

Triumph daytona 1200 95 running to rich loads of black smoke

hi,first place i would look is the choke circuit of the carburettors,if the bike has a cable fitted to the choke make sure that the cable operates freely,and returning fully to the off position,also check that the lever that the choke operates (on the carb)is returning to the fully off position,failing that,you may have to remove the carbs from the bike and check that the plunger(which is operated by the choke cable)inside the body the carb has not jammed inside its casing,failing that,you may have to have the carbs serviced by someone with a syncronizer to optimize the fuel air ratio,sometimes the mixture screws in some bikes have been known to alter with the vibration etc of normal operation,i would say that it is definatley a carb/choke/mixture problem that will not be to expensive to put right..hope this helps...cheers ian

Dec 27, 2009 | 1996 Triumph Daytona 1200

2 Answers

Piaggio nrg mc3 air carbrutor idle screw and air mixture settings

A service manual is a valuable tool with an aging bike. I suggest the dealer/mfr. or Clymer books. In the meantime, go to the library reference section...646 stacks should have what you need.

Sep 30, 2009 | 2006 Derbi Atlantis City 100

1 Answer

I have an 1998 xr250. it ran great and very strong up till today when i decided to clean the air filter (it was very dirty). after cleaning i put it in the bike to see how it ran. the bike would hardly...

There are two causes of your problem that I can think of: firstly, it may be that you, even after changing some jets, haven't got the air/fuel mixture right. If i were you, I'd put the standart jets back in, set the needle position to the middle position, and screw the air/fuel mixture screw 2,5 rotations ( 900 degrees) out from fully screwed in. This should return your bike's mixture settings to approximately standart. Then, using this page
determine if you have a rich or a lean mixture, and adjust accordingly. If you have any more questions, or would like me to clarify something, please ask.

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1 Answer

Rich mixture virago xv250

look up your bike here and i think it is number 13 on the diagram. which looks like its right by where the throttle cable connects

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