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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Plz visit this site it may be of help to you.


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


Driveability Tuning: TPS + Idle Air Mixture

Let me share some information not found elsewhere about how to set your Throtle Position Sensor (TPS) and throtle plate after cleaning the throttle body. This article is about tuning your engine to get an happy ECM not race track nitrous tricks. The on-board OBDII ECM controls just about everything engine wise but for that it relies on a few bases set below. In OBDII era everything is controled with extrim acuracy. If a parameter is off you get bad driveability symptoms if the ECM can not detune the engine enough to compensate. We are not even talking engine code here. You'll get a CEL if something is busted not for driveability issues like misfirings induced by lean mixtures (no CEL but degraded driveability regardless - Trust me I design computers).

Set the throtle plate to be almost fully shut closed plus a quarter turn of the screw so it is not sticking ie. opened as little as possible. At this position you have base idle at which the TPS should read 0.6000 VDC (ie. 600.0 mV) in the car powered by the computer circuitry.
Note that at 610.0 mV you are off idle!! (ECM deactivates vacum engine mounts coil) So adjust acuratly to no more than 600mV +/- 2mV

Set the "Idle Air Mixture" screw to about 1/2 or 3/4 turn opened from fully seated. This is to provide idle air to the engine by bypassing the throttle plate.
More or less air is NOT better - There is an exact amount of air needed to mix with the exact amount of gaz injected at idle.

- Not enough air will give you a surge at pick-up and cause pinging and overall poor driveability at low speeds. The surge is caused by the computer jurking the Idle Air Valve opened to adjust the mixture.
- Too much air will keep the car moving when you let go the gaz pedal AND decrease the vacum available for your break booster.

So better not enough idle air than too idle much air.
By properly tuning the fuel injection you will increase the low-rpm power and you'll potentially save gas as well with increased power.
I find my engine drives around town about 1,100 rpm with amaising tork not always above 2,000 like before tuning!
I also have a TL'05 with the fancy throtle-by-wire, same thing is true. great tork when the idle mixture is set properly which no mecanics ever set. These setings are root to many poor driveability issues. It can not be acuratly factory set or should be retuned every 50,000Mi to match the engine conditions.

The acid test to know when your engine is well tuned: backup a 40% hill slowly. If it is smooth you have it. If the engine surges, misfires or hesitates you are off the chart by as little as 1/4 or 1/2 turn or more. The closer you are to the target mixture the better your engine runs. Aproach the IAM setting on the increasing side: from close to open.
Why backup a hill?? The reverse gear: is actually hard for the engine to drive because it is realy long. Up the hill: is to put the engine under load.

Love tuning these V6 3.2L and crusing around on tork alone while saving green house gases! Third gear WOT is really nice too.

Acura aluminum engines have some electrical ground issues because the ground straps and AL don't like each other (disimilar metals and AL forms an insulating oxide) - Tip: clean up all your ground straps connections including the ECM ground post directly on the thermostat housing and coat them with AL electrical wires compound from Lowes/HomeDepot. Well worth the trouble as well.

on Feb 24, 2009 | 2001 Acura 3.2CL

2 Answers

I have an mgb roadster and it won't run unless the choke is on suggesting fuel deprivation. Has anyone got any suggestions?

Have you been adjusting the slow running screw and fuel screw if this is the case, turn the mixture screw from the full in position then do half a turn at a time until the engine runs in sort of order gradually after a minute or so, gradually try to turn the choke off till it's fully off and at the same time turn the mixture screw half a turn till it runs with the choke completely off and the tick over is holding,
when you have that situation let the engine warm up after it's run a bit gently turn the mixture screw in until it just it's just starting to hunt then turn it back again until the hunting as just disappeared this is the correct running mixture you can turn it a little further to make it leaner if you require, now set the tick over to your liking.

Good luck

Mar 08, 2015 | Measuring Tools & Sensors

2 Answers

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

2 Answers

I have a 125 pit bike and it ticks over fine but when you rev it it backfires does any body no how to fix it.

You can check ur values but some bike do make a we ticking from the values and it will back fire when revved up because of the extra fuel once revved that hasn't brine burn as it revs back down to idle speed.

Jul 19, 2012 | Pit Bike 125cc 4 Stroke Dirt Bike

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

2 Answers

Error code says it is running lean. I replaced the air filter and cleaned the sensor. what other possibilities?

Air/Fuel flow mixture screw needs altering as mix is too lean and will keep causing problems.

Jun 22, 2010 | 2003 Jaguar S-Type

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

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.

Jun 20, 2009 | 1998 Honda XR 250 R

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