Question about 2002 Honda CR 250 R

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How do u know that your air screw is at the right setting?

Well i am having trouble keeping it running, if u start the bike and let it idle, and than crack the throttle it dies. now i have adjusted the air screw 1 1/4 turn from seated position is that ok? with it being like that it runs good. my fuel mixture is at 45 to 1 and the tempature is around 17 degrees. our altitude is at 3700 feet above sea level.

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Air screw adjustment is simply what runs best. All the things you listed do mean something when adjusting the bike, but only to someone with the equipment to properly test all functions of the bike while running. Just make sure your mix ratio is right, and if you have to adjust the air screw for the first time, always run it all of the way in first to find out what the factory set it at. Make sure you write that # down so if you do end up with a problem with your adjustments, you can go back to the original setting and try it again.

Posted on Aug 31, 2010


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What are standard settings for idle and air mixture screws

The idle speed will be dependent on model, particularly if 4- or 2-cycle, 2, 4, 6 cylinders, etc. If your engine uses carburetors, I'd say no less than 600 RPM, maybe up to 850 RPM at idle. If your engine is fuel injected, the computer should set the idle speed and air mixture for you (if it's functioning correctly), and a big twin could idle as high as 1150 RPM .

Your Idle air mixture settings are important for proper idle. A good approach is to let the engine tell you what it likes. For this method you will need either a tachometer or a vacuum gauge. Here are some steps to guide you.

1) If the engine will start and run, go from there. If not, a good initial setting is to turn the idle screw(s) all the way in (GENTLY--don't break the seats!), then back them out about 1 1/2 to 2 1/2 turns.
2) Attach either your tachometer or vacuum gauge to your engine. Tach is connected to the ignition system (usually at the coil); vacuum gauge would be connected to a manifold vacuum port. (The bike's built-in tach MAY work for this, but they are often not graduated finely enough.)
3) If using a tachometer, warm up the engine. Working on only one idle mixture screw at a time, begin turning it IN until RPM begins to decrease. Then back the screw OUT again until you achieve maximum RPM on that screw. Feel free to "play," turning the screw in and out until you achieve highest RPM at at minimum turn-out (if you leave it turned out too far, bike will run rich and foul spark plugs; if not far enough, bike will run lean and hot). Now do the other idle mixture screws the same way. Finally, go back and do all the mixture screws again (and again and again, if necessary) until all throttle bores are synchronized.
4) If using a vacuum gauge, engine temp is not as critical, but go ahead and warm it up anyway. Similarly to the tachometer method, turn the mixture screws in until RPM drops, then out until max vacuum reading at minimum turn-out. If you have multiple mixture screws, do the same on each, then repeat on all screws until you feel they are all synchronized.
5) Throughout the process of adjusting idle air mixture screws, you will probably have to adjust the idle screws to keep the engine in the RPM range you want it to idle. (If adjusting air mixture screws has no effect on the engine idle, the minimum requirement is probably a carburetor rebuild.)
6) Have fun getting to know what your engine "likes!"

Oct 14, 2014 | Motorcycles

1 Answer

When choke is off wont idle

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.
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1 Answer

Overflowing of carburetor

    • 1 Put your bike on the center kick stand either outdoors or in a well-ventilated garage with the door open. You'll need to run the engine, so don't make the mistake of doing that in a closed garage.
    • 2 Set up a powerful fan next to the bike to help keep the engine cool. The cooling fins on your bike's engine rely on the apparent wind created when the bike is in motion to keep the block from overheating. Since you'll be standing still, you will need to keep plenty of airflow on the engine.
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    • 3 Remove any body work or other obstructions so you have clean access to the back of the carburetors.
    • 4 Find the ports for each carburetor on the intake track. The port is a metal tube extending upward from the intake covered either by a rubber nipple or a screw. Each carburetor has its own port. Remove the plug (be it metal screw or rubber nipple).
    • 5 Attach the manometer lines to each of the carburetor ports. With the manometer face up, attach the leftmost line to the port on the leftmost carburetor and work from left to right. Keep the lines free of any kinks or obstructions that could interrupt the flow.
    • 6 Start the bike using as little throttle as possible, and let it idle until the engine is warm. Don't forget to turn on the fan to keep the engine from getting too warm.
    • 7 Locate the vacuum adjustment screws along the top of the row of carburetors on the shared throttle arm. If you need help figuring out what the arm looks like, twist the throttle hand grip slightly and you will see the arm move back and forth. A standard, four-cylinder bike will have three adjustment screws along the throttle arm.
    • 8 Read the manometer for carburetors one and two (beginning from the left). Turn the leftmost adjustment screw to bring the vacuum readings for those two carburetors equal to each other. Turn the screw clockwise slightly and back again to get a sense of the effect on your readings. Do the same for carbs three and four using the rightmost adjustment screw. When your settings are balanced for each pair, use the adjustment screw in the center to bring the two pairs into balance with each other.
    • 9 Adjust the idle (fuel mixture) screw to set the appropriate idle speed. You can call your local shop to ask about the proper setting or check the service manual for your bike if you have it. Make sure you are using the warm idle recommendation as, at this point, your bike is at full running temperature.
    • 10 Tweak your vacuum settings if the idle adjustment threw them off slightly. Keep working back and forth from the carburetor adjustment screws to the idle adjustment screws until you have an equal vacuum for the four carbs and your idle is smooth and running at the proper speed.
    • 11 Turn off the engine and remove the manometer lines. Do not forget to replace the vacuum plugs in the carburetor ports to seal the air intake and preserve the balance of your newly tuned carburetors.

Jan 14, 2013 | Motorcycles

1 Answer

Hi, I own a Pulsar 150 DTSi (2007). I want to know the correct/most effective technique for setting the idling speed and carburetor volume control screw setting. I have already read many articles on the...

First and formost make sure air filter is clean.Then start bike and warm up engine.with engine warm adjust idle screw(the big screw with spring around it)Turn clockwise to increase and counterclock wise to decrease.with bike idling properly the low speed air adjustment screw (small screw located just above fuel bowl on side of carb)Adjust in small increments 1/16 turns at a time till bike has smooth throttle responce.This screw contols air flow during idle and up to 1/4 throttle.From 1/4 throttle and up the needle setting on plunger inside of carb takes care of 1/4 and up.You usally dont have to mess with needle unless you do upgrades to get more power out of bike.But over time the low speed settings can change due to wear on idle needle and air needle.So thats why you have to make adjustments.If bike still dosent respond or idle correctly I would purchase carb rebuild kit and your problem will be solved.

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1 Answer

How do you set the carburetor screws on a 1984 60cc yamaha 3 wheeler? There are 2 screws on the carb one is the idle and I assume the other is the high speed setting. I've adjusted them both all the way in...

Half right, one is the idle the other is the air mixture screw, which really only affects idle mixture. The mixture screw is usually about 1.5-2 turns out from screwing it all the way in. then when the bike is idling it is adjusted by screwing it in a little until it bogs down (rich), then screwing it out a little until the engine revs up and down(lean) and finding a smooth engine speed in the middle.
To initially set the idle, look down the carb throat and screw it in until it just starts to lift the slide.
But this doesnt help the starting problem, there may be a blockage in the carb, or if you have cleaned that already, may have to check further, many of those smaller engines need the suction though the standard air cleaner to run properly

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1 Answer

How to fix a fluctuating idle of a motorcycle? I ready set the timing and adjust the valve but the idle is still fluctuating.

hi there, have you cleaned the carb lately? i have a honda anf 125, a tad bigger that a 100. anyways, usually a mis-tuned or dirty carb makes the idle of our bike go crazy. If your a do-it-yourselfer, dismantling the carb and cleaning the jets, air ports, and choke lines would be best. Not to mention replacing the fuel filter if you have one in series with the fuel line. If you have cleaned the carb and installed it back to the bike, tuning is next. don't worry if you don't know the right position of the air-fuel screw w/c is next to the idle screw. Turn the air-fuel screw clockwise until it stops. Remember the position of the screw. Turn the idle screw clockwise a few turns until you see the throttle piston moves upward a bit. Then, start the bike. Turn the idle screw until the bike is running without stalling(higher than idle rpm. just like the bike is cruising about 40kph) . Now its time for the tuning. Turn the air-fuel screw counter-clockwise count your turns while listening to the sound of the engine. You will will hear the engine runs smoother and the the rpm starts getting higher also. Stop when you do not hear anymore significant change. Then turn the air-fuel screw clockwise a little about 1/8 turn then stop. Slowly turn the idle screw counter clockwise until you reach 1200 or 1400 rpm (well thats the standard value). Now, try revving the engine, if the engine looses power at the high rpm, turn the air-fuel screw 1/8 clockwise more. Do this step until the pooot-pooting stops. Try the bike and feel the power. If it feels the bike is back in shape. try using the bike for a few weeks. After a week, remove the spark plug and look at the tip. If the tip of your spark plug is kinda grayish or slightly redish(depends on the type of petrol you're using). You're setting is good to go. If the tip color is dark gray to black, the setting is to rich. turn the air-fuel screw counterclockwise about 1/8 turn, then test again. if no color change occurs well the engine should be checked and that's another story.

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1 Answer

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1 Answer

Yamaha FZ 750 FM

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Nov 10, 2008 | 1986 Yamaha FZ 750 FM (Japan)

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