Question about 2005 Honda CRF 150 F

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Is there a factory setting on the fuel/air screw to start out with. I seem to remember (many years ago) that it was 1 1/2 turns out or so and then you fine tune from there. Its a Honda CRF150f - Thanks

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One and one-half turns is a good place to start.

Posted on Sep 13, 2010


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Fuel mixture screw settings

Most small engines use a 1.5 turn starting point.

1) Tighten the air/fuel screw in until it bottoms out, taking care not to over tighten the screw, snug is good (over tightening can and will damage the set screw).

2) Back the screw out 1.5 turns and start the engine, but remember that this is only a starting point.

3) Allow the engine to run until it warms up, then back the screw out 1/8 of a turn at a time, allowing at least ten seconds for the engine to get used to this new setting. Continue with 1/8 turns until the engines RPM is the highest. Once the engine RPM begins to drop off after an adjustment, stop and go back 1/8 of a turn and your air/fuel setting should be perfect. :-)

NOTE: This is assuming that your engine is running rich to begin with (which is the most common), but if your engine RPM does not increase by loosening the screw, you may be running lean to begin with and in your case you would need to do the opposite and tighten in 1/8 increments, always making sure to allow at least ten seconds of run time between adjustments before deciding if your RPM has actually increased before adding another 1/8 of a turn.

I hope this helps!! :-)

May 31, 2014 | Tanaka Garden

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If it has been sat for 2 years the fuel will have broken down so a full system flush with new clean fuel is a good 1st step.

If you have checked the carbs was there any sludge build up in the float chambers. If so I would dismantle and carefully clean with new fuel.

Make sure the tank is emptied and has not rusted. When you know you have clean new fuel. Try starting again.

When you get it running you need to use either a pair or easier 4 vacuum gauges to recalibrate the carbs.

This is fairly straightforward and a cheap set can be bought for as little as 8 pounds try Amazon. Obviously more expensive = better quality but if you are careful with them even a cheap set can be quite reliable.

Tip - Check each gauge against cylinder 1 for reading then you know if they are reading the same. Some are adjustable or just mark and set all to cylinder 1.

2.5 - 3.5 turns out sounds about right as a start point as you said.

Good luck

Mar 19, 2014 | 2009 kawasaki Ninja ZX10R

1 Answer

Husqvarna 125b. I have a mess. Blower would only run for.a.few.minutes and shut down. Ifirst changed the l and h carb settings and the spark plug. Didnt help so i took both settings t 1.25 turns. Now it...

The factory will not give carb settings as these machine are set from the factory for the best emmisions, this is why there is a special tool required to alter the screws, the screws are fuel screws not air screws, so as you un screw them ( anti clockwise ) more fuel is let through the carb, your machine is running too lean so the screws are in too far, before making any more adjustments check the fuel filter in the tank is not blocked, check the block the carb is connected too is not loose on the cylinder ( i have seen the screws coming loose ) if all is ok unscrew both screws out a further 1/4 turn and try again.

Dec 02, 2012 | Garden

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Hi, I just cleaned my Poulan Pro. Changed out the gas, opened the carb and flushed it out with fresh gas, cleaned the fuel lines, the spark plug and air filter. I didn't replace the fuel filter though. ...

The fuel pick up or filter should be changed every year but if your saw will start and run good but just not idle then adjust the screw marked T counterclockwise slowly until chain starts to rotate without you depressing the throttle.At that point back it off about 1/16 of a turn until saw will idle but chain doesn't move.Thank you. P.S. If you want to you can go back to factory setting by turning H & L fully closed then open 1 to 1 1/4 turn and very slowly adjust for smoothest operation. Do not adjust H anymore then minimum off factory to avoid engine damage.
If you need further help I would suggest you have a trained tech.service it. Good luck.

Feb 14, 2011 | Poulan Pro Chain Saw 46cc 20"

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I have a huskey chinesaw model 50 trying to adjust carb but haveing no luck what is the proper adjustment please help

Hi, Gerald I will try to help. The high speed mixture screw basic setting is about 1 1/4 turns out from lightly seated position and the idle or low speed mixture screw is about 1 turn out from lightly seated position. To get the manufacturers basic or start out setting, remember the position of the screws before you start any adjustments. Both are done the same way. Turn adjust screw in or clockwise until lightly seated (so the soft metal is not damaged when seating the screw) then turn out or counterclockwise, high 1 1/4 turns and low 1 turn out. Do any adjustments in 1/8 turn increments until you get running. Do not turn the high speed mixture screw so there is less than 3/4 of a turn from seated position, The reason is not to run the engine too lean so engine does not overheat. When turning the screw in, there is less gas in the mixture, therefore when turning out you allow more gas in the fuel to air mixture.
The problem might not be adjustment, it could be many other things causing it not to run properly. Make sure the air filter is clean, the fuel filter in the tank is not plugged up. Spark plug might be fouling up, the fuel lines might have dirt or starting to go. The fuel tank is usually vented by the tank cap and might be plugging up not allowing enough air in. Check the bolts screws and gaskets of the carb so there is no air leaking in.
The carb might need an overhaul, cleaning and maybe a carb kit.
These are suggestions to help diagnose the problem. I might have forgotten other things to check out. I hope this helps you out a bit. All the best and good luck.

Feb 06, 2011 | Husqvarna "Chain Saw - 16" Bar, 3 Hp

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How do you set the carburator back to factory specs. mine wont keep running

Basic settings can vary from model to model, a good starting point for most carbs is screw both H and L screw right in ,then back the H screw out 1 turn and the L screw 1 and1/4 turns, the machine should run well enough to fine adjust from there, they are both fuel screws, so the more you unscrew them the richer the saw becomes, always remember if there in another under lying problem adjusting the carb screws will not always help, before any adjustment clean or replace the fuel filter in the fuel tank.

Feb 03, 2011 | McCulloch 16 Inch Gas Chain Saw MCC1635AK

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.

Hope this helps. More power!

Sep 29, 2009 | 2005 Honda NF 100 Wave

1 Answer

Saw will start an run short period and stop.Only start when adding gas directly into carberator. This is a Poulan 16 chain saw.

If it is a old saw it sounds like your engine seals are failing. when a engine seal fails it allows air in past the crank upsetting your fuel mixture You could try to richin the fuel mixture by turning the screw marked H anticlockwise a quarter at a time untill it runs Ps to set (h) screw to factory, screw it in til it stops then unscrew it 1 & 1/2 turns

Sep 25, 2009 | Poulan Garden

2 Answers

10 year old Craftsman Lawn Tractor won't start

That's really strange. The low-speed fuel adjustment screw may be set way too rich, but that doesn't seem likely. With the air filter off, look at the choke plate if possible as you advance the throttle and see at what point the choke closes. Back it off till the choke opens and then put the filter back on and try to start it at that setting. Another thing that could cause too much fuel is if the adjustment of the carburetor float is off, causing the fuel level to be too high in the carb bowl.

Aug 03, 2009 | Craftsman 21 Hp 42" Deck, Ys 4500 Lawn...

1 Answer

What is the proper way to adjust the fuel mixture screws on the carburetor of a homelite bc800 string trimmer?; What are the "factory" settings--as in turns CCW out from full stop. The engine starts, but...

I always understood that the rule of thumb is to back out 2 1/2 turns. That is the starting point for any other adjustments, but if it still won't start, then the carb adjustment is not the problem. Check spark and fuel delivery.

Jul 06, 2009 | Garden

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