My Honda CRF100 will not idle without the choke being on. Where do I start, spark plug, mixture ratio, check compression, bad fuel?

You will have to check fuel pressure and volume and if that is okay the fuel/air ratio mixture is either off or getting bad data to the computer from the air flow sensor or the computer is no good.

If you need to use choke and there has been a recent clean and/or rebuild. It would be a good idea to check the fuel mixture screw setting. It sounds like it is running a fuel/air mix that is too thin, (lean mixture).

Hi there,

had the same problem before. What you need to do is to cancel out those basics that prevents the engine from running.

1. Check the spark plug, poor spark causes poor engine performance.
2. Poor fuel. Make sure no water is in the carburetor.
3. Idling problem or fuel-air mixture.

Quick Fixes:

1. Rev the engine with the choke ON. rev for at least 30 seconds to drive moisture out.
2. Drain the carburetor for any water deposits. This makes a bad mixture in the combustion.
3. Clean your spark plug.
4. Tune your Fuel-Air mixture to 2.5 turns out... Turn it clockwise until it stops and make 2.5 turns out. That's the standard.
5. Set your idle later if the engine's hot enough for idle run.

Your problem mostly is caused by poor fuel dispersion. Since pulling the choke entails less air and more fuel, it could be that that your engine requires more of it. If you have the time to remove the carburetor for disassembly, i recommended doing so. Remove the carb and clean the jets, make sure you put everything back in order.

That's it.. Let me know if there's any more problems... this is my usual approach.

I hope it helps,
levibit

Being efi (electronic fuel injection) the idle should be higher when starting off cold...in the older days, you used to use a choke, a handheld lever that you pulled out to shut off the air to result in a rich mixture...due to cold air there is alot of oxygen molecules, so a choke increases the fuewl mixture to compensate aiming for that 14.7:1 air to fuel mixture ratio


BUT it should not be that high, what is happening is that is dumping too much fuel in and you are having to go WOT (wide open throttle) to prevent a "flooded" condition..

Why ???? Well, it could be a faulty air flow sensor, a faulty or out of adjustment idle control, bad fuel, bad air filter, fuel filter, fuel injectors bad....etc etc

So, more info is required to solve it......when was the car last serviced, and does it only occur when cold, or do you notice that it is hard to start when hot as well.

sounds like its time to adjust those valves to me 0.003-0.004 on the filler gage or have done at shop.

fuel injected?-was the engine rebuild-higher compression ratio?
pining=detonation which occurs with to advanced timing or lean fuel
mixtures-could be as simple as wrong grade of fuel. carbon deposits in the combustion chamber can also cause pre-ignition.spark plug gapping or even to long of a plug? there is also the posibility of a vacuum leak or intake leak as this would lean out the fuel mixture-scan tool read fuel trim and o2 readings bad sensor or exhaust leaks could cause fuel mixture issues as well. hope any of this helps..

Is the fuel full of something? Dispose of it and try this.
Fuel/Oil Mixture

1. Use a quality 2 cycle oil and mix it to the OIL supplier's recommended ratio. Today I use Stihl 2 cycle oil mixed @ 50:1 in a Pioneer that I purchased new in 1980. There are no gouges or scratches on the piston or cylinder and I have no carbon build up on the piston top. The manual (on stone tablets) recommends 24:1. Over the years the mixture has leaned from 24:1 (Saw Recommendation) to 28:1 (Lawn boy mower recommendation) to 32:1 (Oil provider 8oz/2gal - used for many years) and finally the last 5 (±) years 50:1 (Stihl 2.6oz/1gal)
2. Any fuel containing ethanol is not good with chainsaws. Mix what you expect to use within a few months. Anything over 3 months old use up in a 4 cycle engine.

Start Procedure
Cold:

1. Ignition on/off to on
2. Set compression release – optional step even if saw is equipped with a compression release
3. Pull (close) choke, set fast idle (done when choke closed on some saws); pull starter and listen for an attempt to start. once heard (usually two pulls)
4. Set compression release – optional step even if saw is equipped with a compression release
5. Push (open) choke pull starter until it starts. (usually first pull)

Warm:

1. Ignition on/off to on
2. Set compression release – optional step even if saw is equipped with a compression release
3. Pull (close) choke, set fast idle (done when choke closed on some saws) - Don’t pull with choke closed.
4. Push (open) choke, pull starter until it starts. (usually first pull)

HTH
Lou
If no joy repost with what you have done and we'll try something different. Once flooded chainsaws are very hard to start.