Crf250x help it fires but won’t keep running.

[Todd Howard]

2006 CRF250X
Surely someone on here has had this happen.  I kick the bike (e-start is giving me nothing - I get the rumble start only when I kick it.). I roll the throttle 3X, kick it and it rumbles to life.  When the gas from the accelerator pump burns up it dies.  Opening the throttle kills it, choke kills it.   I never get more than the rumble but it’s definitely firing and burning the small amount of fuel.  What does this mean?  

Here is the setting:  full lower end and top end rebuild.  New cylinder, rings, cylinder head and SS valves tested, intakes at .005 and exhaust at .011.

New spark plug, new cam, basically a lot of new parts.

Surely someone has seen a bike rumble and not go.  What did you do?

Edited May 24, 2020 by Todd Howard

[Jim Dettman]

Check the fuel flow.

1. Open the drain valve on the carb bowl; do you get a steady flow?

2. Disconnect the gas line at the carb; do you get a steady flow?

If not, you can have:

1. A float that is sticking

2. A fuel line that is collapsing internally.

3. A fuel inlet screen that is collapsing (the one in the tank attached to the petcock).

4. A plugged tank vent in the cap.

 If you have good flow, then your float may be adjusted to the wrong height.

Jim.

[Todd Howard]

Jim big thanks!  I have drained the carb a few times to do other work so I know gas is getting into the carb bowl.  I’ve witnessed the AC pump shoot fuel properly.  The float level is a real possibility???  Maybe fuel isn’t getting to the pilot jet?  Isn’t pilot the one operating at idle?

[Jim Dettman]

Todd,

 Yes, float level is a possibility or it being partially stuck. 

 Again, checking fuel flow will pin it down a bit.   It's possible your are getting a restricted flow, which lets you get enough for the AP (which picks up off the bottom of the bowl), but not fast enough for anything else.

 i.e. if you get a flow out of the carb for just a bit, but good flow at the gas line, then the float is stuck.   If flow out of the gas line is not good, then the problem is further up (fuel line is deteriorating/collapsing inside, fuel strainer in the tank is collapsing or plugged,  or a plugged fuel vent).

 If you do get a good continuous flow out of the carb, then the float is out of adjustment, or the slow jet (or pilot) is plugged possibly.   But if you are cranking it and trying to blip the throttle to get it to run and it's not doing that, then it points to not getting fuel in general.

 But I would take the time to double check the fuel flow.  You might be surprised and it only takes a few minutes.   Also be sure to use fresh gas if there is old stuff in there.

 Little more detail would help to....has it been sitting?  Work done recently?  Last time carb was cleaned, fuel line or strainer replaced, etc.  

Jim.

 

[Todd Howard]

When I bought the bike the bottom end had been rebuilt.  I’ve rebuilt the top.  I’m not sure how long it sat before but I’ve ultrasonic cleaned the carb, checked jets, squirted carb cleaner and air through all passage ways I can find.  I pulled the carb today just to go over it again.  I’m wondering if a total carb kit, new air screw, etc might clear up the issue.  Blew air through gas line and float shut off air pretty good at about level.  Wondering if I should allow it to fill further Than level??

[Todd Howard]

Also, When the throttle is rolled 3 x and I kick it it will run until that gas is burned up.  If I crack the throttle it dies, if it’s on choke it dies.

[Jim Dettman]

<<I pulled the carb today just to go over it again.  I’m wondering if a total carb kit, new air screw, etc might clear up the issue.>>

 New slow jet for sure...they are notoriously difficult to clean.   They are about $6 US.

<< I’m not sure how long it sat before but I’ve ultrasonic cleaned the carb, checked jets, squirted carb cleaner and air through all passage ways I can find. >>

 You should pull it apart mid-body and replace the gaskets.  Carb cleaner melts rubber, which is what the mid-body gaskets are made of.   Don't think it's your problem, but I would do them on an '06 with un-known history and that you used carb cleaner.  This is what it can look like inside:

 The ultra-sonic was good, but air doesn't cut it.   You need to use carb brushes, guitar string, or fishing line to get everything out.  The slow circuit air passage from the bell on the air box side over to the slow jet and fuel screw is tough to clean.

<<Wondering if I should allow it to fill further Than level??>>

The float setting is 8mm. On page 131 here:

http://owners.honda.com/assets/OWNERLINK/model/own_man/powersports/2005/2005_CRF250X.pdf

of the owners manual.

Jim.

[Todd Howard]

Wow!  That mid body video!  Hmmm will dig in to that ASAP!

[ramz]

Recheck this:

 

Edited May 25, 2020 by ramz

[Todd Howard]

10-4 on that!  I think I’m all good.  Cracked open the mid-carb this morning.  It looked old and nasty so I’m hoping this was the issue.  I’ve got the new gaskets on the way along with new jets etc for a total carb rebuild.  Probably Thursday before I get the parts.

Edited May 25, 2020 by Todd Howard
Add pic

[Todd Howard]

Hey guys how many turns out on the idle screw?  Not the air.  The one that controls idle (left side of carb with longer flex cable.). Any counsel on beginning setting when I get these gaskets, air screw, jets installed and this carb back in the bike?

Edited May 25, 2020 by Todd Howard
Misspelled word

[Jim Dettman]

Todd,

You need a tach to set the idle speed.   Idle is supposed to be set to 1,700 rpms.   That's to keep the decompressor from kicking in.

The fuel screw is typically in the range of 1 to 2 1/4, with a setting of 1 3/4 turns out as a starting point.   That will vary based on the slow jet size, altitude, and temperature.   

The procedure to follow for that is:

1. Get the motor fully warmed up.

2. Lower the idle speed until the motor is just running.

3. Adjust the fuel screw for the smoothest running.

4. repeat #2 and #3 until you can't keep it running.

5. Bring the idle speed back to 1,700 rpms

 Note that you might want to put a fan on it while doing this so it does not overheat.  When your done, the fuel screw should end up between 1 turn and  2 1/4 turns out.    The reason is that at <1 turn, the needle is so far in the hole, the adjustment is not effective, and > 2 1/4, you have to start worrying about the screw falling out.

 So if your are <1 turn, that says you are trying to cut the gas back, which means you need a smaller slow jet.   > 2 1/4 means your trying to get more, so you need a bigger one.   You should find you need a #42 slow jet and you'll end up around 1 1/2 - 1 3/4 turns out.   If you can't adjust correctly with that, then something is probably wrong (i.e. an air leak).   Ride it after adjusting and if it pops at all on decel, turn the screw 1/4 out.

 If you have the adjustment right:

1. Pulling the hot start *slightly* will give you a rise in rpms

2. Pulling it all the way will kill the motor

3. Pulling the choke will kill the motor.

  If you get the above, it means your slightly rich on the slow circuit, which is where you want to be.   When you are tuning, you always want to error on the rich side.   Being even slightly lean will cause all kinds of issues (motor running hot, bogs, poor performance, etc), where being rich you have to be way rich before you have problems (fouling plugs).

Jim.

[Chuck.]

+1 on the previous.

The engines don't have a thermostat to regulate engine temp and as a result best mixture varies during a ride.  I have a Vapor on my X and the engine temp vary a lot during a ride so I suggest the remote mixture screw for easy adjusting during a ride.

I have a TrailTech fan on my X and this summer I'm going to block off most of the left radiator and let the fan thermostat regulate engine temp like it does on my Trials bike.

[dakh]

I think the question was where to put idle screw so the engine starts at all.  I usually just make it barely touch the slide when putting the carb back in, and then screw it in by half turn to find where it will want to fire up.

[Chuck.]

Best is to measure the number of turn out for the idle speed screw to untouch the slide, then you have the initial setting when you reinstall the carb. Same for the mixture screw except it is number of turn in to seat the screw.

[Todd Howard]

Got all the carb parts in and replaced the mid carb gaskets, and pretty much all wear components inside the carb.  The bike still will not crank.  Very frustrating!

[Jim Dettman]

Hum....and we are sure we have good fuel flow?

If so, I would pop off the valve cover and double check the cam timing.   If you are off a tooth it will be very hard to fire and may not run at all.   When you do that, use the left side marks to line up for TDC.  Lobes on the cam should be pointing back towards the back of the bike.  If not, rotate the crank 360 degrees and line up again.   Note there are two marks there "F" is fire, "T" is TDC.

and curious; what did the carb look like mid-body?  was it a mess?   I don't think what you did there was a wasted effort.  Being an '06, I sure it needed to be cleaned out.

Jim.

 

[Chuck.]

I bought an 05 6 years ago and had to do a complete carb rebuild to get the bike to run correctly, including mod body gaskets, slide gasket, and JD kit. These carbs have been around for several decades and are used on a lot 4T dirt bikes so lots of good help on TT for checking and tuning. My FCR works great and is near EFI.

[Todd Howard]

The mid carb was bad so I’m glad to have that out of the mix.  The carb bowl is always full of gas and I have to drain if I’m going to check jets so I think gas flow is fine.  TDC has been checked also.  I line up the right side punch mark, the two hash marks on the brand new cam, and the second (or right punch mark) on the flywheel.  Cam lobes are facing rearward and slightly up.  Maybe the idle screw needs to be turned in further??   

[Jim Dettman]

<<Maybe the idle screw needs to be turned in further??   >>

 Well it certainly won't hurt to try it.   Just count the number of turns in that you do so you can back it out if it doesn't change anything.

 Besides that, I'm at a loss.  If you can get it to burp, it should run even with opening the throttle.

 The only thing that comes to mind is a massive air leak somewhere.   Check that the hot start nut is not cracked (it's plastic), that the hot start is not stuck in the open position, and look for any flaring/cracks in ends of the boot between the carb and the engine.

 Also see if it will run with the choke on now that you've cleaned the carb.

Jim.