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Out Of Ideas - Hard Starting, Won't Idle

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Hey TT,

     I have a 2009 CRF250R.  She's a pain in the ass to start and keep running, won't idle with the choke off.  Carb is stock (Main Jet #185, Slow Jet #42, Clip is on 3rd groove down from the top).  No airbox mods, bike is stock.  I've dismantled and thoroughly cleaned the carb, ensuring everything is correctly reassembled.  Tried the fuel screw at 1 1/4 turns (stock).  She'll run a smooth high-idle with the choke on.  Dies immediately when choke is turned off.  I'm positive the pilot jet isn't clogged or damaged.  It looks perfect.  I'm also positive I have no air leaks around the card.  What else should I be looking at?  It ran okay a couple days ago (just okay, not great).  I have to use the 'pump twice then kick' trick to get it turned over.  Usually 2-3 kicks.

 

- Matt

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You didn't mention if you turned in the idle adjustment to raise the idle haha. Is the compression really low? 

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Working in that compression test.  As far as the idleading adjust, I have no reference point.  I've had it anywhere from 2 to 8 turns in from initial contact with the throttle.  The manual doesn't specify a factory st letting or a starting point, so it's basically been trial and error uplease until now.  It purrs like a kitten (a very loud one) at very high idle with the choke on, but chokeep off... no go.  Anyone have an initial reference point for the idle adjust screw?

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So sounds like all the internal carb parts are  OEM.

For the Pilot Screw or what I think you are calling the fuel screw, I went after market so you can adjust it with your fingers an 1-1/4 turn out as the start point.

For the idle adjustment screw, I'm assuming that you removed it completely when you thoroughly cleaned the carb but unfortunately I can not find an initial setting for this in either of the 2 manuals I have :(

IMO try turning the idle screw in say 2 more full turns before you start the bike. Start as normal with the choke, then after a minute or once the bike is warmed up, close the choke and see if the bike idles. If not repeat turning in the idle screw 1 full turn at a time.

A HIGH sounding idle with the choke on may not actually be that high cus without at tachometer you really can not even set the 1700ish RPM normal idle speed.

Personally when I first start my bike, I turn the idle screw in about 1/2 turns, pull the choke, start the bike. Once warm, push in the choke, then back off the idle screw until it sounds like its around 1700 RPM.

Another thing, is the hot start functioning correctly?

 

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The hot start appears to be functioning correctly. It opens and fully closes. I managed to get it to idle with the choke off today so far but it has an annoying hanging idle. That was with the fuel screw at 3/4 to 1 1/4 (anywhere in that range) and the idle adjust screwed so far in that when the choke IS on, it's revving pretty good. I'm not understanding the disparity between choke on and off. It should be idling high with choke on and idling 'normal' with choke off. It's revving with choke on and idling somewhat normal with choke off. And then there's that hanging idle (which feels a bit sketchy on a fast motocross bike).

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If it seems better with the choke on and the carb/jets are clean...is it possible you're getting some false air from somewhere? Hole in the air filter, bad air box seal...etc.

 

Just a thought.

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On 3/26/2017 at 0:47 PM, SpyderXLT said:

The hot start appears to be functioning correctly. It opens and fully closes. I managed to get it to idle with the choke off today so far but it has an annoying hanging idle. That was with the fuel screw at 3/4 to 1 1/4 (anywhere in that range) and the idle adjust screwed so far in that when the choke IS on, it's revving pretty good. I'm not understanding the disparity between choke on and off. It should be idling high with choke on and idling 'normal' with choke off. It's revving with choke on and idling somewhat normal with choke off. And then there's that hanging idle (which feels a bit sketchy on a fast motocross bike).

At least on my bike, for a normal setting the idle screw is turned in a lot and to adjust it say 1/2 turns either way its a bit hard with my gloves on and I'm not using a screw driver. Sorry if thats vague :(.

Really the choke is only used for a minute or so when you need to start the bike. For example in the summer when the outside temps are hot, when I first start my bike.

Turn idle up say 1/2 turn

Choke off

Hot Start in

Kick bike and once it starts, pull the choke for a minute. Might give it a few shots of gas but I'm just letting the bike warm up and idling steady

Might give it a couple of shots of gas but once the bike starts idling high with the idle steady, choke in, few shots of gas, then adjust the idle out as needed.

As @Force10 posted, might be an air leak or false air.

 

 

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Somehow picked up a nail in the back tire while test riding and shredded the tube . Had to pull that off, so troubleshooting is on hold (since bike shops are closed on Mondays). Will triple check for false air / air leaks with some carb cleaner/ starter fluid when I get the new tube back in. Seems like these CRFs are finnicky? My '04 WR250F takes a lickin' and keeps on tickin'. Same (almost) carb and they are two completely different beasts.

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Ya its hard to give advice but IMO my 05 is a bit finicky to start but I have not pulled or cleaned the carb in 12 years :).

Another thing is make sure your throttle assembly/tube and cables are clean and running smoothly.

Really is just a carb bike so you just need to be methodical trouble shooting.

Good luck and keep us posted :)

 

 

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Okay, got the tube in the tire, back on the bike... I replaced the floating valve seal (it was missing a tiny piece of rubber, which would cause a vacuum leak). She idles... Still a bit high on the choke, and the pilot screw is backed out past 3 turns. In fact, it actually fell out on a test ride... So, larger pilot jet?

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G2G. Popped in a size 45 pilot jet, replaced floating valve seal, threadlocked the pilot screw, set it to 2.5 to 3 turns. She idles, no low-end bog. So, for future reference, check the floating valve and seal if you're experiencing hanging idle or popping on deceleration (indicates a lean condition) caused by a vacuum leak. Everyone always checks the carb boots for leaks, when vacuum leaks can also occur inside the carb.

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What is a floating valve seal?

carbslide.jpg

Scratch that, let's call it the vacuum plate (its technical term). Some refer to it as the floating valve, which can make it somewhat confusing when referring to the carb float (even though it is indeed 'floating'). If you pull the carb slide out, the vacuum plate will fall off (as will your darn rollers). The vacuum plate has a seal around it. This seal HATES carb cleaner and will shrivel up when exposed to cleaner. The seal is very fragile. If even a tiny piece is damaged or missing, you have a vacuum leak which could cause a hanging idle and popping on deceleration. See the pic...

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