Hanging idle & AP timing issue?

So I have been trying to chase down a hanging idle in my 2001 YZ426. I inspected the cables & found a spring installed by the previous owner on the throttle pulley to help force the throttle closed. I removed the spring & adjusted the cables to get 3mm of free play but still had a hanging idle. I removed the cables, cleaned & lubed them, tested the pulley without the cables in place. Cleaned & lubed the throttle tube. I found the pulley snaps shut fine without the cables.

After installing the cables & noticing the throttle snapping shut fine with the bike off so I ran the bike & disconnected the TPS switch. I didn't notice any difference with the TPS on or off. So the throttle snaps shut when the bike is off perfectly but while running I noticed it will still hang at high idle unless I physically force it closed.

After losing the entire riding day yesterday (more than likely our last up here) I decided to mess with the AP timing. What I found was that if I back the AP timing screw two turns out from it's previous position I no longer have the hanging idle concern. I rode the bike up & down the block & did not notice any bog & my idle did not hang. It seems that maybe while the throttle cables were closed that the AP was still engaged due to a very tight tolerance on the adjustment? Is this even possible to maintain steady pressure on the AP linkage allowing a steady shot of fuel at idle or close to idle which would somehow cause a very high idle? In other words directly off idle it seems like my bike was getting a full squirt vs. allowing you to roll the throttle on slowly increasing the squirt/power? My bike felt like the throttle was a "light switch" making it extremely hard to ride intermitantly when the idle would just jump sky high, on or off.

So now I have a few questions, first what is the PROPER way to set the screw length, I have checked the factory service manual & Clymer to no avail. Also, does this seem like the right way to go? There was no bog after my adjustment but am I covering up another problem by using this adjustment? Everything I research says that there should be a bog as I back the screw out & delay the shot of fuel from the AP? My bike seems to like the delay from the AP. In other words it allows me to turn my throttle a few mm BEFORE the AP squirts, does this make any sense? It sort of seems like what the G2 throttle tube does if I understand the concept correct?

Check HERE for the FAQ jetting guide. In there you will find info for tuning your AP.

As far as your bog is concerned, you could have too early an AP squirt where it actually hits the slide, or too late a squirt where it doesn't provide the fuel fast enough for the revs to build. I have found that I cannot have too early a squirt on my 03 WR; it always misses the slide. But I think the earlier bikes could squirt too early if not properly adjusted.

Aside from mechanical malfunctions, a hanging idle is usually a sign of a lean pilot circuit.

Check HERE for the FAQ jetting guide. In there you will find info for tuning your AP.

As far as your bog is concerned, you could have too early an AP squirt where it actually hits the slide, or too late a squirt where it doesn't provide the fuel fast enough for the revs to build. I have found that I cannot have too early a squirt on my 03 WR; it always misses the slide. But I think the earlier bikes could squirt too early if not properly adjusted.

Aside from mechanical malfunctions, a hanging idle is usually a sign of a lean pilot circuit.

I read the AP guide but what confuses me is that they state turning the screw delays the start, see below:

Turning it in delays the start and turning it out advances the pump action to start earlier. At immediate squirt from idle would be zero delay from the "touch point", where the rod just touches the diaphragm. A setting of 1/2 - 1 turn inwards delays it adequately to keep from squirting on the slide. This, I believe, was the .6mm measurement with feeler gauge. The original BK Mod posting from SUnruh also had the pump stroke set to 1 1/4 turns out from touch point to set the flow. This did not say the pitch of the screw being used and so was a little vague.

My bike seems to respond in the opposite manner. The setting of 1/2-1 turn inward is from what starting point? The screw all the way out I presume? What is the feeler gauge measurement? Where is that procedure located? If I could find a baseline fron the factory I would feel comfortable working from there.

I also feel my pilot circut may be a little lean due to the cold weather up here & should probably wait until the spring for my normal riding temps to adjust my pilot circut but would a lean pilot cause the sysmptoms I have? Would you be able to adjust past a lean pilot with the AP pump timing? Also would it be intermitant & be able to be forced past the high idle with a twist of the throttle?

The factory AP timing adjustment procedure is in the Regular Inspection section of the manual (4-19 for my WR). Adjusting the AP screw at this throttle height is similar to setting the gap between the link lever and the cam follower to .6 mm at closed throttle. This 6 mm measurement would only apply to the 250's, though, because they have a different throttle valve height than the 450's for AP adjustments.

If you also ride your bike in colder conditions you should change the pilot to suit the season; it's one of the easiest jets to change. But if it's an intermittent problem, look for mechanical causes like a frayed cable or a dirty throttle. The AP circuit is only for quick increases in throttle position and has very little, if any affect on the pilot circuit.

I need to check my manual again. I know there is a complete teardown of the carb, maybe it is there & I glanced over it?

Hanging idle is due to a lean condition caused by jetting and mixture adjustment, or air leaks in the intake, or by tight intake valves. If you have a bike that did not use to have a hanging idle, you haven't changed anything, and now it has one, you should first see how it responds to adjusting the fuel screw. If that fails to correct the problem, check your valve clearance before proceeding.

My bike also has a hanging idle with another strange occurance...when I turn the fuel screw all the way in, the bike doesn't die...it keeps running.

Is this normal?

I thought the bike should die when the idle screw is turned in completely.

Mine doesn't die either all the way in and probably wouldn't unless I had a smaller Pilot jet in it. I kind of wished I had tried turning it all the way in and out before switching out the stock pilot for a 48.

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