What's a good idle screw baseline setting?

[mxthump]

Hey guys.

I'm just done cleaning the carb, but in the hurry of getting it clean I forgot to record the number of turns on the idle screw. So now I'm trying to figure out a good baseline (no of turns or throttle slide height), I can't find anything about this in the manual.

Anybody got some good info about this?

Bike is a 2006 crf 450...

Edited January 24, 2012 by mxthump

[nickdawg18]

1600-1800 rpm

[mxthump]

Sorry, I should have been more specific.

I'm having a hard time getting it to start with the kicker after I put the carb together. I've been down this road once before, but non the wiser I made the same mistake again.

That time it would bump start easily if I just opened the throttle a little bit, so I figured I would to that again except all the snow outside makes it to slippery to bump start. I have tried holding the throttle open a little while kicking, but it's kind of hard holding it steady. That is why I wondered what a good starting point would be, in number of turns on the idle screw or maybe throttle slide height.

Hope this makes it clearer.

[Shawn_Mc]

it wont even start with the choke knob out?

With the carb off (or the subframe off) and looking down the throat, give it two full turns past where the slide just starts to move. Once you get it started dont adjust that speed too much until its good and warm.

[William1]

Set the slide to be about 3/32" open. (a drill bit works fine for a gage). There is really no number of turns as the tab it rests against can be bent and the the screw and the tab worn.

Set your fuel screw at 1.75 turns.

Do not touch the throttle during the actual starting.

Once the bike is fully heated, do the following to ge the fuel screw right and the idle speed correct.

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

Remember, unless you have a tach, finish with a what may seem like a elevated RPM. A slightly high idle is much better than one too low. Just because it can idle slow is not a good reason to set it that low. Those 'bangs' each times an engine fires can be tough on it when there is a long pause between events.

[mxthump]

Thanks guys, this was exactly what I was looking for. Will try this after work today (GMT +1). I'm pretty confident this will do it.

[mxthump]

This is why TT is so great! Now my bike starts like a dream again.

I started with setting the throttle with the drill bit method sugested by William1. I only have metric drills, so I used a 2.5 mm drill bit and lowered the throttle slightly after that (this actually was pretty close to Shawn_mc's suggestion).

After this it made noise again, it started almost instantly. I took it for a spinn and after it was warm and nice I ended upp adding 1.5 turns on the idle screw. On this carb its now 5 full turns untill the spring on the idle screw is fully compressed. I don't know if that is usefull for anybody else, but at least now I have a good reference...

Again, thanks to William and Shawn and to TT for being a great source of information.

[Shawn_Mc]

What the screw does before it raises the slide is kinda useless and will be different for just about everybody. If you do the math, two turns on the thread pitch and the drill bit diameter are probably within about ..020" or half a millimeter.

[mxthump]

Agreed, what the screw does before it raises the slide doesn't matter.

What I meant was, if I turn the idle screw all the way in (to the point where the spring is fully compressed) and then back off 5 turns I'm at where I have set my idle (will be a quick reference for me). Still, this is probably only valid for this carb and for someone else it is a better idea to use the "2 turns in from where the slide starts to move" or the drill bit.

[Guadalupe Tejeda Ron Epperson]

Ok so my bike was in high elevation when I bought it and it started really easy. Now I have it home and I'm have a problem getting good it started. Is there a quick easy explanation/fix for this??

Desperate any help would be great it's an 06 crf450r 

[Guadalupe Tejeda Ron Epperson]

Ok so my bike was in high elevation when I bought it and it started really easy. Now I have it home and I'm have a problem getting good it started. Is there a quick easy explanation/fix for this??

Desperate any help would be great it's an 06 crf450r 

[powers145]

What's the elevation difference? Need to know what jets are in the carb 

4 hours ago, Guadalupe Tejeda Ron Epperson said:

Ok so my bike was in high elevation when I bought it and it started really easy. Now I have it home and I'm have a problem getting good it started. Is there a quick easy explanation/fix for this??

Desperate any help would be great it's an 06 crf450r