[narf44]

Sorry it's so long, this is 2 months of work summarized in this post. I'm at my wits end now and defeated.
To start with bike specs
2006 450X
4000'-7000' MSL riding altitute
New carb parts...
needle jet, floating valve, float needle, o-ring kit, pilot jet, R&D mixture screw

Here is the deal, over the past 3-4 months my bike has been progressively getting harder and harder to start(when hot) and getting worse and worse gas mileage. It is impossible to get my idle mixture set properly as well. It started by actually having to use the hot start at first. I Never had to use it in 2 years of riding this bike, so I thought that was weird. Then it got to where I would have to roll it down a hill to get it started. Then it just stranded me a few times in the middle of no where and wouldn't start doing EVERYTHING. But then the next day after sitting all night it would fire right up like nothing was wrong. The valves are spot on to start with. So far I have tried brand new 42, 45,& 48 pilot jets, all three do the same thing. At low idle I can turn them all the way in and the bike doesn't die, it just raises the idle once it's turned all the way in. I have checked for leaks around the carb boot from the carb to the intake manifold, I have removed my hot start plunger, cleaned it, lubed it. It is working well and not sticking. I have replaced the floating valve and double checked to make sure it was installed in the proper way. I have changed the needle jet or emulsion tube what ever you prefer to call it. I have changed the float needle and verified the float level with the manual. I have checked for cracks around the rubber boots as well as cracks on the hot start plastic nut. The carb has a brand new o-ring kit and I have verified it has a good seal at the top of the carb in case for air leaks.
BUUUUUUUT....I still can not get it to start good. Once it's running it runs like a champ, but I can not get the idle mixture set so it starts all the time. I have used the hot start lever and that helps sometimes, but not every time. it's inconsistent. I started with the stock brand new 45 pilot jet, set the idle speed at 1200-1300 rpms, turned the brand new R&D mixture screw all the way in and it died the first time with 1 turn to go. So I turned it out the 1 1/4 turns, couldn't get it started, so I turned it out 3 full turns from all the way in, and it would start good. So, it jumped it up to the 48 pilot jet because it was more than 2 1/2 turns. Finally after a TON of cranking and hot start I got it to start. I set the idle again at 12-1300 and turned it all the way in and it never died, it just raised the idle speed once it was turned all the way in, so then I said screw it, i'm gonna see if the 45 works any better again, but then the second time I could screw the mixture screw all the way in and it wouln't die, so i put the 42 in and I could also screw that one in all the way and the idle would raise up once it was screwed all the way in too. I am at a lose. i've been working on this for weeks, have spend over $150 on this carb in the last few months and it still isn't working!

[JimDirt]

Is it popping thru the muffler ?? , if so , when does it do it , on acceleration or de-cceleration ?? (note: it will always pop on acceleration when on the stand , i am talking about popping while riding)

Are you 100% positive that you got all the OLD O-Ring out of the Fuel Screw orifice ?? , since its inconsistent , i am thinking that when you turn the fuel screw in or out you are moving around the old , most likely torn O-Ring , so this would make the screw adjust properly one time , but not the next , the only other possibility would be a orifice inside the carb is clogged and becoming blocked and unblocked with engine vacuum when giving it throttle and letting off

After making 100% sure there is no old O-Ring left by using a flashlight and looking into the Fuel Screw orifice , making sure you can see the taper of the opening (you may have to use a magnifying glass) , if all is clear then take your hand and momentarily put it over the rear of the carb while the bike is running , if there is debris stuck inside , this may dislodge it or suck it thru , see if it runs better after doing this , if it does , then that will confirm you have something inside one of the orifices somewhere in the carb

Also make sure your header and muffler joints are completely sealed , take some baby powder and sprinkle it near the header where it goes into the head (just blow on it so it goes towards the head while its in your hand , with the bike idling) , do the same at each pipe connection , and make sure the system is not leaking , if it blows out the powder , then there is a air leak , and it can cause these symptoms

You did not mention changing the Needle itself in your list of parts , just the Needle Jet and Float Needle/seat , a worn needle can cause all sorts of idle inconsistencies and make tuning hard because its bouncing around so the mixture will change

My first guess is going to be its the old (or new) fuel screw o-ring that is causing the issue ... (if its not the needle)

This is a basic jetting guide to go by

Jetting Guide for Main Jet:(pilot 45) CRF450R/X

Sea level....165
2000 ft.......162
4000 ft.......160
6000 ft.......158
8000 ft.......155


Temperature/Elevation:
One main jet size (up/down) for every 2,000 feet or 25 degrees in temp.

On a side note , i run 45/162 from 2000 ft to 8000 ft , with just slight fuel screw changes , in between at around 6000 ft , fuel screw set at about 1 1/2

[narf44]

As far as the mixture screw, yes I verified it did not have the old o-ring in the hole before I put the new on in. I used a flashlight and I could see the tape of the hole at the bottom. I checked for air leaks today using a propane tank all around the carb and the idle never raised. I took the tank off and run it with the tank off and checked for leaks again using butane gas and also moved everything around with my hand like the hot start plunger and cable and nothing changed. i'm going to take it off again for the millionth time and check the accelerator pump diaphragm and changed the main needle to a different one to see if that helps.

[JimDirt]

It sure sounds like some kind of intermittent blockage , so needle , or a passage would be my guess , if you can't find it , PM leardriver , if anyone can figure out a obscure carb issue here , its him

[narf44]

My altitude is 4200' and I ride up to 7500'. Okay it starts every time now second kick with hot start pulled and idles very smoothly all the time now. I split the carb in half and cleaned all the passages really well and that what fixed the hanging idle I believe. Like mentioned earlier the slide was up about 1/4" at idle BEFORE I cleaned it and I think on of the pilot passage ways was partially clogged or corroded with some fuel varnish. I started with the 45 pilot jet, turned my idle speed screw all the way out. I started with the idle mixture at 1 1/2 turns out. The first time I started it with the choke but also needed the hot start lever even though it was a cold engine. If ran nice, idled smoothly. I rode it around for a bit and brought it up to temp and I lowered the rpms as low as I could with it still running and slowly turned in the idle mixture 1/4 turn in at a time a waited 10 sec between each adjustment. But It turned all the way to the seat and didn't die, just raised a few hundred rpms. So I put the 42 pilot in, did the same thing with the same results. It starts great with the hot start every time 2nd or 3rd kick (my regulator is not working) with both the 42 or 45 pilot jet turned out 1 turn. Not sure why it won't die when the mixture screw is all the way in but it starts great and idles perfect all the time now.

So in conclusion for those reading this trying to desperately figure out why their POS bike isn't starting or running like crap. the needle jet fixed my hard starting and splitting the carb in half at the middle and cleaning with carb cleaner and fishing line (and new pilot jet) fixed my erratic idle.

[JimDirt]

If the fuel screw can be turned all the way in then that means its way rich , this is confirmed by needing the Hot Start to get it going , since the Hot Start LEANS the mixture , so the blockage is/was air not a fuel blockage , there are 2 jets in the air filter side of the carb inlet , have you made sure a piece of dirt did not get into them ( dirt getting to them also means dirt getting to the Intake valves which leads to the Intakes going bad)

45/160 or 45/158 should be about right on jetting for your altitude , for about anything below 9000 ft you want a 45 pilot , right down to sea level , a 42 for over 9000

If fuel screw goes all the way in and still runs , go 1 size smaller on Main jet (not pilot) , lean it down till it will try to die at about 1/2 turn from all the way in , do this with the main jet and/or RAISING the clip position on the needle this will lower the needle making the mixture leaner for a longer period of time , till the throttle gets up a little higher allowing more air

Unfortunately , this mess is mainly created from Ethanol , its the worst thing to happen to gas engines in the history of bad ideas just to make a profit

[narf44]

You might want to read up on adjusting carbs before giving advice. The main jet only adjust 3/4-full throttle, the slide and needle adjust 1/4-3-4 throttle and turning the fuel screw out to richens the mixtureon a FCR carb. Out of the horses mouth http://www.carbparts.com/keihin/needles ... r_carb.htm

[JimDirt]

You might want to re-read what you read , the main jet covers all ranges , as soon as the throttle moves , so your misinformed , , not trying to argue , but

....Think about it , if the slide and the needle covers 1/4-3/4 , how does it do that you ask ?? , by the throttle slide moving up OPENING the orifice of the MAIN JET that is being blocked by the NEEDLE and ADDING MORE FUEL , so the Main Jet works thru ALL RPM ranges , and if you RAISE the needle you richen the mixture because the main jet is putting MORE fuel output at a LOWER RPM

The fuels screw works for idle and OUT richens , In leans , if your bike runs with the fuel screw all the way in , its too rich , because , when its IN you are trying to starve it , if it does not die then its too rich .... or you have a massive vacuum leak allowing air to feed/suck in all the time keeping the mixture lean enough to idle , but too rich to run right , but you would also get massive popping thru the muffler all the time

Again , not trying to argue , and i was only trying to help with your issue , if you found advice somewhere else that solves your issues , then by all means use that info , and actually , i never claimed i was a carb expert , i was merely giving suggestions of what to try and look for as they are all common issues caused by what i described .... , was not trying to "misinform" you or anything else , i was only trying to help , sorry if my help was not to your liking , was not my intention ... , if i suggest something its usually because i am right about it , i am not claiming i am right , or wrong , just look at my post history and you will see , i don't try to mislead or misinform anyone here

If you want a real "Carb Expert" PM leardriver he IS a carb expert

[Aussiecrf230]

What Jim is saying that if the idle mixture screw is all the way in and the bike still runs the fuel has to becoming from somewhere.

Assumingthe fuel screw being all the way in shuts off fuel from the idle circuit then it has to be sucked from somewhere and in this case out of the main jet orifice (even if the needle almost has it closed off). That is why it is important that there be no bits of old oring or any other crud as it won't seal off. The other possibility is the taper on the new idle mixture screw is different from that in the carb. Seen it before so it can happen. A bit of Prussian blue on the fuel screw and gently seating it will show up when you unscrew it. Again as Jim said not trying to start an argument just trying to solve a problem that is stopping someone enjoying their bike.