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'06 450x Hanging Idle Issue!

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I bought the bike used, seems like a common story, and it had a bad hanging idle when I got it. I pulled the carb apart and rebuilt it. Replaced everything on it that comes in the carb rebuild kit. The bad hanging idle went away but a slight idle increase is still present. I have the idle set about 1750 rpm. It will idle there fine bouncing above and below by 80rpm. If I rev it up to about 2300 to 2400 and hold it and let go, it hangs and slowly idles down to the set idle. It takes about 2-3 seconds. You can feel the throttle snap back. I know its the carb because I put my brothers carb, off his 05 450x, on my bike, with the same jet and needle set up, and it ran perfect. I have done searches here on the forum and couldn't find any answers. Here is a list of what was done on the carb:

 

Rebuild kit

New Slide plate and seal (installed correctly with hole in the plate on the bottom) the old one was completely worn. Attached picture

Crfs Only Accel Pump mod

New Carb to Intake Boot

Fuel Float Height Verified to book spec

TPS set up to book spec

NVCS Needle 4th position from the top

48 Pilot

170 Main

70 Leak Jet

My current elevation is 1,700ft

MSR Fuel Screw 

New Idle adjustment screw as the old one broke

Power Bomb header

PowerCore 4 Muffler

Airbox Slight opened on top only.

New Hot Start nut (Aluminum)

Brass end on hot start/choke polished

Throttle Cables lubed and sliding freely

Hot Start cable operated freely.

All passages blown out with compressed air and shots of carb cleaner. 

Wire ran through the passages to make sure there were no obstructions.

Sprayed for air leaks all around the carb

 

I am completely lost now. Any help is appreciated. I have had the carb in and out 7 times now. I dont like the fact that I have improved on my carb removal and installation time. Setting new records daily.

Thanks.

20140722_181818.jpg

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You've eliminated eletrical/engine issues.

 

I take it you are positive the TPS is working properly and adjusted spot on.

 

Hanging idle (when not caused by a sticking slide, you can confim it by looking at the throttle wheel, even physically confirming it is all the way down) is usually caused by a too lean a pilot circuit and/or a slightly elevated idel speed setting. If anything, your pilot circuit is too rich, having a 48 pilot in it. That is on its' own, suspect.

Have you installed a brand new 45 pilot and tested?

Have you installed the stock or other all brass fuel screw?

Positive the hot start is fully closing.

Have you lowered the idle speed when setting the fuel screw then raised the idle speed, all while blipping the throttle slightly to 'get it to settle' to find the sweet spot? Some bike are notorious for being a little finicky and a deft touch may be needed to find that 'point'.

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So I went back and double checked some things again. One of them being the TPS. When I disassembled the carb originally, I noticed there were alignment marks on the TPS for its position. When I checked the TPS at that position I was getting incorrect reading when doing the math for the position. I had put the TPS to what the calculated values said it should be when I reassembled the carb the first time. I decided to put it back to where the marks are and sure enough it worked. The idle fluctuation is gone. I am not sure where I went wrong in my volt meter readings.

 

In regards to the pilot jet, I checked the fuel screw setting and I am 1.5 turns out. That seems to be the sweet spot. Going to a 45 seems like it would lean it out based on where my fuel screw setting is with the 48 jet.

 

Thanks for your input.

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fwiw , you can run it with the tps disconnected on that bike if you want to do a quick test, or think the tps wipers are bad.  Also most are set by keihin with the slide all the way dropped, NOT at idle speed slide height like the manuals show. It may still be in range but that often cause confusion when guys test them.

 

Sometimes a hanging idle is just a combination of (too high) slide height and idle mixture setting.

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Well, I was wrong. Its still happening. I unplugged the TPS to check and nothing changed. It still did the same thing on the rev down. The TPS checks out between the ohm range. Could the TPS cause the slight hanging issue? On a good working TPS, what happens to the carb when you unplug it? I even tried raising the needle up (By lowering the clip) and that didn't change anything. I know my original slide plate was worn, would that have any effect on the inside of the carb body that the plate rubs against? I am still lost.

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TPS has nothing to do with hanging idle

Needle has nothing to do with hanging idle

Unplugging the TPS does nothing to the carb; it changes the ignition timing.

 

 

 

It's a 'too much air' problem in the pilot jet circuit

 

Usually it is due to a lack of maintenence on the carb.

 

Slide is too high (poorly adjustedidle and fuel screw)

 - this is the most common reason. You must start with a very low idle before adjusting the fuel screw. Raise the idle with the fuel screw to get your desired rpm, not the idle screw

Hot start nut is cracked/loose and leaking

Hot start plunger is not seating and leaking

Slide plate seal is thrashed

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TPS has nothing to do with hanging idle

Needle has nothing to do with hanging idle

Unplugging the TPS does nothing to the carb; it changes the ignition timing.

 

 

 

It's a 'too much air' problem in the pilot jet circuit

 

Usually it is due to a lack of maintenence on the carb.

 

Slide is too high (poorly adjustedidle and fuel screw)

 - this is the most common reason. You must start with a very low idle before adjusting the fuel screw. Raise the idle with the fuel screw to get your desired rpm, not the idle screw

Hot start nut is cracked/loose and leaking

Hot start plunger is not seating and leaking

Slide plate seal is thrashed

Slide Plate and seal are brand new as stated in my first post.

I've sprayed around the Hot Start nut and there are no leaks.

The hot start plunger bore is clean from obstructions. Its adjusted correctly as it worked fine in another carb I put in the bike.

I've adjusted the fuel screw setting 3 different ways and even kept opening it up, once it was set, to get more fuel in and nothing changes.

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You are leaving something out of your trouble shooting

 

If you start with one turn out on the fuel screw, start the motor, get it hot, then adjust the idle for the lowest possible idle.....THEN adjust your fuel screw out for max idle.

It the idle goes too high, drop it with the idle screw, turn the fuel screw in /1/4 turn, and start the bike again, and raise the idle WITH THE FUEL SCREW ONLY.

 

Repeat if it goes to high again

 

Your last adjustment will be with the fuel screw to reach the idle you want, not the idle screw.

 

Once done, you can fine tune the circuit by blipping the throttle and listening for fastest  idle drop. Only 1/8 turn one way or the other should get you a fast drop.

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Okay, I went and did your test. I am confused and relieved. I think my jetting is off. I am confused because of the original idle test I did, it showed a different result as to what I just got but I agree with your test. 

 

I set the fuel screw at 1 turn out and started the bike up. Once warmed up, I lowered the idle till it was just barely running, about 1300-1400 rpm. My pilot jet is a 48. As I started opening up the fuel screw the idle went lower and the bike died before I got to 2 turns open. I turned the screw back in to 1 turn out and kept the idle screw adjustment the same. I started the bike up and turned the fuel screw in till it closed. The idle went up to about 1600 rpm and rev'ed perfect. The idle down was crisp, smooth and fast.  From this I take it that I am lean and I need to step up to a 50 pilot.

I actually noticed it right away when I left the screw at 1 turn and lowered the idle that the throttle response and idle down was better when the bike had a low idle. This proved that I was to lean.

 

I need to get a 50 jet and a retry everything now.

 

Thank for the help.

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With much success the 45 pilot worked to eliminate the slow idle down. Now I can finally ride it an enjoy it. Thanks for your help.

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