Author Topic: Starts and idles at 3000RPM indefinitely  (Read 286 times)

Offline NoGutsNoGlory

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Starts and idles at 3000RPM indefinitely
« on: September 20, 2020, 02:33:06 pm »
I recently acquired a 99 SuperX #124 with all the upgrades (so I am told). It had 15XXX miles and I have put on another 500. During the last 200 miles, it started to randomly jump to 2500RPMs when I would come up on a light or intersection but eventually settle back down to normal range. In just the last few days, when I start the bike and let it idle, it goes straight to 2500RPMs and works its way to 3000ish and stays there for 5 minutes if I allow that.

I was told the ECM was upgraded, new stator and some other upgrades.

Any thoughts please?

Thanks you!

       


               














Offline wytfut

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Re: Starts and idles at 3000RPM indefinitely
« Reply #1 on: September 20, 2020, 03:29:21 pm »
Noglory
Try these to start:
Pull air cleaner and backing plate on front of throttle body.

Are your throttle cable free and move smoothly? To further that thought up by the triple tree neck are your throttle cables real tight?

Lastly, check the air idle control on throttle body. They do get gunky, and it'll hang up, making strange rpms. Clean it out with carb cleaner and cotton Qtips. Activate action on it by turning on ignition switch and off several times. Make sure it operates smoothly. Possibly a lite squirt of silicon to lube smooth action. You'll here it cycle with switch on and off.

While you are there, on top of throttle body is port, that is plugged at the factory with a rubber cap. That cap is very old now, and is most likely cracked and rotten. Go down to your favorite parts house and buy an assortment of vinyl caps. There will be one that fits and not rot out for a very long time, use the pinch clap if it's still there to hold that cap on.

Still got a problem, come back. I'm sure we have more help.

Bruce Whitefoot
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« Last Edit: September 20, 2020, 03:34:01 pm by wytfut »
Bruce
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Offline Donkey Hotey

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Re: Starts and idles at 3000RPM indefinitely
« Reply #2 on: September 20, 2020, 06:35:39 pm »
Seconding what Bruce shared: it doesn't take much fuel to make RPM but, the engine absolutely, positively must have air to rev like that. The air is coming from somewhere that it's not supposed to. Inlet manifold seals, the rubber cap he mentioned, butterflies not closing fully or a sticky idle air control. Less likely but, still possible: the gasket between the throttle body and intake manifold.
Greg
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1663 since 2017 (Deadwood) 0738 since 2018 (Babe) 1940 since 2019 (Sinclair)

Offline blackheart

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Re: Starts and idles at 3000RPM indefinitely
« Reply #3 on: September 20, 2020, 10:53:48 pm »
Mine was that way from day one at 6200 miles.   It was getting to where it would start and rev to 2500, never idle down fully. This last go round I blocked off the IAC port.  Makes you have to hold the throttle open when cold but hot it idles around 750-800
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Offline wytfut

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Re: Starts and idles at 3000RPM indefinitely
« Reply #4 on: September 21, 2020, 09:01:58 am »
I forgot to mention, to note to yourself as you disassemble air cleaner and backng plate.... Are any of those screws and studs loose?.
I've had 2 come thru my shop where they were just barely hanging on or were hand tight.

Rich (black heart)...  Jim McCarthy did that on his hot rod X too. Never knew anyone was doing that until I had spoken with him. Interesting, as they are becoming hard to find.
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Offline Donkey Hotey

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Re: Starts and idles at 3000RPM indefinitely
« Reply #5 on: September 21, 2020, 05:20:07 pm »
Mine was that way from day one at 6200 miles.   It was getting to where it would start and rev to 2500, never idle down fully. This last go round I blocked off the IAC port.  Makes you have to hold the throttle open when cold but hot it idles around 750-800

Have you checked if the engine temp sensor is working properly? It sounds like it might still think the engine is cold and is keeping it in the cold-start tuning.
Greg
1525 since 2000 (Molly) 1989 since 2012 (Jennie) 0333 since 2015 (Beulah)
1663 since 2017 (Deadwood) 0738 since 2018 (Babe) 1940 since 2019 (Sinclair)

Offline NoGutsNoGlory

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Re: Starts and idles at 3000RPM indefinitely
« Reply #6 on: October 04, 2020, 12:06:28 pm »
Thank you for all the helpful feedback! I'm out of town for another week, but will try all those suggestions as soon as I return and post my results. Cheers!