CBR 1000F "Hurricane" 1987-1996 CBR 1000F

Intermittent High Idle

  #1  
Old 06-10-2018, 08:48 AM
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Default Intermittent High Idle

I just cleaned my carbs, and she now runs awesome! It was a small job repairing the airbox boots, but I found this glue similar to Goop that perfectly sealed the cracks up and it's good as new now. I'll post the brand later, forgot the name but it's now the stuff I would always use for that type of repair.

There is one thing that I can't seem to figure out, maybe someone can help. It starts and runs normally, warms up with choke and idles fine after the choke is off. However, with a quick snap of the throttle sometimes it hangs at 4K RPM or so and stays there.But not all the time. If I have the brake on and release the clutch a little to load the drivetrain it immediately goes back to normal idle. It will eventually go back to idle on its own but takes a bit.

If I had an air leak I assume the idle would be high all the time and I completely sealed the airbox boots. The insulators were a little grubby but I didn't notice any tears. I'm going to order some new ones and replace eventually, but as the problem is mildly annoying I don't plan to anything about it yet.

What I forgot/failed to do was clean my idle mixture screws. They need to be reset probably and I'm bummed I didn't do it with the carbs off but that's life. But I've never seen a dirty one either so just an adjustment will probably be enough. And if the mixture was off I doubt the problem would be intermittent.

I have about 250 miles on since the cleaning which I would think is run in enough.

Does anyone have any ideas?
 
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Old 06-11-2018, 04:48 PM
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Think you still have a vacuum leak somewhere, and/or the pilot screw & jet need cleaning. The orifices for the pilot jet are the smallest on the whole carb (thus the most susceptible to crud) and are almost impossible to clean without removing the mixture screw.

Made the same mistake on my 600, and after running multiple cans of Seafoam through multiple tanks of gas, my issues have abated to a small degree, but I can see that the real solution is to pull the whole thing apart again whether I like the idea or not. This time the mixture screw comes out and the idle passages get blasted with cleaner and perhaps run though with a small copper wire.
 
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Old 06-11-2018, 05:11 PM
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One easy, (and cheap if you already have it) thing to try when testing for a vacuum leak is to have the bike idling and take a propane or mapp gas torch (like plumber use when they solder pipes) and open up the valve on it while the nozzle is near your carb boots, not lit of course. If theres a vacuum leak it will suck that gas into your carb and the rpm will change. Ither aerosols will work but the suggested way doesn't leave a mess
 
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Old 06-11-2018, 05:32 PM
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Nice idea. I like.
 
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Old 06-12-2018, 10:46 AM
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For the sake of being diligent, you probably want to make sure the throttle cable is operating smoothly. That'd cause the problem you described

A visual inspection while snapping the throttle back and forth is all it takes. If it lags or sticks, replacements are cheap and (generally) plentiful
 
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Old 06-13-2018, 03:27 PM
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Thanks for the ideas guys, for some reason it won't start now. Last Sunday I went to go for a ride and all it does is whirl over - It sputtered a couple times at first and now doesn't do anything, even with a squirt of ether. I have brand new freshly gapped plugs. It is surprisingly similar to this thread https://cbrforum.com/forum/cbr-1000f...uestion-67137/ , only I used a battery charger the day before. The starter has always been a little weak and I think it sucks too much amperage to fire while it's turning over. A rebuild kit is on the way.

So I'm going to take the carbs back off in the meantime and check things over really good, including the pilot screws. It seems like the throttle is working smoothly, with a very small amount of play in it - How much should I have, it's like a 16th of an inch or something.
 
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Old 06-13-2018, 03:33 PM
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And this old thread, although unanswered may indicate a laggy old starter sucking too much juice. An admin is going to make me start a new thread for this probably lol https://cbrforum.com/forum/general-t...trouble-15424/
 
  #8  
Old 06-14-2018, 12:18 PM
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Originally Posted by GronkFries View Post
It seems like the throttle is working smoothly, with a very small amount of play in it - How much should I have, it's like a 16th of an inch or something.
Rider's preference. I always prefer it razor-thin, but manual recommends anywhere from 1/8 to 1/4"

As for the other gremlins, I'm not sure I would rule out the battery as the cause for the no-start. I know it had a charger on it, but personal experience - I have had more starting problems caused by a weak battery than all other causes combined. Even if the voltage looks healthy after it's been charged, capacity is the issue nine times out of ten. If the voltage drops a couple volts after cranking it a few seconds, that's a pretty clear sign

Couldn't hurt to confirm spark though

If the starter wire is bad, it should show high resistance. That could draw excessive current, but it would likely be accompanied by other intermittent problems (ie no-click). You could try applying battery voltage directly to the starter motor and see if that makes a difference

That said, if I were a betting man, I'd put ten on the battery. I've been bitten too many times before

Hopefully the carb service clears up the racing idle issue. That vacuum leak trick is clever
 
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Old 06-14-2018, 12:23 PM
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Originally Posted by tentacleslap View Post


That said, if I were a betting man, I'd put ten on the battery.

Is that CAD or USD?
 
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Old 06-14-2018, 01:25 PM
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I can't afford real dollars, so let's do CAD
 

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