Uncontrolled High revving from polaris predator 500 - Polaris ATV Forum
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post #1 of 18 (permalink) Old 04-02-2019, 06:26 PM Thread Starter
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Uncontrolled High revving from polaris predator 500

Hey guys, I'm having a problem with my 04 polaris predator 500. It will start up and idle great, but then it it gets to operating temp./ warmed up and idles up extremely high so I run over to it and shut it off. When I am riding it and pull in the clutch it does the same, idles up extremely high. The only way I can control this is having a load on the engine such as applying the brake when it is in gear to keep the rpms were they should be. And no, it is not the idle screw. I swapped carbs from a parts four wheeler and it does the same thing. I also saw the thread when a dude had the same problem and it was his throttle cable. I have yet to get the new one in to see if that is the problem. Leaning towards a vacuum leak but I've coated that thing with carb cleaner and couldn't find anything. Any help would be appreciated!
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post #2 of 18 (permalink) Old 04-03-2019, 06:08 AM
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Idle speed is controlled by spark timing and throttle opening. A vacuum leak is an uncontrolled source of air. The fuel mixture has to be rich enough that a vacuum leak only results in an increase in idle speed. If the leak is minor enough to raise the idle speed without affecting performance in other RPM's, it is easily found using soapy water to spray around the carb holder where the carb pushes into it and where it seats to the cyl head.

Other causes of uncontrolled idle; most common - not enough slack in or sticky throttle cable, not enough slack in or sticking enrichener cable, dirt, corrosion or debris preventing the throttle butterfly from closing against the throttle stop screw (idle speed screw) - less common - a perforated air cut valve diaphragm, high float level, throttle butterfly that has loosened and not closing completely due to binding in the venturi or damaged butterfly shaft, missing or incorrect size air jet in the bell of the carb - more obscure - a bent slide needle or damaged pilot screw orifice.

Good luck - it takes a good eye to see some of the less common to obscure causes - vacuum leaks are easy

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post #3 of 18 (permalink) Old 04-03-2019, 01:19 PM Thread Starter
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Yep that is the problem I am having, no problem when I get on it at high rpms when, for say, I max it out still runs fine, but I mean when it starts to idle up uncontrollably it flat gets it. It doesnt just go up a little bit it goes up to about 3/4 the throttle being pushed in. I will start with the intake connecting the carb to cylinder head. Is this what you would recommend?
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post #4 of 18 (permalink) Old 04-14-2019, 03:21 PM Thread Starter
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Well guys I replaced the rubber intake that connects the carb from the cylinder and it still have the problem. What should I try next or a direction I should head with it.
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post #5 of 18 (permalink) Old 04-14-2019, 07:26 PM
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Did you inspect and correct any imperfections in the carb? The carb controls air - shut the air off and it will slow down.

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post #6 of 18 (permalink) Old 04-14-2019, 11:24 PM Thread Starter
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Yes, I replaced intake flange, and tried using a different carburetor from a donor bike I have, the problem persisted so i tried to find a vacuum leak with soapy water and could not find a single one. I have also went through the carb many times, I am at a complete loss.
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post #7 of 18 (permalink) Old 04-15-2019, 04:38 AM
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Try removing the throttle cable from the carb and see if that changes anything

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post #8 of 18 (permalink) Old 04-16-2019, 02:01 PM Thread Starter
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Well late bird that wasnt it either unfortunately. It was not sticking. Also when I was doing this I looked down the barrel of the carb and the slide was moving up and down with use of the throttle. Have I missed something?
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post #9 of 18 (permalink) Old 04-16-2019, 03:06 PM
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Obviously!

You failed to identify the carb. The original carb was a constant velocity - there is no connection between the butterfly air control valve and the vacuum operated slide.

I now suspect you have a other than original carb. Are there identifying marks like a brand name - maybe you could attach some pics of the carb?

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post #10 of 18 (permalink) Old 04-16-2019, 06:20 PM Thread Starter
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Well I cleaned the carb that was on it. Everything looked slick and span and perfect condition even when taken apart. So I have a parts quad, cleaned its carb and slapped it on and it had the same problem, has anyone you have heard of had this problem and the reason were the valves somehow?
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