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Discussion Starter · #1 ·
When the machine is just sitting or being allowed to run down a moderate slope with no throttle applied, the revs will suddenly increase to a more-than-idle, but nowhere near racing. No throttle has been applied. When standing still, nothing is moved to cause this and it could have been running fine for a couple of minutes, so it does not seem like a jammed throttle cable.

The other trouble is that when the throttle is first applied, the revs die way down then suddenly the machine takes up and if the throttle is not applied very gently it will leap forward. In any sort of confined space this could result in a collision.

This has been appearing more and more in the recent past, and correlates with a worsening gear change, which makes sense if the idle is too high. Anyway, once I sort this idle problem I will work on the gear change.....or should I look at the centrifugal clutch in case it is forcing the engine to slow down, then releasing it occasionally? The gearchange is fine when the engine is not running.

I am wondering if these are connected. But whatever, does anyone have any "most likelies" about this behaviour.

Thanks for any help.

Nick
 

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When the machine is just sitting or being allowed to run down a moderate slope with no throttle applied, the revs will suddenly increase to a more-than-idle, but nowhere near racing. No throttle has been applied. When standing still, nothing is moved to cause this and it could have been running fine for a couple of minutes, so it does not seem like a jammed throttle cable.

The other trouble is that when the throttle is first applied, the revs die way down then suddenly the machine takes up and if the throttle is not applied very gently it will leap forward. In any sort of confined space this could result in a collision.

This has been appearing more and more in the recent past, and correlates with a worsening gear change, which makes sense if the idle is too high. Anyway, once I sort this idle problem I will work on the gear change.....or should I look at the centrifugal clutch in case it is forcing the engine to slow down, then releasing it occasionally? The gearchange is fine when the engine is not running.

I am wondering if these are connected. But whatever, does anyone have any "most likelies" about this behaviour.

Thanks for any help.

Nick
Welcome to the forum.

What year and model atv are we dealing with ? Carbureted , or FI? Is the fuel fresh? Has the ATV been sitting dormant for some time?
 

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Discussion Starter · #3 ·
Thanks for the reply, John1960.

Year and modal? Meh. Sorry, I really have no idea, but old and battered. Carbureted. Yes the fuel is fresh, as I have filled it up myself since purchase. The ATV gets used from time to time, with maybe a month max between. Whether it was left lying before purchase I do not know, but guy mentioned battery would often be flat so I suspect. The battery is pretty shot now and needs charging after a week or so of inactivity. But as I say, this has quite suddenly become worse, but there was "popping, spitting and detonation" as I saw it so charmingly described at some time :).

Nick
 

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Thanks for the reply, John1960.

Year and modal? Meh. Sorry, I really have no idea, but old and battered. Carbureted. Yes the fuel is fresh, as I have filled it up myself since purchase. The ATV gets used from time to time, with maybe a month max between. Whether it was left lying before purchase I do not know, but guy mentioned battery would often be flat so I suspect. The battery is pretty shot now and needs charging after a week or so of inactivity. But as I say, this has quite suddenly become worse, but there was "popping, spitting and detonation" as I saw it so charmingly described at some time :).

Nick
I think the first order of business is to determine what machine we are dealing with. Can you find the VIN number ? That will allow us to positIvely identify your machine. It might help if you can post up some pictures also. This way we can deal with the specifics on that machine.
 

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Hello. I believe the vin is on the rear frame. Right hand side. On a round tube running vertically.
I would put a new carburetor kit in it. Thinking that when going down hill the rim increases. This could pull gas through the needle valve that is supposed to stop gas. Just probably needs it anyhow. It's not too hard n you may as well start getting used to your ride.
I would do a basic tune up . Adjust the valves n put new o rings on the valve caps as they get old n hard, leak. And there cheap. Nip all the rubber vacuum lines a 1/4" or so , so they seal better.
As for the clutch system. I would think it's working good as it moves when given gas. It's just not getting the gasoline metered in correctly. You will need to make sure your fuel system is cleaned up.
Good luck n have fun
 

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If there is a rubber diaphragm in the top of the carburetor. Your carburetor will have 4 screws on the top holding down a tin cover. Take it off slowly as there is a spring in there. Look for a hole in it.
 

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Discussion Starter · #8 ·
If there is a rubber diaphragm in the top of the carburetor. Your carburetor will have 4 screws on the top holding down a tin cover. Take it off slowly as there is a spring in there. Look for a hole in it.
OK thanks, and thanks for the reply. I will certainly have a look at that as it feels right. It would be a way for air to get in but the diaphragm could make it intermittent.

Nick
 

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Air leaks can do this. Check the carb boots on both sides of the carb. Make sure your air filter is in place and clean.
 

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Discussion Starter · #10 ·
Thanks for the reply. Yeah I need to give the carb and airline a good looking at (when I get the time: firebreak time :( )

Nick
 

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Hello. I believe the vin is on the rear frame. Right hand side. On a round tube running vertically.
I would put a new carburetor kit in it. Thinking that when going down hill the rim increases. This could pull gas through the needle valve that is supposed to stop gas. Just probably needs it anyhow. It's not too hard n you may as well start getting used to your ride.
I would do a basic tune up . Adjust the valves n put new o rings on the valve caps as they get old n hard, leak. And there cheap. Nip all the rubber vacuum lines a 1/4" or so , so they seal better.
As for the clutch system. I would think it's working good as it moves when given gas. It's just not getting the gasoline metered in correctly. You will need to make sure your fuel system is cleaned up.
Good luck n have fun
I have similar problems with my 250 4x4 . The replies gave me something more to check . When I was working on mine I pulled the metal cover off the top of the carb and started it . It ran pretty decent . But when I put the plate back on and stuck the screws back in it started running like crap . Finally figured out that I could leave the screws out of one end it runs pretty good . I can just start the screws into the holes , heads still up off the plate and it runs bad . Has new vacuum lines attached . Will have to find out how to check the boot from the engine to carb . Had no obvious cracks . Runs pretty decent with the airbox disconnected .
 
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