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Discussion Starter #1
So I bought a 2003 ZL600 efi (with power valves of course) at the beginning of the season; it runs beautiful except recently it has started to bog out at 3000 rpms from a stop when you give it full throttle. If you ease into it its fine, even it its a bit aggressively. I've looked around and it seems like forums are saying its the apv servo and that its common, however I don't want to just start replacing parts so i figured I'd ask all of you that have more knowledge of the subject. I'm not familiar with sleds at all as far as working on them, this is my first snowmobile that I own and have to maintain lol so bare with me. I haven't cleaned the power valves or done anything due to not really knowing for sure where to start.
 

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TSS(throttle over ride switch) I'm pretty sure on your machine if you follow the wires from throttle down you will see it ends up being 3 wire connector - cut/remove the center prong(male)end of connector then reconect. This will leave your kill switch working but your TOS disconnected, it worked for me fine.If your sled has a 4 wire connector then it is usually the brown wire, still same procedure.
 

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Discussion Starter #3
searching for runaway throttle wire.jpg

So today I did some digging in the harnesses as you suggested and here are my results: the top plug with 2 wires is the kill switch, this is connected to the bottom plug. Before I started cutting, I wanted to make sure that the middle wire on the bottom plug is the one you are talking about
 

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well b4 you cut
un plug both and see how it behaves. if it is the same no need to cut as your problem is else where
 

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An engine acts differently when it's under load than free revving. If you're not getting any codes for catalytic converter or misfire my first check would be the air filter.
Under load the engine uses more fuel. More fuel needs more air to combust properly. If it is restricted by a dirty air cleaner it will bog down, typically mid revs
 

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An engine acts differently when it's under load than free revving. If you're not getting any codes for catalytic converter or misfire my first check would be the air filter.
Under load the engine uses more fuel. More fuel needs more air to combust properly. If it is restricted by a dirty air cleaner it will bog down, typically mid revs
?
 

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An engine acts differently when it's under load than free revving. If you're not getting any codes for catalytic converter or misfire my first check would be the air filter.
Under load the engine uses more fuel. More fuel needs more air to combust properly. If it is restricted by a dirty air cleaner it will bog down, typically mid revs
Sorry Man but I don't follow your post at all. Air Filter ? Their is an Air Box with an Air Horn But no Air Filter.. Maybe a Screen somewhere. I don't know if you were saying open up the air box lid & ck for obstructions( Mice/Dog food etc) A little confused by how you posted.
Ps if you find a solution I'd like to hear about it as one of our 02 600 EFI's is doing the same thing.
 

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Pretty low rpms for APV problems.
I'm not a fan of cutting wires and bypassing the TSS. I'd want to verify that is the problem before even thinking that route.
I had one that did act similar to what you describe. It ended up being the fuel pump. I'd check fuel delivery before going into bypassing parts. Filters first, then verify pressure.
 

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Discussion Starter #11
So I unplugged the plugs for kill switch and supposed TSS and no change. I never thought to check air ways. As for the fuel pump, where is the filter located and how would I check pressure? Something else, if its cold it'll take off like a bat out of hell, once it warms up the bogging comes along.
 

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Discussion Starter #12
To put into words what I couldn't before, if you rev it up so it engages the clutch and pin it, it'll bog- if you hold the throttle, it will die, if you let go 99% of the time it'll come back. Same instance of engaging the clutch, if you ease into it, even a bit aggressively, it'll take off with no issues. Any time you pin it from a dead stop, except for if the engine is "cold" (what I mean is I let it idle for a couple of minutes instead of letting it warm fully up) it'll always bog out, if you hold it it dies, if you let go it'll generally come back. For trail riding it isn't a huge issue, but when I have to put my friends in their place its a bit of a pain ??
 

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Yep that's a pretty accurate description of what one of ours is doing too. It seems to run ok after you get past the bog. We did do the new spring in the smart valves trick & that didn't fix it. Cut the spark plug wires back a little & reinstalled-(nope). Its up North for a few days yet & their going to install a new coil (2ndary) & will report back on that. Have run Seaform in fuel (Nope).
 

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Discussion Starter #15
Don't take this the wrong way, I'm trying to understand where you mind is, but what leads you to an option of compression being a probability since it runs fine otherwise?
 

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Is it a fuel related bog, rich, or lean, or is it a clutch related bog? With the sled having EFI you would think the fueling would be fine so it would not be a rich, or lean condition. If the APV's are stuck open, would that cause a low RPM bog?

Have the clutches been serviced? Either one, or both of the clutches could be sticking and causing a bog, but I'd think that would happen closer to engagement RPM. Does the bogging happen when the track is off the ground, so no load on the drivetrain?
 

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Discussion Starter #18
those are questions that have popped up besides the load bog referring to the track, which I plan on checking into now. To answer some of those questions, service of the clutches are unknown, the guy who had it before me supposedly only used it for ice fishing, the guy before him used it for trail riding (this guy was older than the one I bought it from) but it looks pretty well kept and the old guy supposedly took good care of it too. It doesn't seem fuel related but I'm not ruling it out or setting it on the back burner at all. According to my good friend who has been riding dirt bike since birth and has quite a bit of power valve knowledge said if they were stuck open it would be doggy at bottom end of power band, stuck close it would be doggy at top end of the power band so it crossed my mind. I'm thinking of cleaning them since we have a warm spell and trails are closed just to rule things out
 

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HA, Found the Problem. I guess I'll call this string "NEVER ASSUME" ..So here is the Long Story... Son in Law Bought a Matching Pair of 02 600 EFI's about 3 Years ago. I went with him & test rode it at sellers house before purchase & everything seemed OK. For the most part that sled ran fine the first yr & maybe got 200 miles on it that season. Some where during yr two it started to develop an annoying slight bog off the line. We went through many of the suggestions that was /were mentioned here. I thought we had cleaned the power valves too but ??? that now. So anyhow KIds got back from Up North yesterday & Bog was now pretty much happening at any speed, It would go but you had to really feather the throttle. So in my garage it came, I was cking this string saw the comment on PV not opening till 7K & then saw the above one about sticking open. So I told the boys to Pull the Power Valves & Clean. Not thinking that was it but at least making them do/ learn something. So since they were doing the dirty part, I thought I'd ck the Cables for sync. Popped the Servo cover off & TADA ! Both cables were there, Snapped in with the retainer clip. The only problem was they were not connected to the servo. I Think the prior owner cleaned the PV prior to selling & forgot to rehook them. It worked for a while by air pressure until they got dirty. So with clean Power V, & cables hooked up its fine. Buying used---NEVER ASSUME
 
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