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Old 11-10-2010, 12:39 AM   #1 (permalink)
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1986 Artic Cat Jag 440 Running VERY Rich

I have read so much about this carburetor I believe it is the Mikuni VM38.
I've tried touching the big screw (Labeled 32 on page 2 in this link) http://www.mikuni.com/pdf/vmmanual.pdf
and after looking at this I now know it's just the screw that adjusts the idle. I know now that 29 the air screw is the one I really need to mess with. That screw is currently all the way in which I knew wasn't right but this thing ran perfectly last year.

I believe that the needle isn't seating properly or not stopping fuel flow into bowl because it is running so rich it's just spitting gas out of the carberator. I can barely get it to rev up because it is so rich and once I get it up there it's still too rich to burn all the gas. The plugs are very wet and black when I take them out.

I've cleaned carburetor very well the only part I didn't get to clean was the needle and seat. Due to the fact the pin that holds the arm that moves as floats go up and down looks tough to get out and I didn't want to use much force. Also if you look on page 12 http://www.mikuni.com/pdf/vmmanual.pdf
I am so confused on how to set this. I'm thinking my bowl is filling up and just leaking up and into the carb loading it up and making it run extremely rich.

My floats move well and I tested them with water once to see if they floated and weren't gas soaked.

My plans are to get that needle out clean in there very well and I would love to set the float to the right position if someone could explain what it says on page 12 to me better than they do that would be great.

Also what can I expect the air screw labeled #29 to be good at? What's the best procedure to setting this? It really doesn't idle on it's own at the moment you need to always be feathering and working the throttle to keep it going.

Any input or ideas would be greatly appreciated. Thank you all!
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Old 11-10-2010, 06:19 AM   #2 (permalink)
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If the needle isn't stopping fuel flow, it'll be coming out of the hole on the front intake of the carb, or out the overflow tubes if you have them. Start the sled and see if it's coming out of that front hole.
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Old 11-10-2010, 08:25 AM   #3 (permalink)
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Take the carb and hold it upside down and blow into the gas inlet and it should stop as the float comes to level with the flange!
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Old 11-10-2010, 11:53 AM   #4 (permalink)
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Set the air screw at 1 full turn out from bottomed.
The pin for the floats is just held in place by the weight of the float, it should just push through. Inspect the needle valve tip, if it is worn)(, replace it with the rubber (viton) tipped one. To clean the seat, take a tiny bit of steel wool and wrap it onto a q-tip and apply with a twirling motion to clear the glaze off the brass.
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Old 11-11-2010, 10:06 PM   #5 (permalink)
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Originally Posted by RJ Gleason View Post
Set the air screw at 1 full turn out from bottomed.
The pin for the floats is just held in place by the weight of the float, it should just push through. Inspect the needle valve tip, if it is worn)(, replace it with the rubber (viton) tipped one. To clean the seat, take a tiny bit of steel wool and wrap it onto a q-tip and apply with a twirling motion to clear the glaze off the brass.

I set air screw at one turn out. Still runs extremely rich The needle is seating properly also. This is how I tested, first i took off and lifted upside down and couldn't blow in the hole where gas line attaches. Then I filled bowl up through that hole with gas. then I tried to blow in it and I couldn't so the needle must have plugged hole the way it should have when bowl was full.

It ran the best when it was running out of gas. I'm not sure if the level of gas in the bowl effects how rich it runs? It seems like if I pinch gasline and wait like 5-10 seconds I then get about 10-12 seconds of it running perfectly..

I made a video for you guys I'll try to attach it.
Yfrog Video : yfrog.com/5b8kvz
http://img191.imageshack.us/img191/65/8kv.mp4
<embed src="http://img191.imageshack.us/flvplayer.swf?f=M8kv" width="640" height="380" allowFullScreen="true" wmode="transparent" type="application/x-shockwave-flash"/>

Uploaded with <a target='_blank' href='http://imageshack.us'>ImageShack.us</a>
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Old 11-12-2010, 08:04 AM   #6 (permalink)
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take the needle out and there should be a small clip washer on it. move the washer up a knotch or 2 and see if that helps.
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96 cougar 550 2up bone stock (sold)
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Old 11-12-2010, 09:06 AM   #7 (permalink)
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It kinda look's like the exhaust might be stopped up (silencer) just take the springs off and fire it up. If it runs great VIOLA you found the problem, if NOT then you verified that's ok (LOL) .......
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Old 11-13-2010, 11:24 AM   #8 (permalink)
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I will try unhooking the exhaust I never thought of that before. But I'm not sure where that clip washer is. I'm picturing the needle solid with that little pin out the bottom tom absorb shock. But I'm not sure where the clip washer would be?

What stinks is this thing is a half hour away and I"m always so busy to go and try to work on it so the more ideas before I go the better!
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Old 11-13-2010, 03:38 PM   #9 (permalink)
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most time the clips are about half way. you will see a few notches 4 or 5 i think. just bring it up to the 2nd from top and go from there.
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97 ultra spx slp can geared clutch and 144 studs.(mine)
96 XLT studded with reverse(12y/o son)
98 xcf 440 (wifes sled)
96 puma 340 elec start(kids sled)
96 cougar 550 2up bone stock (sold)
96 XCR 440 clutched (sold)
92 indy 500 bored,clutched. piped(sold)
85 indy 400 (11 y/o son's sled)(sold)
87 yamaha excel 340 (parting out)(sold)


2011/2012 miles :00000000
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Old 11-13-2010, 04:31 PM   #10 (permalink)
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Hey the other thing I've been thinking is make another video of you showing the inside of the carb and working the throttle, full-open to closed (not running !)..... My thought is there is really only a couple of thing's that would "dump" that much fuel into the cylinder,
(if it isn't stopped up exhaust system) and that would be the "main-jet" which is located in the carb bowl IE, fell out, missing, just gone, (seriously !) and the other would be the needle-jet, which is the one you see going up and down as the throttle is worked. Hence why I wanted to see the inside of the carb and you working the throttle full to close again (Not running of course).... I still think check the exhaust first though ? Good luck and PLEASE report back.....
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Old 11-15-2010, 09:36 PM   #11 (permalink)
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Ok tomorrow is the big day.. So for ideas I have..
~ Adjust the needle clip thing. (never heard of it I"ll look haha) IS this the same as bending the tab on the E Bracket that is lifted when the floats rise?
~ Unhooking exhaust.

If you have ANY ideas why it is running so freaking rich please post here so I can resolve this tomorrow..

Thanks,
Ryan
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Old 11-16-2010, 12:15 PM   #12 (permalink)
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with the clip all you have to do is get a pair of pliers and pull it off then move it up 1 or 2 notches. DON"T DROP AND LOSE IT.
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97 ultra spx slp can geared clutch and 144 studs.(mine)
96 XLT studded with reverse(12y/o son)
98 xcf 440 (wifes sled)
96 puma 340 elec start(kids sled)
96 cougar 550 2up bone stock (sold)
96 XCR 440 clutched (sold)
92 indy 500 bored,clutched. piped(sold)
85 indy 400 (11 y/o son's sled)(sold)
87 yamaha excel 340 (parting out)(sold)


2011/2012 miles :00000000
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Old 11-16-2010, 09:05 PM   #13 (permalink)
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OK so after 2-3 hours of trial and error it's running pretty good but not perfect. the mid/high end is like perfect. But it doesn't want to idle too much and when it does it usually loads up a little but not like it did before.

I unhooked exhaust and it did nothing so I put it back on.
Than I adjusted the bowl gas level lower to lean it out a little. It actually ran pretty good after that but still not right especially in the low range of throttle.

Than I realized if you are holding carb upside down to the side of the main jet in the middle is a tunnel to a screw that has a hole drilled in it. I believe it is the pilot jet. This screw was allllll the way in?? What should it be set at? I set it to one turn out and it runs pretty good but I'd like it to run better. Does anyone know what I should set this screw at (Pilot jet screw going up into carb through bowl) and also what the small air screw should be set at that is at the entrance of the carb on the side?

Right now pilot jet is at 1 turn out and that small air screw is at 1 and a half out.

I wanna get it to run better. I'll make a video soon if I have to. I appreciate all the help the more the merrier!
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Old 11-16-2010, 10:14 PM   #14 (permalink)
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try 3/4 out
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97 ultra spx slp can geared clutch and 144 studs.(mine)
96 XLT studded with reverse(12y/o son)
98 xcf 440 (wifes sled)
96 puma 340 elec start(kids sled)
96 cougar 550 2up bone stock (sold)
96 XCR 440 clutched (sold)
92 indy 500 bored,clutched. piped(sold)
85 indy 400 (11 y/o son's sled)(sold)
87 yamaha excel 340 (parting out)(sold)


2011/2012 miles :00000000
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Old 11-16-2010, 10:24 PM   #15 (permalink)
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try 3/4 out
On pilot jet in bowl? Or on air screw on side of carb?
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Old 11-17-2010, 05:00 PM   #16 (permalink)
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you should only have 2 to turn. the air screw and the idle screw. i'm not sure what other one your talking about. the air screw should be 1 turn out but you may have to play with it while it is running. I would say ask RJ about the other one cuz i'm lost.
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97 ultra spx slp can geared clutch and 144 studs.(mine)
96 XLT studded with reverse(12y/o son)
98 xcf 440 (wifes sled)
96 puma 340 elec start(kids sled)
96 cougar 550 2up bone stock (sold)
96 XCR 440 clutched (sold)
92 indy 500 bored,clutched. piped(sold)
85 indy 400 (11 y/o son's sled)(sold)
87 yamaha excel 340 (parting out)(sold)


2011/2012 miles :00000000
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Old 11-18-2010, 05:30 AM   #17 (permalink)
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Yes the air jet is for your 0-1/4 range... And the best way to set is to support the back of the sled fire it up and either turn that little fella one way or the other if that screw is in the back of the carb it controls fuel to air ratio, if the screw is in the front it controls air to fuel ratio. (JUST A LITTLE THOUGH 1/4 turns ) if the bog gets worse go back to your original one turn and go the other way, till your BOG goes away !.... now just drop the sled and see how the adjustment feels on the ground when you hit the throttle. And a reminder NO GOLF TEES !... (LOL) the other is if there is no distinctive change while turning that screw the system is clogged, then you simply get a can of carb/choke cleaner and pull that jet then hit ALL ports by sticking the nozzle into each one and give it a shot. then just reinsert jet and go one turn and fire it up again for final adjustment.
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Old 11-18-2010, 12:36 PM   #18 (permalink)
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Yes the air jet is for your 0-1/4 range... And the best way to set is to support the back of the sled fire it up and either turn that little fella one way or the other if that screw is in the back of the carb it controls fuel to air ratio.
I think I understand what you mean here but I adjusted it to the best spot using the same technique and it's still not like perfect. the idle is kind of random mostly it will slowly drop and stall or slowly load it up so it's spitting out gas as I try to rev it up and it struggles to burn up the gas to get to higher rpms. Or maybe it's not getting enough? But I think it gets too much because if you rev it up let it idle for just a quick second you can rev it right back up again. But if you rev it up and let it idle for about 10 seconds or so it seems to load up and have trouble reving up again. (is this due to pilot screw or air screw?) I believe air screw is in best spot for now so maybe it is the Pilot screw (right side of picture)

if the screw is in the front it controls air to fuel ratio. (JUST A LITTLE THOUGH 1/4 turns ) if the bog gets worse go back to your original one turn and go the other way, till your BOG goes away !.... now just drop the sled and see how the adjustment feels on the ground when you hit the throttle.
In this part are you talking about the pilot jet on the right side of my attached picture? It's set at 1 turn out right now is that a good starting point? Which way do you think I should start doing the quarter turns? It sucks having to take off the carb and bowl each time to adjust this.. EDIT by the way.. This screw had no tension on the threads and there is no spring so I would set it at 1 and it would either vibrate out to 2 turns out or vibrate in to almost closed! I put a THIN layer of that nylon thread tape JUST on the threads so it had a little pressure so it will no longer move. This is why I'm probably the rare case that needs to adjust this screw.. Because my screw vibrates in and out as it wishes changing how it runs..

And a reminder NO GOLF TEES !... (LOL) the other is if there is no distinctive change while turning that screw the system is clogged, then you simply get a can of carb/choke cleaner and pull that jet then hit ALL ports by sticking the nozzle into each one and give it a shot. then just reinsert jet and go one turn and fire it up again for final adjustment.
The golf tee is just because the choke cable is messed up and the plunger wont seat right now.. I don't want to tune it without the tee because I'd be tuning it for running on choke.. But I'll fix the cable after It's tuned correctly. All jets have been taken out carb completely apart every square millimillimeter is spotless with fresh gas and a clean tank

Thanks for your help I'll try to make a video soon of how it is. It's not that bad I'd say about 70% of running potential compared to the 15% it was at a month ago. But last year it was at like 95%

Last edited by IM Buddy8; 11-18-2010 at 12:41 PM. Reason: Threads no pressure.
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Old 11-18-2010, 04:17 PM   #19 (permalink)
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Put a drop of loc-tite on it, that will work better than the thread tape.
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Old 11-18-2010, 04:35 PM   #20 (permalink)
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Your carb is too big. An 86 Jag 440 should be running a VM34 with a starting point of a 300 main jet, 22.5 pilot jet, Q-0 166 Needle jet, 6DH2-3 jet needle and set the pilot screw at 1 1/2 +- 1/4 turns out. Make sure you have the right carb before trying to diagnose any further.
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