1998 Polaris Magnum 425 starts but dies right away.

[BillR94]

I picked up this ATV that had no spark. The previous owner said he was driving it and it died and would not start. He discovered it had no spark. He replaced the CDI and the coil with no luck. He got tired of it and I bought it. I replaced the stater and now it has strong spark. Now, it starts for a second or two then dies. It will not stay running. I have checked the timing and it is spot on. The valves are adjusted correctly. I see no warn issues with the cam. I put the original CDI and coil back on it. Same problem exists. Compression is at 65 psi (has decompression mechanism),

I took off the muffler in case the issue was clogged pipes. No change. I replaced the spark plug. No change. The carb was an aftermarket so I put a Niche carb on with no change. I bypassed the fuel pump and that did nothing to solve the problem. 

I don't know if this is a carb issue or an ignition issue. I am looking around locally for an OEM carb to try out but not sure that will fix the problem. 

Can anyone help me solve this problem. I am running out of ideas. 

Thank you for your time

Bill

 

[Cactus]

I might be way off base here, but have you tested the battery for a dead cell or hooked up jumper cables to see if it will stay running? I've seen dead cells do weird things with electronic ignition. 

[BillR94]

Yes, I have used a battery charger, and a car battery with jumper cables. The battery is fairly new. It made no difference.

[davefrombc]

That sounds like a fuel issue..  Check  the float level is right,  the  line from  fuel tank to  carb  is unrestricted and there are no vacuum  leaks.  Does it rev up at first then  dies on idle?  if s  idle mixture may be too  lean.  Does it run  with the choke on ,or partially on?  Vacuum leak.  I  can't offer more than  those things to  check.. I  doubt it is an  ignition problem but you could  check  it with an  inline spark tester5 to  be sure.. They are inexpensive and handy to  have  when  chasing ignition  and running issues.  One issue  I  have heard of others having  is the  alternator/ /charging circuit when  a diode went bad in the regulator..  It is a bit out of left field  but  when  all else fails  it's worth checking out .

Edited December 21, 2025 by davefrombc

[BillR94]

I have tried 3 different carbs so far. All non OEM but one of the carbs I borrowed from a running ATV. The issue remained the same no matter what carb was used. It does not rev up at all. The best way I can describe what is is doing is imagine starting it (and it starts) but immediately turning it off. No matter where the throttle is at, it does the same thing. Its like it loses spark just after it start. Now to be clear, I DO NOT know if it is actually losing spark, I'm saying it acts like it. I tried a spark tester and it has a nice strong spark but I can't tell if it is losing spark under compression or not. 

I spoke with the previous owner about this and he says that the machine ran fine , started fine, and were riding it around when it lost spark. So the only thing that has changed is the replacement of the stater and pickup coil. It is an aftermarket stater so is it possible, I got a bad one? I have no idea. I am going to borrow the stater from the same guy I got the carb from to see if that is the issue but I am not holding my breath.  I'm going to attach a video  but it is hard to hear clearly that it fires a few times then dies. 

I am pretty much out of ideas. 

 

[davefrombc]

Have you tried connecting the spark tester and turning the motor over using the pull start to see if has spark  that way.?  It could be  it gets power for ignition through the start circuit but doesn't  when the starter is disengaged.  

[BillR94]

No, I never thought of that. I will try it today. Thank you. What would cause it to do that?

[BillR94]

5 hours ago, davefrombc said:

Have you tried connecting the spark tester and turning the motor over using the pull start to see if has spark  that way.?  It could be  it gets power for ignition through the start circuit but doesn't  when the starter is disengaged.  

I tried your suggestion this morning. It DOES have spark when I pull it over manually. Would a bad stater cause this issue?

[davefrombc]

Has  the timing chain  been  off ,  or very loose  by any chance ? It may  have jumped  way out of valve time.  If it has spark  it  has to be fuel  or valve / ignition  timing way out of whack .One more trick to try  before tearing into it.. Have you  left the intake hose to   the filter off and tried  holding you hand over the  intake ? That will tell  you if  it   has intake draw?   With that,  I'm spent.  I don't think there is a problem with the stator  and can't think of anything else to try.

[BillR94]

I have checked and double checked timing. It is spot on. The timing chain is tight. The spark plug is new. I have tried removing the filter and placing my hand over the intake. There is strong suction and the engine will fire when I do that. It just does not stay running. As I said, I have tried 3 different carburetors because it DOES seem like it is not getting fuel ( and/or losing spark) and all three carbs have the exact same results. That just seems suspect to me. I am trying to find an OEM carb to try out but don't want to spend $250 for a part I am not sure will address my issue.  Its hard to "borrow" one. 

I keep thinking it is a simple solution I am missing but I am at a loss as to what that might be or what else to try. 

[davefrombc]

I  keep  thinking  of things to  mention  and the last is  have you checked that the fuel  bowls of the carbs  have been filling?  No  plug  between the fuel  valve and the fuel  bowl.   It definitely has to be something rather simple that we're missing.   You  could try to  use a spray  bottle to  mist the carb and see if the  motor  catches  on those spritzes.  If it does it would definitely be a fuel  / vacuum  problem.

[BillR94]

Yup, tried carb spray directly into the intake. Same issue. Only other thing I can think to try is a leak down test but not sure that will show anything. The previous owner said the machine would start and run fine before the stater went out. But I have to try it!

[Sha35297]

I had this exact same problem on a grizzly 700 just the other day. I'm not familiar with how the starter solenoid works on this particular bike, but the way it works on the grizzly is when the ignition is turn on it supplies power though the starter solenoid which then powers everything else. On the grizzly the power would send to everything while holding the starter button down and then would kill power as soon as the button was released which would cause the bike to kill every time. May be a long shot. One thing I do know from an older Polaris I worked on years ago was that the ignition switch and the power switch on the handlebar are directly linked together and can cause running issues. The other thing with the older bikes is the switch inside of the throttle mechanism on the handlebars. It has to be functioning and adjusted properly. Hopefully this helps. 

[Sha35297]

 

[Gwbarm]

Just watching your video my first impression would also be fuel delivery, but if you carb bowl is full and you cant get it to stay running squirting gas in the carb thats not it unless you have a massive air leak leaning out the mixture.. Spark is good you can hook up an inline spark tester to see if the plug is firing under pressure. The only other thing if you have good consistent spark is timing and compression. Also something could be interrupting spark but you should see that with the inline spark tester.

[BillR94]

Thank you Sha35297, Gwbarm This bike is a little different than the one shown in that video. I know they perform the same task but I did  manually separate the contacts and the problem is still there. Is there a way to bypass this switch or temporarily disconnect it for testing purposes? It looks like it is working correctly but I am not sure. Isolating it from the system would confirm if it's the problem.

[Gwbarm]

It doesnt appear that there is, you can cut the wires and wire it directly to bypass the switch.

[BillR94]

2 hours ago, Gwbarm said:

It doesnt appear that there is, you can cut the wires and wire it directly to bypass the switch.

I unplugged it completely and it did not make any difference. I also took the kill switch apart and cleaned it with no luck. I have tried everything I can think of and everything that was suggested and this bike will not run. I just don't get it!

[davefrombc]

All I  can suggest at this point is to  cdheck the timing again  and make sure it is firing on TDC compre3ssion stroke and not TDC exhaust stroke.  If the motor  hyqas been  disassembled and reassembled,  you need to be sure both valve timigt and ignition timing  aree  right.. if it has compression , fuel  and ignition it should run.  It's amazing how easy to  haqve a motor 180 degrees out of time and  miss it even  when  checking again.  Believe me , you wouldn't be the first  to "check it twice"  and be  wrong both times.  Don't ask  How I  know

[BillR94]

Yes, I get it Dave. In fact, I went over the timing ( removing the valve cover, side cover, recoil, flywheel, stater, stater cover) and checked the marks and aligning them a total of 5 times. Piston at the top. But if it was 180 out, it would not run at all (would it). In the video below, I disconnected the exhaust in case it was clogged and causing the issue. I tried another known good CDI. I took apart the kill switch and cleaned it. I removed the starter solenoid and cleaned all the connections and the ground. I went through all the wiring for the CDI. coil. stater to make sure they were connected and grounded where needed. Still no change. It would not surprise that it is something very simple, or even something dumb I did but for the life of me I have no clue what it would be. Currently, I am looking for an OEM carb and stater to try. Hopefully a local person will let me borrow them for testing purposes. I'm running out of idea! Correction, I AM out of ideas!

 

 

Edited December 31, 2025 by BillR94

[Gwbarm]

I was under the impression that this switch was keeping it from sparking, cant really tell where the switch is located from the photo. Looking a little closer at the photo i see a cable so it must make connection when the cable is pulled, maybe a start in gear switch.

Unplugging it may not work, it may need to make connection to complete the circuit.

[BillR94]

1 hour ago, Gwbarm said:

I was under the impression that this switch was keeping it from sparking, cant really tell where the switch is located from the photo. Looking a little closer at the photo i see a cable so it must make connection when the cable is pulled, maybe a start in gear switch.

Unplugging it may not work, it may need to make connection to complete the circuit.

I'm not sure either. nut no matter what I do with the switch (plugged in or not) it has no effect on the issue.

[Gwbarm]

It may not be the switch at all you can check the continuity with and without the cable pulled and see if it does anything, it appears that when you pull the cable it makes contact with the switch. The contact points look clean but you can try contact cleaner to clean off any corrosion that might be there causing intermittant contact maybr even use a little fine sandpaper or points file.

[jen]

Gwbarm is right on track as usual...continuity test is good. However, if you jumper out something ( by pass to test)  NEVER remove that jumper as you move on to jumper (by pass) test another circuit.  that way if you have multiple "bad" circuits  they can be exposed.... Been there, done that and have the 'spaghetti string  top' ...LOL

[davefrombc]

Back on the 22nd. Bill said he  had spark  when he pulled it over manually but it still  did not start.  Try connecting the spark tester again  and try to  start it..  If it has spark, it's not switches or wiring.  That only leaves timing and fuel  ( or a really serious vacuum  leak) 

[BillR94]

4 hours ago, Gwbarm said:

It may not be the switch at all you can check the continuity with and without the cable pulled and see if it does anything, it appears that when you pull the cable it makes contact with the switch. The contact points look clean but you can try contact cleaner to clean off any corrosion that might be there causing intermittant contact maybr even use a little fine sandpaper or points file.

But if I unplugged the connector and there is no change to the issue, would that not mean the switch would be ruled out? Or am I missing something.?

[davefrombc]

Do you have spark  when you turn it over on the pull cord  or starter?

 

[BillR94]

yes, both ways have spark. You can see it run for a short time in the video I posted yesterday

[Gwbarm]

If you have spark i dont think the switch is the problem, if the switch is the one i think it is it bypasses the neutral light circuit to allow you to crank it in gear, if its on the left hand brake lever. If its unplugged it just wouldnt allow you to start it in gear.

Im also thinking compression or fuel, 65 is too low for an engine to run i know it has a decompression valve but is it working properly it should only come in play during startup , if the fuel bowl is full it should run for a bit longer, so that only leaves compression and timing and you have checked timing, leaving only compression, i would check that again and put some oil in the cylinder and see if it increases. If no luck find the decompression valve and see if it is keeping something open, not sure where it is on this ATV.

[davefrombc]

The way it was turning over in the video  seemed to me like it was firing on the exhaust  stroke rather than on the compression   If it has spark,  it is not an  electrical issue. I  have seen  motors run  with only  65  pounds compression ,  but  not develop any amount of power.  As I've said,  to  me  the problem  is most likely timing of either valves if  they had been worked on, or the ignition timing being  180  degrees out,  or  a very serious vacuum  leak not allowing the motor to  draw fuel from the carb. Yes,  try a little squirt of oil in the cylinder to see if it  raises the compression and check the decompression  to see if it isn't stuck open.

I  just did a  quick search on the  old  Fords Model T  motors  of the early  automotive days..  Some ran with as little   as 35  pounds compre3ssion.  Typical compression  was  40 to 55 pounds. It doesn't take a lot of compression for a motor to  run, but  one  with that litle  would have very little power.

 

Edited January 1 by davefrombc