1998 Polaris Magnum 425 starts but dies right away.

[BillR94]

I just redid the compression test. With the throttle fully open (cuz I knew you going to ask me if I opened it) it was 200 psi. I then did a leak down test and it is leaking badly from the exhaust. I loosened the valve adjustment on both valves several turns and although the leak subsided, it did not stop completely. Would that be a de-compression issue or hopefully your not going to say bent exhaust valves!?

[BillR94]

I then looked at the de compression mechanism install procedure in the book. I took it out and reinstalled it just as the book says. The leak decreased considerably but I don't understand how I got 200 psi. No change, it does the same thing. (sigh)

Edited January 1 by BillR94

[davefrombc]

2 hours ago, BillR94 said:

I just redid the compression test. With the throttle fully open (cuz I knew you going to ask me if I opened it) it was 200 psi. I then did a leak down test and it is leaking badly from the exhaust. I loosened the valve adjustment on both valves several turns and although the leak subsided, it did not stop completely. Would that be a de-compression issue or hopefully your not going to say bent exhaust valves!?

The 425  is not an interference engine so the piston cannot hit the valves even if the timing chain broke.  The  worst it could be is  a burnt valve. and since you have  enough compression the slight exhaust leak isn't the reason for it not running.  I'll  repeat my suggestion one more time.  Check   timing  and be sure it is not 180 degrees out..  Beyond that I  cannot offer any more suggestions.

 

Edited January 1 by davefrombc

[BillR94]

I guess I don't understand. How can the timing be 180 out? I have the timing marks on the crankshaft lined up with the case. I have the two dots on the cam gear lined up at the top of the gear, I have the piston at top dead center. I checked the woodruff keys to make sure they are not sheered, The timing chain is tight, and I have the timing marks on the stater lines up with the case mark. If the timing was 180 out, it would not run at all...... wouldn't it?

Can you please give me more info on how it could be 180 out and how to check it? I'd be glad to check it and get back to you.

[davefrombc]

I  can't help on the timing   of the engine  since I  have never worked on  one of those..  you'd have to  go by the manual. .The  piston  would be  TDC  twice in each cycle.  once  on  compression   (  all valves closed) and  TDC exhaust (exhaust valves open). But  The  timing marks shouldn't be lined up then..  The only thing  might be if  you  are mistaking  something for a timing mark  rather than  using the  actual  one..  .  The  firing in that video didn't sound at all  like a firing under compression to me..  That  is what I  was going by..   To  me it sounded  just like some residual  gas left in the cylinder after the exhaust stroke being ignited  which  would give the piston a bit of a push,  but not enough to  really spin  it  over..  Hopefully  one of the other s has experience  with that motor and can  help..   At 82,  I'm  not that great at  making diagnoses and interpreting what I see in  a picture of the timing  marks to  what I would see if I  was actually there with a motor  open.  With  compression and ignition , I  can  only  see  fuel  and timing being the missing  element  to  it actually running and producing power. .  Giving a shot of fuel  directly into  the  carb  should make it fire at least a couple of times with  force  To  me , that only  leaves timing  as the culprit.

Do  you have a riding buddy that might be able  to look at  the  motor with you  and  maybe spot something missed?   That  was how  my error  was solved on a  car  motor way back  when.

   

Edited January 2 by davefrombc

[BillR94]

1. No. its just me. I don't know any local mechanics that are familiar with this bike. I appreciate your help tho. I'll just have to do more research (or part it out). 

[davefrombc]

Doesn't have to be someone familiar with the bike  or  that particular motor  if you  have a copy of the instructions for setting the  cam and ignition timing.  I  know on some  motors with  a  chain driven  cam and ignition the  timing marks are not  not directly lined up  but so many links apart. Double  check  that  it is actually drawing fuel.  after  spinning  the motor over  several times  with your  hand blocking the carb intake  does the spark  plug  look wet  when you check it ,  or  does it  actually fire when the intake is severely restricted?   I don't know about you, but I'm  stubborn  enough  I'd  keep  at it until  I  got the  damn  thing running  rather than  part it out.  I  like  my mother's saying ...  " I'm not stubborn,  I'm determined".  I'm a bit like she was; and she could be very  determined.

[BillR94]

I'm not ready to part it out yet.

[Gwbarm]

Rotate engine to top dead center, timing marks should be lined up, cam lobes should be pointing toward the ground, valves should be loose. It you really want to make sure its the compression stroke take out plug put your finger over the hole rotate the engine, when you feel pressure on your finger stop and continue up to top dead center by hand, you can put a straw or piece of ridgid wire in the hole, move it until it stops going up, see if your timing marks line up and check that valves are loose.

[BillR94]

As I stated earlier, I have done all that. In fact, multiple times. I have checked timing marks, cam lobes, valve clearance, checked for clogged exhaust, bad grounds, carb, shut off switch, throttle safety, fly wheal woodruff key, timing chain, compression, leak down, stater, coil, CDI, crank gear woodfuff key, carb boot etc etc etc... no joy!

[Gwbarm]

I figured you had done that already , i really dont think its timing, just stated an old school way of double checking. If it was 180 off it would not try to start. I still think it is aa fuel delivery issue, not sure what since you have tried multiple carbs and not sure why you cant keep it running with starting fluid. It still could be an electric glitch you said the CDI has been replaced is it an OEM or aftermarket sometimes the aftermarket ones are not exact and the CDI does control the timing to some degree. Another thought would be a glitch in the pick up coil they can get debris on them to caause not to function properly , but again you have checked all that. So im not sure at this point i would keep trying to start it and see if anything else happens to give a clue as to what is going on. Being that its a 98 it shouldnt have sensors and electronic devises causing this problem. 

[Sha35297]

Another common issue with these model bikes is the camshaft. I have had a couple in the shop that would idle great, but die as soon as any throttle was pushed. The exhaust lobe on the cam was worn down to almost perfectly round. Just enough to allow it to idle. This one could maybe be beyond that point. Grasping for straws at this point. I'm sure you may have said you did this, but check the intake boot between the carb and engine for cracks. Spray some brake cleaner on it while its running and see if it revs up rpms or floods it out. 

[Sha35297]

Damn, didn't see there were several more comments before I responded. So ignore my previous post. I know you have said you checked timing over and over, but it really sounds like either timing or valve adjustment. 200psi compression is very high for that machine. Especially being that it has automatic decompression. Should be closer to 80-90.  Could be as low as 55 and still run good. 200psi is way too much, indicating incorrect valve lash or bad timing adjustment. 

 

 

[BillR94]

Today, I put an OEM carb on it and it did not change/correct the issue. I am now convinced that this is NOT a fuel/carb issue. I also do NOT think it is a timing issue. I am leaning toward electrical so I have a couple of wiring questions. Since I replaced the stater to get spark back (as you may recall, a no spark issue was the original problem) I think it might be related to that. I  discovered that the bike is losing spark AFTER it starts. 

Plug1 picture shows a 3 wire plug with a empty slot. The other side of the plug has 2 black wires going into it opposite side of  the empty slot.  Picture 3 shows a black wire that I found hanging coming off a black box (I don't know what that black box is for) . So, I thought that that hanging black wire goes into that empty spot on the plug. When I plug that hanging wire into that open slot, the bike loses spark completely. 

Picture 2 shows a brown wire pigtail that is part of the stater wiring harness. It was plugged into one of the wires going to the headlight. That seems odd to me.,

So my questions are:

Where does that brown wire go?

Where does that black wire go? If it goes in that plug, why am I losing spark completely?

I put in an aftermarket stater cuz I couldn't find an OEM one. Could it be the wrong stater? 

and lastly, If you were going to replace a stater, is there a specific brand/manufacturer I should get? Please include link if you can.

Thank you

Edited January 13 by BillR94

[davefrombc]

There  is a service manual  in the downloads section that  covers that quad and  related ones  and  also  farther down the Polaris section is  a  wiring diagram  for a 1999 Magnum  that may  be the same as the  1998. Download the manual or  wiring diagram and print out the wiring diagram  and use it  to  trace out the wires. Tedious job for sure.  You'll need to  look for a wire disconnect  or  a possible safety switch  gone bad.  I  don't think the starter itself  is any part of the  problem.

Edited January 14 by davefrombc

[BillR94]

Thank you Dave, That is one hell of a library!

[spock58]

It's possible that your ETC (electronic throttle control) is acting up. They cause issues when the throttle cable isn't adjusted right. Those limiter modules are also known to fail. That's the black box thing next to the ignition coil. I seem to recall that unplugging the black wire would bypass the system (not sure if this works on all models). If you can try another module, that might help in diagnosing this.

[BillR94]

I bypassed the ETC, That was ruled out. I am currently looking for a limiter to try.

[spock58]

https://www.ebay.com/itm/286748237462?pub=5575009733&campid=5337068107