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Discussion Starter #1 (Edited)
1997 scrambler 400 2 stroke



I have been messing with the stator plate because some how the bolts backed out and lost the timing mark, doesn’t seem to matter where I put it most of the time it will fire right up first click the other time it will crank and crank and crank and then it will back fire and blow the exhaust pipe off at the springs connection and I will have to take the mounting bolt off and pull of the exhaust so the springs will pull it back over the exhaust gasket donut or it will just crank and crank and then slowly start to catch and then it will run perfect, once running it’s an animal just sick of these starting issues. Not sure where to start anymore
 

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Discussion Starter #2 (Edited)
I did just rebuild the top end, I have sprayed starting fluid at the head, intake and jug to check for leaks at the gaskets and there are none, new spark plug and have clean and adjusted the carb multiple times, seems to be a spark issue but can’t figure out how


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I wonder if your valve timing got off? check your timing marks, and if those are fine, maybe your flywheel key? Shooting in the dark here.
 

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Discussion Starter #4
It’s a 2 stroke so no valves, I have checked the fly wheel key, it’s a little beat up but still holds it


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Discussion Starter #7
I updated the first post but it’s a 97 scrambler 400, the keyway on the crank and the woodruff key is a little beat up, not bad but I am wondering if the woodruff key is letting the fly wheel spin just a degree or so causing it to do this, I wouldnt think it was beat up that bad, keyway isn’t wallowed out, time to pull it all back apart again and put some more thinking time into it


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Are you sure you're getting spark? I'm just thinking, the reason it'd blow the pipe off would be because something is detonating some fuel in the pipe itself, so I'm wondering if you aren't getting spark, it's just dumping raw gas into the pipe, and the second it fires, it just detonates...
 

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Discussion Starter #11
I would agree, but it does start after a little bit of trying and runs like a new machine, that’s why I am thinking something with timing


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Flywheel key

I updated the first post but it’s a 97 scrambler 400, the keyway on the crank and the woodruff key is a little beat up, not bad but I am wondering if the woodruff key is letting the fly wheel spin just a degree or so causing it to do this, I wouldnt think it was beat up that bad, keyway isn’t wallowed out, time to pull it all back apart again and put some more thinking time into it


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Time to clear up a mis-conception about flywheel keys; they are not there to hold the flywheel in position - they are there to line up the flywheel to assure proper timing without having to reset the timing every time the engine is worked on. The flywheel is "locked" into position by tightening. If the flywheel is properly tightened, the key will never shear or get "beat up". If the flywheel is not properly tightened, the flywheel will eventually shear the key just from starting and stopping the engine. Anytime the key shears it is an indication that the flywheel was not tight, unless the engine is swamped and hydro-locks. In the case of hydro-locking, the piston comes up on liquid and stops instantly. The inertia of the flywheel can either shear the key, break the crankshaft, bend a rod or something else will succumb to the force of the flywheel's inertia.

With that out of the way, let's look at this: "it will just crank and crank and then slowly start to catch and then it will run perfect" - you have just described a classic indication of the engine being flooded. You are not turning the fuel off when done riding, the carb overflows and fills the crankcase.

Now, the timing can't be adjusted far enough to cause starting issues like you describe whether fully advanced or fully retarded. Fully retarded would make starting easier at the cost of high end performance. Fully advanced might cause spark knock when using low grade fuel. Properly set, the starting is easy and spark knock is prevented. I have run both fully advanced and fully retarded with no noticeable change in performance. If you are a stickler for "on the spot timing"; get a degree wheel, a pointer rigidly fixed to the engine and a timing light. Start the engine check the timing, shut the engine off, adjust the stator plate, restart and recheck the timing, readjust the stator plate - repeat the procedure until correct then mark the stator plate for future reference, but each time the flywheel is removed and reinstalled, the timing will change a degree or two just due to the slop in the fitting of the flywheel key. For practical purposes, just set the stator plate midway of the slot and forget about it.
 

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Discussion Starter #13
I updated the first post but it’s a 97 scrambler 400, the keyway on the crank and the woodruff key is a little beat up, not bad but I am wondering if the woodruff key is letting the fly wheel spin just a degree or so causing it to do this, I wouldnt think it was beat up that bad, keyway isn’t wallowed out, time to pull it all back apart again and put some more thinking time into it





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Time to clear up a mis-conception about flywheel keys; they are not there to hold the flywheel in position - they are there to line up the flywheel to assure proper timing without having to reset the timing every time the engine is worked on. The flywheel is "locked" into position by tightening. If the flywheel is properly tightened, the key will never shear or get "beat up". If the flywheel is not properly tightened, the flywheel will eventually shear the key just from starting and stopping the engine. Anytime the key shears it is an indication that the flywheel was not tight, unless the engine is swamped and hydro-locks. In the case of hydro-locking, the piston comes up on liquid and stops instantly. The inertia of the flywheel can either shear the key, break the crankshaft, bend a rod or something else will succumb to the force of the flywheel's inertia.



With that out of the way, let's look at this: "it will just crank and crank and then slowly start to catch and then it will run perfect" - you have just described a classic indication of the engine being flooded. You are not turning the fuel off when done riding, the carb overflows and fills the crankcase.



Now, the timing can't be adjusted far enough to cause starting issues like you describe whether fully advanced or fully retarded. Fully retarded would make starting easier at the cost of high end performance. Fully advanced might cause spark knock when using low grade fuel. Properly set, the starting is easy and spark knock is prevented. I have run both fully advanced and fully retarded with no noticeable change in performance. If you are a stickler for "on the spot timing"; get a degree wheel, a pointer rigidly fixed to the engine and a timing light. Start the engine check the timing, shut the engine off, adjust the stator plate, restart and recheck the timing, readjust the stator plate - repeat the procedure until correct then mark the stator plate for future reference, but each time the flywheel is removed and reinstalled, the timing will change a degree or two just due to the slop in the fitting of the flywheel key. For practical purposes, just set the stator plate midway of the slot and forget about it.


Thank you so much latebird, was recently thinking that the timing isn’t the issue because i have had that plate all over the place and hasn’t change much, the reason why I was curious about the keyway because the previous owner must of run the flywheel not tightened properly, I never sheared a key or anything just the keyway on the crank is a tiny bit beat up so I thought maybe it was allowing it to be out of time, then I started remembering working on lawn mower motors and remembered that the taper and proper tightening is what holds the fly wheel, so I had it all apart again and went to tighten it down to the right specs and it looks like the nut was beat up because it took the threads out of the nut, would you happen to know the thread size and pitch, I knows a long shot lol. Thank you for the very detailed response it helped allot


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Sorry, don't have that info - the Polaris part number is 3083905 - about $6.50

If no one else on here responds with the thread size and pitch, I will order one and measure it for future reference.
 

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Discussion Starter #15
Sorry, don't have that info - the Polaris part number is 3083905 - about $6.50



If no one else on here responds with the thread size and pitch, I will order one and measure it for future reference.


Sorry to keep bugging you lol, I can’t seem to fine the adjustment range for the choke, want to make sure it’s not being held open


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There is no specific adjustment that I use on the enrichener cable other than making sure it closes completely. With the engine running and fully warm, pull on the cable until the engine changes sound - adjust the desired slack out of the cable - I like to leave 1/8 to 1/4 inch of slack. If you find you have to pull the choke cable a little extra to get started when below freezing, adjust a little more slack out of the cable.
 

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Discussion Starter #17
As an update I had a bad cdi, it would give a hard time starting and then ignite all the gas in the exhaust causing it to grenade and pop the pipe off and after a while I completely lost spark, so I bought a new cdi and all of my ignition issues went away


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