Has anyone had to change their CDI box before? My Scrambler all of a sudden won't start anymore. I have good compression, spark and gas to the plug. It will backfire when trying to start it occasionally, and when you try to give it gas when starting it will act like it boggs out even worse but never starts. I have blown out the gas tank hoses and petcock. I have checked the coil to make sure that it is ok and I have even tried multiple new spark plugs to no avail. I am thinking that it is the CDI box only because when I check it with a volt meter I get numbers that aren't anywhere close to what the service manual says. My question is has anyone had this happen and is there a good aftermarket CDI to get?

2000 modded Scrambler 400.

 

Balzak

If you're getting spark then it isn't the CDI. The same thing happened to me last year. I thought it had compression, but what happened was that the piston had deposited aluminum on the cylinder walls and had jammed the rings open. You might have what's commonly known as a seizure. To check it, get a compression tester, insert it in the spark plug hole and give it a crank. If the compression is much below 100psi, you have to do a top end rebuild.

Hope this helps.

 

Mike

I only have 3 hours on this top end now, I just had it bored .020 over and put a new wiseco piston, rings and wrist pin in it. Could this still be happening? The only reason that I say CDI box is because I measure the output with a voltmeter and I am getting between -50 and -70 volts where it should be 20volts. The coil tests good but could the CDI be causing a weak spark? I don't have a compression tester but I did try to fire the bike with my finger over the spark plug hole and it blew my finger off of it so it seemed pretty strong to me.

 

I almost forgot, this was happening last year too before the rebuild. I would ride and it would act like it was running out of gas, sometimes it would fire right back up and at other times it wouldn't until it sat for a while. It might run for 10 minutes or it might run for 2 days I never knew what to expect. I had gone through the old carb at the time and I now have another one so I am certain that it isn't the carb, and I have done the other extensive checks. As the bike sits now it won't even run. But I belive that this all stems from the problems before. I have heard of people having "vapro lock" from the gas tank exhaust being plugged up but I blew all of that out with an air compressor last week and still nothing.

 

Balzak, if I were you I would get my hands on a compression tester and rule that out first. Your symptoms sound alot like what I experienced when my piston gave out. I had enough compression that with my finger over the plug hole I thought it was ok but with an actual compression test I found out otherwise. Like Mike stated make sure it's over 100. If it's a new top end I would hope that wasn't the case but there might have been a problem with the rebuild.
You may be right, it could be CDI related but before I invested much time in checking that out I'd rule out the piston.

 

Crawdad, thanks for the info, I have spent a lot of time on this one already and since I don't have a compression checker I am going to take it to the dealer tonight. While I am there I will have them check the compression with a gauge. Thanks for the help and I will be sure to give an update when/if they figure this one out for sure.

 

The best way to check a cdi is take it off and put a different one on.If your going to the dealers they should have one in to let you try if not maybe someone you ride with.
Hope this helps.
Matt
2000 500 Scrambler
Sadly for sale.

 

Balzak,

I had even less time on my Sport when it seized. It turned out that the bore was WAY oversized for the piston. Like .012 oversized! The normal piston skirt to cylinder clearance is .0023-.0037". It would shut off and then run again after some loud cursing, swearing, speaking in tongues and invokations then shut off again. Just like yours did, although probably without the swearing.

As for the CDI, did you hook the wires up correctly when you tested it? It sounds like you may have reversed the wires when you did the test.

 

Well I took the quad to the dealer last night (The Toy Store in Thornville OH). When I started talking to him about what I had done to check it out he immediately said that he was almost certain that it was in fact the CDI box. He said that he had one in there just last week that was doing the same thing and a new CDI fixed him right up. I tried to get him to test the compression while I was there but he said that there was no need. He seemed to feel pretty strongly about the CDI box. He will call me in the next few days or so and let me know for sure what the problem was.

Is that aluminum scoring a very big problem with these polaris machines?

It was kind of funny when the dealer came out to see the quad he said Gees you have a lot of money tied up in this thing don't you? And of course I had to tell him that apparently I didn't have enough in it yet.

 

Balzak, hope it does turn out to be the CDI. That would be an easy fix. Let us know what turns up.