Vintage Dirt Bike Q & A

My bike didn't come with a spark arrester, how will this effect the performance of the powerband?
I seem to have slow low to midrange throtle responce.

Is thier a basic way to rewire this bike? all I need is a kill switch no lights.

thanks

So you have the stock exhaust pipe, but it's missing the removable tailpiece section? On my bike, all I noticed was a bit more noise when I tried this - the powerband was affected very little. I'm not sure if I have a spare one of these, but if not, the pipes come up on eBay all the time.

The tailpiece section is the second half of the spark arrestor; the first part is ahead of the large tube that the tailpiece fits into. If you look forward into the front of the tube, you'll see 6 or 8 openings arranged around the outside diameter, like a turbine engine exhaust - these are the spark arrestor outlets. If these are clogged (all of mine were either partially or totally stuffed with crap), you'll obviously have a huge drop in performance and throttle response. I cleaned mine out with heavy-duty sharp-edged pipe cleaners I got at a tobacco shop, and I also drilled out the center cone of the spark arrestor (in the center of the 'turbine') 1/2". This added midrange and top end, and increased the noise slightly with the tailpiece in place, without the tailpiece probably even more - but the actual muffler section is inside the pipe body so it won't make a gigantic difference. One of my pipes was really bad, so I pulled it off, soaked it in gas overnight, burned out the spark arrestor with a torch from the rear of the pipe, then finished up with the pipe cleaners - worked great.

I found the stock 52 pilot (slow) jet too big - I use a 48 pilot now, along with a 118 main jet. It would also be worthwhile to check the compression and ignition timing.

The yellow wire from the alternator (motor) is for the lighting - just leave it disconnected after taping it off. The black/yellow alternator wire can be connected to the black/white wire to the ignition coil, with another black/white wire running from there to the stock kill switch (the green kill switch wire goes to frame ground).

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric