Added reply in a thread YZ125 ignition mapping? 6/8/2017 5:41 AM

HPI looks good! Because the original Hitachi Ignition is Analog, nobody makes a programmable CDI box that will work with my Rotor / Stator. I'm going to research if I can fit a 2000 YZ125 Rotor / Stator to my bike and use an HPI programmable ignition ... more »

Added reply in a thread YZ125 ignition mapping? 6/7/2017 6:59 AM

Welp... I looked at the timing last night. It was retarded by about .010", so I timed it to slightly more advanced than factory spec. (Factory calls for .043" BTDC and I set my bike to .045" BTDC). I will report back on any noticeable change in feel.

... more »
Started new thread YZ125 ignition mapping? 6/6/2017 9:20 AM

Hello All, I've finished my motor build YZ125 1979 Race Build and the bike has a boatload of top end, but is still lacking in mid range. I haven't played with setting the ignition timing, but I've got a hunch that the motor will respond well to advancing the ignition ... more »

This forum thread has 6 replies

Added reply in a thread YZ125 1979 Race build 5/17/2017 11:24 AM

I never measured the cranked compression. I assume it would be about 160psi. The math says it should be 183, but that's bogus. My UCCR is actually 13.5:1. After milling the bottom lands, I flipped the head over and milled the Spark plug hole and stud

... more »
Added reply in a thread YZ125 1979 Race build 5/17/2017 10:39 AM

Gotta start somewhere... It's a casting after all! ... more »
Added reply in a thread YZ125 1979 Race build 5/17/2017 10:34 AM

Thanks for the compliments! I'm only into it for about $150. Comparing the astronomical prices of DG, FMF and Webco heads, this was a no-brainer!

See the two flats I milled on the under side of the fins? That's how I got a surface to reference. ... more »
Added reply in a thread YZ125 1979 Race build 5/17/2017 7:37 AM

I'm going to try to upload the pics in order for ya. It was a pretty easy mod.

Before Top Before Chamber After welding. Stud holes drilled and plug hole tapped Machined Chamber (see porosity) Top Machined ... more »
Added reply in a thread YZ125 1979 Race build 5/15/2017 7:27 AM

Couple crappy Pics, sorry.. Got the Cylinder all set, 34mm Mikuni, 6-petal YZ400D reed cage and a modified '74 Penton ISDT125 radial head, and added the RF boost bottle. Gained a bit in the mid, but top end just shreds. Never had a 125 wheelie up a sand

... more »
Added reply in a thread Any experience with plastics? 12/20/2016 9:36 AM

5 gal buckets are made of HDPE. That's what you want. McMaster Carr will have HDPE in different sheet thicknesses. You can heat and form it easily, but you can't bond it. I wouldn't use PVC as it's more brittle and scars more easily as well. However,

... more »
Added reply in a thread Old school mini Mx bikes...50cc-100cc 8/29/2016 11:42 AM

Here are a couple of my mini's. Fun stuff. I seem to crash harder and more often on a 50 than a 250... SMH. QA 50 set up for mini Sumo.

82 YZ60 with a bunch of 80 parts. The only one I "restored" and now can't ride ... more »
Added reply in a thread Something cool happened to me today! 6/7/2016 9:03 AM

Great story!!! IMHO, keep it stock and get it up into that house! Here's mine. That front Number Plate is going to be a tough one to locate.... Good luck!

Added reply in a thread YZ125 1979 Race build 5/11/2016 8:22 AM

I had a little more time to play in the shop. Turned a spigot for the carb boot and installed that. Also noticed that the boost bottle spigot at 90* doesn't really want to fit on the bike, so I cut and laser welded it back on at an angle. I wasn't going

... more »
Added reply in a thread YZ125 1979 Race build 4/4/2016 7:24 AM

LOL!!! Yes, rumor is that even though All-Balls makes great seals, they have a lot more drag than the RateTech seals. Either way, just replace the seal and be done.

Added reply in a thread YZ125 1979 Race build 4/3/2016 7:56 AM

That sounds familiar. It's been a while, but I think I might have had to leave one retaining ring out as well.

Added reply in a thread YZ125 1979 Race build 3/31/2016 12:00 PM

Well, I like playing with ports and engine building, so my time may be different than yours, in terms of "worth it". But yeah, I did the same on a YZ80 cylinder and it made a difference even with small Boyesen ports. The size of the port is limited by ... more »

Added reply in a thread YZ125 1979 Race build 3/31/2016 6:38 AM

New top end has been on the back burner for a while now. I ditched the modified YZ250 re-cast head idea. Might play around with this Sachs / Penton head if it runs hot. All I've done so-far is to have the cylinder welded so I could create boyesen ports,

... more »
Added reply in a thread 89 YZ490 Rebuild 3/30/2016 11:09 AM

I just sold my '87 after a few years of non serious racing and riding. I'm faster on my 125, but I'm starting to miss that beast. FWIW: I ran 92 pump gas and Spectro at 40:1. Never pinged after performing the "Yahoo YZ490 Group" carb mods.

Added reply in a thread YZ125 1979 Race build 3/30/2016 11:05 AM

That drain goes into a waste oil bucket, right? wink wink. I've seen worse oil, but that's pretty ugly. Are you revalving the shock?

Added reply in a thread YZ125 1979 Race build 3/29/2016 1:59 PM

175 - 200 psi should be good. As was mentioned, make sure the separator piston has about 2" of space above it for the nitrogen to compress. If you purge all the air out of it / fill it up completely, it won't move.

Added reply in a thread 1980 Yamaha YZ175... 9/15/2015 6:20 AM

Max, I've thought of that too, but I get a little nervous putting so much heat into a precisely machined cylinder like a fork lower. With my luck it would end up binding at the end of the stroke or something! Both components changed in about 81 or 82. ... more »