Posts
21
Joined
2/27/2020
Location
AU
Edited Date/Time
10/27/2024 4:10am
Hi,
I have a 1980 yz125G that im doing some work on. I have cleaned up the ports and have a Vforce 4 reed block in it. I will have to replace the con rod and mains so will have to split it. I will update squish to btw.
I saw a while back reference to added boost ports and crankcase stuffing for this model, does anyone have any pics and specs ando other info on how it worked with other mods on this to give me an idea on whats possible.
Any help would be much appreciated
Regards
Hi, I TIG welded added material on sides of a stock/unported/unpolished cylinder. Without the extra material you are very limited on how big a hole your can make. With the extra material, I then made largest ovals into the transfer. The nuts where switched to a shouldered so I could get a wrench on it. I worked with the V force tech probably 12 yrs back with different reed cages to find what would fit. I remeber sending ones back/forth till we found a husky one that fit with min mods.Was the Husky 125 model when owned by BMW. The Blaster one was close but not close enough for me. The next 'trick' I done was make my own head gasket, .020 copper which is 1/2 stock. This with the DG head has my cranking compression up there, 180sh I think,been a few years. 110 race fuel. Carb is 36 PWK Keihin from late 80s early or 90 KX125. Pipe stock. Silencer DG from another year made to fit. Intake boot 1981 boiled in water and stretched on PWK. This combination I refined over a couple seasons for max mid range/broad power. Lots of wins and holeshots with it. The 1980 YZ needs a good ignition, and nos stock stator coils are best but hard to get.Often misadvertised on ebay adds. Also important and often oerlooked for power in this is getting a actual dial indicator and tool to set the timing. I found more mid power tuning advance,not just lining up marks. After all the tuning I did on mine, I got to ride another stock 1980 YZ125 at track and he rode mine. NO COMPARISON. Mine I pulled 2nd gear starts and it exited corners with ease as a 125.
The airbox lid I made as well to breathe better and will never fall off like the stocker did. Best to saftey wire stocker on cause it will fall off sooner or later. Sellers think they are gold $$$ when your needing one for next race. Thats why mine has 3 bolts holding it on....If it still fell off on track,they new whos it was...my wife asked why I didn't also weld my phone number in it too,? I've given you a whole combo not just pictures of tiny holes,,,but it works!
Thats great info thanks for that, it has me thinking where to go next.
If you could comment of the below it will help me work refine my direction, a lot is governed by what is allowed these days.
What sprockets did you run on that, i was looking at 12 and 13 with a 50 but you may have it worked out already ?
I am guessing going slow with the tig to avoid warpage on the cylinder is a must, i will get a pro welder as opposed to my own efforts there. The Vforce 4 of my 02 cr125 fits neatly, its about same length as, same stud pattern and all but i do notice that vforce reeds stops fit right up close to the ports wouldnt effect the ports you added but the port just on top middle might be restricted a bit.
I cant really see any pipes that are accessiible out here in Aus, i am looking at making one up after remove the dents from the original and run that initially
On the head gasket, i have a squish level in mind and will get onto a dial guage, was there a timing that worked best for yours ?
I see pwk35 was the carb on the kx's, the vintage guys are pretty hard on later model parts though which is a pity. Maybe a mikuni bored out would still be ok with them.
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12/50 gear. 2nd gear starts. NOS clutch basket ,,need smooth release. Welding I wasn't worried about warpage because of the fins sucking heat out and the shape of head.. Vforce I think I removed their embossment,LOL.I did the bike in 2009.
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