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Project Why-Zee Progress

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Project Why-Zee Progress was created by YZBill

Every project bike I’ve built or rebuilt gets a name and my 79 YZ400F is now called Why-Zee. Actual credit goes to my wife. When she saw it in the garage her first question was; “Why?” When I told her it was free, her second question was; “Why?” When I told her I was rebuilding it, yup, you guessed it; “Why?”

As ugly as it was, the motor was still within the service limits. Because I’m going to use this bike in AHRMA cross-country, and some vintage MX, I decided to use the 79 IT400F piston. Today I bolted the top end back on and it has spark. Last week I cleaned the carb. Now I need to source a pipe and silencer, intake boot since the original is cracked, new air filter and control cables. Once I get the motor running I’ll rebuild the forks using RT emulators and new springs, have the shock rebuilt and replace all the bearings and seals on the frame, swing arm and wheels. Final touches will be re-finish or replace the plastic, new seat cover and new grips.

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22 Jun 2020 23:11 #1

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Replied by YZBill on topic Project Why-Zee Progress

Progress on project Why-Zee has been rather slow. That happens when you’re working on four bikes at one time. Anyway, as I mentioned before, this bike is going to be raced which means it’s going to get dirty. The plastic on the bike was badly oxidized from sitting outside for years. The back fender was cracked, so I ordered a replacement from DC Plastics. I decided to restore the side panels and front fender. This is a tedious process that starts with cleaning using a solvent safe for plastics followed by washing with Simple Green then rinsing with water. Next comes scraping off the oxidized layer with a razor blade. Hold the blade perpendicular to the surface then move it back and forth. Do not apply pressure to the blade as you only want to remove the oxidation, not any plastic. After removing the oxidation, wet sand the surfaces with 400, 800 and 2000 grit sandpaper. Next, use a heat gun to bring a shine to the surface. You want to apply heat until you see the surface just start to turn into a liquid then move the heat away from that area. The final step is to apply a wax onto the plastic.

Oxidized right side panel.


Scrape with a razor blade to remove the oxidized layer.


After wet sanding and using the heat gun to melt the top surface.

There’s still some discoloration visible which I think is due to spooge from oil that on the back side of the panel which covered the pipe-silencer junction. This area will get covered with graphics. It’s not a showroom finish by any means, but will work for a bike that’s going to be raced.
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12 Jul 2020 08:15 #2

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Replied by YZBill on topic Project Why-Zee Progress

Not a lot to report here as most of my progress has been hampered by other projects. The oxidation on the plastics has been removed and a few pieces still need sanding and polishing the carb was cleaned and installed with a new intake boot and air filter after cleaning out the air box and air box to carb boot. New cables were ordered and I discovered the front backing plate is damaged. Luckily a friend has a spare. I took the silencer apart and cleaned out the carbon that has been inside for 25+ years. The main parts I need now are the expansion chamber and a chain.
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08 Aug 2020 18:19 #3

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Replied by YZBill on topic Project Why-Zee Progress

Almost ready to fire it up. Doesn’t look like I’ve done much since my last post, but I replaced both the cracked front rim and the broken front backing plate. Sourced a new DG replacement pipe and installed it, but I need to pickup some new pipe springs. The one good pipe spring that held the rusted, mangled and poorly repaired hunk of metal that sort of resembled an expansion chamber is too short. Also picked up a new 520 sealed chain that I need to cut to length.
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Last edit: 10 Sep 2020 21:20 by YZBill. Reason: Remove sideways photo
10 Sep 2020 21:16 #4

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Replied by YZBill on topic Project Why-Zee Progress

It’s ALIVE!
Project Why Zee runs!
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28 Sep 2020 13:20 #5

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Replied by YZBill on topic Project Why-Zee Progress

So far I’ve done three break-in runs. The first and second time I started the bike it wouldn’t start up cold on the choke and required quite a few kicks until it would light off. Yesterday the jets I ordered arrived. I installed them last night and today I fired it up. First kick with the choke on. A few small turns on the air screw and idle speed screw and it was idling like a big bore 2-stroke. A short run up and down the street and it feels like it’s running much cleaner. The next update will be after some track time.

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Last edit: 06 Oct 2020 20:14 by YZBill. Reason: Add pic
06 Oct 2020 20:13 #6

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Replied by YZBill on topic Project Why-Zee Progress

Ride report... FINALLY!
Yesterday my oldest son and I took out the YZ’s, his is a ‘79 250, for a much needed ride. It’s been 30-some odd years since my 400 has been ridden off-road and I was anxious to see how it performed. Because it’s hunting season and getting close to winter, we opted to avoid the forests and rode over in the desert at a place called Saddle Mountains not far from the Columbia River near the town of Mattawa. While lacking trees, roots and tight single-track, there’s no shortage of sand, rocks, hills and whoops on the fast terrain.

The Good: The 400 motor is superb. It makes power everywhere. You can lug it and it will still pull you around. Whack open the throttle or downshift and there’s plenty of power to increase the fun factor. Like any big bore, you have to be careful how much throttle you give it, but I prefer this to having fan the clutch all day to keep the motor on the pipe. The first real test came about 300 yards from the truck when the trail went down hill then back up another hill. I snickered the gearbox into 2nd and before reaching the bottom rolled on the throttle to WFO. As I’m climbing up the other side I realize the motor and wheel spin is telling me to shift up. I hit third gear, backed off the throttle and it still pulled me up the other side with ease. I could’ve never done that on a 250. There were a few rocky uphills where I found it easier to plonk up in second, but most of the open, sandy terrain was best in third. If traction is minimal, like in deep sand, it’s better to lug the motor in a higher as opposed to letting the tire spin. This 400 motor feels a lot like the motor in my GasGas EC300, so I’m looking forward to spending more time on this bike.

The Bad: I really can’t say anything bad about the motor. Yes, you need to be mindful of how far you twist your right wrist. Yes, if you give it too much throttle in a low gear the back tire will spin and come around on you. Yet the bike is still very easy to ride. Other than getting the motor running and fixing the front wheel and brake plate, I haven’t greased any of the suspension or steering bearings. While I’m sure they need it, along with some suspension work, it certainly didn’t any negative effect on my ride. The only real bad thing I can say is the stock seat cover sucks. If you’re sitting down under hard braking, you’re sliding forward. Same the sitting down under hard acceleration. Both the seat foam and cover need replacing anyway, so I’ll look into more of a gripper-style cover.

The Ugly: We rode a total of four loops. On the second loop I noticed an increase in the free play at the clutch lever. Thinking this was due to the adjuster at the lever, I pulled the cover back and saw it was still where I had set it. I ended up adjusting it out all the way, but I still has too much free play, for my taste. I do need to look into this before I take the bike out again.

Overall: I’m definitely happy with this bike. I wasn’t sure a big bore motocross bike would make a good post-vintage class hare scramble bike, but the motor makes very useable power everywhere. Now I just need to figure out what’s up with the clutch then go though the chassis and the suspension.
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Last edit: 09 Nov 2020 13:59 by YZBill.
09 Nov 2020 13:55 #7

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Replied by YZBill on topic Project Why-Zee Progress

Only a week since my last update. Haven’t even washed it since the ride last week. I did pull the primary cover and adjusted the clutch free play. Did some other minor adjustments. Next up, check/grease the swing arm and steering head bearings. Also need to pull the rear wheel and check the brakes and wheel bearings. Then it’s time to replace the seat cover and foam.
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16 Nov 2020 21:26 #8

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Replied by YZBill on topic Project Why-Zee Progress

Second ride in the books and I have to say that the more I ride it, the more I enjoy it. Although yesterday’s ride was cut short due to my youngest son’s TL125 losing spark, which I’m fixing in this pic, I still got some good seat time in. The ergonomics really fit my neutral riding position, standing on the pegs with my weight low and over the back. The adjustment I made to the clutch after my initial shakedown ride was perfect, but I really don’t need to use the clutch at all since this motor has such a wide powerband.

I let my friend and older son take a spin just to get their feedback. My friend races an ‘87 RM125, but trail rides a KTM XC350. Both of them came away impressed with how controllable the power is. It’s not explosive like you would tend to think of an open class motocrosser. You can lug it in third gear through mud and rocks without worry of stalling, then roll on the throttle and instantly be moving at a good clip.

Next on the agenda is to check out the rear brake. There seems to be a fine line in the adjustment between too much and not enough. Also noticed the rear wheel dragging when rolling it out of the truck last night. Need to make sure the friction material hasn’t delaminated from the shoe.

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28 Nov 2020 20:11 #9

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Replied by MarkT on topic Project Why-Zee Progress

Yes, check the shoes... always a good idea.

These old Yamaha's had touchy rear brakes... one trick we did was to put a foot on the center of the rear brake rod and stand on it... object of this is to bow the rod so it's curved instead of straight. Don't forget to readjust the brake.

Brake is a little more progressive with a good bow in the rod rather than an on-off switch.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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28 Nov 2020 21:16 #10

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