Learning by doing, 79 Scrambler(ish) Build


XS400 Member
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Portland, Or
Hi, I recently bought a 1979 XS400, with the plan to turn it into somewhat of a scrambler build. My daily ride is a Honda 1975 CB550, so this project is mainly to get my hands dirty and learn a little about motorcycles along the way, with the hope that i'll end up with something fun to ride on the street and on light trails/gravel roads. I have basic knowledge of motorcycles, supplemented by youtube videos, a couple different manuals, and annoying my friendly neighborhood mechanic/

I bought the bike in barely running condition, vacuum petcock non functioning and bypassed with an on/off valve. Carburetors leaked gasoline backwards into the air filters, battery was overcharged and dry of electrolytes, old spark plugs, torn seat, straight through exhaust that can wake the dead, head gasket leak, the tires were new but completely deflated.

The previous owner bought it as their first bike, decided that owning an older bike is too much hassle and bought a brand new harley, their loss my gain i guess.

2016-08-17 16.13.50.jpg

First thing I did was clean and adjust the carburetors, replace the spark plugs, and the battery and it ran reasonably well. Compression testing showed pretty good compression, and so I decided to start planning out the build. First thing I wanted to do is get the engine rebuilt, fix up the gasket leak, replace the clutch, measure the pistons etc for wear and get a rough idea of the over all condition of the engine.

Currently the engine is sitting disassembled in my dining room. The Haynes Manual was a great help in walking me through it step by step.

2016-10-10 13.19.31.jpg

I have new clutch disks, and piston rings that will be going on, I've also got a new drain plug, and shift lever as those were both damaged.

I was thinking about replacing the clutch springs whilst I'm in there, and was wondering if anyone has any opinions on that or replacing anything else while I'm in the engine?

the next couple things on my list are replacing the fuel lines, and rebuilding the petcock, replacing the air filters.

I'll also probably overhaul the carburetors, and try to find a replacement exhaust, Mac 2-1 exhaust, seems to be the only pre-made full system I can find? Once the engine is back together I'll put a new chain on it. I was also thinking about changing the drive sprockets, but ill probably wait till i have a better feel for the bike in running condition.

Once its running I plan to replace the suspension, I was thinking about using progressive springs and replace the steering bearings etc. The Brake pads and rotors need replaced, and I'm also looking for some dual sport tires that will fit.

Other than that I'll keep it looking stock-ish, I will be getting some form of "dirt tracker" handlebars and probably raising the front fender (more for aesthetic than anything as I doubt it will see anything other than tarmac or light gravel). I have some vague ideas on replacing the tach/speedo with something smaller and at some point ill replace the seat with something minimal. LED lights might be a possibility in the future too.

I'll update this thread as the build progresses.

I hope I didn't ramble too long and welcome any input to the build.
Nice beginning you've got there! Are there many miles on it? Wondering why you want to do the clutch immediately. Was it slipping when you were riding? If so it may have been adjusted wrong. These bikes seem like they'd be pretty easy on clutches. Anyway good to see a new thread and hope to see more.
The clutch probably doesn't need replaced, the previous owner thought it needed replaced even though I had no issues with it. The bike has around 16k miles on it if I remember correctly. I'm mostly just doing it because I can.

As for sprockets I see a few people change the sizes for lower rpm at cruising speeds. Has anyone went In the opposite direction for a more aggressive ride, and would it even be worth it?
Well mine has stock gearing and it is a joy to ride. Enthusiastic from idle to redline. Carving up the canyon the only thing I desired was a quieter exhaust. Which I now have...sort of...These 1970's things move nicely. Yamaha did their homework so you may want to forestall any gearing changes until you have some empirical/experiential observations of your own.