Tuesday, October 30, 2012

XS750 Restoration, part 7 -- Some Progress!

I've been getting just a bit frustrated working in the garage lately. Parts were breaking, and I was watching the cost of replacements ratchet up while the funds I have to spend fixing up the bike have been dwindling. However, in the couple of days that I've been working in the garage since my last update, I've made some real progress.

First, I got started cleaning and rebuilding the carburetors. For the most part, the carb work was pretty straightforward. The K&L carb rebuild kit that I bought was very complete, and the parts in the kit appear to be very good quality. I was a little perplexed by this, however:
Where, exactly, does the little o-ring go? I looked at the parts diagram at Power Sports Plus, but the only o-ring they show is on the "main nozzle" -- which is about two or three times larger than the o-ring. In the photo above, I've shown the o-ring next to the needle and needle seat to give an idea of the size. In fact, the o-ring is exactly the same size as the needle, making me think it probably should go on the needle somewhere, but 1) there was no o-ring on the needle when I disassembled the carb (and I've cleaned two of the three carbs on the bike as I type this), and 2) the parts diagram doesn't show an o-ring on the needle, so I'm puzzled why K&L would include this in the kit, since I can't find it anywhere. <shrug>

Edit: With the help of the great people over at Yamaha Triples, I finally identified the o-ring. As I believe Sherlock Holmes once commented to Watson, "Once you have eliminated the impossible, then whatever remains, no matter how improbable, must be the answer." There is only one o-ring on the parts diagram. Therefore, there is only one possible o-ring that the tiny little donut in the K&L kit could possibly replace, even though it seems too small. I tried it, and sure enough, the o-ring will stretch to fit over the main nozzle.

I ran into one additional snag, as well: despite claiming to be a fit for XS750's, the Emgo pod filters that I wanted to use have a lip inside the rubber gasket that partially blocks some of the small ports in the intake side of the carb, at least on Mikuni Mk. I carbs that I have on my bike. I tried to cut away some of the lip to open up the airflow to the ports, but I didn't realize that under that lip is a recess that hold the gasket onto the air filter. When I cut away that lip, I cut into that recess, weakening the gasket, and possibly allowing unfiltered air into the carb. I'm still trying to decide if I can engineer a coupler to allow the Emgo filters to fit on my carbs without restricting the air flow to the ports, or if I should just suck it up and spend the extra money on the K&N filters.

Edit: K&N filters are on the way :)

Edit 2: K&N filters have arrived, and are installed. Yes, they are triple the cost of the Emgo filters, but the K&N's don't have a restriction inside the filter that blocks air flow to some of the ports inside the carburetor inlet. If you are reading this while researching pod filters for an XSx50, my advice is to just pony up the extra cash and buy the K&N filters. They're worth it.

However, I did make some progress in the garage tonight. First, the FZR750 front brake perch and master cylinder that I ordered on E-Bay finally arrived today. I fit it on the handlebars, and it not only fits great, but looks good, too. I had to clip the brake switch wires to fit, since the clubman handlebars are much (MUCH!) lower than stock, but that was easy.

Next, I was finally able to get the piston out of the front, left brake caliper. I've been soaking the brake parts in Liquid Wrench, trying to get the old brake fluid and oxidation to break loose, but while I was able to get the piston about an inch out of the calipers, I just couldn't get it all the way out, no matter how hard I tried. Finally, last night, I had an idea. On my wife's bike, I attached a hose from my air compressor to the bleeder valve, and the compressed air blew the piston free. However, I broke my bleeder valves off in the caliper (yes, on both the LH and RH brakes, grrr...)

However, I managed to match up the diameter and pitch of one of the banjo bolts at Lowe's -- it's a metric 8mm x 1.25 bolt -- and bought a couple of new, plain bolts in the same diameter and pitch. Then, holding the head of one of the bolts in a monster Crescent wrench that I own (seriously, it's got to be like 18 inches long!), I drilled a hole lengthwise through the bolt. Then, I used a drill bit that was just slightly smaller than the nozzle on my air compressor to radius the hole in the head of the bolt, screwed the bolt into the caliper, and pressed the nozzle into the bolt. It took a couple of tries, but finally, there was a sound like a gunshot in the garage as the piston broke free of the caliper. Woohoo!

While the inside of the piston looks pretty gnarly, the inside of the caliper is surprisingly clean, as is the outside of the piston. If I can find new pistons that aren't terribly expensive, I'll probably replace them, but if not, I think I can clean these up enough to reuse.

That only leaves the busted bleeder valve in the calipers, and I think I know how to repair them. The passage from the brake cylinder to the bleeder valve is completely blocked (at least on the LH caliper; I haven't checked the RH caliper yet) with dried brake fluid and/or rust. I am currently trying to drill it out with a small drill bit. I have also spent a little time trying to drill out the remains of the bleeder valve. Once that's done, I'll pick up a slightly oversized (9-10mm) thread cutter, and install a plain bolt where the bleeder valve used to be. SV Racing sells banjo bleeders -- banjo bolts with brake bleeders built into them -- for under $20 each. Rather than use a separate bleeder and banjo bolt, I'll just use the banjo bleeders to bleed the front brake lines, and block off the opening where the bleeder valves used to go.

Gotta say...after several days of breaking parts and finding out that components I've spec'd for the bike won't work out of the box, it was nice to make some progress tonight :)


  1. Hi Mike. I tried to contact you on G+ but wasn't sure if you check that a lot. I'm working on the motorcycle as you are..an XS750 and it looks like I have the Mikuni Mark 1 as well. I just wanted to ask if the jets supplied in the K&L kit that you linked to worked out? I'm thinking of buying the kit but wanted to double check before I do..


  2. Hmmm...I didn't see a comment on G+, but I don't check it *every* day. Anyway, I have yet to run the bike -- it's still significantly disassembled -- so if you are asking if the jetting was right with the pod filters, I couldn't tell you. However, if you are asking about whether the kit contained the right parts for a stock configuration, yes, it looks like it. I'll try to remember to post back here once I've got the bike running, but it might be a while, so you might have your XS750 running before I have mine put back together ;)

    In any case, good luck on your project!

    1. I'm sure there's no way you check this anymore, but I'm rebuilding those Mark I's right now and from two of the three, a tiny spring and ball fell out. I don't have any idea where from, I checked for that sort of thing carefully and then they fell out while I was disassembling them anyway. Any advice or help would be amazing. The third one didn't seem to have this check ball and spring. At least, I assume that's what they are.

    2. Hey, sorry to take so long to reply! It's been about two years since I last opened up the carbs, but I don't remember seeing a check ball or spring in mine. About the best recommendation I can make -- assuming you haven't sorted it out already -- is to ask on the Yamaha Triples forum (yamaha-triples.org) or Facebook group. If you can't get a good answer there, you can search for a parts diagram for the carbs on-line (I've got a couple of links to on-line diagrams in one of my posts). Best of luck with your project!