my new (ol' but low cost) ride

[WebPilot]

Backing up … a few words concerning the removal of my front caliper's piston.

The trick is to heat up the caliper and 'press out' the piston by blowing compressed air through the banjo bolt fitting for the brake hose. The loosely fitting clamp acts to prevent the piston from becoming 'air borne' when it finally emerges from the caliper.

I used a hot air gun instead of a torch because I didn't want to repaint the caliper just yet.

I tried to use a little portable air compressor that I use for miscellaneous stuff and blowing up tires. It didn't work, but then I didn't use it with a tank. I did use my 2½ HP 220v air compressor with tank and it did push the piston out; but not completely. The piston 'hung' about 7/8 ths of the way out.

I cleaned its outside surface, put some brake fluid on it and pushed it back in with the clamp. I tried it again with the same results. I figured I could seriously heat it up and try again, but I thought "why do it?". I'd have to lose my pads and rotor for the piston to come out that far so I decided to reuse it as is.

PS
I've just determined my garage DVD/MP3/CD player, plays data cd's that are filled with mp3's. I like to hear 'blues rock' so I just filled 1 cd with Ten Years After's first seven albums!

I find this all simply amazing.

[WebPilot]

I put the caliper back together, installed new brake pads, and mounted it back on the front end. I cleaned both ends of the brake hose's banjo fittings and connected everything back together.

Now comes time for the bleeding.

[WebPilot]

Brake hose ends were made tight to MC and caliper.

I filled the reservoir and started working the lever. The MC is bone dry and I kept seeing bubbles in the reservoir. Undaunted I kept at it and refilled the reservoir at least three more times. There was NO improvent in lever resistance.

I cracked the hose fitting at the caliper and found NO brake fluid had made it here, yet. I removed the banjo bolt and the bleeder valve and filled the caliper with fluid - it doesn't take much since the piston is backed up into the caliper.

I refitted the banjo bolt and bleeder loosely. Several minutes later (when I wasn't looking, of course), brake fluid came trickling down through the hose and out of the lower hose connection. I tightened it up, replenished the reservoir, tightened the bleeder and commenced serious bleeding.

I would squeeze the lever 3 times, hold it at a point before the lever would strike the grip, open the bleeder and the close it. At times I would see a mix of air and fluid coming through the tube I had affixed to the bleeder valve. I kept doing this as more and more resistance was felt at the lever. I quit when I could discern no difference.

This all took about an hour. I now have a front brake!

[WebPilot]

I got the front brake working by last Friday. I took the bike out Saturday for a spin and it would not run right; it was breaking up badly, as if there was a gas problem. I could get it going but about 45 mph max. It seemed to me at mid throttle it was running on only one cylinder; back the throttle off, and the other cylinder came back to life.

It was either carbs or electronic ignition. I'd have to buy parts if it was ignition.

Having nursed the bike back home, I killed the engine and pulled the air filters. I noticed my vacuum petcock was malfunctioning and allowing gas to go to my carbs. The float was stuck on the right carb and I saw a trickle of gas in the venturi around the jet and needle.

So I pulled the carbs for the third time; this time armed with better information that I found on the I'net.

[tufty]

Not sure if it has rubber pipes between the carbs and engine casing, but these are a source of frequent frustration on the XTs - the slightest (and usualy pretty much invisible) crack, and it won't run right, usually with bogging at higher revs. Might be some help.

Also, it's worth regasketting and generally overhauling the entire carb, in my experience.

[WebPilot]

Thanks Simon.

The 1st time I took them apart was to thoroughly inspect, remove jets and clean them and passages. I have a manual, but it wasn't very helpful here. I reassembled and tried them out only to realize I had the floats set too high - thus, the 2nd removal.

I should replace gaskets but more importantly the slide diaphragms. They were running $100 a piece. Mine pass the test, but I still need to find a pair for < $50.

I am now following an overhaul manual-ette from a user's group and found this anomaly with the pilot circuit mixture screw - THE TIP HAS ENTERED THE VENTURI! The one in the other carb is still back up in its hole.

[Viv]

Hi Forrest

Just a small point but those screws had a habit of falling out occasionally so it may have been replaced with a screw of the wrong taper, maybe worth comparing it to the other carbs screw to double check.

It wont be the first time on a rebuild of an old bike I found the carbs were not identical ;-(

Viv

[WebPilot]

These pilot mixture screw settings are set at the factory and then covered by a brass plug so they cannot be adjusted unless the plugs are removed.



I see no evidence that anyone has tampered with the mixture screw on either of the carburetors. It should be noted that these are the correct carburetors for this particular model year.

[tufty]

the caps can be drilled out so you can get to the mixture screws, I have a carb overhaul manual somewhere (for the XTs, but the majority should be relevant for your XS) which explains what you need to do; I'll try and get a copy to you sometime during the day today.

[tufty]

Here's a mikuni carb tuning manual from around that era, might be of some help. I'll try and dig out the Yamaha-specific stuff later.

Mikuni-carb-tuning-manual.pdf

(1.2 MiB) Downloaded 234 times

[WebPilot]

Yes, they can and thanks for the manual - I think I have that carb on another bike.

I drilled through the 'pilot' hole with a drill whose diameter matched the root diameter of a sheet metal screw I have. I inserted the screw, began to twist it into the hole with a wrench and before long the brass cap began to rotate free in its hole. It was then just a matter of pulling while twisting to get the plug out.



I did the same to the other carb.

The one mixture screw was the correct 3 full turns from being fully seated; the other had been 'run fully down' and left there!

It must have been a 'bad hair day' at the factory that day. I don't know how the previous owner put 20 thousand miles on the bike with this pair of carburetors.

[WebPilot]

It's been raining 'round here quite a bit as of late.



Prior to this, I just took off the tank (which was a trick since my vacuum petcock is malfunctioning and fuel will NOT turn off regardless of lever position) and removed the carburetors. It started to rain so I had to push her back into the garage.

[WebPilot]

Watching this great flic again tonight ...

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[WebPilot]

$5.00 US buys you a gas shut-off valve from your local lawn mower repair shop.