81 seca brakes/ fuel shutoff

I received the the master cycl. kit (xj forever vendor) with piston and seals etc. . Is there any step by step instructions/ videos for the install. Kit was costly and would like to get the rebuild done right. Also and most importantly what is the overall length of the XJ 750 Seca 1981 (frame mount) front master cylinder piston?. The original piston is gone.

Lastly, When I shut off the fuel petcock to primary or 3 o'clock position it still drains. I have to dial the valve to the on position to stop the gas flow. Checked the gaskets/ valves they are good and set right.

Thanks

 

if the 750 is the same petcock as most of the other xj's, then Prime is permanently ON
the "ON" position is switched on by the engine running and causing a vacuum to the diaphragm petcock

 

Very cool that explains the Fumes in the shop after the last ride. It was high octane. Appreciate the reply. Have any idea on the master. cyl. piston size for the 81 xj . ?.

 

You will have to find or buy another MC to get that piston. That or ask someone on here if they have one for you. One of those live and learn things.

Fuel petcock I would change out to a "on-off-res" type only without the vacuum line going to it. On all my carb bikes, when I am done riding them I physically turn the fuel off. I just don't trust the vacuum style. That and if the carbs are "wet set" they should not leak back fuel if the vacuum portion fails.

 

For Front brake Master cylinder Rebuild. I think I used a generic video on Yamaha MC rebuilding.
Get a vacuum bleeder if you have a compressor. The kind that hooks up to the compressor and has what is a modified paint sprayer on the front. worth its weight in gold.
For rebuilding MC, there is a clip that you need a long snap ring pliers tool to get in there and pull open.
I got a cheap one but had to grind some of it to better fit in to grab the rings.
I also ground the outer edges to create a grabbing flair (hard to describe)
https://www.amazon.com/gp/product/B0886L4Y4B/

 

I am confused on the question as you stated the kit from XJ4ever had the piston, which I believe they sell an OEM kit

Anyways, the size is:

Length 25.5 mm
Diameter 17.5 mm or more commonly referred to as 11/16

 

If the length is 25. mm for the piston and the depth of the cylinder is 19.05 m.m.+- or 3/4". How would the Piston seal even work. See attached pictures. If the pictures aren't clear, I can send more. I do have the OEM kit.

 

That depth should be 62mm or about 2.4 inches. I can't see what you are bottoming on in the picture - perhaps the old piston is still in there??

And I believe that added note for item one in the parts diagram is the dust boot for the plunger

 

Over the course of the last ten years I've found that the el cheapo master cylinders on eBay are less expensive than a master cylinder rebuild kit. If you're looking to do a concours restoration then the rebuild kit makes sense, if it's a typical "rider" then save yourself a lot of hassle and just replace it.

 

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I have a picture of the stamp on the side that has 11/16" for depth of the pist. cylinder. The old piston is out with the snap ring.Also, I measured the overall depth with the 1/4" fluid passage, and it was 1.25" (31mm). To the snap ring notch is .75". Also, the piston and snap has been removed.

 

11/16" (17.5mm) is the bore of the piston / cylinder, not the length/depth............