14mm bore Mc

Recently changed my big old master cylinder because of snagging on the clocks, the Mc I fitted only has a 14mm bore and I'm sure the original was a 16mm or 5/8th could this be causing the brakes to feel spongy? I have tryed every way I can to bleed the front brake but can not get a good feel to it nor is there any air coming out.

If its twin disc set up you need a 5/8th (16mm) mc to get good feel. If it is a twin disc I assume it has a splitter on the lower yolk. If its the old kz v shaped one air can get trapped in the front of the v when its on the center stand. Easiest way to resolve is to un bolt the splitter from the bottom yolk and let it hang so the splitter feed is the highest point. Then reverse bleed by feeding fluid in from the bottom pushing all the air back out the mc.

Yes it's a dual disk setup, I have tryed the stacking method while reverse bleeding that did get a little air out but I guess the difference in lever feel is the difference between a 14mm and a 15. 8mm bore size

New SS braided brake lines?

Just curious. Did you get a new aftermarket master cylinder or a used one? There ought to be dozens of choices for a dual disk. I got a very good condition Fr brake master cylinder from a late model Honda CBR500 for pretty cheap on EB (12.5mm single disk)

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