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  #51  
Old 26-09-2018
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Quote:
Originally Posted by dwb79 View Post
We fitted these perches to some DLC/Kashima CC forks on a KTM 350Excf.

When we first fitted the JBI Pro Perches, my tester said he could feel them hit the oil which caused a spike in damping half way through the travel.

We lightened the fork valving a little, but this made it worse because the forks used more stroke and the perches hit the oil more frequently.

So we went firmer on the fork. This reduced comfort a little overall, but kept the perches out of the oil more often and therefore reduced the frequency of the spike in damping.

We then removed the Pro Perches and fitted a single sided Huck Valve. My tester has not asked to try the Pro Perches again since.

I did speak with JB about his perches and explained the problems we were facing. He suggested a lighter shim stack on the perch, but we never got around to trying it.
Awesome, thanks for the update!!!!
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  #52  
Old 5 Days Ago
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Further update;

My JBI perches were in the mail when I asked DWB about them, so I was already committed.

I got them installed and had my first ride last weekend. I was mindful of the damping spike DWB described so I set the oil level at 280 and 300mls so that they wouldn’t both hit the oil at exactly the same fork position. This was not at the recommendation of JBI.... I just made a decision to do so after reading about other riders only running one JBI perch etc for different applications.

Short story is I did appear to use all of the travel of the fork but did not feel it. They forks are still smooth all the way through the stroke, no harshness detected anywhere. Another rider with Ohlins RXT forks had a go and made a similar comment. I rode the RXT’s and thought they were good which built confidence but then had random spiking which wasn’t so great.

Anyhow, more to come but right now I am the happiest I have ever been with any fork and running out of things to complain about.
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  #53  
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Thats a good result.....and lucky that it was, because the WP CC Huck Valve is NLA.
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  #54  
Old 3 Days Ago
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Quote:
Originally Posted by dwb79 View Post
Thats a good result.....and lucky that it was, because the WP CC Huck Valve is NLA.
OK, I didn't know that....that was my backup plan if the JBI perches weren't so hot!

The JBI's were attractive since they are easy to install/remove, and relatively affordable at US$250.

I will get some more time on them this weekend. It would be nice to flick back and forth on same day/same trails but not sure I will have time to do that soon.

I have read about other riders going as low as 250mls. I don't really know at what stage the JBI perches come into play relative to fork travel and oil level. Jeremy Wilkey indicates they might be working in the lower 2/3 of travel, and specifically states that they are not an anti-bottoming tool here https://mx-tech.com/blog/some-conten...-thumper-talk/

JB reckons they are a good anti-bottoming tool on his website. https://www.ridejbi.com/jbi-pro-perch/

Best way to find out was to get some and ride.

I wasn't looking for a fork that could do supercross.....I was looking for a bit more control because the fork was running through the travel faster than I liked at speed. I seem to have achieved that without making the fork firmer at the top of the travel....it seems like a win so far but will do more riding......

I was also thinking about how these perches might make the fork stiffer in hard pack braking bumps for example. Running the oil through a perch with a narrower orifice on compression raises the question about how it gets back below so that the oil is available for use at next compression. The nylon spacer is narrower than the groove it sits in. It slips on the perch on rebound and exposes return holes, which look small to me. When the fork is chattering back and forth quickly, does the oil have time to get to where it needs to be to add significant comp damping? I doubt it if just relying on gravity, but it would also be subject to the air spring which I assume is always going to be at the top and would be forcing the oil back through the perch under some pressure during rebound (certainly when deep in the stroke).

On the other hand it is probably more likely to drain back to the bottom of the fork completely after taking off for a jump when the forks get to fully extend and stay there for a moment, which should be a good thing as this is the kind of condition where you want the perch to be more effective on landing. Question is, do you want the oil returning to the bottom of the fork quickly or not?

I don't have any answers, but I would be interested to try and measure this out of interest.
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