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KTM 520 experiences

Joined
Feb 5, 2001
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#16
BTW the low rpm hesitation are well known to Yzf riders ...but they can happen to KTM 400/520 also (same carb..) clean the acceleration pump and have a look at the membrane ,replace if necessary...

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mechantloup
GRRRR!!!
KTM 520 EXC 01
Japanschrott?!Nein danke !!!
 
Joined
Feb 25, 2001
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#17
Merchantloup, thanks for your tips. Do you know anything about the P-38 Lightning carb mod by R&D Racing?

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01KTM520EXC
91Yam WR250 4sale
86XR350
74TM125
 
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Jun 18, 2000
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#18
I have the P-38 lightning on my '01 520sx. I took the "throw money at it first" scenario. It did make my bike run a little stronger but I still had the hesitation.

At 3000 feet Factory R&D recommended 1 step leaner on both the pilot and needle. I tried that but my bike still had the hesitation. The best thing I've done so far is play with the plunger rod on the accelerator pump. I'm guessing this has been the problem from the beginning. I just started with it this week so I still have some learning time left.

Does anybody know what the right amount of play shoud be with the adjuster fork?
 
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Aug 15, 2000
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#19
Originally posted by JohnnyMac:
Does anybody know what the right amount of play shoud be with the adjuster fork?
The standard Keihin setting (according to Sudco) is .6mm. This affects when the pump starts pumping, (at .6mm this will be just after the slide opens), while your R&D cover shortened the pump stroke. If you’re curious the guys at Factory R&D can tell you the stroke length you ended up with. Stock should be about 3mm on the slant FCR.

Some WR guys on Thumpertalk are going crazy with all kinds of accelerator pump modifications, including disconnecting the thing altogether. The R&D cover shortens it a fixed amount (differs for diff. models I’m told), but I’ve heard two really good ideas for adjusting the pump stroke on the slant FCR that are cheap and easy and allow different lengths (some guys are down to 1 mm and love the results):

1) Place shims under the pump diaphragm of different thickness, where the desired reduction in stroke is the shim thickness.

2) Drill and tap a hole in the bottom of the cover for a set screw. Turn in to shorten stroke, out to lengthen.

Another invaluable FCR tuning tip is the use of an air screw in place of the fixed pilot air jet. Sudco carries these parts (screw and spring) for about twelve bucks. It seems an improvement can be had by shortening the pump stroke, going richer on pilot and needle and larger on the pilot air jet, but with the optional air screw you don’t have to swap the jet each time you want to change it and it is more adjustable.

I think those guys have too much free time on their hands…

At any rate JohnnyMac I think a larger pilot and pilot air jet may be worth trying (but check your pump timing first).
 

PK

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Feb 27, 2000
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#20
I got hit by some roost by one a few days ago and I got the bruises to prove it. Lighter than my YZF400, more snot, better equipped stock, little more maintenance but very good reliability so far. Go for it...

Pat
 
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Feb 25, 2001
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#21
I haven't got my 520 yet (there is still 2 races in the SETRA Enduros). But I have an experiance to share from the current owner. He was racing, and saw some smoke coming from the engine area. He pulled in the clutch, and more fluid squirted from the hydraulic clutch line, and started a fire. Luckily, he was in Florida and had access to wet sand to put it out. Anyway he has switched to a Enduro Engineering stainless steel braided clutch line so it shouldent happen again. All 520/400 or other KTM owners be aware of this potentially bike melting problem!!


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01KTM520EXC
91Yam WR250 4sale
86XR350
74TM125
 
Joined
Apr 5, 2000
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#22
Just as an iteresting addition to the FCR discussion, the Carb on my YZ250F has an accelerator pump bleed jet that determines the volume of fuel injected. I forget what Yamaha's exact terminology is, but is is one of the five jetting circuits in this complex carb.