Legends carbs (was Re: Hello from Nova Scotia)

[Bob]

Those Legends racecars that race at Scotia Speedworld near Halifax have basically the same motors (actually new Yamaha XJR1300s from overseas) with the same carburetors so I've been swamped tuning those things up to get them ready for the upcoming race season.  If you ever need a hand with your carbs or valve adjustment, etc. give me a shout. 

Greg,
A local motorcycle mechanic that's also a Legends racers says that since they can't modify the carbs, used ones are a great swap for an FJ.  He says that the old carbs 'wear out' and that a nearly new (for an FJ) Legends carb is a noticeable improvement.

Any truth to that?  I've asked him to keep an eye out for a good set of carbs.  I've cleaned and rebuilt mine far too many time (in Boone, under Frank's tarp, at night, in the rain), and I just can't seem to get them dialled in right.  I'm good above 3.5k, but they're sluggish below that.  I've changed needle height, I've adjusted the float level, I keep the carbs sync'ed... I can get them to be ok, but not great.

Should I consider a used set from a Legends car?

Thanks

[Dan Filetti]

What's there to 'wear out'?  I guess some of the mechanical bits in the throttle can wear out, but the bodies don't seem to be wear-out-able to me...  Maybe Old Slow Guys can chime in as to whether he's ever seen a truly worn out set of carbs.

Dan

[gdml2]

Bob I tend to agree with Dan.  There's very little to wear out in this carbs.  The needles do wear against the needle jets, but both are easily replaceable.  Usually these carbs are discarded only after someone breaks one of the float hinge tangs off (because they tried to "punch" out the hinge pin instead of pressing it out), or if they strip some threads.  I've heard that the slide bore can wear, but haven't actually seen it myself.  Most low rpm trouble is usually due to restricted pilot jets.  Don't just blow them out and expect them to be clean.  Take them out and look through them (at a light) and you should be able to see clear light through them.   Most new carbs come with stock 37.5 PJ, they are replaced with 40s for racing.  This cleans up the bottom end, but will probably hurt your mileage a bit on the bike.  Clean the tip of the mixture screws off and make sure the little O ring and washer are in place in the mixture screw hole.  Check your carb inlet boots for cracks, make sure you don't have any tight valves, and you should be good to go. You've said that you've sync'd the carbs.  You may have to resync. them if any valve adjustments are done.  Sometimes, if various pieces of aftermarket carb. kits are installed over the years, you have to go back to basics.  The pilot air jet should be a 155.   Make sure your choke (enrichment system) rod is working properly and that all 4 "choke slides" are opening together.  Let me know how you make out.

Greg

[gdml2]

Oh yes, one more tip... Check your slide diaphrams for leakage by pushing the slide up with your finger.  Block the vent hole (the oval top hole on the air box side of your carb) off with your thumb, let the slide go and it should slowly fall back down to the closed position.  If it falls too quickly the diaphram is leaking, or the choke plunger is stuck out a bit.  This is a quick check that's easy to perform once you have that cursed air box out of the way.  Note: I'm new to this forum and haven't had much time to look around yet, so most of this info. is probably already posted somewhere.  I don't want to "step on anybody's toes".

Greg

[Bob]

Bob I tend to agree with Dan.  There's very little to wear out in this carbs. 

Sounds right to me.  It's the 'wearing out' comment that I had trouble with.  My carbs got new needles and seats three years ago, and have been well cleaned.  I think I just need to adjust them better.  I balance them a couple of times each season, and I've done my best to get the float levels the same.  But that's about the limit of my carb tuning knowledge.

Here's how they looked at one point 

[gdml2]

Bob, you've got something to work with there.  I wouldn't replace 'em.  Just need a little "tweeking".  Does it start and idle fine, then go flat off throttle?

Greg

[TRoy]

What's there to 'wear out'? 

- jet needle/ needle jet

- slides/ bores

- throttle shaft/bush 

- choke plungers

[Bob]

Bob, you've got something to work with there.  I wouldn't replace 'em.  Just need a little "tweeking".  Does it start and idle fine, then go flat off throttle?

Yup, that's exactly it.  The bike feels really sluggish moving from a stop; especially before it really warms up.  Once it's up to speed (over 3.5k) it responds well.

[gdml2]

Bob, sounds like a simple cleanup of the idle system (mixture screw passage) and off-idle system (pilot jet, pilot air jet).  Remove the mixture screws c/w tiny washer and o ring (these may want to stay in carb - I use an old jet needle with a slight bend in the end to remove these), the pilot jets, and the pilot air jet.  Spray carb cleaner into these passages, and through the jets.  Blow them out with compressed air, take a look to see if they are indeed clean, check the number on the pilot jet and the pilot air jet and reassemble.  I set mixture screws at 3 turns out, but on a street bike you can probably go 2.5 - 3 turns out.  Bench check your carb. sync. prior to reinstalling carbs by looking at the relationship of the closed throttle blades to the 1st transition port in the carb.  Each carb. should have the same amount of this hole exposed.  I find that the initial idle speed is close if approx 1/8 th of this hole is exposed.  This is what works for me.  If you can't see the the 1st transition port open the throttles using idle speed screw, get them all set the same, then return your idle speed screw to where it was.  Install carbs, sync. on the bike, fine tune idle speed by adjusting the "master" idle speed screw found on the underside of the carbs.  If it still hesitates, and it has 37.5 pilots in it, you might want to try 40s.  If you can't find any let me know.   I guess we maybe should have posted this in the maintenance section instead of introductions.  Kind of getting strung out a bit.

Greg

[Marsh White]

I guess we maybe should have posted this in the maintenance section instead of introductions.  Kind of getting strung out a bit.

Greg

Done!

[racerrad8]

All of the parts that are subject to wear are replaceable. If you are having low speed issues I would inspect the emulsion tubes and slide needles for wear. That is the mid-range fuel mixture and as those parts wear the mixture gets richer.

Randy - RPM

[gdml2]

Thanks Marsh,

Greg

[Bob]

Thanks Greg... nice to know we have some carb depth on this list ... you and David Raforth would get along just fine (legendary carb dude on the Yahoo list) 

[Paul Dodge]

Howdy folks! Bob,i didn't see you mention the miles on the carbs. If they have a LOT of miles on them you may have an issue with wear on the throttle shafts and/or the holes the shafts pass through. If there is a lot of wear the carbs will "suck air" around the shafts and make syncing the carbs difficult. You can check this out by spraying a little WD-40 on each side of each carb (tank off of course) If the idle changes there is an air leak there. New shafts would probably help that situation , but i'm curious to know if there is a machinst out there that could bore out the bodies and press some brass or nylon sleeves into the carb bodies. Or it might be possible to slide a snug fitting "O" ring on each side of the carb and make sure it's snug against the carb body. Also if you still have the carbs stripped down see if you can find a shop with an ultrasonic carb cleaner. That process will insure that all the passages are spotless. As usual i've rambled on!!!!!!LOL but thats my two cants worth. Ride Safe!!  Paul

[gdml2]

Bob, I "googled" on David Raforth (sorry, you probably all know him already) and found some good reading on FJ carbs, petcocks, etc.  Good stuff!  I'm new to this forum thing and like I said before, I don't want to "step on anybody's toes".  Just puttin' my 2 cents worth in to try to help a fellow FJer.  I've been rebuilding carbs since around 1980 and have found these ones really user friendly (have rebuilt / setup approx. 23 sets this year already).  Pretty near ready to take some time off to go biking.  I'll be looking for advice from folks on the forum when I get a chance to work on my own stuff.  Looks like lots of good quality knowledge here.   

Greg