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Ironhead Sportster Motorcycle Talk (1957-1985) For all those that wanna talk about Ironhead Sportster Motorcycles

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  #1  
Old 25th October 2009
BLIGHT BLIGHT is offline
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Default 40mm CV Carb Swap Today

Hi guys, I'm feeling kinda lazy today... I was gonna pull off the front head today and check the rod play and just look around for what is causing the knocking sound. (That's all in another thread...)

Then, the mailman delivered the last part I needed this morning to do my CV carb swap on the '77 XLCR, so I figured, that's an easy job. I decided to take a bunch of pics, I hope there are not too many, but I wanted to show all the steps along the way. Took about 2 hours of easy work.

I first took some pics of the Screamin' Eagle K&N air filter kit I bought used on ebay. I drilled out the plug over the pilot jet and adjusted it 2.5 turns out from being lightly seated. Here's a good set of tuning instructions for the 40mm Keihin CV carb:

http://www.nightrider.com/biketech/hd_cv_mods.htm

Here's a few pics of the carb & aircleaner. Notice the velocity ring! I still need to get a couple of rubber plugs for the holes in the filter back plate. I put some duct tape over them for now.







I decided to mount the VOES switch I also got on ebay to the new filter back plate:



Here's a pic of the stock air filter protrusion from the gas tank:




Next, I removed the old carb and air-cleaner back plate:




I bolted up the carb using the rubberized flange adapter:



Here's the VOES wiring being connected... one wire to ground, the other to the ignition (MSD) control unit for vacuum ignition retard.



I fabricated a simple aluminum brace to support the carb:



Next, I installed the air cleaner element, connected up the fuel line, and throttle cable. I'm not using a return cable, because the pull spring is pretty stiff. If it were to stick, I can always hit the kill button! The original carb never had one, and it worked OK for 32 years, eh?





The air cleaner cover I got with the kit was chrome, and not all that perfect, so I decided to paint it wrinkle black. I used the XLCR center medallion and I think it looks cool. I didn't modify the stock cover, and it's put away safely.




The filter sticks out about 1" farther than before, but it doesn't look bad!

I fired up the bike and it runs pretty decently, with a stable idle. I took it for a little ride, and there is a lot more mid-range punch. It's weak on the top end, though. It's got the stock (emission) jets in it, so I'll be installing a DynoJet kit in it with a lighter slide spring, custom needle and larger main (180 or so) and a 45 pilot jet. Then, it should be perfect! It's a pretty easy swap once you get the right parts.

Here's a view from the rider's seat.



Hope this info helps anybody considering the CV swap!

Cheers,
BLIGHT

Last edited by BLIGHT; 25th October 2009 at 01:19.. Reason: Forgot one photo link
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  #2  
Old 25th October 2009
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ericfreeman ericfreeman is offline
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Nice job fitting the CV carb to your XLCR. Here's a pic of the vintage Mikuni-Solex carb that I'm running on both of my Ironheads. Fell in love with this carb back when I had one on my new '77 XLCH. I've managed to find and restore 4 of them, although it takes some serious work since most of the parts are no longer available. Fortunately, jets and some other critical parts are. Twin 36 mm butterflies, superb fuel atomization, excellent economy and throttle response second to none. I've also run the stock Keihin and a Super E and the Mikuni-Solex is my favorite by a long shot.

The air cleaner backing plate is a K&N but I've cut off the cover support to allow running a Ramflo foam element and cover. Luckily, the backing plates are nearly identical in size for both filters.

Eric

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  #3  
Old 25th October 2009
BLIGHT BLIGHT is offline
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Default

That's very cool! I have always thought that the H-D's should have an individual carb for each cylinder. The twin choke Solex is a very nice solution.

Question... how much more does it stick a lot more than the original Keihin side-draft? My 40mm CV sticks out about 3/4" or so more than the original setup.... so just curious.

I'm sure you have a LOT more power with this setup, but is it a lot more, judging with the SOTPD? (Seat o' the Pants Dyno)

Cheers,
BLIGHT
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  #4  
Old 25th October 2009
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ericfreeman ericfreeman is offline
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It sticks out a couple of inches further than the stock carb, about the only drawback for guys wanted a sleeker look. Fortunately, I don't have long legs so I can tuck in just behind the aircleaner on the stock mid controls. I use the highway pegs as well but my right leg rests against the air cleaner.

Never done a dyno run but I remember back when my '77 XLCH was nearly new and I swapped the stock Keihin for the Mikuni-Solex: Difference was like night and day! The stock carb seemed a bit flat and you really had to crank on the throttle to get some action going. With the M-S, the response was instantaneous and just kept going.

Here's a pic showing how the carb sticks out with the K&N filter, before I fitted the Ramflo.

Eric

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  #5  
Old 25th October 2009
GA_Ironhead GA_Ironhead is offline
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Quote:
Originally Posted by BLIGHT View Post
I fired up the bike and it runs pretty decently, with a stable idle. I took it for a little ride, and there is a lot more mid-range punch. It's weak on the top end, though. It's got the stock (emission) jets in it, so I'll be installing a DynoJet kit in it with a lighter slide spring, custom needle and larger main (180 or so) and a 45 pilot jet. Then, it should be perfect! It's a pretty easy swap once you get the right parts.
Before you go down the Dynojet path, I would try changing jets and/or needles. It is said that the slide can oscillate with the lighter spring, especially if you drill the slide. Jets should be all you need.
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Old 25th October 2009
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Schutzhund Schutzhund is offline
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Great job documenting the carb swap. I run the vilocity ring on my old bendix. It looks really cool, but I'm not sure it does any thing to enhance the performance.
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Old 25th October 2009
BLIGHT BLIGHT is offline
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Quote:
Originally Posted by GA_Ironhead View Post
Before you go down the Dynojet path, I would try changing jets and/or needles. It is said that the slide can oscillate with the lighter spring, especially if you drill the slide. Jets should be all you need.
Yeah, I used the DynoJet kit for my Triumph Thruxton 900 (dual 36mm CVK's) and it worked like a champ. That kit recommended NOT drilling the slides with the lighter springs included in the kit.

Last night, on ebay I did buy just a simple jet kit with a custom needle specifically for this 40mm carb. The seller says you don't need to drill the slide or change springs with his kit. The pilot and main jets included were exactly the range I was looking for.... so, we'll get it in a coupla days and see how it works!

Cheers,
BLIGHT
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Old 25th October 2009
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Default CV carb

Excellent info BLIGHT !!!

I will also put on a CV carb on my ´77 xlcr but i will keep my original cover for it!
Will fit a K&N filter in it too!!

Did you use the stock manifold?
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Old 25th October 2009
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You'll love the CV. I did mine last year...just a simple rejet and it's never ran better
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Old 25th October 2009
BLIGHT BLIGHT is offline
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Quote:
Originally Posted by xlproject View Post
Excellent info BLIGHT !!!
I will also put on a CV carb on my ´77 xlcr but i will keep my original cover for it! Will fit a K&N filter in it too!! Did you use the stock manifold?
Thanks, XL... I used the original intake manifold, but used a rubberized flanged adapter to the carb. (The other way is a billet adapter that press-fits on the carb spigot with JB Weld!) The aircleaner assy. is the HD Screamin' Eagle kit that comes with the K&N filter in the pics.

I could have used my original XLCR cover, but the chrome one the seller included in the ebay sale already had some extra air holes in it and the chrome was not really right on the XLCR.... so I painted it with black wrinkle paint. I can always slip my stock "ham can" shiny black cover back on if I ever want to.

Should run like a top once I get it jetted correctly.... then, it's time to tear down & re-do my top end

Cheers,
BLIGHT
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