Speaking of cv carbs

[Hybredhog]

 90 degree/ "v", it doesn't take much, Start small & get the feel for it. As mentioned before, drilling a hole in the butterfly can be an option, but a lot more sensitive in its location & size, like .030". But I've only used that on the early '89 xl CV's that don't have an accelerator pump, and some older Jap bikes w/ CV's. They have to be a bit richer pilot jet, & It kind of blows down across the transition orifices & creates its own accelerator fuel pulse.

[JW113]

Note that for the idle circuit, it does not operate from air flow over the idle jet hole like the main jet or transfer ports. At idle, the idle jet hole is behind the 'closed' throttle plate, there is almost no air flow at all, and intake manifold vacuum alone sucks fuel from the idle jet hole. You can put an idle air bleed hole almost anywhere in the throttle plate, and it won't make any difference. FYI, the one on my CV51 on a 113" TC is at least 1/8", maybe a little bigger...

The whole point is that at idle, you want fuel being sucked from the idle jet only, so you can control it. If the throttle plate needs to be opened enough to keep the engine running but crosses over the transfer ports, then you've lost fuel metering control from the idle jet circuit. My approach was to keep drilling the idle air bleed hole larger until I could see that the throttle plate at idle was between idle jet hole and transfer ports.

-JW

[david lee]

Note that for the idle circuit, it does not operate from air flow over the idle jet hole like the main jet or transfer ports. At idle, the idle jet hole is behind the 'closed' throttle plate, there is almost no air flow at all, and intake manifold vacuum alone sucks fuel from the idle jet hole. You can put an idle air bleed hole almost anywhere in the throttle plate, and it won't make any difference. FYI, the one on my CV51 on a 113" TC is at least 1/8", maybe a little bigger...

The whole point is that at idle, you want fuel being sucked from the idle jet only, so you can control it. If the throttle plate needs to be opened enough to keep the engine running but crosses over the transfer ports, then you've lost fuel metering control from the idle jet circuit. My approach was to keep drilling the idle air bleed hole larger until I could see that the throttle plate at idle was between idle jet hole and transfer ports.

-JW

another good reply

[Hybredhog]

   In my experience, I went with a hole to blend in flat spots during throttle movements, and I located the  small hole appox. a 1/4" above the transition orifices. I've used notches on the butterfly edge on all kinds of rig & carbs for the same reason, and it helps in cold blooded circumstances to ease into running temps.
   My CV51 on my 124+ is virtually untouched, other than a leaner needle. I believe it takes a really big engine to make them work right, and almost anything smaller may have issues of one form or another. If you were to talk to Bob Woods about his modified 51's , & why he get the big $$ for it, he's machining out the stock orifices, & inserts a plug with a new pattern. I believe he did use a BF hole on his smaller (42mm) rebuilds, & those are orifice located.

[76shuvlinoff]

Well this OF is learning a lot. I'd run out to the barn and diddle it but tuning on a shovel in MI in January seems iffy at best.
(At least that's my excuse today) 

[JW113]

Well I can't say about a CV51 needing a 124" or more to work right. HD was selling them at a time when their biggest displacement SE stuff was 113", which is what I have. I don't think it's the cubes that is the issue regarding how they performe at idle. There is hardly any air flowing through until you have the throttle opened up quite a bit. I think the problem that I had was with the cams, i.e. a whole lot of duration and overlap. That is what messes with carburation at idle. After adding an idle bleed hole to the throttle plate, it purrs like a kitten at idle and has no flat spots anywhere through the throttle range. Not to mention very polite street manners until you bang the throttle open. Then hold the <cuss> on.


Speaking of the engine size and CV, to me the whole point of using a CV type carb is that they are fairly immune to displacement. They act like a small carb at low throttle openings, then turn into a big carb at WFO. Here's an example. I had a 1000cc BMW twin with TWO 40mm Bing CV carbs on it. That's 40mm of carb for 500cc of displacement per cylinder. Contrast that to a TC88, which used one 40mm CV to feed 1450cc. The Beemer ran great, never seemed to be "over-carburated".

I think it is with large throat butterfly carbs like the S&S G and especially D that you want to avoid on anything less than large displacement motors.

JMHO!

-JW

[Burnout]

"S&S G and especially D that you want to avoid on anything less than large displacement motors."

This goes for an E on a small motor, I liken them to a barn door for air and a fire hose for fuel.

You need a certain amount of pressure drop across the carb to create a responsive fuel signal.

This is the CV advantage, it also benefits by accelerating the air flow across the feed point adding to the signal and promoting atomization.

[Hybredhog]

    When HD came out with the 51cv, I think they were just shooting in the dark for "something" to sell. People drank the Kool-Aid for awhile, but most had unsatisfactory results with them, same as the Holley two throat they tried selling. I have several 51's on the bench for extra parts, and they all came off bikes with "95" phase 3" builds, and ran like turds. A less aggressive cam would make them better for "mid-size" motors, but as you've found out there was "some assembly required", and you were creative enough to tinker with it, but most people weren't. Yes, a CV is a great concept to cover up engineering/ EPA flaws, like for a stock 883 before F.I. came along. But Harley brought a 12 ft. culvert to go under the driveway, and created more problems than not.
    HD sold theirs with an updraft manifold to get tank clearance, and semi-defeated the purpose. I, on my life's path to do "Potty mouth" the hard way, machined a S&S "G" manifold to fit, but it was to close to the tank (FXDXT), & eventually cracked the plastic dome. So I whittled a low clearance dome (1/8" shorter), from a block of aluminum, to feed my stubbornness.   

[FSG]

......  to feed my stubbornness

I like that     but isn't that we all do riding HDs   

[Ohio HD]

......  to feed my stubbornness

I like that     but isn't that we all do riding HDs   

   Yes         

[xlfan]

J01696   SCREAMIN' EAGLE® BIG BORE 44 mm CV CARBURETOR KIT, 27934-99

I have a Screaming Eagle sitting out in the garage, it has a Black plastic knob to pull up for enrichner. Needs to be gone through as that will be done in the Spring. It has been a while since I looked at it, it has a what appears to be a Black Plastic type of adapter on one end of it, I don't see it in the parts break down drawing you attached, any idea what it is used for ?

You describe a completely different carb than the CV. The SE carb you describe, is the early style high perf butterfly Keihin, also sold as an Andrews carb.

[76shuvlinoff]

Bump!
I need to service my TC EG brakes and the shovel sitting on the lift untouched for nearly 9 months finally got to me. I uncovered Obnoxious and felt pretty bad when I saw the feed and mice "Potty mouth" on the seat. Didn't find any other rodent damage... yet but she's dusty and crusty, even a little rusty.

I turned on the fuel and it flowed out of the bowl overflow line just like when I parked it. Imagine that.  First order of business clean the bowl out, drop the float and flush it all out. 
Got the 44mm CV to hold gas. Next I popped a 3/32 hole in the butterfly, got it hot,  adjusted the idle and now I can kill it by adjusting the idle mix screw in. Thanks JW!

Wiped her down some, no more tweaking until I get fresh fuel. Man I have missed the sound of a good sized shovel barking through a Thunderheader.



Thanks all.
Mark

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[Hossamania]

Yeah, you missed it, didn't you?

[jls 64]

Really nice scott.congrats

[Burnout]

That particular Thunderheader is one of the "all time best" pipes made for power and drive-ability. Very desirable.

You might find a pipe that makes a little more power up top, but you will give up a butt load on the bottom.

[76shuvlinoff]

That particular Thunderheader is one of the "all time best" pipes made for power and drive-ability. Very desirable.

You might find a pipe that makes a little more power up top, but you will give up a butt load on the bottom.

It's showing it's age these days. I don't like the idea but it may end up BBQ black in a year or two.

[76shuvlinoff]

Yeah, you missed it, didn't you?

I sure did. I'm thinking one of these rainy days the 3 degree neck cups are going to come out and maybe the chimps too.  I'll likely keep the late front end if only for the brakes.