Venture Carb Conversion

[cbx550]

Since the Venture/VMAX motors are also 70 degree V's with four valve heads and of similar vintage to the Vision, I reasoned that the same team probably designed these motors and the Vision's, and that two Venture carbs might work and be simpler to tune as they are CV carbs turned sideways. I bought a whole intake setup for a Venture (vintage unknown), everything from the rubber intake manifolds to the air box at a swap meet to experiment.  I stripped down the carbs to use the main pair that connect directly to the throttle cable. 

So far, I've mocked this up on the parts bike. Using the Venture carb manifolds rotated so that the oval ports lines up with the oval ports in the Vision heads, this looks like it's going to work while retaining the air box.  I'll need to make up an adapter for the misalignment of the manifold and the threaded holes in the Vision heads and cut back some of the manifold for bolt clearance.  The choke cable looks like it will work, but I need to make a different throttle cable mount to clear the air box. The bottom of the airbox is at about the right elevation for the Venture rubber velocity stacks, but will need to be modified for the different carb spacing using either the bottom of the Venture air box or some aluminum plate.

[cbx550]

Venture carbs track tested.  Starts well, no stumble, strong mid-range.  Throttle and choke cable moved to be side-pull.

[lexx790]

Nice going, now if you could just make the pictures a bit smaller so I can see it all in one go without scrolling.

[jefferson]

A friend of mine did a vmax carb conversion and widened the carbs out to match the airbox. I think he used the stock manifolds.

[PwrManDan]

Nice going, now if you could just make the pictures a bit smaller so I can see it all in one go without scrolling.

Here's a tip that works for me - right click on an image in the post and then select from the menu open in a new tab or open in new window.  Depending on your resolution you still may have to scroll a tiny bit, but it will fit in the window a whole lot better.

[Rikugun]

Venture carbs track tested.  Starts well, no stumble, strong mid-range.  Throttle and choke cable moved to be side-pull.

Good deal! Looks like a tidy installation. It looks like the bowls can be removed with the carbs in place which is convenient.

How is the side pull cable arrangement working? Any cable routing issues to the throttle pipe?

[lexx790]

Nice going, now if you could just make the pictures a bit smaller so I can see it all in one go without scrolling.

Here's a tip that works for me - right click on an image in the post and then select from the menu open in a new tab or open in new window.  Depending on your resolution you still may have to scroll a tiny bit, but it will fit in the window a whole lot better.

thanks that worked a treat

[cbx550]

My way you avoid the problem of connecting the throttle shafts and extending the choke shaft for wider carb spacing. No change in the Venture carb spacing. I have the choke cable operating side-pull on the outside end of the pair of carbs using the Venture shaft lever arm.  I don't think the side - pull throttle cable is much worse than the top pull of the original Venture setup. Either way the cable must turn forward. If the stock airbox wasn't used I could have probably used the Venture cable setup.

[cbx550]

Photos of the throttle cable and choke cable mounts. Throttle cable mount came off a set of Honda CBR600 carbs (came with a set of cables I once bought). I adapted a Honda throttle cable because it provided more range of adjustment than the Yamaha style cable and a more secure mount at the carburetor end.  Choke cable mounts uses some parts from the Vision carb to hold the cable and to connect the cable end to the enricher activation shaft crank.

[cbx550]

I have been using the best two of the four carb slides. The Venture carbs look very similar to the downdraft XV535 Virago carbs.  In other markets there was a smaller displacement XV400 Virago.  I bought a pair of XV400 diaphragms from Ali-Express to replace the worn out diaphragms on the Venture carbs.  Fit perfectly. 

[Walt_M.]

Good find. Oh and Merry Christmas to you.

[allstateguy]

if you have pix or descrips of how you adapted the Venture inlet manifolds to the Vision bolt pattern, I'd sure like to see it.

[cbx550]

I used the pair of Venture carbs that connect to the throttle cable and picked the Venture carb boots that best fit the Vision motor.  The carb bolt hole locations are different.  I aligned the oval ports of the carb boots to the oval intake holes in the Vision heads, and checked the spacing with the Venture carbs.  There is enough meat in the Venture boots to carve away clearance for cap screws with a Dremel tool and drill new mounting holes in the flange.  There is aluminum core in Venture carb boots, probably because they need to support the weight of the V-boost cross over manifold, the carbs and the air box all stacked on top.  The photo shows a trial fitment on a parts bike motor.

I made a flange template from the Vision boots to locate the holes in the Venture boot flange using the oval hole for clocking alignment.  If you have a Vision gasket, that should work as well.  My gaskets were too torn up after carb boot removal.  The Venture boots have O-rings for sealing to the head, so they don't need gaskets.

Bruce

[allstateguy]

Thanks! I'll give that a shot

[cbx550]

I found the stock Venture pilot jets are too small. Running air box and no filter. Field fix at the track by drilling out pilot jets. Idle and mid range much better. Jet block is accessible from the side.  I'll order some proper pilot jets.

[cbx550]

Updated choke linkage.  The clevis is now fixed to the arm and no longer rotates.