batman wrote on 03/21/19 at 14:34:37:


  The cylinders are 45 degrees apart, but the firing order is most definitely not 45 degrees too. If it was, the second cylinder would be coming up on the compression stroke 45 degrees behind the first cylinder. Try kicking one sometime with the ignition off to see for yourself. Bring it up on a compression stroke, let the kickstarter ratchet back to the top so you can get a full kick from it, and give it all you've got then. No matter how hard you kick it it will only go thump one time for each kick. You will never spin the engine fast enough for the second cylinder to make a compression stroke with one kick.

Hotrod:  I bet the install is almost identical to the Mikuni VM.  If the DellOrto is the particular design I have in mind it's pretty much the same as a VM.  Has a round slide and the cable comes in through the top and hooks into a slot in the slide.  It should be easy to install that type of carb.

Good luck with your project and keep us informed.

I suspect that the LS engine will run at approximately twice the speed of the Harley to achieve similar jet circuit transitions.  For instance, out of the box, the S&S utilizes a .040" airbleed which brings the main jet on-line at about 3000 rpm.  With that same .040" airbleed, the LS engine would probably have to run about 5000 or 6000 rpm to bring the main jet into play.  So I'm guessing I will need to use a smaller airbleed on the LS.  Finding just the right jet combination to allow the carb to transition from the low speed circuit to the high speed circuit will be tricky.  I may have to try unorthodox stuff like increasing or decreasing the number of holes in the emulsion tubes.  The Harley is pretty much a 5500 rpm engine until you really start to breathe on it.  The S&S E runs very well on a 5500 rpm Harley.  Our engines are 6500 rpm engines and I'm looking to increase that to about 7000.  That's the redline on the DR so I think the valve train will be good to 7000.  That should make application of the S&S carb a little easier, but still difficult (at least for me).
 
I don't think it will be a cakewalk.  I think it will most certainly be much more difficult than adapting a Constant Velocity or Variable Venturi carburetor.  The fixed venturi will be a big challenge.   If I don't get it to work properly at least I will learn a few things.

Thanks for sharing the info on the Weber setup Dave.  That may turn out to be quite useful to me.  Do you think that a change to the throttle linkage (less throttle plate movement per inch of peddle movement) might have helped.  I could possibly fabricate an elliptical pully for the throttle shaft so that at the lower throttle openings the throttle plate movement to twist grip ratio would be less than at higher throttle openings.  Do you think something like that might have improved conditions on your six-cylinder application.

Lancer loaned me three more carburetors to test. A BIG mahalo to Lancer for trusting me with his valuable mixers.  The new candidates are a Mikuni 36VM, a Mikuni 38VM, and a QuiuckSilver 38mm.  I tested the three new carburetors using the same process as the stock carb, Kehin 40, and S&S Super E.

Here are the results of the tests:

Box Stock Head

Mikuni 36VM:            149 CFM @ 15” (no  airbox)            109 CFM @ 10” (airbox installed)

Mikuni 38VM:              153 CFM @ 15”       (no airbox)            113 CFM @ 10” (airbox installed)

QuickSilver 38:              157 CFM @ 15” (no airbox)            117 CFM @ 10” (airbox installed)

Modified Hammer Head

Mikuni 36VM:              172 CFM @ 15” (no airbox)            126 CFM @ 10” (airbox installed)

Mikuni 38VM:              178 CFM @ 15” (no airbox)            130 CFM @ 10” (airbox installed)

QuickSilver 38:              184 CFM @ 15” (no airbox)            132 CFM @ 10” (airbox installed)

To get a feel for what we could expect from an air filter/airbox change, I installed Lancer’s Uni Pod filter on the QuickSilver 38.  The Uni filter flowed 134 CFM @ 10” H2O, an increase of 1.5%.  That was with the red outer sock removed.  When I installed the sock it flowed 132 CFM, the same as the modified airbox.

Let’s look at the Mikuni VM setup.  It looks to me like it would be an easy installation.

The VM36 is almost identical except for a slightly smaller throat.  The QuickSilver also looks like an easy installation.  The throttle cable might be a little tricky but nothing we can’t handle.

IMO, the three Mikuni carburetors should be very easy to setup for most applications.  The 36mm & 38mm VM carburetors will provide a boost in performance, and the stock CV carburetor will probably provide the best mixing qualities for trouble-free everyday street use.  The Kehin 40mm CV, the QuickSilver, and the S&S E are the flow kings, but I’m betting they will be difficult to setup.  The 38VM is so close in terms of flow that only the most discerning performance seeker will be able to tell the difference.  It looks like the other five contenders will have a very hard time outperforming the 38VM overall.

Thanks again to Lancer for the loan.  It allowed us to gather a lot more comparative data.

Knowledge is power.

Best regards, Mike