The main reason I did it was because I just couldn't get my 40 tuned right. On occasions it would cough from the carb just when I'm turning on a busy highway...and I said enough of this. The 42 is so much more responsive and more power when you need it. Very easy to tune, in fact mine came from Maxir and it was pre-tuned. All I had to do was install. No carb heat anymore. If you are not having isues with your 40 and are comfortable with your bike then there's really no reason. But if you want more responsive riding and loads more torge and power, then the 42 is the way to go.

When someone suggests taking a core piece of the fuel induction system and changing it I scratch my head especially when it such a nifty device as a Constant Velocity Carb, Performance modifications almost always involve a trade off and ditching the CV for a direct slide is no different .

Aside from the loss of the TPS and timing advance or the hassle associated with getting it working again I have heard some folks feel the HSR's can be a bit "touchy".  That is, small changes in the slide throttle can give instant changes in speed, which can feel jerky and cause vibrations or chugs in the driveline and others have said that holding steady speeds is sometimes tuff because of this sensitive nature and others report that snapping the throttle open suddenly, can cause the engine to cough and stumble until the revs can pick up enough to achieve sufficient air speed through the bigger opening to restore the venturi effect. At which point you finally take off .

Sometimes I need to remember what is important on a lazy Sunday afternoon on top the bike in the middle of nowhere a nice smooth ride and lots of distance between gas stations or some bars on a graph from my latest Dyno run.

May I ask what the total cost was shipped to your door ?

X2

coalstoves wrote:
When someone suggests taking a core piece of the fuel induction system and changing it I scratch my head especially when it such a nifty device as a Constant Velocity Carb, Performance modifications almost always involve a trade off and ditching the CV for a direct slide is no different .

Aside from the loss of the TPS and timing advance or the hassle associated with getting it working again I have heard some folks feel the HSR's can be a bit "touchy".  That is, small changes in the slide throttle can give instant changes in speed, which can feel jerky and cause vibrations or chugs in the driveline and others have said that holding steady speeds is sometimes tuff because of this sensitive nature and others report that snapping the throttle open suddenly, can cause the engine to cough and stumble until the revs can pick up enough to achieve sufficient air speed through the bigger opening to restore the venturi effect. At which point you finally take off .

Sometimes I need to remember what is important on a lazy Sunday afternoon on top the bike in the middle of nowhere a nice smooth ride and lots of distance between gas stations or some bars on a graph from my latest Dyno run.


I don't know what trade-off you refer to? I've been running this carb for 5yrs, and have had no issues that you speak of nor have talked to anyone who has experienced those issues. Oop's sorry, I did experience the last issue you mention, but that wasn't only a fault of the carb, I gained an extra 6 hp and the clutch spring couldn't handle it so I was slipping in all gears, a mod to the clutch spring 75k miles ago and have not had any issue since. I've tuned both stock carb and the 42HSR to AFR values and get the same mpg's as well. As far as the TPS mod, it's not that hard to come up with a way to do it or to send it out and have it come back professionally done. All I can say is this carb runs smooth as silk, has all the power there when I need it and a bit quicker response as well, great gas mileage too.

Since this subject is still rockin tell me:
One of my favorite places to go when I can is BrianHead ,UT.
From here to there about 216 miles with a change in elevation up to
10,,ooo ft. in some areas.What kind of problems would I run in to with
the 42. May loose some power with my 40,but no real issues.And even locally
my elevation may change by a few thousand.2ooo here in vegas up to 9000 at Mt.Charlston,Mt. Springs about 5500.

I've never ridden in such drastic elevation changes with the 42 enough, so I cannot give you a correct answer. I'm in Ga now, about 1k elv. been up to the mt's a few times, maybe up to 4k, 4.5k elv, don't recall issues with the 42 at least on the pilot ckt and mid-range. But do know the CV carbs due to atmospheric conditions and that the slide moves up due to vacuum is quite capable to elevation changes.

But any way, if you really want to know, suggest you contact Mikuni directly and talk to their tech. Yrs back it was a guy by the name of Lee, not sure if he is still there tho. He is more familiar with the 42 on a HD then on our bikes, but regardless, it's a general question on how this carb would work with extreme elevation changes, if anyone would know, it would be this man.

+1 with what Erb says. The 42 is like going from a 2-barrel carb to a Holly four barrel for those ole car buffs. With the Maxair mod, they install you TPS from your old 40 carb. Main reason I switched is because the 40 was coughing. Not the carbs fault I might add. But the 40 is very senitive. The Maxair came as plug and play and that's what I did and now my bike starts right up, idels smoothly, and when you ride it it's like I'm super charged! You can hear the carb sucken the air! If you do it right, like I did and pay the xtra $$$ you will be a happy camper. The total cost was $730. I bought some extras like new throttle cables, TPS mod, fuel pump mod, jet kit, etc. Maxair installed everything, tuned it and sent it to me. I also got the Yamaha ported manifold, Maxar stainless choke cable, Maxflo air filter, and the two into one exhuast. It runs better than it ever has. I recommend it too anyone if you really want so power when you need it. I haven't done the mpg calculation yet since I just got it but I will and post it. I see folks get big air kits, after market exhaust, re-jet their 40 and I would think they do this for better performance so why not take it one step further? Because if you don't your not getting your bikes best performance and wasted good money on the other stuff. Just my two cents.

For Coslstove's comments, looks like your bike is pretty much stock and that's fine. Mine ran great stock. Nice and quite and a big difference coming off a Royal Star Tour Deluxe. My Roadie is more like a sport car feel to me. If you don't want the expense or the hassle of supercharging you bike, that a okay in my book but for me, working on it is as much fun as riding it!

Starkruzen wrote:
For Coslstove's comments, looks like your bike is pretty much stock and that's fine. Mine ran great stock. Nice and quite and a big difference coming off a Royal Star Tour Deluxe. My Roadie is more like a sport car feel to me. If you don't want the expense or the hassle of supercharging you bike, that a okay in my book but for me, working on it is as much fun as riding it!


I agree my bike runs like a bat out hell and 42 made it even better