Is the Mikuni 42HSR Worth It?

[Blackbeard]

Hi All,

I'm sure this is a topic that has been discussed before, but I thought I would bring it up again. I bought my RoadStar 1700 approximately 2 years ago. It was already converted to a pumpless system when I got it. It has a Pingel High Flow Petcock, and a vented gas cap. The bike has a MaxAir air filter on it, but it still has the OEM Carb. I feel like the bike is not jetted correctly as it seems to slowly decel when I snap off the throttle. Instead of spending money to play with re-jetting the 40mm, I started looking into the 42HSR. It seems like this option gets rather expensive by the time the carb is jetted, the TPS is installed and everything else is done. Are there cheaper ways to achieve this same result?

Can anyone provide any guidance if this is worth the money? Or, is there a general jetting on the OEM that people tend to like?

Thanks for your help in advance.

[AR. Hillbilly]

For what it’s worth
JD, Curt and Dave J all ganged up on me ant talked me through the jetting on mine. I went from a hyper charger to a K&N so I had to change the everything to get it right. I went pumpless while I was at it. They got it spot on first try.

[Bikerron]

Easy to jet. Simple carb, but you’ll be without the throttle control sensor that adjusts the ignition timing according to load demand.

[Flashback]

If you can do the work yourself and get the carb at a reasonable price then go for it............. that said, the stocker is fine when jetted right for your setup and well proven changes are readily available here..........

[Duke]

I have 2 Road Stars, 1 having a modified stock CV carb, and the other bike having the 42 HSR with the TPS installed. I myself would stick with the stock carb. The CV-40 stock carb is good for 80 HP if you do the right mods. The 42 HSR is a good carb, but you will not get good fuel mileage and the performance gain is not worth the expense in my opinion. The quick throttle response the HSR gives can be done with the our stock carb by modifying the CV slide.
I will be putting a stock carb back on my bike that has the HSR on it, and will be selling the 42 HSR soon as I get it done.

[Doc_V]

What are the mods to the CV slide? Drilling bigger holes in the bottom? ...Also, as an aside to quicker throttle response, properly set fuel level in the float bowl makes a bit of a difference. If the fuel is too low, it takes longer to get sucked up the tube, and you get slower response. Conversely, if it's too high, you get over spill and intermittent rich conditions that can stall the engine when coming to a stop or braking too quickly. Stock settings on many R* are too low. They came from the factory at 3-4mm *below* the float bowl seam, but updated new spec is 5mm *above* the seam. [this is for the new guys]

[Duke]

Doc,
The mods I've done to make a quicker throttle response is drilling the slide vacuum holes out to 7/64"(A), max is 1/8" (B), chamfer (C), and reaming the emulsion tube bottom 6 holes out .001" (E). Along with this I chamfer the pilot jet and emulsion tube holes (F).
I keep my float level at 2mm above the bowl flange, about 2mm lower than factory specs.
This works for me and have had good response with out any adjustments to the excelerator pump.

[Doc_V]

Another one of Duke's Tips to add to my To Do List. We may need to start your own section.

[Spydr]

Me too, on All those points. My Roady has nearly 85K on it (all but 2k by me), and the only mechanic it has ever known is me.
Anything I was ever unsure about, Somebody here was on the spot with help & advice.

[Jclevesque]

Hi Duke. Would you mind explaining why drilling and chamfering the bottom 2 holes of the slide? Also why chamfering the holes on the pilot jet and increasing the emulsion tube holes? Would like to know how it works to create the increase. JC

[davej]

Easy to jet. Simple carb, but you’ll be without the throttle control sensor that adjusts the ignition timing according to load demand.

He can make a mount for the TPS. I think there are some sort of directions in the tech article and there may even be someone that still makes them. Smokescreens might be able to help.

[Bikerron]

From the old site.

https://wayback.archive-it.org/10073/20180223182925/http://roadstarclinic.com/content/view/231/96/

[Doc_V]

Damn Ron! Bonus points for you referencing the archive!

[Spydr]

LOL! Geeeze Ron... I don't know of Anybody that ever built that contraption!

[davej]

Doc,
The mods I've done to make a quicker throttle response is drilling the slide vacuum holes out to 7/64"(A), max is 1/8" (B), chamfer (C), and reaming the emulsion tube bottom 6 holes out .001" (E). Along with this I chamfer the pilot jet and emulsion tube holes (F).
I keep my float level at 2mm above the bowl flange, about 2mm lower than factory specs.
This works for me and have had good response with out any adjustments to the excelerator pump.

Good mod!!! I haven't gone as far as you have drilling but I always like to at least drill the slide holes. That alone makes a difference. Modding a CV carb like this is old Harley stuff.

[Duke]

Thanks Dave. I know WE are always trying to get every little bit of power and response out of our engines.

[Questcap]

Totally FWIW, Beard, but I've had 3 carbs apart to install jet kits, due to K&N air filters, ported manifolds, DYNA 3000 ignitions, all kinds of freer-flowing exhausts, etc... and for ALL of that, with each bike, the jet kit instructions had me spot-on the first time, with no other tweaks necessary. If you don't know how it's jetted, and they don't have numbers to tell you, and it's just not right. For the price of one kit with instructions, if you get the same fine results I did each time... You'll realize it was the most cost effective way to go.

Oh, and there's also this... It's been quite some time now, but someone once posted dyno results of the same bike, after switching from the stock to 42, and there was NO appreciable gain or change in the results worth the cost and trouble. Someone here might remember who that was.

[Jaybo]

I did the HSR 42 to mine and it accelerates so much nicer and is all around a better performing carb than my stocker. However it drastically changed my mileage. I was around 40-45 on normal rides a little less when I was making noise. 42 gives me about 32 all the time. that's a 100 less miles so I'm rather worried around 120 miles, instead of 200.

[texasscott1]

The 42 is fine as long as the bike is kept at the same altitude. Any big increase and the bike will be running too rich with a 42 while the stock carb will compensate for changes in altitude.

[Doc_V]

Well I'll be damned... I'm glad to hear all his truth-takin, cuz I'd always heard how it was such a great way to go... Feelin better now.

[Smokescreens]

i had the 45 on my bike and they are basically the same as the 42 i was able to get 50mpg no problem. a tps bracket will keep your computer happy but other than ease of tuning and a little better throttle its not like your bolting on big hp. was i happy with it? yes. would i do it again? yes. because i like to tinker. was is needed? only if you want to go pumpless without "ever" worrying about starving for fuel. though most are good to go with the grizzly valve

[Spydr]

How did you get 50mpg with it, Jason? Did you push it the last 10miles? LOL!

[Smokescreens]

found the magic jetting, was very gentle on the throttle, and im sure the 65t rear pulley helped

[Spydr]

Ahhh... so it weren't really the carb or the jetting, it was cruising easy & better gear ratio. Gotcha.

[davej]

I did the HSR 42 to mine and it accelerates so much nicer and is all around a better performing carb than my stocker. However it drastically changed my mileage. I was around 40-45 on normal rides a little less when I was making noise. 42 gives me about 32 all the time. that's a 100 less miles so I'm rather worried around 120 miles, instead of 200.

If your MPG change with the same style riding your jetting is not correct. The only way your mpg would change with the same riding style and conditions is with a change in AFR not the amount of air in itself entering the engine. For instance an AFR of 14 at 60 mph requires the same amount of combustible fuel regardless of the carb.

[Jaybo]

If your MPG change with the same style riding your jetting is not correct. The only way your mpg would change with the same riding style and conditions is with a change in AFR not the amount of air in itself entering the engine. For instance an AFR of 14 at 60 mph requires the same amount of combustible fuel regardless of the carb.

Dave,

Huh, it runs really nicely and never seems to be rich or blubbery even in the high desert. It seems crisp everywhere much more so than the CV40. I followed jetting specs posted on the old site for the carb as well. Would using that HD doodad to do the advance be the reason? Duke can also do the TPMS mod to the 42's and I was thinking about having him do that for me. Thoughts?

[davej]

My understanding is that the HD VOES advance is just a switch that is on or off. It is either at no advance or full advance. If you are properly jetted (and I don't think you are with that MPG) something else is wrong and the Voes may be the issue. I have no experience using 1 so I can't comment further about it other than timing will make a difference.

[Jaybo]

My understanding is that the HD VOES advance is just a switch that is on or off. It is either at no advance or full advance. If you are properly jetted (and I don't think you are with that MPG) something else is wrong and the Voes may be the issue. I have no experience using 1 so I can't comment further about it other than timing will make a difference.

Dave, yeah I am thinking I am going to have Duke adapt the TPS bracket to my 42 and see if there is a difference, because I really do miss the good MPG.

[Duke]

Jaybo, I'll be glad to do it for you. If you wait a little while I will be removing a 42 HSR off my bike so I can use it for a pattern.

[Blackbeard]

Thank you all for your guidance. This is very helpful.

[Bobbin-Martin]

I did the HSR 42 to mine and it accelerates so much nicer and is all around a better performing carb than my stocker. However it drastically changed my mileage. I was around 40-45 on normal rides a little less when I was making noise. 42 gives me about 32 all the time. that's a 100 less miles so I'm rather worried around 120 miles, instead of 200.

Hello. So im new to the world of the roadstars as last year I picked up a 2002 XV1600 midnight star. Me never being able to leave good enough alone, want to squeeze a little extra out of the engine. Got it from the previous owner with a Kuryakin Hypercharger installed. However I dont think the Hypercharger was the right one for this model as the Hypercharger didn't exactly have a straight shot to the carb and would foul up the filter something awful and rather quickly. Hypercharher kit broke while removing it, so now I need a new air kit. I was thinking of running those FP 2-1 pipes if I can find em, Barons BAK, and trying to snag up a Mikuni 45mm and ported intake from Pacific Coast star. I'll be honest though, reading up on this, all this talk of pumpless(don't know if your referring to the AIS or if there's a fuel pump on this thing), vented gas caps, and bigger petcocks, and im starting to realize, it won't be as easy as just bolting on parts and having someone jet the carb for me. Didn't even know these carbs had throttle position sensors. Usually im used to seeing TPS on fuel injection equipped vehicles. Im getting off topic though. I saw you run a similar setup to what I would like to run and wanted to ask how you like it? Pros and cons kinda thing. Thanks