With my new experience in trying to put a HSR42 carb on my roadstar I've found there is not one place that tells all you need to know BEFORE starting on this adventure so I'm starting this thread to gather info about the HSR 42 and everything that is involved to put in on our Roadstars.
TPS mods, voes, jetting, cable mods etc. If you have any info or pics to add please post in here. When I have gathered all the info together I will make up a tech article and have Gram post in the Tech corner.
I look forward to seeing what info you have If you get info from another source please give me the original author so credit can be given.

Thanks,

Steven

Man there is nothing better than letting someone else blaze the way!
Its on my list of to-do's since I think our carb is the one piece of crap Yamaha put on the bike. I'll be watching for it.

I think one of the best places to start is to go to the Mikuni site and read the info in the Tuning Manual. Another thing is to forget how you tuned the stock carb, and don't compare the 2. The 42 has a much better separation of ckts and can be tuned individually where as I see there are more over lapping of ckts in the stock carb. I have run this carb without mods, with VOES mod , and TPS mod, I highly suggest the TPS mod and not even to bother with the VOES, there is enough difference to feel just by the seat of the pants, and does help with mpg's in city riding.

Some items to have on hand
#50 pump nozzle (leaner than standard #70)
and leave pump ckt at factory set-up
#98 needle (leaner than standard #97)
needle plays more of a roll in cruise mileage (65mph as per Mikuni manual)and is more geared for economy tuning, use the #97 if tuning for performance
Main jets same as stock carb (large head)160 is standard, have on hand 165, 167.5 and no need to drop floatbowl for only a main jet change, a 17mm nut is on bottom of bowl, main jet is right there.

Also might want to consider getting the short idle screw adjuster, I found that the standard idle adjuster gets a little tweaked since it will bend up against the push rod tube.
I'm using a mikuni choke cable since I was never 100% certain the choke was shutting off completely using the stock carb choke cable, however, the Mikuni choke cable is either on or off, there are no indents like on the stock carb cable


Yost Power Tube, if being used, be careful on seating it, it does not seat flat on it's collar, so don't try to force it, it is that way by design.
Be careful when removing needle, there is a brown washer that fits into a slight recess (e-clip on needle rests on this), it usually will not come up with needle removal, just need to ensure that it did not pop out of that recess. Do not use an extra washer for half-step adjustments either.

I will also suggest tuning by AFR. I am using the AFR table from this site: http://www.daytona-sensors.com/tech_tuning.html I have mine tuned to the leaner side (economy) of the AFR that they show for each ckt (use #98 needle) if you decide to use AFR on the richer side (performance) use the standard #97 needle

Good info!!

Steven

Good info Erbman02....but, why no half step on the needle?

MidStar07 wrote:
Good info Erbman02....but, why no half step on the needle?


The way the needle is kept in place, if you use an extra washer for a half step, that piece will possible bend, then if you take the washer out, you will have slop in the needle, so you would need to remove the carb, take that piece out, bend it back to original shape and re-install. Not worth the effort. This needle is held rigid in place, not like the stock carb where the spring and cap hold the needle in place. On top of that the options of different needles will get you where you need to be. As I've said before, forget how you learned to tune the stock carb, this is a much better carb to tune, and has a few options in tuning that cannot be done on the stock carb.

I will also suggest tuning by AFR. I am using the AFR table from this site: http://www.daytona-sensors.com/tech_tuning.html I have mine tuned to the leaner side (economy) of the AFR that they show for each ckt (use #98 needle) if you decide to use AFR on the richer side (performance) use the standard #97 needle[/quote]

Can you tell us all HOW you determine what your AFR is for each circut and what device / meter are you using ?

sailrider wrote:

Can you tell us all HOW you determine what your AFR is for each circut and what device / meter are you using ?


I use someone that has a portable dyna, which he also uses the "sniffer". All that a "sniffer" is, is an oxygen sensor shoved into the tailpipe. And thru the wonderful world of electronics, the sensor takes those gases, and the electronics converts that all into voltages, and the voltage reflects the Air/Fuel ratio. 14.7 afr is ideal for combustion, that is the proper ratio of gas and air. 14.7 does not reflect the voltage tho, there is still a bit of electronic wizardry that makes the numbers for afr. 14 is the leanest afr that my bike runs, and that is at cruise speed (65, 70mph max and 50mpg)after that my carb starts to go richer, at WOT my afr is aprox 12.5. At a constant 80mph I'm at 40mpg. I can set this carb to get 45mpg at 80mph, but I have no need to, seldom do I run at that speed for any length of time. another thing is my set-up, if doing 80mph in 5th gear, I don't need to drop a gear to pass, if I set it up for 45mpg @80mph, I would need to drop a gear to pass. I've played quite a bit with this carb, probably at least 20 to 30 different jettings, and have seen how the bike performs, and where the AFR's were. I've also spent a number of hours on the phone with the head tech over at Mikuni, and as well as Bob Yost, and have gleaned quite a bit of info on this carb, the biggest issue were neither one of them was familiar with this carb on the Roadie, both are HD guys. My biggest help was that AFR table in the article I mentioned. I've also ran this carb at a 13 afr for cruise, and with a 1 point difference in afr at this point there is a seat of the pants difference in performance from mid to wot, but at only a half point difference (@ 13.5)could not tell by seat of the pants.

You are a wealth of info Ebrman02!
Steven

Steven,

I have a "sniffer" if you want to borrow it.

We would just need to find a place to meet as close to Santa Monica as you could get.

Gram