HSR42 vs. HSR45 ?

[Jaybo]

The price diffewrence is not that great so who wants to tell me why or why not? Stock 1600 engine, Curts Manifold, BAK Freedom Combat pipe. Would I see a significant boost with the 45, or just worse mileage? I see both carbs are common upgrades for the HD 1340cc motors, but is there a lot of actual difference?

[HotRod]

Its all how they are set up. I am running a HSR 45 on my 02 1600. The only reason is, I got it CHEAP!!! It was missing a lot of parts, I sent it to Curt and he worked it over for me. It was set up and jetted for a 1600. Your engine is only going to flow what it is going to flow, a bigger carb is not going to make it flow more, A stock CV40 is plenty of carb for either the 1600 or the 1700. The biggest difference you will see between a CV and a HSR is in throttle response, a HSR carb has very instant throttle response where as the CV tends to "think about it" a bit then respond, which also can be corrected for if you are willing to INVEST the time in tuning it properly.

The CV on the stock carb stands for Constant Velocity. This constant velocity allows the fuel/air to flow faster at lower rpm but still giving the proper mixture, thus allowing a fuller charge in the combustion chamber. At higher rpms the slide opens to maintain the same velocity with a higher rate of fuel and air flowing to meet the demands. The HSR 42 or45 have a larger diameter opening which leads to fuel/air flowing at a lower velocity at lower rpms because it doesnt have the slide.

Now all of that said, I never noticed any loss of power on the low end, nor did I notice any power increase on the top end, just much better throttle response throughout the rpm range. If I were going to purchase a new HSR for my 06 I would go with a 42 over the 45, still plenty of carb, a little less costly and could theoretically give slightly better performance than a 45 on a pretty much stock motor. Even if you were to go Big Bore with cams and valves the 42 would still be enough carb to supply the demand. Just ask DaveJ,

Rod

[Jaybo]

That's kind of what I was thinking as well and the throttle response is the biggest thing to me, I hate the CV carb for the "think about it" delay. There is about a $40 difference between the 2 and that would almost pay for my VOES as well. Going to need to get some jetting specs for it as well as far as where to start. I saw one with 98 needle, 170 main and 25 pilot. That sounds lean to me, since 97 and 165 is what the jetting is for the 1340HD. Guess I'll order 170 and up mains and a 96 and 98 needle to go with the std. 97. Time for more research/googling

[HotRod]

That's kind of what I was thinking as well and the throttle response is the biggest thing to me, I hate the CV carb for the "think about it" delay. There is about a $40 difference between the 2 and that would almost pay for my VOES as well. Going to need to get some jetting specs for it as well as far as where to start. I saw one with 98 needle, 170 main and 25 pilot. That sounds lean to me, since 97 and 165 is what the jetting is for the 1340HD. Guess I'll order 170 and up mains and a 96 and 98 needle to go with the std. 97. Time for more research/googling

Look at my profile page and go to the "about" tab, it has my jetting for the 45. I would imagine you would want to mimic that. Again, Curt set it up not me, so take it for what its worth, 97 needle 3rd groove, 167.5 main, etc.

Rod

[Jaybo]

Look at my profile page and go to the "about" tab, it has my jetting for the 45. I would imagine you would want to mimic that. Again, Curt set it up not me, so take it for what its worth, 97 needle 3rd groove, 167.5 main, etc.

Interesting! leaner than the stock carb. Better efficiency perhaps?

[HotRod]

Well remember that you are dealing with 2 different carbs and the jetting for one will give completely different results than for the other.

[davej]

It's not leaner than a stock carb. The difference is in the design and dia of the needle. The stock needle has been referred to as a tree trunk by some when compared to any aftermarket adjustable needle.The HSR carb even has a choice of 3 different dia needles to tune it in nicely. The thinner the needle is the more fuel can pass by it so you can use a smaller main jet and still be richer than the larger stock main jet. The best efficiency and performance comes from a properly tuned carb not necessarily a lean tuned carb. I have a HSR45 on my big bore but also for the reason of getting it at a good price used. A HSR42 is all that is needed for a stock bike but if a 45 can be picked up cheap it can be tuned down to fit your needs.

[Jaybo]

Dave, wasn't referring so much to the needle as I was the main and pilot. I'm running a 170 and 37.5 in my CV40. - I get it though two totally different carb designs. Also, the jetting for the HD 1340cc motor is real close to our 1600 jetting and that seems odd to me too.

[davej]

I understood you were talking about the main and pilot. The dia and taper of the needle directly effect the amount of fuel flowing to the engine.from the main jet The thinner dia of needle the smaller main jet can be used,

[Jaybo]

Oh, I totally got that one too, but I have a pretty slim needle in my CV with the pipes and BAK. Was just looking at the needle profiles of the HSR42 needles and they are quite a bit slimmer.

I did the off road thing with 2 strokes for 20 some years and I got to be pretty good with jetting a 250cc 2 stroke, but that was with Keihin PWK carbs its all relative though, its just learning what needles are what with the Mikunis. Wish I had all of the needles and jets for the Mikunis that I do for Keihins!

[Jaybo]

Will I need a different throttle cable?

[davej]

best if you get a new cable. Shane at ss customs can help. Just tell him that you are putting the hsr on your Roadstar.

[Txulrich]

If I remember right, the pull cable will work fine. The push cable can be made to work (the mount at the carb is different) but it's best to just replace it. Might as well do both while you're doing it.

[Jaybo]

OK, pulled the trigger and ordered the HSR42 a handful of jets and a couple needles to go along with my purdy new air cleaner