Carb set up

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8541Hawk
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Carb set up

Post by 8541Hawk » Tue May 28, 2013 6:40 pm

Carb set up

This thread has been around for a while on the US forum with many good results.
Just bringing it over here in case someone hasn't seen it or are not happy with your current set up.

Another way to put this after reading more on this forum and Roger D.'s post, this is more of and based on the Bob H. carb set up as he is the one who got me started with it and gave me my first base line settings for my HRC jet kit.

I will also ad a bit of new stuff at the end as I've been running the Al stack for a while now and have changed my opinion on a couple of things.
So here it is though the pic is missing..... though it is not really necessary.

As I've been asked a couple of time and with all the issues I've heard about with carb set up I guess it's time to pass on what I have learned in the last 14yrs of owning a SH (yes I picked mine up in 97)

Note: The following set up works with a stock airbox and stock air filter. If you want to run a aftermarket filter or airbox mods, you are pretty much on your own trying to get it dialed in correctly.


I have arrived at this set up by taking the info I have received from Dan Kyle, Bob Hayashida and HRC. Then by a little experimentation and looking at how HRC did things, I have come up with what I feel is a very good base line set up. As with all tuning, this is just a starting point and you will need to fine tune for your bike.

First lets cover a couple of things. First is the old axiom that the bigger the CV carb, the harder it is to tune. As this bike has the largest CV carbs factory installed, it is no wonder you hear about all the problems getting them "right". I've read many posts where people state that "the bike runs great, except at..... insert low end, mid-range, etc here.
To me this is unacceptable.

Then there is how the aftermarket jet kits (except HRC) deal with the stock set up. They address the low end /mid-range lean condition by running larger mains and a different needle profile and in the case of DynoJet by getting the slides to open sooner & quicker. While these methods work well with most bikes, on a SH there is IMHO a better way.

The HRC kit comes at things a bit differently. Though it is really for a full race set up and if you want to run ram air or a real high flow filter, then their method of plugging the air bleeds and running small jets is the way to go. On a street set up, this really isn't all that good of an idea. I'll just leave it at that for now. It can be discussed later but really doesn't have a lot to do with what this is trying to accomplish.

The main thing a street rider can get from the HRC set up is a modification they have done on the slides and their recommendation to run #48 pilots. The slide mod is useful to widen the power band on a bike with stock velocity stack. It also can be used for racing where the set up is 2 short stacks. This same method is what is needled with stacks like the Dr. Honda units which go rich in the mid-range. Though I am getting ahead of myself, so I'll explain the mod and what it does in a bit.

So back to the stock set up or starting point. The problem with a stock bike is it is a bit lean on the bottom and mid-range and pretty close on the top end by what I have seen. The good part is the stock needles actually are very good. In fact they are some of the best stock needles I have ever seen. Which leave us with how to get the best performance from the bike.

So here we go. The first step is to install a set of #48 pilot jets (per Dan Kyle & HRC). You will here people say they have tried this and it didn't work. The reason for this is that they have done it along with installing a jet kit. As I stated earlier, aftermarket kits install larger mains and different needles. When you change both, you end up too rich with a stock motor. It's a one or the other with this bike. By upping the pilots you cure the low end leanness and also add a little to the top end as the pilot circuit doesn't turn off, so larger mains are not required.

Then you need to shim up the needles. While they have a very good profile, they are a little too long for performance. The question here is how much do you shim them. Around .040" is a good starting point but will need to be tuned to each bike. Also there is more to it than just shimming both needles .040". One of the set up tips from HRC is to use one more shim on the rear needle than you use on the front (this tip might be helpful to try on bikes with an aftermarket kit also). So what I do when setting up a set of carbs is remove the stock thin washer that is under the front needle and leave it in place on the rear. With this method you actually end up with the front needle approx. .030" higher than stock and the rear .040" higher than stock which seems to work well.

So You can stop at this point, put it all back together and start with the pilot screw set at 2 1\4 turns in the front and 2 1\2 turns rear as a start and the bike will work pretty good but it can be better.

This is where the HRC slide mod comes into play. What is this "secret" mod? Well it really is quite simple. We'll start with this hijacked pick once again

Carb set up-slide-jpg

The 2 holes are called lift holes. It's where the slide gets the pressure differential signal which causes the slide to open. That is why DynoJet has you drill an extra hole, to cause the slide to open sooner, but that is the wrong way to go IMHO.

Because of the different length velocity stacks what is really going on with the bike is the front cylinder slide opens too quickly causing the front cylinder to go rich in the low to mid-range. FactoryPro even recommended running an emulsion tube from the rear in the front to help cure this problem.

Now the HRC cure for this is to supply a slide with one lift hole. This will lean out the low & mid while not effecting the upper mid-range and top end. So the last step would be to use some epoxy and seal one of the lift holes in the front slide.

This will give you a very good baseline set up. Yes some tuning will be required but all it involves is adjusting the washer stack ( you might need to raise or lower the needles a small amount) and set the pilot jets per the service manual.

The HRC type slide is also the cure for the Dr. Honda stacks which cause the over rich mid-range. The problem here is the stacks create too good of a vacuum signal to the slides causing them to open to quickly. So in this case you would plug one hole in each slide. This will eliminate the rich condition without causing a lean condition on the top end.

Hope this is some help to you guys.

This thread might help if you are having the common why does the bike go rich when I mod questions:
viewtopic.php?f=9&t=36367&p=378469#p378469
Last edited by 8541Hawk on Sat Apr 04, 2015 6:23 pm, edited 2 times in total.
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macdee
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Re: Carb set up

Post by macdee » Tue May 28, 2013 6:57 pm

hi hawk great post
just one question
what size are the washers that you use to lift the needles
in thou or millimeters
you yanks really need to start using metric :lol: :lol:
told you not to but oh no you knew better

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8541Hawk
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Re: Carb set up

Post by 8541Hawk » Tue May 28, 2013 7:03 pm

macdee wrote:hi hawk great post
just one question
what size are the washers that you use to lift the needles
in thou or millimeters
you yanks really need to start using metric :lol: :lol:
What is funny is I had to convert my numbers to inches for the damn yanks as all my stuff was done in mm

What you want is .5mm thickness washers. That is what I used but they are all but impossible to find here.
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lloydie
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Re: Carb set up

Post by lloydie » Tue May 28, 2013 7:10 pm

i just phone up dyno jet and order needle washers from them cheap too
( dyno jet uk 01995 600500 ) :thumbup:

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8541Hawk
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Re: Carb set up

Post by 8541Hawk » Tue May 28, 2013 7:46 pm

I found this the other day and while I have to give it negative points for not giving links to some of the statements listed in all I found it does a good job of explaining a few things.
Yes it is written for an RC51 so you need to change power commander adjustments for carb adjustments and such but as far as late "90s on Honda airboxes and stock air filters to be right on.

http://www.hondavtrsp.com/forum/viewtop ... f=5&t=1032


K&N's Taking them off.....

Postby sparkysp2 » Tue May 01, 2012 5:08 pm
Testing of aftermarket airfilters on the RC51 has yielded poor results. Typically there are no real world benefits to aftermarket filters for the RC51 as small hp gains can be obtained on topend, but only with a trade off for mid-range hp. Truth be told every single Honda sportbike in the last 10 years has had losses in power at some point in the rev range or even throughout it from the addition of K&N , EMGO, BMC filters etc... The only real exception being the Airbox Plus kit developed for the 900RR from Factory Pro tuning which does increase hp throughout the rev range on the 900RR, but in my experience requires some pretty extensive jetting to get it right and it uses a filter system inside the airbox at the end of each intake snorkel tube.

Since this article was originally written we've also had multiple issues with drivability on the Honda 919 that resulted in small stumbles and hesitations at lower rpms. None of these were able to be ironed out with mapping changes, but simply swapping out the K&N filter & reinstalling the OEM air filter instantly fixed the problem. I don't think much else needs to be said on that...

Interesting info #1: Flow testing on the stock filters performed by Brian Sheridan of Sheridan Racing Design proved to us that the OEM filters are more than capable of flowing more air than the engine can use


Interesting info #2: Dyno Testing on the BMC filters showed a definite decrease in topend horsepower with only a very slight gain in the mid-range. dyno charts from testing on 02/23/02

Note: when testing new high flow filters it is imperative to allow them to be broke-in properly by getting some miles on the bike at normal riding speeds. The oil applied from the factory can be initially too thick & can cause flow problems which can mis-lead dyno results in either direction. You may initially get good dyno results, but when the oil dissipates & the flow increases your dyno results may worsen or vice versa. Simply put with the extra oil in the filter you might get a good or bad initial dyno run, but after the oil is thinned out the dyno results may change (& usually do) just depends on the bikes flow characteristics

Additional common dyno testing discrepancies are discussed here dyno tuning basics



Back in the old days all the bikes benefited from slapping some individual pod filters on & adding some larger fuel jets... Things have changed greatly in the last decade whereas it's not uncommon for today’s custom jet kits to use smaller main jets with slimmer needles etc... to gain more horsepower & a more linear power delivery instead of just following the old cliché of bigger is better.

Since originally posting this page I have received hundreds of further inquiries about testing methods involving ram-air & how do I know the aftermarket filters don't work etc... Well there are more ways than just dyno testing to get results. Utilizing an Air/Fuel meter while riding in real world conditions will reveal alot of what your bike is actually doing, but even then not everything may be as it seems, sometimes a rich condition will be reported when the reason is that too much air inside the airbox is causing turbulence & stalling the airflow etc...

Some airfilters do work on certain bikes & some don't affect performance at all, but most aren't worth a damn for the overall performance advantage. The OEM filters are tuned to a specific resonance inside the airbox & once you go altering that you get various results. You might get better top end, but poor low end or vice-versa or you might get better performance with a bad stumble that lasts only for only a 200 rpm range or you may simply get a dip in power at some point. The combination of results is almost infinite.

The main thing to remember is that on streetbikes you need drivability. If you were to put a graduated scale on your throttle housing & make a mark on your throttle grip you would find that you rarely exceed 10% throttle while riding around, yup no crap, 10%! Even when aggressively leaving stoplights & such you really don't open up the throttle all that much. So you need to have your bike as responsive as it can be at low throttle positions & in the mid-range of the bike where you ride the most. Way too much emphasis is put on peak hp when in fact you rarely ride around at redline with the throttle pinned to the stop... It's all about better mid-range performance & that is coincidently where the high flow filters usually hurt performance.

Honda's are definitely more applicable to this issue than the other manufacturers. It would appear that Honda spends more R&D time than any of the other manufacturers to insure that the intake system on their bikes is finely matched to the flow characteristics of the motor. The airbox is perfectly tuned to accept x amount of air thru the filters & deliver it to the carbs or throttle bodies in a metered volume & every thing works perfectly in sync in the state of tune they must be in to pass EPA Emissions testing. Typically an alteration of the filter leads to too much turbulent air entering the airbox & usually ends up either leaning out the motor or stalling the airflow altogether.

What would be more beneficial for creating more horsepower would be a larger airbox, which would make a larger amount of air "available" for the motor to use as opposed to a greater volume of air that the engine would be "forced" to use if you went with hi flow filters or filterless. What you don't want to end up doing is putting more air into the airbox than the engine can mix with the fuel. If that happens then you have screwed up your air/fuel ratio & you will lose power.

I'm not going to outright say that there is nothing to be gained from aftermarket filters, but I will say that most top-notch tuners will sway you a different direction especially if you are riding a streetbike as opposed to a racebike. Citing drivability issues as the number one concern.

Another point routinely thrown in my face is that the aftermarket filters are "re-usuable" Which simply put means that not only are you spending $80-$100 for a filter, but you also now have to purchase an additional cleaning kit so that you can wash, dry & oil your expensive filter, but in less time that it takes you to just wash the re-usable filter I can remove my old OEM filter, throw it away, install a new one & be off riding... If you are one of those people that are going to argue the cost savings of aftermarket vs OEM filters then you are into the wrong sport as nothing about a sportbike is cheap, not the cost of the bikes, insurance or maintenance period & you should be prepared to pay a few bucks every 4000-8000 miles for a filter.

Let's take a different look at it. If K&N filters really were the instant bolt-on horsepower that they are claimed to be in those ridiculous tv commercials then why doesn't K&N simply put a picture of the dyno chart showing the gains over the the stock power curve right on the box for every air filter they make??? Could you think of a better marketing strategy proving to the public that the filters actually work? Unfortunately they don't always make horsepower and sometimes decrease performance so obviously this simple tactic won't work... Caveat Emptor

In the end one thing is for certain if you are going to use aftermarket filters & get any appreciable gains from them it's going to require a Powercommader, alot of dyno time & probably some creative airbox mods too, maybe even to the point of fabricating custom bellmouths to get it dialed in correctly & you must also consider that in some cases there are no gains to be had & in many a loss of performance or drivability can occur!

BTW because someone always brings up the fact that they use K&N filters in their car or truck & they do work under those conditions I must add that I too use K&N filters in my vehicles & they do show definite increases in power & throttle response, but cars are differerent from current bikes in that they have a closed loop Fi system that can compensate for the air flow variance whereas bikes use an open loop Fi system that cannot automatically compensate. Adding supporting evidence to my theories of airbox turbulence you will be interested to know that K&N has developed many different types of turbulence diffuser inserts for many different makes of cars & trucks that lessen intake turbulence when using their filters to increase performance. So far nobody has developed a way to even test for turbulence on motorcycle induction systems let alone cure it...

(C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 http://www.rc51.org ROGUE
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Re: Carb set up

Post by sirch345 » Wed May 29, 2013 7:05 am

Thanks for posting this 8541Hawk :thumbup:

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Griff1977
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Re: Carb set up

Post by Griff1977 » Mon Jul 01, 2013 9:24 am

This is where the HRC slide mod comes into play. What is this "secret" mod? Well it really is quite simple. We'll start with this hijacked pick once again

Carb set up-slide-jpg

The 2 holes are called lift holes. It's where the slide gets the pressure differential signal which causes the slide to open. That is why DynoJet has you drill an extra hole, to cause the slide to open sooner, but that is the wrong way to go IMHO.

Because of the different length velocity stacks what is really going on with the bike is the front cylinder slide opens too quickly causing the front cylinder to go rich in the low to mid-range. FactoryPro even recommended running an emulsion tube from the rear in the front to help cure this problem.

Now the HRC cure for this is to supply a slide with one lift hole. This will lean out the low & mid while not effecting the upper mid-range and top end. So the last step would be to use some epoxy and seal one of the lift holes in the front slide.
Hawk, interesting reading, thank you. I have gone the route of the Factory Pro 1.7 kit using their adjustable needles and drilling the main jet air holes. What are your thoughts about if I'd discover benefits with blocking a front slide lift hole? I'm assuming once the hole is blocked with epoxy resin you've got to make sure it's smoothed out properly to avoid interference with its operation?

I'm running #50 pilots which I've discovered makes it to rich at 0-1/4 throttle position so I'm planning to lower to #48s and up the mains to 182f/185r (FP jets) and prob reduce a/f to your base setting. I might just block the front slide hole at same time, depending on what you suggest.

Thanks again for your advice. Regards, Griff.
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Re: Carb set up

Post by Gazfirestormowner » Mon Jul 01, 2013 9:38 am

What would be the advantage of blocking an air hole I only ask as when rebuilding my carbs the other day I noticed one of mine was covered with what would look like epoxy resin I just presumed it was standard cant remember now though if it was front or rear carb.

I will have a look when I raise the needles so I can remove the baffles.

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Re: Carb set up

Post by 8541Hawk » Mon Jul 01, 2013 4:38 pm

Griff1977 wrote: Hawk, interesting reading, thank you. I have gone the route of the Factory Pro 1.7 kit using their adjustable needles and drilling the main jet air holes. What are your thoughts about if I'd discover benefits with blocking a front slide lift hole? I'm assuming once the hole is blocked with epoxy resin you've got to make sure it's smoothed out properly to avoid interference with its operation?

I'm running #50 pilots which I've discovered makes it to rich at 0-1/4 throttle position so I'm planning to lower to #48s and up the mains to 182f/185r (FP jets) and prob reduce a/f to your base setting. I might just block the front slide hole at same time, depending on what you suggest.

Thanks again for your advice. Regards, Griff.
Well I have not used that kit before but blocking a lift hole on the short stack should work in this application also.

The jet sizes will be different as the larger air bleed will require larger jets to flow the same amount of fuel, so you are kind of on your own to figure out what your bike wants.

Yes you smooth out the epoxy after you plug the hole but it is actually rather easy to do.
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8541Hawk
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Re: Carb set up

Post by 8541Hawk » Mon Jul 01, 2013 4:47 pm

Gazfirestormowner wrote:What would be the advantage of blocking an air hole I only ask as when rebuilding my carbs the other day I noticed one of mine was covered with what would look like epoxy resin I just presumed it was standard cant remember now though if it was front or rear carb.

I will have a look when I raise the needles so I can remove the baffles.
The reason for blocking a hole in the front carb slide (when running stock stacks) is the the front cyl. goes rich in the mid-range due to the slide opening too fast.

Another side benefit is that is stops the slide noises at idle and low RPM as the slide no longer slams open and closed.

In short it is just one of those things that helps smooth out the powerband. :wink:
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Re: Carb set up

Post by Gazfirestormowner » Mon Jul 01, 2013 6:13 pm

A benefit that it is blocked then bonus

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Re: Carb set up

Post by ptynan » Tue Jul 09, 2013 1:09 pm

great post
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