Carb tuning a 40 yr journey

[8541Hawk]

Well as an old guy I have been starting to get a bit of a mixed feeling to some of the carb threads running around right now.

While I could just sit and laugh at some of the things going on, I actually would like to help out some of these guys but it is not easy.

Part of it is my writing style and the other part is how misunderstood carbs are now...... even worse than the old days when they were all we had.

So I am going to try and cover some general stuff that I hope might save some time and grief for the folks that want to try and really dig into their carbs.

First and most important......carb tuning is more an art than a science.

Some folks don't get this but the easiest way I have found to convey the idea by relating it to cooking.
Just because you have a cook book doesn't mean you are the next Gordon Ramsay.

That is how you need to look at all the charts and graphs you find on the net or anywhere else.
They are just a recipe. While they will get you in the ball park, you are not going to get a 5 star result without much more added effort.

Another thing to remember about tuning a VTR. You are working with "economy" carbs not "performance" carbs (if you need this clarified, let me know ) which limits your tuning options and also adds a bit of complexity to the task of getting everything to work together.

Then we have the dyno....... yes a good tool but not the end all. be all of tuning.
To me it is one of the most misused and misunderstood tools out there.

When I use the dyno I first need to know what the engine configuration I'm working with (talking bikes here) as you tune differently for a Inline 4 (I4) than you do for a V-Twin (V2) or a triple for that matter but we will only deal with I4 & V2 to keep it simple. Though none of the charts and graphs you see mention this......
In the most simple terms with a I4 you tune for peak HP. With a V2 you tune for the best torque curve.

So when I get a chart there is an order I look at things. I4- HP curve, Torque curve, A\F ratio. V2- Torque curve, HP curve A\F ratio.
The peak number is irrelevant, you just want a nice clean curve with no holes or dips on the street.

Had to catch myself there as with everything relating to carbs, there is an exception..... Yes for a track or serious street I4 peak numbers can be important but I tend to default to V2 tuning because that is what I do.

The reason I assign the order of importance for a V2 of :Torque - HP - A\F is because Torque is a V2s life and the ultimate is not a torque curve but a torque plateau.
Which is what a well tuned VTR does. Around 50ft\lbs @ 3K and 70ft\lbs @ 7.5K with a straight line in between.
With the HP curve, just look for dips or holes, other than that not a real big deal.

The A\F curve, It is nice to see it in the "proper" numbers but it is more to see what is causing dips (if you have any) in the other 2 curves.
The reason it is not the most important is that it will be the first thing that changes when you take the bike out of the controlled environment of the dyno room and start rolling down the road.

If you stop to think on it, even the factory gives some clear clues that optimum A\F ratio isn't the best for the "real" world.
My example is the pilot circuit. When setting it, per factory specs, you go to peak RPMs (optimum A\F ratio) and then open it up 1\2 (now rich per the dyno) because in the real world that gives the best rideablity.

Another saying from the past that might have been forgotten : The larger the CV carb, the harder it is to tune.
Taking that idea as a "truth" and then looking at the 48mm carbs (the largest ever on a production bike) you have to accept that they have to be damn close from the factory or the bike wouldn't run at all.

So the whole idea of installing a jet kit and a slip on will get you a big power bump just isn't the case with this bike.
There is no hidden power. All you can do is clean up the slight lean issues that are due to emission regulations.

While each bike will require a little different set up, minor changes are all that is needed with a stock bike with slip ons.
Now if you start changing things, It's a whole different story and can be very difficult to sort out.

This is also where things get tough, and the whole "art" thing comes in.
For me, I can "feel" what the bike is doing and what circuit I am on (with some help from what RPM I am turning) and adjust from there.

I wish I could give a better answer on fine tuning but it just clicked one day after 10-15 yrs of doing it.

My take on modifying parts.

99% of the time you would be better off just taking the bit over to the dust bin and throwing it away.
Sorry but it is the truth. The tolerance of the machined parts can be in the +\- .0005 in range or +\- .0127mm (with the possibility of the +\- being .0000)
Even the loosest tolerance is +\- .005 in or +\- .12 mm
Do I even need to explain why cutting, grinding, filing, drilling these parts is a bad idea?

Before you start in about lift holes, well like I said before, there are always exceptions (you just have to learn them all).
The slide is designed to be drilled there. It is how you "fine" tune the lift speed.
Kind of like the pilot circuit, you have a main bleed and then the number of lift holes is kind of like the number of turns out on the adjustment needle.
Like the number of turns out on the pilot screw, there is a range you want to be in with the lift holes, so that is why I stay away from the 3 hole slide.

The last bit I have to say on this topic is there is a lot of good info already out there on how to set these bikes up.
Lately though, it seems, that many are looking for a "new" way.

I will admit that I have been offended ( I am only human....lol) by some of the stuff I have seen saying this or that doesn't work.
Stuff I have been saying works for years and now all of a sudden someone is claiming I have no clue on what I am talking about....but then I take a set back and remember the learning curve.....lol

What I will say is there really is no need to reinvent the wheel here.
Kind of like I'm going to cook a roast but the cook books are all wrong so I'm going to figure it all out myself, even though I have only read about cooking.

On this board there are around 3 different carb set ups.
All of them work well.
This shows, that again like cooking, there is more than one way to get the desired result, in the end.
It depends on what your tastes are.

Now if you change things (the OCMD crowd) then things can get tough as you must first figure out what changed (the dyno can help here) and then what to change to fix it.....that is where the black magic comes in.
There are many tricks and it will take a while to figure it out.
There was a reason, even back when carbs were all we had, that finding a good carb tuner wasn't easy.
Just like finding a good dinner....not everyone can do it.

The last tip here, TPS.
Just a fine tuning bit though not critical. In fact I would bet that 8 out of 10 people couldn't tell the difference if it was unplugged.
It really does make that little of a difference on this bike.
Yes it is worth the time to set it but again, no big gains just a little better idle characteristics
Also to help the bike pass emissions.
That is why they are not set to "spec" (Yes Honda does have a calibrated ohm meter....lol) but it is set when they run in the engine on the dyno for the idle emission.
That is why they are also all different.

Now you could fit some flat slides and have all the adjustments you could ever want and yes you can get it dialed in perfectly........ today
Though as soon as the weather changes, so will you carb setting and you get to start all over again.
That is why they use CV carbs on the street.

I think that covers the basics and I will say good luck to everyone you wishes to dig into the carbs.
It can get confusing and it is also easy to head down the wrong path.
That is why I say look to the set ups that are "known" to work.

Though again. as soon as you change something, you get to start over.
My set up is no longer like what I posted..... yes it is still based on it but with each change I have made, I have had to figure out what changed with the carbs and what I needed to do to compensate for the change

Hope this is of some help and if you guys have any question, ask away.
Otherwise I'll just at the carb threads as they can be entertaining.......

[TheGingerBeardMan]

Now THAT was an interesting read!

I've always been a bike rider, and not a bike modifier (as in not ferking around with the running/internal performance of it). In my time, I've come across many folk big-boring, porting, skimming, polishing, carb swapping, tricking out etc....and all on road bikes.

Me? I'm just happy to get on the damn thing, and ride it for what it is. If it has performance faults, then I either live with them, or trade the bike for something else.

Unless taking the bike onto a track, I cannot see the point in tweaking a road bike just to get an extra 4 bhp, or save 2mpg extra on the tank range. I also can't understand why the need to change gearing and sprockets for rocket performance when leaving traffic lights. Yeah, fine for pulling away sharpish, but shite when over 30mph in top gear.

I know people have been spannering and modifying bikes for generations. Old Brit stuff, the Café racers, the ton-up boys, the Ace Café and all that stuff from by-gone days.

How fast can you make yer bike go? was THE thing back then. And it still is today. There's always gonna be folk who want their bike to go that extra 1mph faster than Johnny neighbours. But I can't understand it.

Brit bikes in the day struggled to reach the ton. But this modern jap stuff can do nearly 200mph in STANDARD trim. So why the hell need to modify and tweak it?

Don't get me wrong, if that's what people want to do, then fine. But it ain't me.

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These modern Japanese bikes (like the Firestorm/SuperHawk) are designed and built for the road from the "get go". They've been made to suit the majority of users needs (those that want a sporty bike), and thus to perform where needed. In that respect, I am happy to leave everything the way Mr Japanese bike manufacturer had it kicked out of the factory. My Storm will get away from a set of traffic lights and leave a car standing, should I want to wring it's neck. It will trundle...erm...it will lump and lurch...through a town at 30mph, but she will also fly effortlessly into illegal figures, passing traffic like sh1t off a greasy shovel when on an open road, and the space is there to run the bike on almost full chat. And ALL in standard trim.

That said, I have changed my end cans. The only reason I changed them was for the noise it made, and to let it "breathe". Which is a bit daft using that term "breathe", as that's an old farts British bike term from back in the day. Yes, it probably uses more fuel with no baffles/db killer fitted, but that's a price I'm willing to pay to hear the sound of the V-twin growl. I doubt if it's added anything to the bhp or take off speed. No re-jetting was carried out, timings were not altered, cranks were not fiddled with. I just run a standard factory engine, with open ended cans.

In old days, that would have been a case of "all show and no go". Sounds like yer doing 50mph, but yer only doing 15 !

But, modern tech bikes with open cans easily, and effortlessly, do 140mph +, and don't hang about getting there, even with no baffles. And no need to fart about with carb settings.

The only other things I've changed are the tyres, ('cos there's better rubber out there, and better suited to my riding style and the roads I have where I live), and I've got Goodrich braided lines fitted. There was nothing wrong with the standard lines in my opinion, but it does improve the stopping performance. So that's another safety mod. My safety, not the bikes!

As for carb tweaking and modifying to the extent you talk about , I understand and agree with you (although I've never done it myself).

I think, (in fact I can be 100% sure), that of all the bikes I've ridden in all the years, I've only ever had ONE bike into a workshop to get the carbs balanced. And that was in 1990, with a GPZ900R that was stripped and cleaned after sitting in a shed for years with old crusty fuel in the carbs. The bike was trailered to the bike shop and set up properly (as per factory settings), as I didn't have a manual (or the knowledge) at the time to do it myself.

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I am impressed with some peoples tweaking and modifying though. Some folk can do stuff that really blows my mind. How to extract extra oomph and zoom out of their machines. On a track, superb!, but to me, useless on a street.

I was always one to shy away from buying a bike that has been heavily modified internally, or "race parts" fitted - as it means the bike has more than likely been hammered and thrashed within an inch of it's life. That in-turn, means premature internally stressed components, and probably will lead to an early death of the engine. Perhaps. Some folk are lucky, and can buy a modified/tweaked bike and it lasts years. But I won't take that chance. Ok, an un-tweaked bike can still go tits up after buying it, but the odds are in it's favour it if it's been looked after properly and serviced at regular intervals.

I make exceptions to modifications that have been done to SAVE the engine. Like with the CCT mods done to the Storm. It's not directly affecting or altering the performance of the bikes motor.

Carb tuning (or balancing), to me, is necessary now and again, (if things need re-balanced after a full carb strip down and rebuild), but you'll never get me Dyno-jetting, or running the nuts of a bike on a Dyno-bench, just to get some top line figures to go "oooh" at.

The bike in standard factory trim can already do more than twice the legal speed limit in the UK (145-150mph), and I can't see any reason to want to screw an extra 10mph out of it.


Ok, this blurb probably has nothing relevant to do with your post, and if it did, I've probably gone waaaay off topic, but, I just thought I'd share my thoughts. All in all, I'm happy with the bikes I ride as they are.

The old saying "ride what ya like, and like what ya ride" is true for me. And also "if it ain't broke...don't fix it". (And yes, I can hear people saying "I ALSO like what I ride, but I like to ride it a bit faster with this, that and the other done to it...)

Now, I know it'll rattle a few cages in here, but if it has, then I hope folk understand that it's a personal choice, and, if stuff works for you and keeps yer happy, then I give you both my thumbs up!

Again, don't get me wrong. I can hear folk shouting "why is he on here if he's not interested in mod-ifi-cating his bike?". I enjoy reading and viewing the photos on this forum of all the folk who take the plunge and really transform a bike. Be it changing wheels, swing-arms, bars...whatever it is. But, I'll keep the Storm as standard as I can (personal preference n all that jazz). In the meantime, y'all crack on with the welders and angle grinders...

Best regards.

Dave.

[Cadbury64]

To Hawk and GingerBeard, thank you both for taking the time to express, so eloquently, your views on modifications. It is posts like these that keep forums alive, in that they are thought provoking and informative, and uncover a lot of the man behind the message.

I've done a little delving into carbs on a previous RF900 to correct some wear and tear (emulsion tubes) but also to correct for filter and pipe changes; for the latter I simply followed FactoryPro's suggestions and luckily just nailed it. Given the sensitivity of the VTR, I am reluctant to break into the carbs unless I need to, but if I do, I will be looking to Hawk's helpful posts.

I'm probably more in Ginger's camp in that I like my bikes to run well and sound good doing it, but don't need them to break any land speed records or hoist 100 mph wheelies. So I've left the engines alone from a major mods perspective but have enjoyed (OK obsessed over) maintaining them as well as I am able. To that end I can proudly say that on both my bikes (I also own a VFR800) the valves are adjusted within spec, the carbs/starter valves are perfectly synched, the air filters are clean and fresh oil is circulating through a new filter. They are also cleaned and lubed, and kept polished, because even though they were cheap, older bikes (in total the two bikes are worth less than 1/3 of a new VFR800), they deserve to be loved.

I will say that the TPS adjustment was worthwhile on my VTR, it comes off idle more eagerly now that has been set, and idles like a metronome.

My modifications have been more targeted towards chassis improvements, as these are areas where the original design and intervening years have left a fair bit wanting. With the suspension working well, you can use more of the available power, under more control and in a safer, more relaxing manner.

[Pete.L]

Good posts Boys!

Just because you have a cook book doesn't mean you are the next Gordon Ramsay.

Great analagy Hawk. I too used to get upset with some of the infomation posted, especially if it wasn't right or simply misleading or ill informed. I don't get so wound up about it now and like you said, there is a learning curve and I think it's great folks want to share there investigations/ mods and results. This would be a poorer place with out it. I also think It great people don't just "flame" ( to steel an americanism ) for the sake of it but they are not worried about speaking up if they feel something said is fundamentally wrong.
Keep posting Hawk, commen scence and good knowledge will prevail in the end

GBM,
Something to be said for "if it ain't broke, don't fix it" Personally I think people will always try to personelise what they have, even in some small trivail way, furry dice in a car or type of air freshner, it's human nature. That said, there is also quite a bit of satifaction in keeping something as close to original as possible. I too love all the pics and reading about the modifications and seeing the skills of others.

Cadbury,
Hello brother from another mother! I too used to have a RF900. Easiest thing in the world to fit a dyno kit and get better results out of
I'm from your school my self, I've only done mods to improove safety i.e some niosy pipes so people know I'm coming... which then led to some engine tuning so as not to damage valves. Better suspenders, for increased braking and handing capabilities. Well, that's how I justified it

Pete.l

[fabiostar]

and that is why in two years of owning a firestorm i havnt touched my carbs, balanced my carbs or even know how to find my TpS ,iv also still to ride a storm that pulls better than mine so im leaving well alone..

[uk13iker]

Great posts and the original post is a good read. My bike had a nice loud set of cans on when I bought it that would of been the only thing I would of changed but was already done. When I serviced it found it had a pipercross filter on then after 1000 miles of riding and coming up to 16k I took it to a mechanic for a full service when I went to collect the bike he gave me the pipercross filter and told me he's put an original back in. The bike runs much better and pulls smoother through the revs and even runs better at lower speeds and low revs can't imagine what a faster bike would be like lol

[Stephan]

Hope this is of some help and if you guys have any question, ask away.

how to get rid of transition between pilot and needle circuit? I struggle with it for a long time, details here

http://www.vtr1000.org/phpBB3/viewtopic ... 5&start=15

Now I really don´t know, where to go. 4-5 area is dull, but definitely rideable. Change from one slide hole to two seems to me good way to go, but I am not certain about needles, as this change came with slide holes.

Currently I have oem needles, but top end seems to me slightly affected by this change, so now I consider to go back to FactoryPro needles with two slide holes, just 0,5 mm up from current setup to get leaner condition. Another thing I have in mind is to richen pilot circuit by pilot screws to get richer condition, so there would be smaller change between pilot and needle.

Please take a look on blue and red lines, any suggestion would be great.

[8541Hawk]

Hope this is of some help and if you guys have any question, ask away.

how to get rid of transition between pilot and needle circuit? I struggle with it for a long time, details here

http://www.vtr1000.org/phpBB3/viewtopic ... 5&start=15

Now I really don´t know, where to go. 4-5 area is dull, but definitely rideable. Change from one slide hole to two seems to me good way to go, but I am not certain about needles, as this change came with slide holes.

Currently I have oem needles, but top end seems to me slightly affected by this change, so now I consider to go back to FactoryPro needles with two slide holes, just 0,5 mm up from current setup to get leaner condition. Another thing I have in mind is to richen pilot circuit by pilot screws to get richer condition, so there would be smaller change between pilot and needle.

Please take a look on blue and red lines, any suggestion would be great.

Well I even impressed myself after looking at your chart..... the reason being my first reaction was....are you dealing with an aftermarket exhaust system...... then read the link

I do know what you have been going through as the Akro system has been a bit of a pain for me also......lol

In your situation, I would go back to the FP needles mainly because they are easier to adjust as any of the "normal" needles will give a good result.
Then go to 2 lift holes in each slide.
This should gt you close and then adjust stuff from there

[Stephan]

thanks for that, I came to the same conclusion. Just come back to FPro with two slide holes, but adjust them for one slot to get leaner settings, rear 0.5mm up. This could solve the top end which seems to me a bit worse now with oem needles. It is strange, but when we tuned it, I saw that change of needle can do it.
In the past I ran one setup with strong mid range, it lead me to believe that these FPro needles are tuneable.

Just for curiosity, rear cylinder with needle set for leanest condition, ran quite badly - too lean, and we ended up with shim in the middle. As it was end of the day and we ran out of time, we left this setup.

From pictures I see akra system is very similar to mine.

[8541Hawk]

thanks for that, I came to the same conclusion. Just come back to FPro with two slide holes, but adjust them for one slot to get leaner settings, rear 0.5mm up. This could solve the top end which seems to me a bit worse now with oem needles. It is strange, but when we tuned it, I saw that change of needle can do it.
In the past I ran one setup with strong mid range, it lead me to believe that these FPro needles are tuneable.

Just for curiosity, rear cylinder with needle set for leanest condition, ran quite badly - too lean, and we ended up with shim in the middle. As it was end of the day and we ran out of time, we left this setup.

From pictures I see akra system is very similar to mine.

Yeah with your stg1 set up you might try running the rear needle 1mm higher than the front to see if that might be helpful

[VTRDark]

Fantastic reading guys. good thread.

Some great analogies there Mike and I agree with the majority of what you say, though I do disagree with the weather not affecting things. Yes they are a constant velocity carb which by their very nature of design are not as sensitive to temperature and altitude changes, but for some reason with this bike I can feel the change. Maybe it's because these carbs are so bloody big and temperamental. I have been out on a hot day and the bike runs better in the cooler evening coming home than during the hot day, which suggests running a little rich. This could go the other way when tweaking the fuel screws or the weather is drastically different the next day. It definitely rides different according to the weather a bit like the way it gets choked up when in lots of slow moving traffic and fly's like a bird released when opened up on open roads, which kinda frees things back up again. Saying that though my setup is probably right on that borderline a fine balance from running a little lean to rich.

Thanks for the info on the slide holes. I never thought of them as a fine adjustment to the needle circuit like the fuel screws to the pilot circuit. That makes perfect sense, though harder to tune. Unlike the fuel screws which fine tune mainly the pilot circuit and a little to the lower end needle circuit as they cross paths. With the needle circuit being in the middle any adjustment affects both the pilot circuit and the mains. This is why I guess it is best to start one end or the other and not try to tune from the middle. Either start at the mains and work your way down like in the FP CV carb tuning instructions or start the other end at the pilot.

I totally agree with "there is more than one way to get the desired result, in the end.
It depends on what your tastes are." another one is "there is more than one way to skin a cat"

The TPS is a funny one. For some folk it works well and for others it does not. Back in the early days for me personally it done exactly as factory pro suggested and smoothed out the steady state cruise. My idle was better too. It also had a side affect of alleviating the carb fart and odd cutting out at lights along with a carb balance.

My bike is not exactly standard any more either. Having adjustable needles if one has Dr Honda stacks etc or changing the filter from standard is a must to get things tuned right IMO. Like you say in your carb set up with a standard filter and stacks you can get away with shimming the original needles which IMO are bloody good needle profiles. Stick a K&N or equivalent in and your on your own

My bike ran smoothest with the standard filter but felt a little flat. I have also tried a K&N which made the bike lively but harder to tune and very temperamental. I settled on the BMC street filter as a compromise and I am happy with it. At the moment if I give it the beans on the right type of road surface and happens to be at the right speed and revs it will power wheelie (little wheelies) in 2nd gear when I slam the throttle open. It's fun at the moment

We all speak from experiences and we can give advice and this is either taken onboard or sometimes one has to experiment and learn for oneself. It's kinda cool that people are still willing to experiment and push boundaries. Sometimes it works and sometimes it does not and we can all learn from each other as a collective Some people see drilling out a jet to a larger bore as being wrong and others feel it's OK to do so it's a bit like Potato pronounced (pot tate toe) and Potato pronounced (po tart toe) or Tomato pronounced (tom mate toe) and Tomato pronounced (tom art toe) as long as the end goal is reached.

(:-})

[sirch345]

I must admit I've enjoyed reading this, thanks for posting guy's

Chris.

[kenmoore]

After 3 years with my bike I can fully understand most points of view.

We all do different things to our bikes for different reasons, we all experience different usage as well.

About 2 years ago I modded my engine to get more power and then realised that it ran like sh1t.

I addressed the carbs with jetting etc and was very happy with the result so I have left it well alone except for syncing from time to time. Even drilled the slides only to find that it ran shithouse and then returned to standard slides and it ran great so left it like that.

I must admit that with the setup I run I reckon that it reacts differently to different weather conditions, however because it performs so well over a wide variety of conditions I have chosen to leave well enough alone.

I do admire those that continue to seek improvement even though their bikes perform and run well.

Sort of like a holey grail!

I watch this debate/ discussion with interest , and still believe that one of the most alluring things about this bike is the fact that it has carburettors.

One day there will be no one that has a clue about how these things work, glad I won't be around to see that!

I feel lucky that I have a set up that works after reading about others experiences ,and am now too scared to change anything in case it stuffs the way that it runs.

Having said that, if something came along and there was enough evidence that it improved the bike, if I was bored I would probably try it.

Interesting ready for sure!

[rollingthunderx2]

Probably picked the hardest carbs on any bike to tune

[kev64]

Good read this , thanks, since ive owned my storm for 10 months, the carbs have been
on an off more than I can count, I like trying new ideas, at the moment
I think mine is running well but is in truth probably running worse than when
I bought it !!
One thing I will say is that at the moment im running with a k&N filter and dyno jet needles,(and 3 lift holes front and back)
set to 3rd slot from the top and runs with no flat spots, and good midrange, and gets a return of approx. 110 miles before red
fuel light comes on, I reckon im not far away( in my eyes)
I will carry on tinkering (because I enjoy it) , next up suspension !!!
Good read guys