a question for the rejet/carbs specialists here !

[FLATSIX]

I don't know that much about combustion / rejetting etc. in order to gain power.

But I have a question, something that is bothering me : -when you have the piston that goes down and sucks the right mix air/fuel into the cylinder, this filled cylinder get the spark and BOEM there is the power.

When you give more air through the airbox, and you compensate that by putting bigger jets in the carbs so that the mix air/fuel again is O.K., will there be a change into the piston goed down, filled cylinder and BOEM - more power ??

How can this be, as the cylinder and the piston stays the same , so the chamber is normally filled the same - so the BOEM stays the same (no gain of power) and I give more air and fuel, but a filled cylinder stays the same filled cylinder??

AM I WRONG - please explain because I don't get how by giving more air/fuel there can be more power ?

(I ask this because with that history of the "foam" I now have the opportunity to play with the amount of air by adding less foam, or no foam at all, then compensate with bigger jets - I run now #78)

Thanks for your replies,
 

[Bone]

Well I don't qualify as a carbs specialist. When changing the air and fuel with the jets we are changing the air/fuel ratio. Basically the same volume is in the cylinder.
Now when you add a Blower, Turbo-Charger, etc. you are forcing a larger amount of mixture into the same cylinder. Usually a BIGGER BOOM

[FLATSIX]

Yes, I understand that by using a blower - turbo the BOEM will be bigger as there will be more to let explode into the cylinder - a bigger BOEM in my pocket also !!!!!!!!!

But I am speaking only about the carbs like they are now on the bike : WILL GIVING MORE AIR AND AT THE SAME TIME COMPENSATING THIS BY PUTTING BIGGER JETS GIVE ME MORE POWER, or will all stay the same as before like OEM.

That's the question 

[dreamaker]

That is a really good question !!! I am shooting from the hip on this one. But in a chamber you have three elements, fuel, air and ignition. I would think if I wanted more power I would have to consider how efficient the fuel is. We all know liquids don't burn but vapor does. Gas has to be a vapor to burn. So even if you fill the volume it doesn't mean you get max power. So when the cylinder fires and there is liquid gas it just goes out the pipe. It seems that to gain max power you need total fuel vapor not just compressing the cylinder with a supercharger. So of the top of my head it would seem that you would just be dumping more fuel out the pipe with larger jets unless the demands of the cylinder is greater then the carb is producing.

Dan

[Ferris Leets]

If you have not opened up the exhaust you won't get as much extra but the carb/intake works on suction.  If you restict the opening (filter) less air can get in to the cylinder in the time that the valve is open.  If you lessen the restiction more air can get in in the allowed time.  Thus a higher air to gas ratio (leaner).  So you have to put in less restiction on the fuel, larger holes, so the fuel air ratio can be correct.
On the exhaust side the same thing if you have restrictive (quiet) mufflers the exhaust pressure has a smaller exit path.  
Combining open intake and open exhaust gives the best flow through and the most power.  However this can be overdone.  There needs to be a balance.  That balance point is what you are looking for.  Nothing is going to be perfect for all conditions.  Drag racing is different than cruizing and if you get too much elevation that will change the mix also because of the thinner air.  Actually you should retune your engine everyday as the barometer pressure changes.

[humshark]

FLATSIX -
Let me try my hand at this.
1) change air filter to let more air move easier
2) change jets to compensate and restore the normal fuel air mixture

Piston and chamber are the same - what changes is HOW EASILY the gas air charge gets into the cylinder.  Since the downward motion of the piston draws the gas/air charge into the cylinder, and now it does so more easily, there is less power USED to do this job, which means it is MORE power available to you to use as you see fit!  Burnouts, wheelies, whatever! 

Also - at higher RPM, the easier moving flow will move faster, meaning that just before the valve closes, you may actually have MORE air/gas charge in the cylinder VS. stock components.

Whadayathink?! 

[Ferris Leets]

At higher RPM there may be a little more flow and therefore more compression but the valve timing is still the same.  Only open for a certain # of °s, but shorter time.

[FLATSIX]

With my second airbox-cover I can give as much air as I want : with the OEM foam 10mm in it the Lady get's just enough if OEM jets #78 in it, so if I take a smaller foam (or no foam at all like your bikes) and I would put your jet in it , your OEM is #100 I believe?? then theoreticly the Baby should fly ??

[Madmike]

http://www.factorypro.com/Prod_Pages/prodh78.html

What is the advertised HP of the European model??

[FLATSIX]

I bought it for 98 HP in '97.

[Robert]

There are two things that remain the same the correct fuel mixture for maximum power and the volume of air that a cylinder can draw in without changes to stroke or forced air induction. Having said this the power gains from rejetting are for two reasons one our Valks are lean for emissions. Which means that given a set amount of air being drawn in instead of it being a 14 to 1 ratio it may be a 15 or 17 to one ratio of  air to gas. By changing the jets you are correcting for that mixture even if you dont move any more air through the engine. Now with the opening of the air box and exhaust or any other thing that cuts down on restriction or generally allows more air to pass through the engine a corrected amount of fuel needs to be added to bring the mixture back to the ideal. By taking out the foam in the air box you are not really allowing much more air in but cutting the vacuum in the airbox and thus the engine doesn't pull as much fuel into the engine. The foam really is not enough of a restriction to stop the air from being pulled into it but it is enough to change the pressure differences in the airbox. If you ever pulled your carbs and looked at the engine side you would see that the hole out of the carb is quite a bit smaller than the hole in the head. This restricts air flow into the engine but is that way because of the low volume of air at idle compared to full throttle, its always a trade off. If you would run at full throttle all the time then you could change the size of the carb body to let in more air and compensate with the correct jets. If you put a exhaust on then you are allowing more air out and there isn't as much of a restriction so then you really need to rejet. Most of the time again Its really not a major difference and would be more felt than really cause trouble but again you could rejet to bring the mixture back to ideal. So to sum it up you can correct for the factory's lean condition by rejetting and bringing the mixture to the ideal with or without any change to foam, filter or airbox. Next if you remove the baffle or foam or filter change then you need to correct for the lack of vacuum in the air/ fuel mix being pulled into the engine and any increase in air flow. Any time there is more fuel to correct a lean mix you will get more power, but not if you go to rich. If you cut restrictions out or change how the air flows into or out of your engine then there will need to be the correct amount of fuel added to the mix. I dont know why in Europe they use 78 jets it could be allot of reasons but I know that Factory Pro has already done the homework and you could call them and ask them to explain what jets will work best for you. The real money is spent in finding out what will work the best under what conditions,which is called tuning and good tuners get quite a bit of money and the only difference is they have already done the leg work for you to see what will work best and are acquainted with variables on what you are working with. You can experiment if you like that by changing the jets and either getting a dyno run with a gas analyzer or you can take the plugs out and look at the center electrode. White lean, tan good, black to rich .

[Ferris Leets]

What is the spec for the US horsepower?

[Saloth Sar]

When you remove restrictions in your intake system the mixture becomes leaner, as you mentioned.  You add fuel to make it a proper mixture and you get a bit more power.  You question is a good one.  The volume of the combustion chamber did not change...but the cylinder charge can.

When you go to K&N, match port, or otherwise create easier flow into the cylinder the air can rush in a bit faster.  When the piston hits dead bottom the intake valve closes.  At the instant before it closes the air coming into the cylinder is slightly compressed by the inertia of it’s flow.  This gives part of the power boost, the engine will actually have more fuel and air in the cylinder.  It the same as a turbo or blower boost but on a tiny scale.

The second part is that an engine is an air pump, it takes horsepower to move air in and out. 

[FLATSIX]

   I am beginning to see some light in the dark now ....

The people of Factory Pro seem to have experience with "export Valks who have #78 main jets" - I will sent them an E-mail and ask how to rejet such exportbike - and the question of the restrictor taken off.

I am curious what they will have available + at their answer.

I'll let you know!

Thanks for the technical explainations - you really do make me a lot smarter ! 

[FLATSIX]

They wrote :

Hi Jos -

Sorry - swamped over here, so short answers..... :-(

Verbinnen Jos wrote:
Hello Guys !
 
I am the proud owner of a beautiful HONDA VALKYRIE 1997 - exportversion - here it's called : HONDA F6C (FLATSIX).

Yep!  

 
This motor is equipped standard with mainjets #78 + the airbox has an airrestrictor by means of a foam with thickness 10mm. that is put into the air-intake of the airbox.

Yes..


 I know that when this foam is taken away there is too much air for the motor - rpm's exceed hardly 3500-4000 rpm - machine does not work anylonger as should, even by putting 8mm instead of 10mm of foam, there is an hesitation at those rpm's , then motor continous pulling.
 
My questions: 1) do you have experience with the rejetting of this type of exportbikes - so with the airrestrictor and the standard #78 jet ??

My feedback is that the bike will be larger than 78, but smaller than 100.
More like mid 80's.

     
                      2) do you have a rejetset selling for this type of Valkyrie - what needles should I put in order to have more power?

Our Euro kit has smaller jets -


Do I need to touch at the airrestrictor (take it away fully or what ??)

Restrictor.... remove -

 
                      3) do you have an idea what the amount of horsepower can be by giving much more air by taking away the inside foam + rejet to get the mixture air/fuel back to normal??

I can only guess, based on  US modles -
Remove top plastic intake restrictor that is riveted to the airbox lid, K&N filter = 4 to 5 hp.

 
My 1997 standard is called : type SC34 (GL1500C2) on the homologation-paper that is with the bike.- rated to be 74 Kw..
Changes made : - cut the piggies at the exhaust - only the piggies (left 1" of them there)

Exhaust changes are 1-2 main jet's worth of change.


                         - K&N filter but with the prefilter and not oiled - normally this must come near the stock-airfilter

stock USA air filter = aprox the K&N with the prefilter.
Remove the prefilter and you need 1-3 main jets larher.

I'd guess that if you
mod exh
mod airbox lid
K&N w/o prefilter

would use
our pilots
our needles in /3 or /4
between 85 to 92 main jets

So - you'd get a special jet kit from us -

Thanks -

Marc

.
                         - for the rest all is standard as it was new.
 
Thanks for your response (with prices , ref.numbers and delivery time if possible)
 
Many thanks and ride safe,
 
Jos (FLATSIX VRCC#25005)
 
 


--
Marc Salvisberg

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Factory Pro Tuning
415 491-5920

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