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To: 'mail@awol.co.za'
Subject: FW: AIRBOX,
----- Original Message -----

Carl Talbot
Monday, February 05, 2007 4:59 PM


Knowledge means nothing if you do not eventually pass it on for the benefit of others too.Consider the following may be of benefit to other Vmaxers too.

Those that know me also know that I take pride in the fact that from the start I have done all servicing , maintenance and fitment on my Vmax.

Can we improve the Vmax performance?

Most of us are happy with the Vmax engine performance.Many make changes.If for example you change the exhausts(like most of us

usually do) some minor jetting could be beneficial.Changing(modifying )the air box will also require some jetting and other changes.The Vmax is old school and there are no computer aided adjustments etc.etc thus no power commanders and electronic engine adjustments.Everything must be done manually by human hand.

More airflow ?

I have purposely stayed away from individual air filters because the engine breather flows through the air box and in my opinion the air box is better in very wet and rainy conditions because it encloses the air intake and filter.Most people will start by fitting an air filter that flows more air.This however will not give a substantial increase in performance because the std air box on the Vmax is restrictive to air flow in any event.All standard Vmaxes have air boxes and exhausts that had to pass noise and emission control regulations in the USA at 4750rpm.The air box and exhaust is a compromise between being efficient at all altitudes(height above sea level),at all rev ranges and to keep engine noise and emissions at levels set by the authorities.

My exhaust

My home town is approximately 4200 foot above sea level.Some of the neighboring towns are as low as 3000 foot above sea level. I run the std exhaust headers with two slip on turn out slash cut pipes (manufactured by Lu Hao) that are pretty much free flowing and no baffles.I had specially made up exhaust piping that balance off the two rear exhausts in the same way that the front exhausts are balanced.Cylinders 1 and 4 are paired to the left muffler and 2 and 3 are paired to the right muffler thus 4 into 2. 

The air box and why ?

Most Vmaxers have removed the Y piece on their air boxes to flow more air in conjunction with a K&N or similar type of filter.When I did this(removing the Y), my range of engine performance was effected.At 4000 rpm the engine was" bogging " and lacked performance.What had happened?Simple...that engine range was now running leaner due to more air flow .Solution...remove the needles shim them (thus making the needle shorter so that it does not stick so deep into the needle jet and richening up the fueling). This is a very easy procedure requiring 4 small copper(brass) washers available at most bolt and nut shops.The effect was a better throttle response and improved low end performance.I can ride my Max in 5th gear at as low as 1500rpm and when I twist the throttle there is no lurching or transmission snatch...it just starts pulling.


I also are of the opinion(maybe wrongly) that the diaphragm springs are too heavy and I have lightened(shortened) them by tying them down with copper wire(5 coils tied back).It works fine on my bike for more than the last 20 000 km.

Air box modifications

My next step in trial and error was to open up the air box with the idea of flowing more air.Making more power is simple in theory ....flow more air and fuel mixture to the cylinders.In practice a lot of factors make this not such a simple procedure.What might work on your Max might not work on your mates Max.Why....well he might have a different aftermarket exhaust on that is more or less restrictive than yours,he may have other main jets ,needle jets,needle length difference,different needle taper,different float level settings,different diaphragm spring strength etc. Another huge factor is height above sea level and it is well known that the best performance is obtained at sea level with higher octane fuel.

Modified air box-a 175 jet would probably work here


MModified air box.This works with 170 main jet and ran highest top end .Maybe a 175 jet and remove the Y?

Changing air box changes fueling

In opening up the air box to flow more air you are making the bike run leaner because it now gets more air in relation to the fuel.There are various fueling stages in the engine,depending on what rpm you're in  so changing the air box changes all the fueling stages;

-the main jet will determine mainly the top end performance(obviously it must be coupled to the right amount of air flow and height above sea level) however it also  effects the other fueling stages

-the float level and needles the mid and upper range

-the pilot air jets effect idle ,off idle and lower range

Running out of air

What I found was that in 5th gear my Max started running out of breath at 8000 rpm.I proceeded to open the air box up by cutting the hole in the air box to match the air filter Later ,I proceeded to then cut some of the material on the inside of the air filter itself and thus opening the air filter up to its maximum size.

My results as follows

The main jet of Vboost model Vmaxes is  a 152.2 Mikuni jet.The equivalent size for Dynojet jets is 162.2.My results with air box mods in terms of top end runs where;

-Std main jet with Y removed and needle shimmed                                                                                          =130 mph  /  209km/h

-Std main jet with Y removed and needle shimmed and air box cut  bigger                                                         =135 mph   /  217kmph

-165 Dynojet with Y  on  and needle shimmed and air box cut bigger  and air filter cut open to max size               =140mph   / 225km/h.some lean surging occurred at 8500rpm and therefore I went to 170 main jet

-170 Dynojet with  Y on and needles shimmed and air box cut  bigger  and air filter cut open to max size      =150mph / 240 km/h

Why the Y

Now you may ask why the Y was replaced.Remember I was in trial and error mode.Once you cut the air box lid(and the Rubber lips off the K&N filter) it is permanent.Because the hole in the air box had become bigger(maybe too big) I needed to replace the Y to restore smaller size and make air intake leaner.The point is if you want better performance you  need more air than simply removing the Y and you need bigger main jets to cope with the increased air flow.

Take note 

REMEMBER all above works on my bike at altitude from 3000-4200 foot above sea level and with the setup I run.BE CAREFUL.We tried  170 main jet set  on my friend  Dok's Vmax. He had Y removed only with shimmed needles and a Marving 4 into 2 exhaust.This exhaust is probably a little restrictive and has a baffle in.He was only able to reach 135 mph and stated at that speed the engine was "surging".What probably was the case was that the engine needed more air in relation to the higher fueling which only can be achieved by more air through the air box out the exhaust..

You decide

So as I said it is not as simple as that.I have merely tried to relate to my fellow Vmaxers what my personal experience has been and in no way am I an expert in this field.I provide these observations not to boast or brag about having a fast Vmax,all Vmaxes are fast.All I am trying to say that there is possibly more performance available without going into major engine mods.My deductions are based on what I saw on on the speedometer( yes speedos  do overhead) however  I can assure you that before this my Max had never seen 150 mph on the speedo .My other deduction was that when cruising at 125 mph  /  200 km/h I can  now whack open the the throttle and there is an instantaneous boost of power that propels you forward.In the past the only difference I could feel with V boost on and Vboost off was that V boost accelerated you faster and helped a little in the top end.Now I can feel a difference from 125 mph  /  200km/h....without Vboost from this speed there is little kick but with V boost on from this speed there is a serious kick. I  reached 145 mph sitting feet forward straight up (with a fly screen)and do not know if that is the fastest it would go and chose to back off.I cant explain it but the engine felt free and unrestrained.I would never attempt this in other than windless days on long straight open wide roads .Maybe now would be an appropriate time also to fit a steering damper too.  

I will be using my Max at  sea level in October 2006 and will know what it does at lower altitude too. 

Finally I guess the question on everyone's lips are what about fuel economy...Well it seems that fuel economy might be up a bit. but not noticeably for me.That being said when riding  very hard I  tend to get 11 km to the litre.That equates to about 143 km  / 90 miles then reserve comes on.By that time I in any event stop for fuel and to stretch my legs.When riding at 120 km/h  / 75 mph  I generally reach a distance of 115 miles / 184 km  before going on to reserve.All this to me is irrelevant in any way...If fuel economy were my reason for riding then a 125 cc would have been my choice of bike.To me the Vmax is all about old school  attitude ,muscle and power. 

   I hope you Maxers that read this respond with your own ideas and observations.Our technical page is about sharing ideas and tips and  is there for the benefit of all Maxers. 


Carl Talbot 

        ps       Keeping at 5500 rpm in 5th gear I can go 100 miles before the reserve light comes on.


Carl's Follow-Up Article
"the Vboost modification known as "T-Boost"

Tuesday, July 03, 2007 10:47 AM

The discussion on how Tboost works,the circuit diagram,how to do it etc is very clear in  Terry Campbell's TBoost Modification article. Apart from my bike I have done the mod on  3 other Vmaxes for Vmaxers I know and it really is not that difficult.

I believe that this is a Vboost modification first done by a Vmaxer named  Terry Campbell.Long before the 2007 model Suzuki GSXR 1000 sportbike came with its 3 power settings this idea already existed and was used by Vmaxers worldwide.I used Terry Campbells electronics diagrams for T boost however I added a further option of switching Vboost off entirely.I therefore have Vboost on/off and a choice of Vboost at 3000rpm or 6000rpm.  

As we all know ,Vboost is an electronically activated servo system that starts to open up a butterfly in the lower carburettor manifold and enables each cylinder to run on the air/feul mixture of two carbs instead of one.The result is a turbo like increases in engine power.

 Vboost raises the horsepower(at the Crankshaft)  from 100 hp to 145 hp at 8500 rpm.V boost also increases the maximum  torque.If you had to look at the dyno graph of the Vmax you would see that from 1000 rpm the Hp increases all the time and peaks at 8500 rpm and then starts to taper off.Similarly torque from idle increases and peaks at 6000 rpm and then starts to taper off.Clearly there are two aspects to measuring the engine performance.

               -Horsepower.In theory,the more horsepower you have the faster a bike can accelerate in relation to its mass(weight).If you want a bike to accelerate faster then make more horsepower or put the bike( and rider )on a diet and loose some weight.Anyway the point is horsepower is what makes cars and bikes accelerate from 0-220km/h faster(in a quicker time).Multicylinder engines usually make more horsepower in a given capacity engine.

              -Torque.This is the measure of an engines ability to do work under load.In other words the pulling power (at lower revs) or its ability to pull or push.Engines of higher piston displacement normally make more torque than smaller ones.Torque is not what causes acceleration.

I have been a spectator at drag racing and it is not always the car or bike that makes the most horsepower that runs the fastest quarter mile times.Many things like gearing,rider ability,having a good launch,rider weight,bike weight,aerodynamics ,good traction and useable power are all factors.When the wheel is spinning or when a rider is burning the clutch for example all add up to slower accelleration.  

VBoost activation at lower rpm ?
What will happen if we activate Vboost at 3000 rpm instead of 6000rpm?Will the overall horsepower increase?....no.Will the top speed increase?......no.Will the bike pull faster from 3000 rpm in 5th gear?.......no.Will the horsepower with Vboost open at 3000 rpm be higher versus Vboost open at 6000 rpm?......no. 

Ok, so why then make Vboost open at 3000 rpm instead of 6000 rpm ?

The answer lies in the following :
-if you want maximum engine horsepower from the engine you need to be in the 7000 rpm zone.Vboost normally starts opening at 6000 rpm and is fully open by 8000 rpm.With Vboost activated at 3000 rpm it is fully open at 4000.The effect and sensation is that vboost comes in earlier and and gets to 7500 rpm quicker.From 7500 rpm to redline it pulls the same.So if you are in 1st ,2nd or third gear at 3000 rpm(and vboost is activated at 3000) ,you will accelerate to 7500 rpm quicker than with standard Vboost.In 4th gear it will feel a little  less so and in 5th even less.Opening up Vboost at 3000rpm gives you a "stronger" mid-range.Of course you will need to be in the proper gear.

   -Riding in town I set boost at 3000 rpm.At 3000 rpm you are going 80 kmp/h in 5th gear.Here you can still enjoy V boost in the lower gears without  breaking the speed limit too much and fuel economy does not suffer.

     -Riding above 80 km while cruising longer distances with 3000 v boost effects fuel economy and is only useful when serious bouts of acceleration are required....I then switch V boost to 6000rpm.

     -Riding at long distances at above 6000 rpm and cruising long distance one can switch off Vboost as it saves a little on fuel economy .Switching off Vboost cuts engine power from 145 Hp to 100 Hp (measured at the crank). Even without Vboost the Vmax is an awesome performer.

     -There is no denying that Vboost at 3000 rpm accelerates you faster to 7500 rpm than with vboost activated at 6000 rpm.

    -In wet conditions Vboost can be switched off

    -The difference between Vboost on/off in regard to top speed is that with Vboost top speed is approximately 5-10 mph faster(depending on the wind and steepness of an uphill).What Vboost really does is it gets you to top speed faster...thus faster acceleration.

With a free flowing exhaust and open air box with bigger jets and shimmed needles the Max really runs exceptionally well(for a 23 year old bike).The Vmax motor is even older than the Vmax.The V4 engine found in the Vmax is a souped up version of a late 1970's engine that was fitted to a touring cruiser called aYamaha Venture Royale.This engine was upgraded with stronger parts and Vboost was added.The engine is a tribute to solid engineering and dependability.Vmax engines are generally bullet proof and have been running strong since 1984.

Why has the Vmax endured for almost 25 years ?

In my opinion that is due to  two reasons:

-that unique V4 power and sound

-that unique style.Vmax is not a copy of anything...there is nothing that looks like it....therefore its style can never go out of style or be outdated.Vmax is instantly recognisable and even today people want them. 

ps Caution The Vmax does not have a rev limiter and will keep reving until ..........it destroys itself. 

Vmaximus Maximus

Carl Talbot 



This page was last Edited
Saturday, 09 January 2016 10:18

Kindly forward any complaints in respect of spelling and grammar mistakes to Mr B. Gates .

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