Removing 95bhp restriction

VMAX  Forum

Help Support VMAX Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

johnpclynch

Well-Known Member
Joined
Apr 18, 2007
Messages
1,015
Reaction score
3
Location
Cork, Ireland
Removing the restriction on a 3UF VMax (95bhp > 145bhp)

DSCN0210.jpg


The Japanese model of the Vmax is restricted in a number of ways
- VBoost, there is none so try to source a VBoost kit (expensive)
or do as I did and install VBoost elimination tubes first
- Carb diaphrams, get new diaphrams or carefully cut out the restriction
- Carb jets, get a jet kit - you should have tried this already
- Exhaust, simply replace with an aftermarket system, slip-on or full
- Speed restriction, don't go over 190kph, buy a Speed-Restriction Modification from Speed & Dyno Shop in Oslo
or modify the speedo to allow you to go over 190kph

Step 1: Getting Boost back!
A solid block of aluminium lives where the Vboost butterflys should be
DSCN0108.jpg


You can replace them with identical but hollow tubes (similar to the stage 7 jet kit)
DSCN0111.jpg


or with a manually operated VBoost
Dscn0606.jpg


or (as I finally got around to) a FULL Vboost system! servo, controller & butterflys

Step 2: Removing the restriction on the carb diaphram
Because of the restriction on the diaphram the slides can only open 80% of the way.
IMG_0414.jpg


The removal is a simple cut. If you are doing this with the restrictor still attached to the diaphram then beware of the rubber diaphram, do NOT touch it with the saw or the results will be disastrous!
IMG_0423.jpg
IMG_0425.jpg


Remember to clean the surface with a file or light sandpaper and do NOT allow any shavings or dust back into the carbs. Air jets could easily become blocked.

Step 3: Removing the speed restriction
On the back of the speedo-needle a disc with two different diameters is mounted.
On idle, one end of this disc is between the two legs of the switch.
Normal running, the disc is turned away from the switch until you reach 190kph.
Over 190kph, the other end of the disc reaches in between the switch, blocking the circuit. This activates the restriction (disables some of the cylinders)
1 - Take a pair of cutting nippers and remove 2/3 of the greater disc opposite the idle-position. Now the disc is still between the switch on idle but the rest is long gone = Full Throttle available! (Nothing's blocking the switch)
2 - or instead of removing 2/3 of the disc, simply bend one edge of the disc so that when it comes full circle it will hit the side of the switch and stop, your speed will keep increasing but the needle will remain at 190kph.

This is the circut in the speedo that restricts your speed.
Note the large (IR/magnetic?) switch in the center, this is what the disc slides between. I didn't want to modify the circut so I modified the disc instead
DSCN0216.jpg


Step 4: Re-Jet the carbs, they will be all over the place
New spring vs. old spring
DSCN0316.jpg


Old needle vs. new needle
DSCN0318.jpg


Step 5? Inspect the cam timing
According to the book, when cylinder 1 is TDC (on the compression stroke) the small holes (A / GREEN) will align with the marks on the bearings (B / ORANGE)
Dscn0087.jpg

Dscn0091.jpg


And as you can see from the above pictures my exhaust cam was out by around 3 teeth on the sprocket !!!

Step 6,7,8,....
Get yourself a full exhaust system, with turbo, nitrous, supercharger, etc.. :biglaugh:
 
Last edited:
I would sell it and buy a different one before i went through all that.
 
Your forgot the CDI swap!

The French ignition curve of the digital CDI (89=>) is very different from the US one.
More advance at 4000, less advance at top end, lot more vacuum advance.
Give smore torque at part throttle at 4000 but kills poneys at high end!

Solution : Buying an US CDI or a Dyna3000 one (no EU curves in it, only US shapes)


Regarding valve timing events mod, never heard of this on french ones and no speed limiter in France, but ours are 2EN, not 3UF...
 
Excellent observations and great write up....Glad I don't have a neutered one :biglaugh:
 
Your forgot the CDI swap!

The French ignition curve of the digital CDI (89=>) is very different from the US one.
More advance at 4000, less advance at top end, lot more vacuum advance.
Give smore torque at part throttle at 4000 but kills poneys at high end!

Solution : Buying an US CDI or a Dyna3000 one (no EU curves in it, only US shapes)


Regarding valve timing events mod, never heard of this on french ones and no speed limiter in France, but ours are 2EN, not 3UF...

I did swap the CDI but I wasn't aware of any difference in the map - I only replaced it because it was newer and it came in the box of parts I bought with the Vboost servo & controller

1993 Restricted CDI
attachment.php


2000 Full Power CDI
attachment.php
 
I checked cam timing events of French motor :
-little hole for rear cylinders
-Big hole for front cylinders.

It seems to be the same as US one..

So timing for Japanese is different (Anyone has a japanese tech book?) or the timing of japanase is the same as others and your engine was badly overhauled by the previous owner.
 
So timing for Japanese is different (Anyone has a japanese tech book?) or the timing of japanase is the same as others and your engine was badly overhauled by the previous owner.

That was always one of my worries, because the cam almost lines up with the big hole.
They may have forgotten what page in the book they were looking at and set it up like the front cylinders :confused2:
 
That's some good info there John. Nice one!

If I were to take a guess, I'd say that the switch in the speedo is a infra-red switch. (Not that it makes any difference.) I'm thinking it probably works the same as the infra red beam they put across shop doors so that when someone walks in it sounds a bell.

THREE teeth out on a cam gear ... that's bat shit crazy! I'm surprised it didn't bend valves.
 
That's some good info there John. Nice one!

If I were to take a guess, I'd say that the switch in the speedo is a infra-red switch. (Not that it makes any difference.) I'm thinking it probably works the same as the infra red beam they put across shop doors so that when someone walks in it sounds a bell.
That's a good point, it would make for much simpler electronics

THREE teeth out on a cam gear ... that's bat shit crazy! I'm surprised it didn't bend valves.
So am I, but it may have been a sloppy valve job/overhaul by the previous owner
 
Manual VBOST . Think you need both hands on handle bards when bosts opened ;)

Yeah, that was a bit crazy. I only used the Vboost on long rides and turned it off around town

but I did hear of someone using a bicycle grip-shift to operate Vboost while riding - throttle on both hands
 
Hi all. I have a Japanese spec model without vboost. Over the past month, bought all the parts listed above from ebay or sean morley. Also, to make it easier, changed the wiring bundle as the Jpn version didnt have the vboost wires, which then required changing my switches and ignition key wiring.

Can now see why everyone raves about the vboost. Just need to get used to riding at higher rpms.
 
Looks like somebody is enjoying the vboot in metro manila now :) you might forget that you have an harley lol

Sent from my SM-N9005 using Tapatalk
 
Hi chaps

Were all jap max's resticted?....i'm looking at a jap import that the seller assures me is full power

I'v not been to see it yet so what the easiest way to tell?

Thanks in advance....the mongrel
 
If the airbox is off, you can visualize the cable and linkage moving the VBoost mechanism, while it makes its noise.
 
Removing the restriction on a 3UF VMax (95bhp > 145bhp)


DSCN0210.jpg


The Japanese model of the Vmax is restricted in a number of ways
- VBoost, there is none so try to source a VBoost kit (expensive)
or do as I did and install VBoost elimination tubes first
- Carb diaphrams, get new diaphrams or carefully cut out the restriction
- Carb jets, get a jet kit - you should have tried this already
- Exhaust, simply replace with an aftermarket system, slip-on or full
- Speed restriction, don't go over 190kph, buy a Speed-Restriction Modification from Speed & Dyno Shop in Oslo
or modify the speedo to allow you to go over 190kph

Step 1: Getting Boost back!
A solid block of aluminium lives where the Vboost butterflys should be
DSCN0108.jpg


You can replace them with identical but hollow tubes (similar to the stage 7 jet kit)
DSCN0111.jpg


or with a manually operated VBoost
Dscn0606.jpg


or (as I finally got around to) a FULL Vboost system! servo, controller & butterflys

Step 2: Removing the restriction on the carb diaphram
Because of the restriction on the diaphram the slides can only open 80% of the way.
IMG_0414.jpg


The removal is a simple cut. If you are doing this with the restrictor still attached to the diaphram then beware of the rubber diaphram, do NOT touch it with the saw or the results will be disastrous!
IMG_0423.jpg
IMG_0425.jpg


Remember to clean the surface with a file or light sandpaper and do NOT allow any shavings or dust back into the carbs. Air jets could easily become blocked.

Step 3: Removing the speed restriction
On the back of the speedo-needle a disc with two different diameters is mounted.
On idle, one end of this disc is between the two legs of the switch.
Normal running, the disc is turned away from the switch until you reach 190kph.
Over 190kph, the other end of the disc reaches in between the switch, blocking the circuit. This activates the restriction (disables some of the cylinders)
1 - Take a pair of cutting nippers and remove 2/3 of the greater disc opposite the idle-position. Now the disc is still between the switch on idle but the rest is long gone = Full Throttle available! (Nothing's blocking the switch)
2 - or instead of removing 2/3 of the disc, simply bend one edge of the disc so that when it comes full circle it will hit the side of the switch and stop, your speed will keep increasing but the needle will remain at 190kph.

This is the circut in the speedo that restricts your speed.
Note the large (IR/magnetic?) switch in the center, this is what the disc slides between. I didn't want to modify the circut so I modified the disc instead
DSCN0216.jpg


Step 4: Re-Jet the carbs, they will be all over the place
New spring vs. old spring
DSCN0316.jpg


Old needle vs. new needle
DSCN0318.jpg


Step 5? Inspect the cam timing
According to the book, when cylinder 1 is TDC (on the compression stroke) the small holes (A / GREEN) will align with the marks on the bearings (B / ORANGE)
Dscn0087.jpg

Dscn0091.jpg


And as you can see from the above pictures my exhaust cam was out by around 3 teeth on the sprocket !!!

Step 6,7,8,....
Get yourself a full exhaust system, with turbo, nitrous, supercharger, etc.. :biglaugh:
 
Back
Top