So, the bike I am building will have a Mikuni TM40-6 carb. It has a (capped) vacuum port at the rear of it.

I am using an Ultima ignition system that works with VOES.

Is it worth adding a VOES switch to the bike - and if so, what version should I go for? They seem sot be available in different "Inches of Mercury" settings - 4,6,8 "Hg etc...

The bike is a 1980 FXWG and will be pretty stripped down in terms of weight. It will be a solo only bike. Standard 80", but blueprinted, trued and balanced motor with 9.5:1 CR, Andrews #2 grind cam and generally set up really well mechanically. Single plug heads.

Standard 4 speed 'box, with (currently) 25/51 sprockets.

Any thoughts from those of you experienced with this?

 

with that compression i would use the 8 inches as a start, you want to pull timing out early not later as would be with a lower number < lower number switch is a sporty

and yes i would and have used the switch when i use the ultima ignition

the cam choice you have is also too narrow in duration, the valves are closing early it will have lots of static compression < the valves closing early gives the piston compression travel greater squeeze ie - higher static compression - and you may have to adjust it for more if it pings 10 even 12 inches

9 - 1/2 should have a B andrews for hyd lifters

 

Thanks John,

8 inch VOES switch it is then.

The #2 grind cam came recommended by Scott at Hillside. But your note makes sense. I'll see how it goes and then switch the cam out if I am not happy with it.

 

you will need a professional to install the springs on the heads with a # 2 cam - the travel will be the issue from the bottom of the top retainer to the top of the valve guide seal - the stock retainers top and bottom wont do it, its too short - the top retainer will make contact with the top of the valve seal you need .575 travel for a .490 cam - aftermarket springs and retainer set is a must and you still need to check it

the BH is a much easier cam to install for a home owner then a # 2 is all i am getting at

 

:-) No worries John. The engine has been set up by a very well regarded shovel engine builder over here. So hopefully no issues on springs - all done properly already. We've done Manley valves, springs, guides, etc... cam chest clearances etc...

But. I am not sure if this is enough for a B or BH grind if I do want to change cams later. Looks like very slightly less lift on those cams, so should be OK if already clearanced for the #2 do you think?

I think what I am trying to say, is if the motor is already properly set up for a #2 grind, then most other aftermarket cams with equal or less lift should work - even though it was originally an '80 motor with known issues that need worked for aftermarket cams?

 

first - yes a lower lift fits with no issues

today the camshaft companys have gone from seat of the pants to computer models

while its all math can be a strong argument, the adding machine is not riding a bike

tryed and trued cams have been a trial and error thing since motorcycles started racing each other before the first world war

as a believer in dont fix whats not broken i also attest to what we know works you stay with,


we add duration when you want it to go faster - its an air pump the more you can take in the more pressure / power you get back = dont need a computer to tell me any thing different