help jetting a big bore 750cc kit on vm34's

[rugburn]

any one have a base line jetting set up for
a 750cc motor with mikuni vm34 roundslides
with 41mm open headers. my jetting was
nearly perfect with the same set up on the 650cc
barrel but i suspect i'll need to update it for the
increase in volume.

-burn

 

[XSLeo]

I have a set 0f 76 carbs on my 75. When I added the 750 kit I thought some changes would be nessary. After a week of fooling around I ended up right where I was.
If your carbs where right as a 650 I doubt they will be wrong for the 750.

 

[DetroitMuscle07]

I'm running 27.5 pilots and 200 mains on my bike. Mix screws are about 1 turn out each.

 

[Patches]

I have a set 0f 76 carbs on my 75. When I added the 750 kit I thought some changes would be nessary. After a week of fooling around I ended up right where I was.
If your carbs where right as a 650 I doubt they will be wrong for the 750.

Really? I just don't see how this could be? Not calling young liar, just really surprised.

 

[5twins]

There's not much difference between a 650 and a 750. Look up the carb specs for the old TX750 twin Yamaha made in '73-'74 and compare them to the 650s for those years. They were virtually the same. I would be inclined to tinker, at least try some larger mains, but wouldn't be surprised if I ended up back where I started.

 

[XSLeo]

So was I, surprized that is.
Leo

 

[Stoop22kid]

So stock carbs should work on a 750 kit? What about with pod filters? Which jet would I have to change?

 

[XSLeo]

Yes, I run a set of 76/77 carbs as well as an 82 set of BS34's on my 75 as a 650 and a 750.
With pods, not the K&N style pleated ones, use a foam pod. Like the one UNI Filter makes. Work much better. Try one up on the pilots and two up on the mains. Start with the air mix screws and needles set to stock.
Leo

 

[ebb0tk]

Yes, I run a set of 76/77 carbs as well as an 82 set of BS34's on my 75 as a 650 and a 750.
With pods, not the K&N style pleated ones, use a foam pod. Like the one UNI Filter makes. Work much better. Try one up on the pilots and two up on the mains. Start with the air mix screws and needles set to stock.
Leo

Are you referring to the BS34 on that tuning? two up on the mains and one up on pilot?

Im about to bore mine to 700cc, mildly cleaned ports, open exhaust with free flowing mufflers from cone eng, uni pods, stock cam and crank 277 rephase.

So any input regarding jetting would be nice. I will get the bike dyno'd after break in, but before that i dont wanna run it too lean.

 

[XSLeo]

On the carbs I worked with the one up on pilots and two up on the mains seems about right. On your set up it may or may no work as well. Nio two bikes arte the same. That's a good baseline to start at and test and adjust from there.
The carb guide has a section "Tuning For Mods" that explains how to test and adjust.
Leo

 

[ebb0tk]

On the carbs I worked with the one up on pilots and two up on the mains seems about right. On your set up it may or may no work as well. Nio two bikes arte the same. That's a good baseline to start at and test and adjust from there.
The carb guide has a section "Tuning For Mods" that explains how to test and adjust.
Leo

Indeed. I just disassambled the needle and needle jet. they are mikuni oem buth the canadian version.

Id rather try to run these than buying new ones.
Settings are:
Pilot Jet 45
Main Jet 132.5
Stock Air Jet 130
Needle 5IX11 (Second slot from top)
Needle Jet 336 Y-0

Anything i should consider swapping? Pilot Jet is a VM22, should i change to a BS30/96? Up one size? Raising lower needle to prevent running lean?

Thanks

 

[grizld1]

Re. pilot jet series: question asked and answered. Refer to Carb Guide.

 

[ebb0tk]

Re. pilot jet series: question asked and answered. Refer to Carb Guide.

Yes just did. Thanks