OK so I swapped out my stock VM26ss for a 28mm vm series from a '85 YZ 80 (apparently a vm28(or24?)-606.
Specs are
26MM 32.5 Pilot, P-6 NJ, 5j22 JN, 2.0 slide co.
28mm 35 Pilor, O-0 NJ, 4j13 JN, 2.5 slide co
Everything can be swapped out between the two except for the needle jet.
The P-6 NJ has a I.D. of 2.68mm the O-0 2.60mm
The good news is that the 28mm has no TORS, a standard idle screw, standard cap, quick change jets(bowl), slightly more airflow, and the same o.d. of the spigot and inlet, meaning it fits perfectly/ same as stock.
The problem I am having is that the 28mm carb uses series 249 or series 332 needle jets only. Both come in O-0 size, one comes in the ever so slightly smaller N-6. That is the only sizes I can find. Possibly oem Yamaha might have different sizes in the 249 series which might be hard to find
The series 249 needle is an OEM Yamaha series, the 332 is Mikuni series.
If i could find the specs for the 5j22 needle I could match up one that was.08 mm thinner overall (or at least at the top).o
I did order 2 different needles a 5j11 and a 5fp17, the first starts out thinner than stock by .070mm and has the same taper angle as stock (different start point for taper).
The second is a dual taper needle it starts thinner than stock (to make up for a smaller NJ) and initially has a shallow taper angle, then goes to a sharper than stock angle.
AFAIK this helps lower throttle ranges where airflow and loading are minimal and a richer mixture isn't needed(low speed cruising), then opens up substantially to avoid lean conditions as you get closer to middle throttle position where more efficient flow and heavier engine load benefits from more fuel.
It is my hope that these needles in the 28mm with the O-0 NJ will give similar results to the 5j22 with the P-6.
A scenario that snuck up on me was rebuilding, porting and rechamber in the engine before my throttle cable arrived and before I was able to do baseline jetting on the stock motor with current bolt ons.
Which leaves me pretty close to starting from scratch.
I need someone who has alot of experience with tuning mikuni carbs (of various bore sizes), on modded blaster engines (moderate trail porting: ex port up 1.3mm/+2mm wider, open lower transfer tunnels, moderate sized boyesen ports, minimal intake cleanup), with common bolt ons (A box lid-, dual stage reeds, Toomey, +2 timing advance).
Don't know who that is but they gotta be lurking around here somewhere.
Maybe once I actually get my top sent off,and Ken can get his eyes on it, and ever stop laughing or crying at what I have done to my cylinder, he might have a good idea of where to start.
Specs are
26MM 32.5 Pilot, P-6 NJ, 5j22 JN, 2.0 slide co.
28mm 35 Pilor, O-0 NJ, 4j13 JN, 2.5 slide co
Everything can be swapped out between the two except for the needle jet.
The P-6 NJ has a I.D. of 2.68mm the O-0 2.60mm
The good news is that the 28mm has no TORS, a standard idle screw, standard cap, quick change jets(bowl), slightly more airflow, and the same o.d. of the spigot and inlet, meaning it fits perfectly/ same as stock.
The problem I am having is that the 28mm carb uses series 249 or series 332 needle jets only. Both come in O-0 size, one comes in the ever so slightly smaller N-6. That is the only sizes I can find. Possibly oem Yamaha might have different sizes in the 249 series which might be hard to find
The series 249 needle is an OEM Yamaha series, the 332 is Mikuni series.
If i could find the specs for the 5j22 needle I could match up one that was.08 mm thinner overall (or at least at the top).o
I did order 2 different needles a 5j11 and a 5fp17, the first starts out thinner than stock by .070mm and has the same taper angle as stock (different start point for taper).
The second is a dual taper needle it starts thinner than stock (to make up for a smaller NJ) and initially has a shallow taper angle, then goes to a sharper than stock angle.
AFAIK this helps lower throttle ranges where airflow and loading are minimal and a richer mixture isn't needed(low speed cruising), then opens up substantially to avoid lean conditions as you get closer to middle throttle position where more efficient flow and heavier engine load benefits from more fuel.
It is my hope that these needles in the 28mm with the O-0 NJ will give similar results to the 5j22 with the P-6.
A scenario that snuck up on me was rebuilding, porting and rechamber in the engine before my throttle cable arrived and before I was able to do baseline jetting on the stock motor with current bolt ons.
Which leaves me pretty close to starting from scratch.
I need someone who has alot of experience with tuning mikuni carbs (of various bore sizes), on modded blaster engines (moderate trail porting: ex port up 1.3mm/+2mm wider, open lower transfer tunnels, moderate sized boyesen ports, minimal intake cleanup), with common bolt ons (A box lid-, dual stage reeds, Toomey, +2 timing advance).
Don't know who that is but they gotta be lurking around here somewhere.
Maybe once I actually get my top sent off,and Ken can get his eyes on it, and ever stop laughing or crying at what I have done to my cylinder, he might have a good idea of where to start.
