TOPIC:

I've took them to 29.5 as is the common mod for these.
Could push them to 30 but it will leave only 1mm wall thickness beneath the carb boot location groove.
Not much of a drop from 1.25mm i know but the castings aren't that constantly precise around the full circumference so avoids any low spots and potential breakthroughs.

Motor is high comp 900 bored to 1015.
Ported head.
will have bellmouthes and free flowing pipe.

Yeah I thought they were probably 26s,but wasn't sure.
I think its the 28s that can go to 31.When I saw them on your 1428 post it got me thinking theyd have a hell of a bottem end punch,but might tend to hold yo down up top!

zed,it looks as tho you bored them concentric to the original bore.

is that right?

leon

531blackbanshee wrote: zed,it looks as tho you bored them concentric to the original bore.

is that right?

leon

Yes! just followed the original bore.
Only real option for accurate repeat operations on the lathe.
Trying to oval bore for better response as is claimed would still end up breaking through on the topside of the boot groove.

wireman wrote: Yeah I thought they were probably 26s,but wasn't sure.
I think its the 28s that can go to 31.When I saw them on your 1428 post it got me thinking theyd have a hell of a bottem end punch,but might tend to hold yo down up top!

Yeah! i really should change the title now.
The 28's actually have slightly less meat on the boot side and are very thin if boring to 29+ . going to 31 would destroy them.
As for the 1428, that is waiting in the wings for the next project.
It's going in a Zed frame with a supercharger when i find one and possibly two S&S carbs linked side by side just to be different.

To be honest, I would have thought that the 28's and 26's were the same castings, just machined different. The designation's are different but they are stamped which says it's after all else is done. I think wiredgeorge was doing the bored out carbs but he hasn't been doing anything lately that I'm aware of? Wish I could pull off a deal like this but I tried it years and I mean YEARS ago without success. I done a lot of things to aid in HP but carbs other than a good ole quadrajet were beyond my capabilitys.

Les

I had read previous that the 28's were thinner on the boot side and having both types here i can confirm that to be correct.
They are a fairly slack fit in the tight fitting jig i made for the 26's.
I don't know the reason, maybe they made a fresh mould for them as this type did appear later in the model run and i can't see them boring 1000's of 26mm castings out.
There's not that much in it though and still scope to go to 29mm safely.

I was figuring that they just changed out the core pins to achieve the smaller bores, going off the casting lines in the face of the bore. Guess I was wrong on that one.
I done the same thing quite a few years ago without much success. 20 plus years later I'm quite sure my skills have improved greatly so I may have to try this again myself.

Les

zed1015 wrote:

wireman wrote: Yeah I thought they were probably 26s,but wasn't sure.
I think its the 28s that can go to 31.When I saw them on your 1428 post it got me thinking theyd have a hell of a bottem end punch,but might tend to hold yo down up top!

Yeah! i really should change the title now.
The 28's actually have slightly less meat on the boot side and are very thin if boring to 29+ . going to 31 would destroy them.
As for the 1428, that is waiting in the wings for the next project.
It's going in a Zed frame with a supercharger when i find one and possibly two S&S carbs linked side by side just to be different.

It's looking good!!!

My highly modded yz 250 2 stoke has its carb bored with a divider and low circuit mods for RB designs. Modding carbs produces great results when done right.

I thought about the dual S&S's before I bought my biggy E, but it isnt worth it.(are you just trying to out do me cause I got the E and you wanted it??? lol ) Your better off with these dual throttle body setups, WAY easier to fab up mounting, no linkage required, more room friendly, look how nice the rear would mount to our supercharger plates, less time to install, list goes on. There are the S&S ones too.

I thought of using two super B's as i already have one and they are more common and easier to find.
It will be a simple job of linking them by using one long shaft connecting the butterflies.
Should be more responsive at the bottom end than one massive carb too.
I aim to use a more modern screw SC which draws from one end so the inlet will be somewhere near my right leg and there should be plenty of room for the linked carbs.

zed1015 wrote: I thought of using two super B's as i already have one and they are more common and easier to find.
It will be a simple job of linking them by using one long shaft connecting the butterflies.
Should be more responsive at the bottom end than one massive carb too.
I aim to use a more modern screw SC which draws from one end so the inlet will be somewhere near my right leg and there should be plenty of room for the linked carbs.

Ya the 2 smaller would be quite more responsive and the big single will have better top end but probly not worth the low end trade but what ever, I'm not the fab superstar you are so that shit is easy for you. But I still think you will get more throttle response and more ponies out of an FI throttle body setup. I've just got too much building going on to tackle that too.

Hollywoodmx wrote:

zed1015 wrote:

wireman wrote: Yeah I thought they were probably 26s,but wasn't sure.
I think its the 28s that can go to 31.When I saw them on your 1428 post it got me thinking theyd have a hell of a bottem end punch,but might tend to hold yo down up top!

Yeah! i really should change the title now.
The 28's actually have slightly less meat on the boot side and are very thin if boring to 29+ . going to 31 would destroy them.
As for the 1428, that is waiting in the wings for the next project.
It's going in a Zed frame with a supercharger when i find one and possibly two S&S carbs linked side by side just to be different.

It's looking good!!!

My highly modded yz 250 2 stoke has its carb bored with a divider and low circuit mods for RB designs. Modding carbs produces great results when done right.

I thought about the dual S&S's before I bought my biggy E, but it isnt worth it.(are you just trying to out do me cause I got the E and you wanted it??? lol ) Your better off with these dual throttle body setups, WAY easier to fab up mounting, no linkage required, more room friendly, look how nice the rear would mount to our supercharger plates, less time to install, list goes on. There are the S&S ones too.

Oh I like those throttle bodies!