ESE's works engine tuner

[TZ350]

Yeah,? The RG 50 with a dreadfully compromised transfer arrangement (opps, like the TF) worked better with 28 than 26 or 24 from same family.

The better performance from the bigger carb may not be because it can pass more air but because the fuelling curve is more appropriate for the amount of air the motor is consuming.

A 28 on a 50 seems really out there, but whatever works best is what works best, whatever it is .....

[Frits Overmars]

The better performance from the bigger carb may not be because it can pass more air but because the fuelling curve is more appropriate for the amount of air the motor is consuming.

True, and the same goes for smaller carbs, different pipes, heads, etc, etc. One should re-optimize carburation and ignition timing after every change, before jumping to conclusions.

A 28 on a 50 seems really out there
whatever works best is what works best, whatever it is .....

I would call a 28 mm carb on a 50 cc engine average. I've seen 50s doing quite well with a 34 mm carb, although I admit that seems rather big even to me.
But your second remark is pure gold. I often use it when questioned about jet sizes: 'if the engine feels happiest with a 678 jet, fit a 678'.

[F5 Dave]

Thanks Rob, that is what we'll try then. Esp as I got him to buy a 24 oko. We'll run it std first and then machine it.

I had considered taper boring it at the rear as shown in your early picture, could also be combined with front bore so centre section where the needle is as 24. But that leaves a nasty transition at the slide.

I am still a bit uncertain as to if you bored it right through surely the emulsion tube would lose it's seat. Where I've bored carbs before you offset to only lick this area, but 30mm this would not be possible. OK I'm confused again.

[TZ350]

I am still a bit uncertain as to if you bored it right through surely the emulsion tube would lose it's seat. Where I've bored carbs before you offset to only lick this area, but 30mm this would not be possible. OK I'm confused again.

The OKO is easy to hold and does not crush like softer carbs made from pot metal.



The rib around the bell mouth fits neatly into the grove in the chuck jaws.

This is a 24 bored out to 30mm. It was bored parallel straight through and had a small 24mm section pressed back into the engine end. Next time I would machine it so it had a short (5mm) venturi shaped section of the original 24mm bore left. The original OKO has no venturi at the slide, it is parallel straight through.



With the 24 bored out to 30mm there is still some sealing area for the slide, (blue line). Being parallel bored there is no venturi section at the slide. The sharp edges facing the wind were radiused (yellow line) they were worked until they felt smooth when sliding a finger down the bore and the needle and pilot jet holes still had enough seat area left (black line).



Adding a tube to the air correction jet hole moves it's intake out into high pressure air so it is not suffocated by the partial vacuum back in the bellmouth.

[F5 Dave]

Wow ok. Guess the original was based on the 28 pwk so beloved by me and RZ owners worldwide

Thanks for the pics. So you bored right through then right like 60mm in, flared in to 24mm. Then presumably out to create a venturi?

What's the torrent bit in left air intake?

[TZ350]

So you bored right through then right like 60mm in, flared in to 24mm. Then presumably out to create a venturi?

Yes but the venturi bit was a separate bit pressed in and only the front half at that. The pressure recovery (flared out) part is in the rubber manifold.



Cut at the yellow line, carb on the left, manifold part on the right. Keep the larger parallel part in the front of the carb as long as possible. If I make anymore I intend leaving a 5mm or so section of the original 24mm bore at the engine end of the carb for forming the front part of the venturi.



This is a complete venturi pressed into a carb but if you are machining a venturi into the end of the OKO carb you can make only the front part in the carb, the other part can be a separate part in the manifold.

You could of course just press a complete venturi section into the carb. The venturi bit does not have to be formed from the original carb casting to be a 24mm equivalent but it does make a neater job and retains some of the original OKO manufacturers 24mm bore and the bush lawyers would be pushing it up hill trying to argue with that.

[F5 Dave]

So why didn't I start off with a 28mm pwk?

[TZ350]

So why didn't I start off with a 28mm pwk?

Because the OKO has a neat little "24" on the side.

[F5 Dave]

I can probably punch that in with my punch set. 39mm pwk off my based into the mix?

[TZ350]

I can probably punch that in with my punch set. 39mm pwk off my based into the mix?

Well it is "Buckets" everything is on the table, or is it called "thinking outside the box".........

[Frits Overmars]

..........

[Lightbulb]

Happy Fathers Day to all the Kiwi Bikers out there. Ride hard and return home safely.

[TZ350]

For anyone wondering what this 24 thing is about, its a class restriction, F4 2T's over 104cc are restricted to a 24mm carb.

So why didn't I start off with a 28mm pwk?

You certainly could have if you have one, and I would, but a 30mm OKO special flows more air than a 28mm Keihin.

The reason I use 24mm OKO's and partly bore them out to 30mm for the Team ESE bikes is that they are cheaper than a 28mm Keihin, readily available, clearly labeled "24" on the side for all to see, machine better and don't crush in the lathe easily like the pot metal Keihin or Mikuni do.

Also having some of the original 24mm bore left in the engine end of the OKO meets MNZ's carburetor measurement for size clarification.

Starting with a 24mm OKO helps to silence the sideline and armchair critics and other amature legal beagles who so often label anything they have not thought of or are using themselves or plain just don't understand, as "not Legal" or "against the spirit", all the while conveniently forgetting that cleverness and thinking outside the box is the very essence of Bucket racing.

But my reasons don't have to be your reasons.....

[Grumph]

For anyone wondering what this 24 thing is about, its a class restriction, F4 2T's over 104cc are restricted to a 24mm carb.

Starting with a 24mm OKO helps to silence the sideline and armchair critics and other amature legal beagles who so often label anything they have not thought of themselves or are using or plain just don't understand as, "not Legal" or "against the spirit", all the while conveniently forgetting that cleverness and thinking outside the box is the very essence of Bucket racing.

But my reasons don't have to be your reasons.....

I quite deliberately left the 29mm marking on the carb on Kevs bike. There were a lot of rumours about how big capacity it was and I was trying to tempt someone into a protest...Bit sorry now it didn't happen, LOL.

[Yow Ling]

I quite deliberately left the 29mm marking on the carb on Kevs bike. There were a lot of rumours about how big capacity it was and I was trying to tempt someone into a protest...Bit sorry now it didn't happen, LOL.

I dont recall a single protest in Chch buckets in the last 15 years, that doesnt mean there is no reason for them as i have seen plenty of evidence that not everyone plays by the rules, the score is still zero