Flatslide carburettors and boost

[Reinhoud]

I'm looking for new carburettors, mine are 40+ years old.

There's not a lot of choice, Keihin CR is very expensive and hard to find, so I was thinking of Mikuni RS, had these in the past, sold them unfortunally.

 

Anyone on here who has tried flatslides on boost?

 

Thanks

[Gixer1460]

The only flatslides i've ever seen used with boost have been Keihin HSR's used on draw through installs. The general wisdom is - if used with blow through, the air pressure acting on the slides stops / hinders the closing action making them heavy to close even with a push / pull throttle. Obvs this is a problem in an emergency situation as open throttle will allow fuel & air = boost / power! So, yeah but with that caveat!

[peter1127]

I'm wondering why flatslides would have an advantage in a boosted application.  NA  you have a bit more power but for boost you just add 0.1psi and you're there.

[Reinhoud]

19 hours ago, Gixer1460 said:

The only flatslides i've ever seen used with boost have been Keihin HSR's used on draw through installs. The general wisdom is - if used with blow through, the air pressure acting on the slides stops / hinders the closing action making them heavy to close even with a push / pull throttle. Obvs this is a problem in an emergency situation as open throttle will allow fuel & air = boost / power! So, yeah but with that caveat!

That's what I've read too.. But is it true? That's why I asked..

In theory, theory an practice are the same..

[Reinhoud]

19 hours ago, peter1127 said:

I'm wondering why flatslides would have an advantage in a boosted application.  NA  you have a bit more power but for boost you just add 0.1psi and you're there.

I'm looking for new carburetors,  Mikuni RS is a out the only affordable set I can find.

[Duckndive]

I,ve ran HSR's on Draw Thru,s and they close fine with a push pull cable 

Have you considered cheep Ali Express CV carbs  

[clivegto]

A friend bought Ali Express carbs for his 6 cylinder motorcycle says quality is good just change the jets for proper mikuni one's. 

[Gixer1460]

31 minutes ago, Duckndive said:

I,ve ran HSR's on Draw Thru,s and they close fine with a push pull cable 

Not the same Clive - Atmospheric air pressure as opposed to boosted air pressure or more correctly low velocity against high velocity!

[Duckndive]

1 hour ago, Gixer1460 said:

Not the same Clive - Atmospheric air pressure as opposed to boosted air pressure or more correctly low velocity against high velocity!

Yes i appreciate that the comment was ref draw thru use 

[Reinhoud]

8 hours ago, Gixer1460 said:

Not the same Clive - Atmospheric air pressure as opposed to boosted air pressure or more correctly low velocity against high velocity!

Velocity should be about the same with blow through and suck through..

Velocity is set by the amount of air what goes into the engine, that should be roughly the same with either set up.

Pressure is different.

 

I was thinking, not sure if I'm right, the pressure in blow through is different, higher,  but it's higher on both sides of the slide.

Edited December 20, 2025 by Reinhoud

[Reinhoud]

8 hours ago, Duckndive said:

I,ve ran HSR's on Draw Thru,s and they close fine with a push pull cable 

Have you considered cheep Ali Express CV carbs  

I didn't know Ali sells cv carbs..

I'll have look

[Leblowski]

On the old oss site i think  there was a german guy wich had a boosted gsxr using flatslides i even think it was twin turbo. Blow through using TMR's  I think his name was David Mitzlaff ish.. 

It worked on his bike but why would you use flatslides? I can recall they where a bitch to set up and get the whole system working properly.

If youre carbs are toast dump em and go efi so much easier.

Edited December 27, 2025 by Leblowski

[TraxX]

2 hours ago, Leblowski said:

On the old oss site i think  there was a german guy wich had a boosted gsxr using flatslides i even think it was twin turbo. Blow through using TMR's  I think his name was David Mitzlaff ish.. 

It worked on his bike but why would you use flatslides? I can recall they where a bitch to set up and get the whole system working properly.

If youre carbs are toast dump em and go efi so much easier.

Yep that was David or Nitro or Moloch-Fighter ... he used TMR 40s in the beginning of his twin turbo 1100w build (had them on the bike when it was n/a), but changed over to efi quite fast. He said the 40s were running ok but still a little to big for turbo usage. He would´ve liked to try some tmr 32 or 34 on an oil cooled build.

 

He still builds Suzuki Turbo Stuff and has Instagram / facebook ...  

Edited December 27, 2025 by TraxX

[Leblowski]

4 minutes ago, TraxX said:

Yep that was David or Nitro or Moloch-Fighter ... he used TMR 40s in the beginning of his twin turbo 1100w build, but changed over to efi quite fast. He said the 40s were running ok but still a little to big for turbo usage. He would´ve liked to try some tmr 32 or 34 on an oil cooled build.

 

He still builds Suzuki Turbo Stuff and has Instagram / facebook ...  

Yeah indeed i have him on fb he does a lot of dragracing and builds everything himself, he stopped using w engines and went busa. He is quite handy!

[clivegto]

There was an Australian guy on the temp site ran flats ides on a Pepsi slingshot if I remember correctly.