carburetor for big bore 86cc?

jakan · 29 November 2009

I have previously had a 28mm carburetor for my Big Bore 86cc horizontal minarelli engine
the question is whether it pays of to use a bigger carburetor like 30mm or 32mm instead? the cylinder is tuned

Nick L Møller · 3 December 2009

i use 30 mm

jakan · 3 December 2009

Nick L Møller said:
i use 30 mm

the idea is to test both 28mm and 30mm in a dyno and see what works best, maybe even with a 32mm carburetor

did you tested any other than 30mm carburetor for your big bore engine?

Velo · 4 December 2009

Take a look on what two stroke crossers are useing.

And remember that Both Cagive Mito 125 Evo and Aprilia RS 125 both use carbs less than 30 mm.

tiba_karotsu · 4 December 2009

Velo said:
Take a look on what two stroke crossers are useing.

And remember that Both Cagive Mito 125 Evo and Aprilia RS 125 both use carbs less than 30 mm.

that is bcoz they are road versions & not the race/GP versions, we have an HRC RS125GP & it has a 38mm carb standard.

Velo · 4 December 2009

tiba_karotsu said:
that is bcoz they are road versions & not the race/GP versions, we have an HRC RS125GP & it has a 38mm carb standard.

Yes, I belive you, but those bikes have much much larger reed valves and transers. And personally I have a theory that the last is the reason why BB performs so badly. (Compared to 70 cc)

Rydah1 · 5 December 2009

Velo said:
Yes, I belive you, but those bikes have much much larger reed valves and transers. And personally I have a theory that the last is the reason why BB performs so badly. (Compared to 70 cc)

wassup Velo, can you expand more on your theory.

tiba_karotsu · 6 December 2009

Rydah1 said:
wassup Velo, can you expand more on your theory.

what he means is that the BB kits are restricted by the area of their reedvalves, our RS125GP bike has a huge reedcage which allows for a big 38mm carb, in order to extract more power from the 77cc-94cc kits we must also increase the size of the reedvalves in order to use a bigger carb to flow the volume of air required to make more power.

add to that is teh size of the transfer ports & tunnels, it simply must be enlarged so the bigger 77-86cc MHR kits can breathe & make more power.

jakan · 6 December 2009

tiba_karotsu said:
what he means is that the BB kits are restricted by the area of their reedvalves, our RS125GP bike has a huge reedcage which allows for a big 38mm carb, in order to extract more power from the 77cc-94cc kits we must also increase the size of the reedvalves in order to use a bigger carb to flow the volume of air required to make more power.

add to that is teh size of the transfer ports & tunnels, it simply must be enlarged so the bigger 77-86cc MHR kits can breathe & make more power.

interesting, as I said, I have already enlarged the transfer ports and tunnels of the cylinder
any suggestions on what can be in order to increase the volume of the reedvalves on the minarelli dd block? have you any picture or measurements of the Rs125GP reedvalves?

waxhead · 7 December 2009

Start welding
there simply isnt the material there

Sonic-speed · 7 December 2009

waxhead · 7 December 2009

I can see why they did it that way for the room, but it looks like it firing is straight a the crank which is technically wrong

jakan · 7 December 2009

waxhead said:
Start welding
there simply isnt the material there

yes, it would be good to have a reedvalve to go after

Sonic-speed said:
picutre

any more pictures of that engine?

waxhead said:
I can see why they did it that way for the room, but it looks like it fsiring is straight a the crank which is technically wrong

no matter how you twist and turn on it, it will probably always be that way
unless you move it foward towars the cylinder?

Tommy · 7 December 2009

For minarelli is vl14 from malossi big enough, you don`t need a big reed valve from a 125cc or something. 34mm or even 35mm works very well with a vl14 on 86cc engine

Rydah1 · 8 December 2009

when i get my big bore kit i just planned on using a 28mm pwk carb. my bike is a streetbike anyways so that should be good enough.

Sonic-speed · 8 December 2009

Tommy said:
For minarelli is vl14 from malossi big enough, you don`t need a big reed valve from a 125cc or something. 34mm or even 35mm works very well with a vl14 on 86cc engine

You ever tested a bigger membran to ensure that statement?

Sure it does perform good, and also more peake than with 28 mm. This is after all not much an foundation to conclude that a bigger membran wont be better, or a vl14 is "good" enough.

Tommy · 8 December 2009

Yes I did and yes this are findings of me. If you have other results, no problem But I can quess that you haven`t tested a 34 or 35mm otherwise you would have an other conclusion about it.

Sonic-speed · 8 December 2009

Tommy said:
Yes I did and yes this are findings of me. If you have other results, no problem But I can quess that you haven`t tested a 34 or 35mm otherwise you would have an other conclusion about it.

On what engine did you tested it? and what membran.

Sonic-speed · 8 December 2009

And i bet you costomized the inlet before you mounted the bigger membran.

jakan · 8 December 2009

Tommy said:
For minarelli is vl14 from malossi big enough, you don`t need a big reed valve from a 125cc or something. 34mm or even 35mm works very well with a vl14 on 86cc engine

Tommy said:
Yes I did and yes this are findings of me. If you have other results, no problem But I can quess that you haven`t tested a 34 or 35mm otherwise you would have an other conclusion about it.

so you mean that it did not give any noticeble effects of using a larger reed valve? and that I can use a 34-35mm carburetor without problems?
I consider to use or testing a "pro flow valve" instead of the vl14

Rydah1 said:
when i get my big bore kit i just planned on using a 28mm pwk carb. my bike is a streetbike anyways so that should be good enough.

I have not mentioned it but i use the engine for sprint 150m

carburetor for big bore 86cc?

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