I need info on Carbs???

[05BlasterManiac]

Hey, I am getting eventually the LA SLEEVE 240 BBK and it says it is recommended to get a Keihin 36PWK carb. Now I see people post up like whats the difference between a 28mm carb and a stock and how people want a 35mm, but what does it mean in mm with carbs? I know what carbs do and everything, but that's one thing I don't understand.

Thanks!

 

[Blaaster]

The numbers in mm are the bore diameter of the carby!

The larger the mm the more air fuel mixture can delivered to the motor because of the greater diameter, lesser resistance to air flow and superior atomisation.

 

[Blaner]

bigger carb = more air = go faster!

 

[Blaaster]

bigger carb = more air = go faster!

+ more Adrenaline!I:II:II:I

 

[05BlasterManiac]

Alright so how do you know how big you can go until basically u blow something up?

 

[slickerthanyou]

Alright so how do you know how big you can go until basically u blow something up?

Your not going to blow something up with too big of a carb, you will sacrifice some possible low end, for some top end.

Not saying you can't go too big but your not going to blow your motor as long as you jet it accordingly!

 

[slickerthanyou]

I have a 35mm on stock cylinder, its ported, stroked , and piped i gave up a little bottom for top on that one.

My new build is going with a 33mm this is premium for a stock/ported/stroked modified set-up. I should have great power in all ranges!

 

[yamaha28]

how does the jetting work if you jump form a 28mm to a 35mm with the same mods? do you jet bigger?

 

[05BlasterManiac]

I have a 35mm on stock cylinder, its ported, stroked , and piped i gave up a little bottom for top on that one.

My new build is going with a 33mm this is premium for a stock/ported/stroked modified set-up. I should have great power in all ranges!

O ok, but does the LA Sleeve BBK go for low end or top end or mid? Also, the 36mm carb it recommends, is that low end or top? What's the highest mm in carb people have gone or that you can go and what's the lowest? This way I can know if I am going to low or high end. The Blaster stock goes for low end doesn't it?

 

[slickerthanyou]

how does the jetting work if you jump form a 28mm to a 35mm with the same mods? do you jet bigger?

Well, for example, a stock carb is a mikuni and with a toomey and my mods I'd start at about 350-380.

My keihin 33pwk- I'm starting at 168.

Usually when you go to a larger carb the number on the jet is lower, but it all depends on the make of the carb too!

Mikiuni and Keihin are very different even the jets are different model number and hole size system!

 

[slickerthanyou]

O ok, but does the LA Sleeve BBK go for low end or top end or mid? Also, the 36mm carb it recommends, is that low end or top? What's the highest mm in carb people have gone or that you can go and what's the lowest? This way I can know if I am going to low or high end. The Blaster stock goes for low end doesn't it?

Ya know I have no experience (hands on that is), But I would say a 35/36 is perfect!

a 38/40mm is used for draggin. This is all from reading!

 

[yamaha28]

sounds like finding the jets when bumping up carbs can be a PITA, good luck!

 

[05BlasterManiac]

Ya know I have no experience (hands on that is), But I would say a 35/36 is perfect!

a 38/40mm is used for draggin. This is all from reading!

Kk thanks and sorry for my stupidity, but what do you mean by draggin with a 38/40mm carb?

 

[slickerthanyou]

Kk thanks and sorry for my stupidity, but what do you mean by draggin with a 38/40mm carb?

Drag racing! sorry.....

 

[brandoz28]

sounds like finding the jets when bumping up carbs can be a PITA, good luck!

there's enough info on here that you can get pretty close after doing some research.


i had a 36mm mikuni on a pipe/carb/reeds motor, and it was a doooooooog. probably a 1000rpm usable power band because the low end was completely gone

 

[sicivicdude]

I'm running a PJ38 on my stock bore stock stroke drag engine with a power jet..... I'm willing to sacrifice ALL low end power for top end power because it's a drag engine....

LA sleeve recommends the 36mm carburetor for good reason, it's a darn good carburetor and the right size for that engine combo.

On a hefty ported big bore kit, a small carburetor will actually restrict the engine at top RPM because it simply cannot pull enough air in through the throat (the hole's just not big enough)

You CAN damage an engine by having too large a carburetor (but it's really unlikely) Putting a 44 mm lectron on a completely stock blaster would result in the main jet not having a strong enough "vacuum signal" and failing to draw fuel up from the float bowl to match the incoming air (to keep the mixture right). OBVIOUSLY, this is an exaggeration because no one in their right mind would put a 44mm carb on a stock blaster....

Keihin isn't the only make of carburetor in town either, the Mikuni TM34-38 carburetors are also fine 2 stroke carbs and can be had relatively inexpensive HOWEVER getting jetting help will be harder as most folks run Keihin carbs (either the PJ or PWK).

 

[slickerthanyou]

There ^^^^^ what i was trying to say but couldn't get the words out!

 

[05BlasterManiac]

I'm running a PJ38 on my stock bore stock stroke drag engine with a power jet..... I'm willing to sacrifice ALL low end power for top end power because it's a drag engine....

LA sleeve recommends the 36mm carburetor for good reason, it's a darn good carburetor and the right size for that engine combo.

On a hefty ported big bore kit, a small carburetor will actually restrict the engine at top RPM because it simply cannot pull enough air in through the throat (the hole's just not big enough)

You CAN damage an engine by having too large a carburetor (but it's really unlikely) Putting a 44 mm lectron on a completely stock blaster would result in the main jet not having a strong enough "vacuum signal" and failing to draw fuel up from the float bowl to match the incoming air (to keep the mixture right). OBVIOUSLY, this is an exaggeration because no one in their right mind would put a 44mm carb on a stock blaster....

Keihin isn't the only make of carburetor in town either, the Mikuni TM34-38 carburetors are also fine 2 stroke carbs and can be had relatively inexpensive HOWEVER getting jetting help will be harder as most folks run Keihin carbs (either the PJ or PWK).

Alright thanks, that helped a lot!

 

[sicivicdude]

LA sleeve did their homework on carburetor size for that particular setup. The 36mm carburetors give the best top end without sacrificing too much low end.

Carburetor size is always a bit of a give and take.... the 36mm carb is the best compromise on that engine.

 

[Blaner]

think about a pea-shooter...if your selected pipe is too small, you will not be able to maximize your breath through it. In other words, your potential is greater than what the pipe allows you to transmit through it and your "power" of the shot will be weak.

On the other hand, if you use a 40mm waste water pipe as your pea-shooter, you will not have enough breath to power the shot and your "pea" will not be propelled very far as your air speed will be low (the volume of the pipe is too big)

So you need to find a pipe of the right diameter which allows maximun transmission of your breath through it that results in the right power of projection.

Same thing with carbs...too big and it will only perform when your air speed moving through it is fast and because the volume is to big, this will only occur when the motor is revving its guts out.

On the other hand, if its too small, the motor will be sucking and it will not be fed the correct amount of air that it has the capacity for and so the power output will be limited. (Like trying to breathe with a blocked nose!)

I hope this practical explanation helps!