carbs? why what size when? OPEN DEBATE

[camatv]

ok. i've been reading here and there about different things and seen a LOT of thread jacking and misleading info. SOOOO i'd like to start a series of different threads that are SPECIFIC to certain issue's not sure how much discussion will get put down. BUT i hope a while bunch of bickering and testing and real WORLD results will come to light..

 

this will be the carberator thread!!

 

soo i'll start it off MYTH OR FACT? you dont need any carb larger than a 33mm on ANY banshee even a drag bike..?

 

stock carbs work/ ( wont work at all) on cubs. ??

 

38mm pwk air styker carb on a dune? port is wayyy to big..

 

35mm pwk's will result in a LOSS of bottom end and response..

 

boost bottles work GREAT!

 

so lets here it !!

 

and from time to time i may stick my head in and give my OPINON on what i FEEL works for me..

[shogs]

Stock shocks work better on +3+1 arms than elka dune editions do. They have to have at least 6 years of wear on them though

 

Oh woops were talking about carbs. Well 2 into 1's work way better than any duals...20% hp gain bottom end and they pull on the top more than a drag ported cpi pipe having 35mm running bike even though mines trail ported.

[camatv]

THANKS BROTTHA

 

gotta LOVE banshee HQ~!

[BlasterKX]

Stock shocks work better on +3+1 arms than elka dune editions do. They have to have at least 6 years of wear on them though

 

Oh woops were talking about carbs. Well 2 into 1's work way better than any duals...20% hp gain bottom end and they pull on the top more than a drag ported cpi pipe having 35mm running bike even though mines trail ported.

i disagree. my good friend has a 2 into 1 carb setup and he really doesnt like it. said stock carbs worked and responded better. if you have your stock carbs jetted right i think the will work fine until you start to do strokers and higher hp motors..

[Sandfrk33]

I've been wondering about carb sizes myself. I have a dune port 4 mil. I still use my stock carbs, but they are bored to 28 mil. It runs really strong, great top, better bottom than stock stroke. How much of a difference will bigger carbs actually make? Who has made the switch and has an opinion?

[jbooker82]

Stock shocks work better on +3+1 arms than elka dune editions do. They have to have at least 6 years of wear on them though

 

Oh woops were talking about carbs. Well 2 into 1's work way better than any duals...20% hp gain bottom end and they pull on the top more than a drag ported cpi pipe having 35mm running bike even though mines trail ported.

 

I would believe your first statement before I would believe your second one.

[BigRed350x]

First off I will say that I don't care about dyno results. I ride big dunes and drag race with friends out on the dunes. All of my testing is real-world testing in real life. Not sitting on some dyno in a shop.

 

On my 4mil Duner (4mil gorr ported stock cylinders, vforce3, cool head, 19cc domes noss cut to my spec, reed spacers(just to get the carb bowls off the clutch arm), upp intakes, shearer pipes) I've run 33pwk's, 34PJ's, 35PWK's, 35PWK AirStrykers, 38mm PWK Airstrykers, 39mm PWK's, 34mm TM Flatslides and 35.5 TM Flatslides. Every single carb setup was run on methanol, so my results might be different than you gasser guys.

 

The 38's provided the best power and best top-end speed. The 33's made great throttle response and good low end, but you could feel them holding the bike back on the big end. The 34PJ's were the carbs I ran the most and liked the most for dune riding and play racing on this particular setup. They felt like they gave the best of both worlds - throttle response and top end power. When I'd go somewhere just to drag race and do WOT straight runs I'd swap out to the 38's. The 39's were pretty similar to the 38's, I just prefer the airstryker design with methanol.

 

Its a mix and match between providing your engine with the most CFM you can/it wants and getting your intake velocity high enough to efficiently pull the air and fuel into the engine. The velocity is affected by porting though, so it will vary bike to bike. The bigger carbs are going to have lower velocity through the carb and less of a venturi effect on the jets in the carbs. The smaller carbs will be just the opposite, but will also restrict the CFM available to the engine at your target rpm.

 

If 33's worked on any engine setup out there, you'd see 33's on everyone's bikes, including the big drag bike setups.

 

I run stock carbs on my stock stroke duner, 34PJ's on my 4mil duner, and 41's on my drag bike. I think my drag bike would cave in a set of 33's and suck them into the engine. LOL

[shogs]

I would believe your first statement before I would believe your second one.

Yea lol that was a joke if some of you thought it sounded believable. 2-1 is easier to tune and in my opinion hits on the bottom a tad harder. If I had a choice I would go back to duals though...just no cash flow at the moment.

[papa_smurf49319]

Ok first off i dont know a whole lot about what made a difference and where, but i will say that a guy that needs to run 35mm keihens really isnt lookin for a ton of bottom end anyways. After speaking to Alot of the builders on this topic they said that 35mm keihens would probably be my best bet. One thing i love about these carbs is the massive bowls they have stock, now i know they use more fuel but with the dual pingel and those bowls, i think youd have to be puttin down some serious power to run em dry. I do trail ride quite a bit and i have no room to say on my current setup if it will be trail worthy or not seeings how i only have an hour or two on it thanks to the lovely michigan weather. But most of the riding i do is fire roads and i can cruise in 4 to 6th gear threw most of it. That being said, i think carb selection is the last thing you should do after building your motor, if you have a high winder that likes to rev and you run it threw the r's than ya your going to want carbs on the bigger side, now if your just trail riding then your going to want a set of smaller carbs such as 28's. I think almost everybody can benefit from a little bigger carbs though.

 

 

Hope that wasnt to long of a blah ta blah rant .

 

 

 

Cody

[278]

As Big Red explained, you have to find a balance with carbs. The one size fits all definately doesn't apply. As you make more power and in turn increase air/fuel flow, you will need bigger carbs. However, you can "over carb" an engine. This is where finding the balance between the velocity of incoming air/fuel, and pushing as much fuel and air into the motor as you can. The best thing to answer your carb questions is to use a reputable builder (we have some of the best here on the HQ) and see what they suggest for carbs. The size will depend on your porting, exhaust, elevation, and generally how the motor is built. As far as 2 into 1 carb set-ups, many people have said they believe there is an increase in low end power, however Snop. does have dyno tuning numbers to show that all your really doing is cutting some of your top end. So the only real advantage to this set-up is simpler tuning, but its only a good option if you ride tight trails and only need low end.

[camatv]

GREAT!!

 

i will say this almost ALL the kehien carbs i have seen/ worked on/ tunes were WAYYYYYYYYYYYYYY rich on the bottom end of the throttle range.. this made them feel very very boggy.. and made the illusion that they lacked lower end.

 

i just slapped on a set of 35mm airstrykers and went from a 52 pilot to a 38!! its got excellent throttle response and has tons of low end response under load. its even stock non ported ( for now) cylinders.

 

if your tuning your bike on a dyno rember this unless the guy riding your bike is making jetting runs acording to throttle POSIISTION you are seeing the bike under load responding with the MAIN jet ONLY..

 

just because at the lower rpm's it seemed rich/lean dosent mean the slows are lean/ rich..

 

 

almost ALL dirt bikes from the modern era had at least 35mm - 38mm pwk's on them and the cc size of the paltry banshee is at least 175cc per cylinder..

 

in my OPINON the 34pj's, preferably 35mm pwk air stryker should be the smallest carb you should think of.

 

also the newer intakes should raise your carbs up enough to work..

 

any alky drag bike even a 350cc should use at least a 38-39mm carb.. i pefer the 41's.. and i also really prefer the lectron carb over any other's..

[dajogejr]

When I first built my 4 mil cub motor, all I had were stock carbs and T5 pipes.

I wanted to run the motor, but I didn't have bigger carbs and better pipes or the money to buy them...

It ran like crap. Absolute crap.

Quite a few people told me it was because of such small carbs and trail/dune exhaust.

It ended up being a bad air leak at the base gasket, a bad flywheel AND the deck surface of a brand new cylinder had a little dip causing water to seep in.

 

Once I got that fixed, it flat out ripped with stock carbs and T5 pipes. Even made 84 HP and change on a dyno.

(Within a month I had 35's on gas and inframe RDZ/Shearer, but that's not the point)

 

My point is...will smaller carbs and more restrictive pipes work on a larger engine?

Yes.

 

Safe to say anyone could tell you you're not going to get the most HP out of that setup...but they will absolutely work, hands down.

[Pasi S.]

Very good topic! This is the one I´m going to follow closely.

I´m going to use 35.5 PWK´s in my motor, don´t know yet how they will perform.

 

-Pasi S.

[drap660]

Lets just posts the fastest radar runs with each set of carbs. I have a 4mill stroker/stock cyl, on stock carbs running nice, I swapped out to 35 PWK's and didnt gain a .1mph. Stayed at exactly the same mph. I then tried a set of 39's and guess what same shiet. The only difference is that with the big carbs I can only run for 1/3 of the time due to gas consumption. All tests were done in a 1/4 mile

Edited January 29, 2010 by drap660

[broncbob]

Larger carbs will allow more air to enter the engine and any given time, the hope is that that air will bring in more of the bang water in with it.

 

You will lose low end throttle response with a carb that is to large for a given application. The problem being that the velocity of the air that moves through the carb will be too low to cause enough of a low pressure condition to get the fuel into the air that you need for a instant hit of power, things have to catch up.

 

But if you go too small on the carb, you will choke you engine and power out on the top end, basically you will be using every thing that carb can give you in the higher RPM range.

 

The trick to all of this is to find a crab that works for you the way you need it to. Do you need a nice low end hit, do you need to have every bit of air and fuel you can to keep it screaming way up top, or do you need something in between?

 

If you keep these things in mind, you won't have the stock carbs on a 421 that you want to go drag race with, and you won't have 39's on a trail bike. There are just better things for each application.

 

For me, and the 4 mill stock bore I have planed, it's going to be 34's. This is going to be a dune/hill shot type of set up, and I ride fast dunes. I'm not putting around, I'm not trying to run tight trails, I want this quad to shine from mid range on up, with enough grunt on the low end to get to the pipe.