[stpltn250r]

Just as the title says. For people who have actually used these carbs what are you likes and dislikes of each.

[bubba297]

Chris you can easily get parts and support for the lectrons, not many mess with the crankshop carbs around here.

[Tate]

Does anybody sell a bigger carb then the 54 crankshop. Can you bore the 54 bigger to a 56+

[stpltn250r]

I know. Thats all I have used but with the new big lunger, I dont know if a 50mm Lectron will be big enough. Pretty sure they are only available in HV which means the taper @ the slide is like 46mm +/-. I see Eric @ OMW has machined a 50 into a 52. But its $$$. I have seen some crankshop carbs. They look like they go all the way up to a 56mm. And some use mikuni jets.

Crankshop Gas Carb

Modified Alky Crankshop Carb

[average_joe]

im wondering if you could get a idea of what carb to use if you knew how good your engines scavenge process was ? and how much flow can actually go through the reed block ?

[bubba297]

Or possibly start thinking about a custom setup feeding 2 smaller carbs into one intake. A pair of 39-39.5mm carbs would same the same area as a single 56mm carb. You would also get great throttle response and probably easier jetting. More money and time involved too LOL!

[Tate]

Well for my needs. I dont really need a snappy throttle per say. The 53 lectron thats on it just isn't enough. Motor need alot more air. This a 4stroke also.

[stpltn250r]

A guy has a motor just like ours but its smaller cc's. He has a custom intake that has dual 40 lectrons on it. So that by itself would be 80mm carb with a [censored] load of flow, but then you have two carbs to mess with. Trying to get two carbs tuned in on one cylinder seems like it would be a major pain in the butt.

Here are some pics of the set up, this is a snomo intake grafted to a stock 500 cylinder:







They will actually putting this set up on a dyno along with a CS carb to see what flows the best and the best over all performance

[Sculpter]

2, 40's does not equal an 80 in area,it would take 4, 40's to match the area of 1, 80,,, 1 40 equals 1256 square mm so double that and you get 2512 square mm's 1 80 = 5024 square mm's

one thing you have to remember is if you increase the size of the bore you decrease the signal strength and that is where two carbs will be a tuning nightmare if you cut the signal in half with two carbs,

2 40s will have the same area as 1 56.5 bore somebody correct me if i am wrong that will put things in a different light, the signal strength and velocity at half throttle or even WO would be better with the 56.5 than 2 40s hands down

lectron is coming out with a larger carb soon I myself only run actual 48 venturi lectrons on a 98 bored twin, but I would like to test some 52's that is roughly 17% more area , the key here is matching the cfm requirement you are looking for to sustain the rpm range you are building your engine for. if your engine is over carbed, it wont have the signal strength to keep the air fuel ratio consistent throughout the rpm range

here is a drawing of 2 40mm circles in an 80mm circle to help show the point and 2 40's and a 56.5

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[bubba297]

Hello, I said around 39.5 pair for 56mm????? LOL @ Tim

He knows I'm messing with him, I was just rough figuring.

Chris, you have to do the area of a circle basically and calculate like that. A= pie X radius squared. So you would add the 2 smaller ones together after you figure each one, then compare it to the single larger one.

[Sculpter]

sorry Bubba, I missed that but good eye if you would have put a picture up there I would have looked at it! lmao JK


what are some thoughts on "laminating" 2 columns of flow into the main intake?

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[stpltn250r]

Well, with the stock cylinder and stroke. The carb that worked best was a 50 mm lectron on a 87 intake. Big reed cylinder.

The stock stroke was 86mm and the stock bore was 86mm.

The stroke now is 84mm and the bore is 102.5mm.

[bubba297]

Tim that pic is plain "creepy" lol

I think there could have been more thought put into that intake design. That is a long piece of rubber tubing, althoug I understand the need of seperating them. Everything should have been done in aluminum and only very short pieces of hose used IMO. If thick enough wall tubing had been used then it could have been flowed smoothly on the inside even with some angles in there. I think also that if the effort was going to put into making something like that it could have been done as to not have to suddenly change the air direction a couple of times. I would have tried to get the intake area lowered and angled down a little bit to help straighten out the air stream.

Keep in mind too that a tube of a certain ID does not have to be exactly round. You can ovalize it to fit better or to make a better design and it still flows the same area. I would think a manifold to fit the huge 87 reedcage could be done fairly easy for 2 carbs, but I'll quit on this one for awhile. It would require some extensive time and welding to get right for sure.

[average_joe]

on a single cylinder 400cc or bigger its best to have the carb as close as possible to the reeds because the pulse signal gets weaker as piston size increases ?

[dirtracer]

there are things you can do with the reed cage, manifold and carb to increase the signal at the needle when running a big carb.

[gpr]

2, 40's does not equal an 80 in area,it would take 4, 40's to match the area of 1, 80,,, 1 40 equals 1256 square mm so double that and you get 2512 square mm's 1 80 = 5024 square mm's

one thing you have to remember is if you increase the size of the bore you decrease the signal strength and that is where two carbs will be a tuning nightmare if you cut the signal in half with two carbs,

2 40s will have the same area as 1 56.5 bore somebody correct me if i am wrong that will put things in a different light, the signal strength and velocity at half throttle or even WO would be better with the 56.5 than 2 40s hands down



I'd like to discuss this more.

I aggree with some of what you are saying. The part about 2 40's not equaling an 80 is dead on but the part about tuning and signal strength with two little carbs I disagree. If you are running two 40's instead of an 80 you will have a higher velocity and a higher signal strength at the carbs versus the 80, thus better throttle resonse and easier tuning and here is why:

There is only a certain amount of vaccum an engine can create. On one big carb the signal is lower because it has a larger area the vaccum is sucking through which inturn lowers it. The same is true with part throttle. at 50% throttle on 2 40mm carbs the area is still smaller than 50% throttle on a 80mm carb, thus higher velocity on two 40's versus one 80mm carb, easier tuning, and better throttle response and typically more power with higher velocity.

the only examples i have of this is in the 4 stroke world. On 660 raptors they have two carbs feeding one cylinder. Yamaha did this for throttle reponse over one big carb. Also even on the large DS 650 engines often times two carbs are used instead of one big carb. Mostly because the biggest lectron is 50mm. But two 39 actually work better and flow more because they have an area of 2388mm and one 50mm carb is 1962. The only time two carbs become hard to tune is when the signal is poor from being two large in the first place, but any time a carb is too large you will have the same issue no matter if its 1 big carb or 2 big carbs.

[camatv]

with that big long 2 40mm intake didnt that also add to the lower ends cc volume? and also possibly as to how the pipe is going to react to the motor overall? the long distance from the throttle slides has to make that a sluggish pig if it was actually rode around..??

i have an idear on one way to solve this issue but i dont think i;d like to talk about it. it dosent involve using a over price carb either..

[Moser Racing]

Check out crankshops diad carb, two bores in one body, highy used in snowmobile grass / ice drag racing. 1 wide slide with 2 needles, 2 main jets and 2 pilots. On dyno they sound a little weaker down low compared to 57mm single bore carb but diads "turn on" up top(above 8000 rpm) and make more hp. easy to tune, uses standard mikuni jets, 2 smaller mains compared to 1 huge main with a bigger bore carbs. On rotax 1000 triple(using CP Panther cylinders, making 280hp at 9600) 57mm mre carb needed 840 mains, diads needed (2) 320 mains. 2 smaller mains will atomize fuel better, and 2 smaller bores will have faster airflow and pull more lbs/hr of fuel thru smaller mains. maybe diads would work well on big bore single atv's. custom intake boot needed

[pipe-ster]

stpltn250r, on 04 February 2011 - 08:48 AM, said:

A guy has a motor just like ours but its smaller cc's. He has a custom intake that has dual 40 lectrons on it. So that by itself would be 80mm carb with a [censored] load of flow, but then you have two carbs to mess with. Trying to get two carbs tuned in on one cylinder seems like it would be a major pain in the butt.

Here are some pics of the set up, this is a snomo intake grafted to a stock 500 cylinder:







They will actually putting this set up on a dyno along with a CS carb to see what flows the best and the best over all performance

Thats what i'm working on with my new Saber engine.