Why doesn't anyone know if a 2-stroke carb will run a 4-stroke bike?

[Studytime]

No one seemed to answer the previous threads that asked this.

No one knows? How different could the fuel requirements really be? I don't see what the big difference would be.

Please give some insight if you have any to offer.

Studytime

[Quickonstep]

You are the engineer, you SHOULD beable to figure this one out.. but ill throw you a bone.

a 2 stroke, has alot more velocity than a 4 stroke and is able to pull air in through a bigger diameter carb and venturi.. The 4 stroke doesnt have the velocity to do it.. altho with some work it MAY work, the work vs. benifits or lack of, wouldnt be worth it.

Hope you are able to understand that.

Jesse

[Studytime]

You are the engineer, you SHOULD beable to figure this one out.. but ill throw you a bone.

a 2 stroke, has alot more velocity than a 4 stroke and is able to pull air in through a bigger diameter carb and venturi.. The 4 stroke doesnt have the velocity to do it.. altho with some work it MAY work, the work vs. benifits or lack of, wouldnt be worth it.

Hope you are able to understand that.

Jesse


Didn't really understand all of that.

As for a 2-stroke having more velocity that's not really relevant. There are two factors that determine how much air the motor will require- displacement and engine speed. The two-stroke would have the same instantaneous velocity as a 4-stroke, but would have twice as many intake strokes as a thumper and therefor would flow 2x as much- but at the same velocity. For each pressure drop they'd be close to the same action I guess.

If both bikes are requiring around 12:1 AFR the fuel requirements are the same really. They both have to provide the proper mixture for idle, part throttle, and WOT. They should both be close I would think.

Of course for a 250cc 4-stroke you wouldn't get a 250cc 2-stroke carb, you'd get approximately the diameter of the original 4-stroke carb.

If anyone has any other information please contribute. I don't know everything and the 2-stroke stuff I said above may or may not be wrong. If it is feel free to admonish me.

Studytime

[OldSchoolin86]

It's a carb, if you match the flow to the motor it will work. I'm highly supprised you don't know that.

[Studytime]

Oh, and I'm not sure that saying a 2-stroke has more velocity through the carburetor is an accurate statement. The 2-stroke carb has a larger diameter.

Assuming a 200s and a cr85 both spun to 6200 RPM then the 200s would actually have more velocity at the carb (22 mm) than the cr85 (28 mm).

For TWO crank revs you'd be fueling

a) 200cc through a 22 mm hole

b) 170cc through a 28 mm hole

Of course we all know that when you increase the size of an orifice the flow through it will, of course, slow down.

So, i'd say this 2-stroke has LESS velocity through the carb.

Some a bone to chew on.

Studytime

[Quickonstep]

heres an idea, put a 2 stroke carb on a 4 stroke and then come back and tell everyone if it worked..

Jesse

[KASEY]

ok i guess i will chime in on this one,,, the carbs are the same its the internal parts that are different,,,,, you can take a four stroke carb and convert it to run on a 2 stroke,,,, but as much trouble as i see on all the boards with jetting i would not recommend it ,,,, cause your going to have to go through every aspect of the fuel range,,,, the needle jet is the only part that is totally different, but needle ,slide cutout , and jets will have to be changed to get proper ratios,,,,,,,,,, the bodys are the same ,,,,,

[BLAZERONE22]

If you need to find information, do what I do. Use the internet and search, I've been searching for information on my Tri Z all day. Here I found this one for you on google, its good reading, scroll down http://www.ohv.8m.com/
hope it helps.

[greenhuman]

Two stroke carbs do work on 4 strokes. I use 28mm CR80 carbs on my Project X ATC 70's because of their compact size. All I change is the needle. I replace the Keihin CR needle with a stock Banshee Mikuni needle. They couldn't run better. I have also used a 38mm Keihin PJ carb on my 550cc 350x with very good results also. The 350X had a modded FT500 head with huge valves as well. I still have this if anyone is interested.
Most of the aftermarket carb kits which used to be available for the early 4 stroke ATC's were Mikuni 2 stroke carbs. The 28mm flat slide kits for 200X's were also 2 stroke carbs off a RGV500.

[hotroddal]

well i have experience with putting a old polaris snowmachine carb on my 200x, but before i put it on i cleaned her all out, it did start wiht it on but only ran for about 40 secnds,then after that i just decided to put th original back on, but maybee if i played with the settings alittle it pssibly would have ran longer.

[Blown 331]

My cousin put a DT400 carb (2-stroke) on a TT500 (4-stroke) and it worked fine, he didn't even re-jet.

Why does every one think a 2 stoke uses a bigger carb than a 4-stroke??? Weird.

[4cylinders]

hey, put an 81 kawy 440 ltd carb on the 750x/cb750, with a 4 into 1 intake. had to jet, but works great. kinda sounds like a car, but flies.