carb

[J25]

ok do you guys think i should get a keihin 39mm pwk carb for my 400ex, he also has a 38mm, the only mods i have are full pipe and jetted and k and n so u think i shold get one of theme???

[J25]

someone ne one???

I"m not sure if I understand exactly what those carbs are but they sound like carbs for 2 strokes. FCR is the only keihn carb offered for a 400ex I beleive..:confused:

[wilkin250r]

I'm with Rico on this one. I'm pretty sure the PWK is a two-stroke carb.

[whatwasthat]

im curious, what makes a 2 stroke carb differ from a 4 stroke carb?

[wilkin250r]

Well, for one, I don't think two-strokes are too keen on accelerator pumps. You won't find accelerator pumps on PJ or PWK carbs.

In basic theory, all a carb does is mix fuel with air in the proper ratio, right? So in that sense, any carb should work. However, when you start looking at DYNAMIC requirements (as things are changing) two-strokes and four-strokes are very different. You need to tailor the needle taper and idle-jet locations differently for the different engine characteristics so the carbs work well over a wide RPM range.

[whatwasthat]

very informative wilkin, thanks

[wilkin250r]

That's what I'm here for :)

[YZROOSTINYA]

PJ = Power Jet

Same as accelerator pumps but controlled by a solenoid

Every 2 stroke MX bike since 99 has a PJ

TPS = throttle position sensor

2 stroke carbs probally flow more. a 2 stroke compared to a 4 stoke at the same cc's generally uses alot more fuel.

not sure about the latter though

[wilkin250r]

Originally posted by YZROOSTINYA
PJ = Power Jet

Same as accelerator pumps but controlled by a solenoid

Every 2 stroke MX bike since 99 has a PJ



:huh

A solenoid controlled accelerator pump? Solenoids are actuated by electricity. There are no electrical wires going to the carb. How can it have a solenoid accelerator pump?

[Evan]

On the newer dirtbikes there are wires going to the carb- for example-my cousin has a 250SX KTM, it has the exact same carb as my R (38mm A/S) but his has wires going in the side where as mine does not, just a flat spot.

[YZROOSTINYA]

a solenoid can act as a pump. My 99 yz 250 had it.

straight from the YAMAHA website for ther yz 250

"38mm Keihin PWK carbuerator with power jet and throttle position sensor (TPS) ensure precise fuel/air mixing and extra-crisp throttle response throughout the powerband. "

take a look at all the 99' and up 2 stroke bikes. Its in there, like RAGU!

You perticular carb may not have it. but there is solenoid carbs out there.

[wilkin250r]

Ok, I believe you. I'll be the first to admit I don't know much about dirtbikes.

However, I'm not sure the PJ really means it has a solenoid accelerator pump in it. My quad has a 36mm PJ and it certainly doesn't have an accelerator pump or a throttle position sensor. In fact, I would say NO aftermarket carbs for quads have them, the only place you will find them on quads are the new YFZ450 and the TRX450R.

Isn't the stock 250r carb a 34mm "PJ"? And I KNOW it doesn't have a solenoid in it.

PJ doesn't always mean a solenoid actuated power jet, right?

[hondafox440]

Only Kawasakis have Power Jets.

TPS doesn't have that much to do with the carb. The electronics of it are in the engine - they sense what speed the engine is running at, and it's demand for fuel. I think it is all mechanical from there, as in the engine "demands" more fuel, so it tricks the carburetor into giving it more fuel.