Carb Difference: RWJ4 or WJ39

[Nitroman]

Saw this very briefly discussed in the 390 vs. 394 thread.

So which is better in terms of flow? Can I get more power out of my 394 with the RWJ4? This was implied as being larger.

Thanks.

 

[Chainsaw Jim]

Basically you have to hog out a WJ-39 to equal the venturi size of the RWJ-4. It's a popular addition to the saw to compliment a good port job and wouldn't really be necessary or show much gain on a stock running saw.

 

[Nitroman]

Kewlness. Since I happen to have a wildly modded 394, I think I'll eBay up that carb.

 

[wigglesworth]

If u wanna get rid of your WJ39, let me know.

 

[Big1066ih]

Any mods needed to make it fit/work or bolt on n go?

 

[jacob j.]

Kewlness. Since I happen to have a wildly modded 394, I think I'll eBay up that carb.

If u wanna get rid of your WJ39, let me know.

The 394 he got from me already has the RWJ-4 on it.

 

[jacob j.]

Any mods needed to make it fit/work or bolt on n go?

It's not a bolt and go on the 394. You have to switch everything over to external pulse, or drill the carb for internal pulse.

The 394 uses rigid block and the pulse passage is in the block. The 395 (like the 371/72 and 385/90) uses a rubber boot and external pulse. So the RWJ-4 is a bolt and go for those saws. The WJ-39 would have to be configured for external pulse if using on the 372, but that's easy enough.

 

[Derf]

Hopefully this isn't a detail of this thread, but can anyone explain what is involved in converting an internal pulse carb over to external pulse, or visa versa.

 

[Chainsaw Jim]

Hopefully this isn't a detail of this thread, but can anyone explain what is involved in converting an internal pulse carb over to external pulse, or visa versa.

No problem..
Converting from an internal body impulse location you take the pump side plate and drill an appropriate size hole to press or glue in a barb. Usually there is a bossed area for this location. If not you match it to that version of the carb. If you have each version of the two carbs then swap plates.
Most of the time the gasket area will plug the existing hole in the carb body. If not then jb weld it. It can be easily drilled out later if needed, so it is never a permanent conversion.
You'll have to drill that hole in the carb body to do it the other way around. There is usually a mark in that location to guide you, and it only needs punched through from the outside as the internal part of that passage is pre drilled from the factory.

 

[Iron.and.bark]

No problem..
Converting from an internal body impulse location you take the pump side plate and drill an appropriate size hole to press or glue in a barb. Usually there is a bossed area for this location. If not you match it to that version of the carb. If you have each version of the two carbs then swap plates.
Most of the time the gasket area will plug the existing hole in the carb body. If not then jb weld it. It can be easily drilled out later if needed, so it is never a permanent conversion.
You'll have to drill that hole in the carb body to do it the other way around. There is usually a mark in that location to guide you, and it only needs punched through from the outside as the internal part of that passage is pre drilled from the factory.

A quick question.

Anyone tapped the rjw-4 for an internal impulse signal?

Cheers

 

[Chainsaw Jim]

A quick question.

Anyone tapped the rjw-4 for an internal impulse signal?

Cheers

It would be easier to tap the cylinder for an impulse barb and run a line. The impulse connection mostly disappears if you hog out the intake block to match the rwj4.

 

[Iron.and.bark]

It would be easier to tap the cylinder for an impulse barb and run a line. The impulse connection mostly disappears if you hog out the intake block to match the rwj4.

Sorry, intended application already has a larger intake than the rwj4

 

[jacob j.]

Sorry, intended application already has a larger intake than the rwj4

It sounds like you need an 084/088 carb then...

 

[Iron.and.bark]

It sounds like you need an 084/088 carb then...

Nah, an 084 carb would probably be an overkill. Just going on a poulan 6000/152. Intake block is aperture is prob around a 1mm greater than the carb throught of the rw4j, which in turn is prob 3-4mm greater than the stock walbro carb. The rw4j also maintains the existing physical dimensions avoiding custom work.

Secondly I would also like to see if the diveder within the carb helps with torque, like the old motorcycle theory.

Looks to also be a very nice upgrade for the solo 690 & 603

 

[Chainsaw Jim]

Sorry, intended application already has a larger intake than the rwj4

All the more reason to install a barb and fill in the mating surface nice and flat for the carb. There won't be any room on the carb to drill a passage.

 

[farminkarman]

I know this is an old thread, but figured it would be a decent spot to ask the question. Has anyone seen any performance gain from running an RWJ-4 on a ported 395xp vs. the normal WJ carb?

 

[farminkarman]

I know this is an old thread, but figured it would be a decent spot to ask the question. Has anyone seen any performance gain from running an RWJ-4 on a ported 395xp vs. the normal WJ carb?

I guess I will have to add this to the list of experiments to try....I have an aftermarket 395 carb that I could sacrifice to experimentation with venturi size.

 

[srcarr52]

I guess I will have to add this to the list of experiments to try....I have an aftermarket 395 carb that I could sacrifice to experimentation with venturi size.

Enlarging the venturi by hand and thinning the throttle shafts is only worth a few %. It's only noticeable with a stop watch.

 

[farminkarman]

Enlarging the venturi by hand and thinning the throttle shafts is only worth a few %. It's only noticeable with a stop watch.

I usually thin the shafts, but I haven’t messed with the Venturi on any of my builds so far.

 

[srcarr52]

I usually thin the shafts, but I haven’t messed with the Venturi on any of my builds so far.

Don't be afraid to give it a little tickle.