Custom Saw Intake Choices

Things to know, adapting the larger RWJ-4-1 (X-Torq) intake setup uses components from the 372XT, 385/390XP and carries with it some minor drawbacks. Because the carb is larger it pushes the HD filter a tiny bit to the rear, resulting in slightly crushing the top rear of the HD filter. In order to use the RWJ-4-1 the carb boot from the 385/390XP must be used, this setup does not seal the carb box as well as the standard 372XP setup. Lastly, the RWJ-4-1 requires the blue choke lever from the 372XT be used, which is slightly longer than the standard choke lever resulting in the lever protruding about a 1/16 inch further out of the saw when in the off position.

Voting on this portion will begin Sunday July 13

 

What are the differences between the two carbs?

 

Rwj-4 is a bigger venturi.

 

How would it perform differently?

 

There's not a big difference in power between carbs. It has the potential to flow more air/fuel.

 

Any downsides?

 

Just what he mentioned about the filter and stuff not fitting quite right in the air box. Personally I like the tillotson that some 385/390s have. They seem to tune easier than the walbros on the same saw.

 

Since this saw may very well get ported by Mdavlee, either carb will work in a ported or non ported saw. Putting a larger carb on a saw that cannot take advantage of the increased venturi area is not likely to make a noticable difference in performance. So that means that IMO the RWJ-4-1 will produce the best results on a ported saw, especially since the crancase volume is the same between the XP and XT saws. The porting will also change the port timing of the engine which will take better advantage of the RWJ. There is a stainless steel divider in the RWJ between the choke and throttle shafts which divides the air flow into the carb, the air above the divider is 'dry' (no fuel) this was done to aid the strato design on the XT saws. The divider there or not has no effect on saw tuning since the carburetor has enough adjustment range to negate the effect of the divider.

 

Vote casted

 

Per Mdavlee, on the Tillotson, it does tune better than the RWJ-4, however it has the same fitment issues as the RWJ.

 

Slave to fashion, eh?

 

For non-professional firewood use, does the HD filter make any difference in comparison to a standard filter? I kind of assume that the point of an HD filter is that you don't have to clean it as often because it's got more surface area, but maybe that's off-base?

 

Low top looks too much like a 346 to me and the filter isn't a good when ripping and milling.

If I'm going to change it the tillotson is my favorite.

 

The 'crush' is about 5mm.

 

Do you mean 5mm deep or a patch 5mm across?

 

It puts about a 5mm crimp in the filter paper, I'll put up a picture.