Opening up exhaust flow for off-road use only

[Thumper]

Are you turning your bike into off-road only and want to remove the restriction of exhaust flow in the headpipe bulge? The process is pretty easy if you have a sawzall, grinder and a welder (or know someone with a welder).

The honeycomb is in side a steel cylinder that is nested inside the bulge (TWO layers of steel column).

I used a sawzall to make the two cross cuts, and the grinder with a cutting disk on it to make the longitudinal cut:


Peal back the outer steel skin, and then use a heavy screwdriver to pry out the inner steel skin, The inner steel layer is connected to the honeycomb column, so it resists. You can use heavy channel lock to pry it open.

Once exposed, use the heavy screw driver to get behind/around it on the right side and left side and pry the honeycomb tube out.


I peeled off the residual honeycomb outer layer that was stuck to the steel, then cut the inner flap off (why not?).



The header pipe both input and output side are visibly clear at this point, and you can see them inside, so...
Now it is ready to close. Work it back into place and use a steel wire wheel to prepare the surface for the weld.

[Thumper]

Here is a pretty bad photo of the cleared header pipe (input side). You can see it is wide open now.


Here is the wirebrushed seam. I worked it around to even out the gaps all around for welding That gap on the left is a little wide here:


Once I get this welded, I will update this thread with more on the end result. I am hoping I will have no trouble installing the heat shield after installing it back on the bike. Rejetting the carb will be the next step!

[franque]

Just be really careful with the catalyst... cadmium (what's in the cheap stuff) is highly toxic, especially if breathed in!

[Thumper]

Originally Posted by franque

Just be really careful with the catalyst... cadmium (what's in the cheap stuff) is highly toxic, especially if breathed in!

I thought catalysts were platinum (why they steal the catalytic converters to sell for scrap metal!). It is sitting in a pile ready for sale to recyclers. I wonder what they will say?

[franque]

More expensive ones are, but more likely that is cadmium plated steel... Additionally they will buy the whole catalytic converter (off of a car), but they won't buy the remnants of one (because that could easily be stolen, with no paper trail, to boot!), and the little tiny ones off of motorcycles, even if intact, would likely not be worth their time in terms of recycling.

[Thumper]

I need to put a plate under the catalytic converter in my truck. Apparently it has two of them. But with 18" clearance under the converter, it would be easy to get a sawzall up in there. I have some hardened 16th inch plate (eats up jigsaw bits and needs to be cut with a cutting torch!). I will use it for this shield. I can tack weld the bolts in place after install to make it a little harder to get to. Maybe it will be enough to deter?

[Thumper]

I am pretty sure I didn't overdo it:
Carb is coming off next...

[Thumper]

I gave it a coat of high temp engine paint, then reinstalled and I started it with the new holes in the exhaust pipe too. It is not excessively loud and came off choke without stalling right away... Cool!

Even in the warm Summer temps last year, it stumbled and wouldn't idle properly for a minute-needed half choke to idle. NOW, with the exhaust opened up, it settled into a smooth idle immediately, and would start without choke after less than one minute. And the garage is ~ 40 degrees cold right now!!

Could the high flow resistance in the exhaust system be the real problem?

I am not sure it even has to be rejetted if I leave it like this, but I'd like to get the torque and horsepower up... Actually, running lean isn't good for the engine, so I will definitely rejet to get it on the slightly rich side. But it just runs better. The honeycomb must have really created back pressure.

I haven't opened up the airbox side yet. If I do, I will bet that all of a sudden it will need rejetting and needle height adjustment to run right at all.

[Thumper]

Mods so far on the Bashan Storm:
-Emptied the cat blimp,
-drill the exhaust,
-shimmed the jet needle about 2mm, and
-opened the airmix screw from 3.5 to 4

Also changed the dual sport OEM tires to Tusk Dsport rear and Shenko 425 front MX tires. The Dsport is closer to MX than dual sport, but corners reasonably on pavement considering what it does for off road fun!

I took it out into sub-freezing conditions, into the partilly snowy partially dry conditions and did some turns broken loose in the dirt and snow, and some climbing. YAYY
The DSport needs to have the pressure dropped, and the low temps keep the lugs too hard, but the Shenko 425 is already performing GREAT on downhill control and turns and slippy corrections (inspiring confidence), even in the snow and loose weeds. Very impressive.

It idles right away coming off a cold start without choke within a minute after start! The engine is definitely spunkier and revs MUCH more willingly with the breathing room and more enriched midrange. It breaks the rear tires loose easily, wheelies more easily. Great!

High end is obviously stronger. It feels more torquey (holds speed on hills) at 60mph, gets there to 60 more quickly, spinning up more willingly. It is amazing how the stuffed up exhaust and leaned out carb is such a factor on these bikes. I have heard it over and over, and now I see the little 229cc clone can be unleashed.

I still haven't done anything with the airbox. I am waiting for jets before I do that. My guess is I can close in on 20hp pretty easily.

Limitations? Suspension, suspension, suspension. These grippy tires and additional power made the front end limitations immediately obvious, bottoming out on deep troughs and bumps.

Who needs a new cheap carb and a new exhaust system? Not me. If I want more performance, I will look at a SSR 300 or something. No use spending big money on this bike. The PZ30 carb works fine. It just needs a little adjustment

[franque]

Glad it's working better! If you're running 4 turns out on the mixture screw, you need to make the pilot jet one or two sizes leaner. I would go one leaner and then see what messing with the airbox does, as more airflow typically means leaner mixture. Anything more than 2 turns out means you need a leaner pilot jet (for a fuel screw), and less than 1 or 1/2 turn out means you need a richer jet.

[JProDLX]

Haven’t ridden it yet since removing the cat on my DLX. But did start it and it sounds way better and throttle response has improved a lot.

[JerryHawk250]

Actually on the PZ30 the pilot jet and mixture screw are for fuel. The PE30 and PWK30 will be air mixture.

[franque]

Also, the pilot jet only controls the amount of fuel. Like Jerry said, other than what you're theoretically trying to describe, you're spot on if it's an air screw. My advice is correct.

[Thumper]

I am so sorry I don't have video
I decided to take advantage of 50s weather and test the new setup with opened up exhaust and shimmed needle, and put some feet (not miles!) on these new tires to see what they can do.

There is a housing development nearby that is desolate on weekends, There are ponds, a seasonal creek or two, and lots of big rain eroded clay with schist on steep slopes with mounds and ridges and it is pretty brutal in some places. Oh, I can get used to this
Got some mud and caught some brush.



Oh, and who says a 15hp dirt bike can't wheelie
The right bump, and the front end lofts with ease. Go where it takes you, and it is an extended wheelie. That's what I love about knobbies!!!
And BTW- the exhaust note is GREAT! Those drilled holes were perfect
It is so ridiculous watching youtube vidoes where they want to wheelie a dirtbike on flat pavement

[Thumper]

Originally Posted by franque

Also, the pilot jet only controls the amount of fuel. Like Jerry said, other than what you're theoretically trying to describe, you're spot on if it's an air screw. My advice is correct.

It is not an air screw. It is a fuel screw. It needs a bigger jet, not a smaller jet. 4 turns out is ridiculous, but I am waiting for bigger jets on the way.