Model 94 expansion chamber fitment issues

[matt glascock]

Just for fun, I scored a J&R Power Pipe expansion chamber for a model 94 Wombat. I have a few questions for the forum. First, is there any magic formula for rejetting the carb beyond going way rich on the main jet then dialing them back to a point where it no longer four-strokes? Secondly, there is one mounting flange on the pipe at about the front of the baffle cone. Between that and the nut that mounts to the exhaust spigot, is this 2-point mounting set-up enough or do I need to weld on another mounting point? Lastly, the way the pipe is shaped, there is contact between the stinger and the right top shock mounting bolt. Is this an issue beyond the obvious cosmetic concerns? As always, thanks to all!

[socalhodaka]

Matt lets see a photo

[matt glascock]

Hi Kelly, This was a model 94 basket which was stripped (dig the great wiring arrangement) and was likely a woods weapon/trail bike previously (I reinstalled the rusty crusty spare chain links onto the clutch cable - cool). My plan is to keep it as a piston port MXer. It runs well now. I restored the stock pipe but was hoping for a little better midrange hit and ideally a scosh of overrev with this period-correct expansion chamber. If I get none of the above, it still reminds me of the fiddling and diddling we did back in the 70's to try and wring a few fractions of a pony out of our thrashed bikes. That's cool by itself. The first shot depicts the whole set-up. The middle shot shows the current mounting flange arrangement. The bottom shot reveals the lack of relief between the stinger and the top shock mounting bolt. I'll look forward to your suggestions. Thanks Kelly!

MAtt

[socalhodaka]

I dig the pipe it looks cool and sure it will work. I fixed up your photos a bit, hope you don't mind.

[matt glascock]

Thanks Kelly. Looks much better. I don't know why when I publish photos on this forum they always turn out looking like they are 2.5 stops underexposed. They sure don't look like that before I upload them. Did you copy them onto your photo processor and edit them? Anyway, yeah, its a typical, cool, old-school Southern California 2-stroke chamber with original paint and decal. The bike actually runs well with no carb adjustments giving rise to the concern of a lean condition. Its kind of tricky to do jetting assessments with the upcoming -40F wind chill we are slated for this weekend. Thanks Kelly!

Best,

Matt

[Bullfrog]

I think the long term reliability of the mount system would be greatly improved by providing some means of holding the pipe "in" by some means along the top-side of the pipe. The photo shows a modified Combat Wombat style setup. The metal bracket is completely stock CW, but the bumper is "new" to replace the decades old bumper. I made the bumper out of a short length of small diameter radiator hose which was glued in place and filled at the same time with black silicone sealant. This system helps control my "high, right-side pipe" and reduces the "hinging" stresses on the lower mount at the middle of the pipe.

[Bullfrog]

hmmm, that should be, "hingeing" or flexing
Ed

[matt glascock]

Very crafty set-up, Ed. I see what you mean about the "hingeing" effect, in this case downward, by two points of fixation. Although this is a high right-side mount, it does ride a bit higher than stock bringing it nearly in contact with the seat bottom and in direct contact with the top right shock mounting bolt as seen in the photos. The bracket I'm using is the stock aft pipe hanger from the model 94 simply attached from below by the stock u-bolt. I might try "untucking" the pipe a bit by rotating it outward at the spigot and resetting the bracket as I'm not happy with it in contact with the shock bolt. I do like the over/under mounting points and the spring just may be the way to go. I'm going to have a closer look at my CW. I might "steal" your bumper mod to sit interposed between the pipe and frame to keep the pipe off the shock bolt. Good stuff, Captain. As always, thank you (and Kelly too).

[motovate]

What holds your bumper to the pipe? To keep from loosing it if the pipe moves a round a little??

LBM

[Bullfrog]

The bumper is "glued" to the CW bracket (silicone sealant surrounds the mushroom shaped stud sticking down into the bumper) . . . and the spring pressure keeps the pipe snugged up against the bumper. It has been in place for several years and seems to have worked well.
Ed

[matt glascock]

Well, I have the relief issue solved between the pipe and shock mounting bolt by rotating the pipe outward at the exhaust outlet. That move did bring the stinger out a bit wide, but not bad for MX work - not advisable for woods. I'm going to look at top mount possibilities just beyond the baffle cone.