Combat Wombat

[dcooke007]

Started a new thread since the original post has gotten so far off course from oil migration.

There has been some delay on Will's Combat Wombat due to a broken reed. Sourced and installed new reeds and testing continues. If you recall there was some discussion concerning a restricted exhaust. Removing the spark arrestor improved the engines performance but was very loud and would not rev out well on top. Decided to modify the arrestor and see how that would work. As you can see I cut off the end of the arrestor and welded in a piece of tubing the same length and id / od as the original piece....but with out the internal restrictor. Basically ended up with a stinger instead of arrestor. The large end still retains some spark arrestor function. The results of this modification was a very nice improvement in mid-range and top end reved out cleanly. Had to raise the jet needle one position higher...clip was in the middle notch. Also went from a 270 to a 290 main jet. Noise level was a good bit louder than stock but much quieter than the open pipe.

Now you are going to wonder why I put in the effort on the stock exhaust. Curious minds just want to know I guess. Any way I have a moderately damaged Torque Engineering pipe to try. Repaired the damage and installed pipe for testing. Ended up raising the jet needle all the way up and a 320 main jet. The modified stock pipe had more low end torque, would lift the front wheel in second gear and float the front wheel just off the ground in third gear for a short distance. Modified stock pipe reved out well on top. The Torque Engineering pipe had less low end torque and really starts to pull a little higher in the rpm range. Reved faster and harder in the mid range with more top end rpms and power. So....going to go with the Torque Engineering pipe.

I do not have the mounting brackets for the Torque Engineering pipe. Just installed the pipe with exhaust springs from the exhaust spigot and some cable ties. Any one running one of these pipes that could take some pics of the mounting brackets?
Thanks,
Danny

[viclioce]

Hope you get an answer Danny! That sounds like it will be a better racing pipe! ; D Victor

[Bill2001]

Very good report. I'm playing with the exhaust right now on mine. New-to-me Wombat 94, new engine. The spark arrestor was gutted (nothing upstream of the mounting flange). Needle was set all the way up (super-rich) and who know what the main jet really is (I'm going to run it by a set of jet drills and verify that 160=160). Maybe I'll plat around with exhaust and mixtures later on, but since everything is new I'll go stock til things check out.

--Bill

[Bullfrog]

I would like to throw in a comment I received from Harry Taylor a few years ago. We had been talking about the concept of "making a Combat Wombat engine be all it can be . . . without turning it into something else." Meaning that I was looking for AHRMA legal, piston-port performance which had a nice wide power band (since I just am not very good with peaky engines and corner clutch work and get into enduro type situations requiring some "grunt"). Naturally, we talked about pipes. I'd ask if Harry had any knowledge about this-or-that pipe from the past . . . or an AHRMA legal pipe spec. that would be good for me. And every time we talked about pipes, the following comment would come up, "You know kid? The Combat Wombat pipe is a pretty good pipe."

With assistance from Harry and Paul, I tested nearly half a dozen pipes from the days of yore (plus a "one-off" from Harry) . . . and the Combat Wombat pipe with a custom stinger and modern spark arrestor/silencer ended up in the top two. Which confirmed Harry's comment.

Ed

[michael_perrett]

Harry told me the same thing. Ed, could you get detailed on the custom stinger and modern spark arrestor arrangement?

Mike Perrett

[Bullfrog]

Hi Mike!

In the next few days I'll come up with a response to your question . . . which may also be of use to Danny.

Ed

[---]

Bill,

Be aware that Mikuni main jets are sorted by their flow rate, not by drill size. There is no exact corresponding drill size to a Mikuni 160 as there would be with other brands. Even as between two new Mikuni 160 main jets, the actual bore size of the jet may vary slightly, but the flow will be within tolerance.

Unless someone has taken a drill to your main jet, a 160 is a 160. If you need a different jet size, new jets are readily available.

[Dale]

Interesting note regarding the main jets. I have also found that not all needles are created equal. I have had several needles that did not match the spec sheets. I recently had four different 4E1 needles that did not exactly match each other. I would say that three of the four were probably within tolerance, but one was clearly shorter and richer than the other three. Miss-stamped perhaps? It is something to be aware of...
Dale

[hodakamax]

Hi Mike!

In the next few days I'll come up with a response to your question . . . which may also be of use to Danny.

Ed

Hey Ed, I'm also interested in something for the end of my 94A exhaust that I'm using on my project. I was going to find some expensive innards for it but I'm open to an optional set up with a spark arrestor that might be less restrictive. Any ideas would be appreciated!

Max

[MTRob]

I think I might have an original spark arrestor laying around I'ii look for you. I have one on my 125 Wombat 94A and it cuts down
the noise but really doesn't effect performance to much. I'll get back to you
MTROB

[socalhodaka]

look here how we mounted a tourqe engineering CW pipe

viewtopic.php?f=1&t=482&p=1652&hilit=Socalhodaka#p1652

[MWL]

Ed, could you get detailed on the custom stinger and modern spark arrestor arrangement?

Ed
Didn't you do an article about that a while back? I don't remember where I saw it? Resonator or maybe the old forum......

Mike

[Bill2001]

Bill,

Be aware that Mikuni main jets are sorted by their flow rate, not by drill size. There is no exact corresponding drill size...

Good point. I did a "relative comparison" to check that my jet had not been drilled. It passed a #56 drill but not a #57, as did a new 160 main jet. So I assume that it is not drilled. I may futz around with jetting and mufflers later on, but this will get me riding for the Summer.

--Bill

[Bullfrog]

The very same thought occurred to me in the middle of the afternoon. I'll have to research just where the information on the Combat pipe might be.

But here is some "seat of the pants" information regarding the Model 94 exhaust system (along with a substantial dose of personal opinion).

In my view, the Model 94 exhaust pipe (and the DS 96 and 01, Road Toad 99 and 02 and the Wombat 03 - with appropriate head pipes) provided a semi-stylish way to channel exhaust products from the exhaust port to the rear of the machine. Since it succeeded in doing that . . . it was a good pipe. Engine performance enhancement was never a part of the design of the 94 pipe (<- blatant personal opinion). Soooooo . . . doing a custom stinger and modern spark arrestor/silencer is not likely to result in any significant performance gain. However, since I haven't tried it, I surely can't rule out a performance gain.

ODD NOTE: Some years ago I did discover that the 94/03 exhaust system DOES "come on the pipe" at some where around 8,000 RPM. This "hit" can be noticed ONLY in the most sensitive of situations such as:

I was ahead of a guy on a Bultaco Sherpa 125 (in my class!!!) at Steamboat Springs and negotiating a big sweeping, long, slightly downhill, off-camber which had been freshly watered and was slicker than (pick your own adjective). I was in 4th gear at high R's with a VERY careful hand on the throttle, just maintaining speed or ever-so-slightly trying work up a bit more speed - while staying inside the traction limits of the slimey off-camber - . . . and suddenly . . . the rear end broke loose and a 40 yard "J-turn" was started. To this day I maintain that it "came on the pipe"(!?) and set me free. Cuz I was being as cautious as a church mouse stealing cheese from a tiger with the throttle! Ennnneywayeeeee, without a situation like that, I don't think you could ever feel the "hit" from coming on the pipe with the 94 system.

Ed

[---]

Here's my guess: the 94 is not and never was a performance machine. Building a pipe for it without doing major surgery everywhere else would be an expensive excercise in futility. I don't think the 94 made any more power than did the 100B. It was a street bike with high fenders, like the B+. The first modification to make a 94 into a stronger bike would be reed valves. After that's porting and a bigger carb. But, always a but, the iron cylinder is a hold back. I wouldn't try to make a screamer out of the 94 because it will overheat.

So, a bit more free flow from the pipe can't hurt. A finely tuned carb can't hurt. Carefully setting ignition timing can't hurt. But in the end you still have a mild mannered machine. I would aim at making it durable and rideable rather than fast. Better rear shocks for example, or paying attention to the weight of fork oil for you and your riding style. These will give you a nice, rideable little trail bike that can last for years.

If you really want to build a sleeper, start with one of the alumiferric cylinder bikes and go from there.

[DGardner]

This is the pipe that TTR is making for my wombat. Hope to have it on the dyno in two or three weeks.

[racerclam]

Just a suggestion, the 93 Super Rat pipe works great with a iron wombat cylinder has real broad power band , all one must do is chop off the attaching flange and nut from the wombat pipe and the right amount from the rat pipe and weld it on so you can use the big nut method . I have this on a dirt squirt I had built for my ex wife with a mildly ported and reed valved wombat engine with a 26mm carb and a super combat head , the bike is friendly and snappy. The 93 Pipe is available from who ever got Bill Cooks stuff , I am the one who orchestrated the reproduction of it .

Rich

[Bullfrog]

See Volume 1, Number 8 of the Resonator Revisited for the article on tweaking the later model of the Combat Wombat pipe.

On reviewing the article, I was reminded that Harry Taylor recommended 23mm ID as the proper diameter for the stinger on our 125cc Hodies.

Ed

[dcooke007]

look here how we mounted a tourqe engineering CW pipe

viewtopic.php?f=1&t=482&p=1652&hilit=Socalhodaka#p1652

Socalhodaka thanks for the link. Made my tab a little larger to attach the spring to. Opposite end of spring location to be determined.

The stinger end of the Torque Engineering pipe is much larger od than the original pipe. Worked on making a new mount patterned after the Combat Wombat. Still need to make the mounting stud and weld to fabricated bracket.

Ed,
Thanks for the info on modifying the later model Combat Wombat pipe. The early pipe responded well to my "stinger modification". Simple enough and yielded good results.

Danny

[dcooke007]

Finished fabricating the mounts for the Torque Engineering pipe today. Installed the rear mount with the springs on bottom so the spring ends would be less likely to catch on anything. Pipe is designed for two heat shields and one of them is missing. Will fabricate the missing shield and refinish the pipe and mounts.

Ended up selecting Maxxis tires rated for intermediate to soft terrain..... 100/100 x 18 rear and 80/100 x 21 front. Tires seem to work well and engine has enough power to break the rear wheel loose when desired. No mud yet but nice open tread pattern that looks promising.

Getting close now to having this completed. Using a different two stage reed that shows some promise.

Danny

[socalhodaka]

Danny, great work as always. Now I have an idea from you as I still need amount for my rear of pipe.
Kelly

[dcooke007]

Kelly,
Happy to return the favor. I made a replacement for the missing heat shield. Copied the one I have but the bend angle, length and bolt center lines are a bit different. Not going to the trouble to chrome, just going to blast and coat both parts.
Danny

[---]

This is the pipe that TTR is making for my wombat. Hope to have it on the dyno in two or three weeks.

So how did the pipe turn out? Dyno results yet?

[Kels]

I heard 30HP at 10,000 RPM...

[---]

Or was it thirteen??? Have him post the dyno sheet and list the mods. Might as well find out.