I am doing some work on my old Gas Gas JT25 and when I removed the center muffler it feels very heavy. I read recently in a Montesa forum about people opening these up to clean out and repack. Is this something that makes sense on the Gas Gas?

I guess some people split them at the seam and rewelded, while others cut "windows" in the sides and made cover plates. They said it improved sound and performance.

Thoughts?

Hi, I am one of the posters from the Montesa Forum who has repacked multiple times with multiple products (stainless wool, regular repacking etc.). Personally I found it to work for me, thee existing packing was very soaked and definitely needed doing, after the bike ran and sounded much better. I guess it depends on how well you think your bike is running at the moment, if you think it needs doing it is quite a simple job - I used the window method and poprivited a cover place backover it when repacked.

Whatever you decide, good luck!

Always worth doing, really affects the bike's performance.

see: My blog post

Do you think this would quieten down my 97 JTX 250 as it has a real "crack" to the exhaust and is significantly louder than newer bikes which always makes me feel a bit anit-social.

Hoggy, Have you repacked the rear silencer? When I did mine I found that the packing was badly soaked and compacted. I repacked with fiberglass fairly firmly and it did tone down the bike some. I have not gotten the bike back together after burning out the center muffler so can't really say what effect it will have.

I had a TY350 a few years ago that was pretty loud even with good silencer. I welded an elbow on the outlet end that directed the exhaust down toward the ground and it really reduced the "crack." I did not detect any performance change.

Probably, when you open it up you will likely see that it is either gunked up, or that the orginal packing has disintegrated, both of which are likely affecting the noise level. My Montesa had a noticably softer tone to it when I repacked it.

I typed a follow-up on my center muffler but I guess it did not post so here it goes again.

When I took the denter muffler off the Gas Gas and looked inside it was totally black and I could not see any holles in the inner pipe. Some probing with a bent clothes hanger indicated there were holes but they were completley blocked. So, I sooked the muffler in diesel fuel overnight then drained it and lit the inside to burn off the diesel.

It did burn and smoke for quite a while but I did not feel it had burned all the diesel and did not want it to start buring or smoking when I ride in the future. So, I took my propane torch and held it inside one end and it got hot enough that the oily goo inside got hot enough to burn really well. Note that the muffler is steel so I was not worried about getting it too hot like I would if it was aluminum. After quite a while it stopped burning. After it cooled I used the same coat hanger and all the small holes in the inner pipe are wide open.

I am going to hold off on cutting windows to replace the packing until I have a chance to test it. I expect this should make a difference in the running because the gases will be able to expand through the holes as intended. I will report after I get the bike back together and test ride.

Here is a follow up. I put the bike back together and found that it was running poorly. I realized that the very old air filter was causing an over-rich condition so replaced that as well. Between these 2 changes I needed to correct the jetting by adjusting the clip on the carb needle.

The bike now runs better than it has since I bought it several years ago. Smoother running, better torque and great sound. Not louder, just more clean running sound. In my case, I think it was well worth doing.

Nice to know Five

just gotta be brave i think and cut a hole in my center box, seems worong cutting a hole in it when its not finished though!!!

I have had good results with caustic soda, but its hazardous to work with and needs to be done with caution! No cutting open, pour the flakes inside, dissolve with water, shake it around for a few minutes,it will heat up, pour out , rinse with fresh water and repeat until you are happy.

A bit of boring elf n safety stuff on Na0H..

Rule of thumb for mixing any basic or acid chemical is to make sure you add the chemical to the water. Never add water to any basic or acid as some will give off toxic fumes and some even create heat to the point of combustion.

Sodium hydroxide Na0H aka caustic soda or commonly called lye is fairly safe, if anything it can irritate the skin and sting your eyes if you get some in them. If you do rinse thoroughly with water mixed with orange cordial (a mild acid that will neutralise the effects of a strong base (alkaline).

Safety bit over, now for some caustic soda fun! Get a 1 ltr bottle of water and put a table spoon or two of sodium hydroxide inside it. Quickly screw the lid on and chuck it - makes a good bang as the co2 builds up pressure inside the bottle! Just don't throw it towards other people...