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1972 Yamaha 125 Mid-Range

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I was riding the Yamaha this weekend and noticed it ran good starting out and near the top end.

But in the middle it pops and splits, cuts out some.

I made a baffle to cut down on the noise a little, you think that's effecting it?

Would the jetting need to be changed b/c of this?

Any ideas?

David

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Try checking the points or look for exhaust restrictions. Did it run well before the exhaust baffle? I'm having the same problem on my MX175. I cleaned the carb well including the pilot jet. Bike has stock main jet, I've tried different needle positions. It still runs very flat with no power until I get in third gear then it seems to clear itself out some. Compression steps up to 120psi after 5 kicks. Spark seems OK but I do want to check the points. After inspecting the points I'm going to look at the exhaust, maybe its clogged? There is a stange vortex type of baffle in my exhaust that may be restricted.

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That "strange vortex baffle" you talk of is the patended Krizman spark aresster from the 70s' . Most of the bikes back them had it and clogged easily.

Time to BBQ that pipe.:smirk:

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Memorial day weekend is always a good time for a BBQ! You are refering to a way to clean/decarbon my pipe right? The pipe is in nice shape and I'd like to keep it. Can the Krizman spark arrester be removed? Thanks!

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Memorial day weekend is always a good time for a BBQ! You are refering to a way to clean/decarbon my pipe right? The pipe is in nice shape and I'd like to keep it. Can the Krizman spark arrester be removed? Thanks!

Should be one screw that holds it in. It might have a little packing too.They can be hard to pull out,use channel locks..

BBQ the whole works,then when it's done smoking and REALLY hot,blow into it with compressed air and watch the carbon embers fly!!

DSCN5975.jpg

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Thanks again scalejockey! Do you think I can use a hand held gas torch instead of grilling it?

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Thanks again scalejockey! Do you think I can use a hand held gas torch instead of grilling it?

Not really... the whole inside of the pipe needs to act like a blast furnace. The carbon\oil build up inside will fire up when air or O2 is blown in. It sounds like a big blow torch when you get the right amount of "air\fuel". Most of the pipe can glow orange when done right.

Then chunks of carbon will fly out. :smirk:

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Sounds kind of like a chimney fire on a smaller scale. No pun intended. Thanks for all the advice, hope you're having a nice holiday!

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A fall bonfire is perfect for the yearly "roasting of the pipe", but for now, you're to have to grill it.

Seriously: we used to have a nice bonfire every fall when it got cold, after the fore got good and hot, we would take our two stroke pipes (already apart, with any heat shields and baffles removed) and put them in the fire. After the cooking and smoking was complete, we would pull all the pipes and parts out of the fore, and toss them in a 55 gallon water drum. All the paint would get cooked off, but all the carbon was gone as well. Leave them out in the sun for a few daysafterwards to dry, repaint, and reinstall. Always looked like new for Christmas. The baffles would get the treatment twice a year, with the Krizman turbo checked really well for chunks of carbon. If you use synthetic two stroke oil, you won't have to do this again.

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I pulled the pipe off of my MX175 today and I used a hand held torch to heat the part of the pipe that contained the Krizman spark arrester. I got pipe orange hot then dipped it in water then tapped it with a hammer and repeated that process 3 times. Lots of carbon plus that darn spark arrester came out of the pipe. After things cooled down I reinstalled the pipe minus the Krizman arrester but with the end baffle in place. This bike runs much better now, some carb tweaks and it should be good to go! Thanks for all of the advice!

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I pulled the pipe off of my MX175 today and I used a hand held torch to heat the part of the pipe that contained the Krizman spark arrester. I got pipe orange hot then dipped it in water then tapped it with a hammer and repeated that process 3 times. Lots of carbon plus that darn spark arrester came out of the pipe. After things cooled down I reinstalled the pipe minus the Krizman arrester but with the end baffle in place. This bike runs much better now, some carb tweaks and it should be good to go! Thanks for all of the advice!

You actually need to remove the baffle and then the inner part as well, roast it and you'll get even more out. If it isn't bare, rusty metal, you aren't done.

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You actually need to remove the baffle and then the inner part as well, roast it and you'll get even more out. If it isn't bare, rusty metal, you aren't done.

:ride::thumbsup:

Love a good BBQ!!

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:ride::thumbsup:

Love a good BBQ!!

Yes, but the flavor isn't what you're used to, and it can be tough on teeth.:lol:

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I think the pipe is clean enough for now to get the bike running properly. It still seems very flat until I hit 3rd, 4th or 5th gears, in 4th it really seems to run OK. I think I have more work to do on the carb. Should the A/F screw stall the bike when turned all the way in? My idle screw is turned almost completely in to get an idle. Something doesn't seem right. The carb does have stock parts in it and they are clean the only thing I know that is missing is the retainer that holds the MJ needle down in the slide. I cut a piece of plastic into a semi circle that seems to do the job. I looked at the points but did not actually check the gap, could this be an ignition problem? I have to get this thing running decent before I mess with anything else on it.

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