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Discussion Starter #1
Hi everyone. I've got an 03' KTM 125sx. Factory engine with an FMF Fatty Pipe and Shorty Silencer. Gearing is set at 13 front 48 rear giving me a ratio of 3.69. I live in Northern Maine and there's hundreds of miles of railroad beds to ride (obviously no tracks lol) which is why I've got it set with taller gears. I understand when you add or take away from one end you get the reverse effect on the other but my bike is just about nutless on the bottom end. Has anyone tried or had any luck using flywheel weights. After some research it sounds like a 6-8oz weight is what I'm after but would like to hear from other riders. Thanks for any advice.
 

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Hello & welcome

Unfortunately I am unable to help. I am sure someone will be along shortly to assist
 

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I know its not what you were asking about but check out the STIC block that is available for Keihin carbs, it will give you loads more bottom end grunt, even on a 125.....


The downside of the STIC block is the price compared to a flywheel weight.
 
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Discussion Starter #4
I know its not what you were asking about but check out the STIC block that is available for Keihin carbs, it will give you loads more bottom end grunt, even on a 125.....


The downside of the STIC block is the price compared to a flywheel weight.
I did a quick search and I'm wondering if I've got the right part. Is it a carb insert?
 

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Its a metering block that replaces the original metering block of the carb, its changes the way that the carb atomizes the fuel. I was a sceptic with regards to the device until the inventor sent me one to test, it really is quite a shock with regards to the bottom end torque that it helps the engine develop. The downside is that they are not cheap. You can see the block at 17-18 seconds into the vid.
 
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Sidecar are the carbs now flyby wire?
Not to my knowledge, obviously the later (larger) engines are TPI. I did not want to hijack this thread but as the OP wants more bottom end then I know that the STIC block can give this in spades. Pushing up the CR and sorting out the squish will also help assuming that the CR is not already high on the 125 engine. (which is may well be).
 

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I would suggest that putting a FWW on a 125 will make it a bit trialsy .... so better for slow speed clambering ..... but potentially worse than it currently is elsewhere. Dumping the shorty in favour of a standard can might improve things generally. Might be better with higher displacement?
 

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The stic block is an excellently engineered solution to the classic 2 smoke issue. For what it does I think that’s a cheap performance gain. Flywheel weights are great for calming pipey engines and assist in finding traction as opposed to spinning out when they come on pipe but they won’t increase torque Per se. Bumping the compression will give an increase everywhere but by the same percentage so the perception will be that the strong part of the range got better but that the weak area got weaker because 10% of fuck all is, well, fuck all. As ship said your pipe set up is wrong for what your doing. If you can find one the 03 mxc pipe with an exc silencer would work well but that would probably cost more than the stic block. Obviously this is just my opinion ;)
 

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Bumping the compression will give an increase everywhere but by the same percentage so the perception will be that the strong part of the range got better but that the weak area got weaker because 10% of fuck all is, well, fuck all.
You've read the same book as me, from memory it was AG Bells book on 2 strokes. He mentions that when the engine is operating out of the powerband that the effective CR is so low that there is nothing to compress, I think that he might not have used the words "fuck all", if not he should have!
 

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You've read the same book as me, from memory it was AG Bells book on 2 strokes. He mentions that when the engine is operating out of the powerband that the effective CR is so low that there is nothing to compress, I think that he might not have used the words "fuck all", if not he should have!
Haha you could be right, many moons ago long before the Internet I begged and borrowed all the tuning literature I could find and that was one of them. Good find on the stic block, that’s genius!
 

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Discussion Starter #12
Thanks for the advice, I appreciate the input. Without sounding like money is no issue I don't mind paying the price for the stic metering block, however my bike (the way I bought it) came with a Keihin PWK 39 not the 38 and after quite alot of search time I cant seem to find a stic metering block for the pwk 39. If anyone knows a site could you please drop the link? Also as Chalky 1 mentioned about the wrong pipe set up (FMF Fatty/ Shorty Silencer) I agree and so I have ordered a Pro Circuit Platinum w/ R304 Silencer, and a Thunder Products Quad Flow Torque Wing along with various other non performance parts like new front/rear sprockets, chain, bearings etc ... just to freshen up the bike a bit but when it comes in tomorrow i'll let you guys know how the torque wing works.
 

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Discussion Starter #13
Oh and one more thing. After searching for a performance cylinder head with no luck can anyone tell me what was changed from 2003 - 2007 because thats the latest year back I can find a cylinder head. Would an 07 fit on my 03?
 
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