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108 tuning, jetting, etc....

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maximk

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Discussion starter · #1 ·
Ok so as some of you already know, I'm running a 108 stroker, TM24. We've been playing with it all day. I got someone who knows their **** over here to look at it. He helped get it jetted and tuned, but we ran into a road block. Right now its got a 20 pilot and a 170 main. Idles great, and up to 3/4 throttle things are perfect. But above 3/4 it just dies. Its had the same issue from 135, 150, to 170. He wasn't really familiar with the engine but suggested i get a new plug to match the rebuild, from the forums we found the NGK CR8HSA. Not readily available at advance. So may have to get it ordered. He also thought opening up the exhuast might help (it has a catalytic converter). But these are all just guesses on his part, and i'm clueless. Any ideas on what to do next? Really want to get this sorted.



Thanks
 
#2 ·
have you tried going smaller and see if it cleans it up? that sounds like a lot of main jet for a 108... My 141cc is happy on a 102 main throug a stock CRF pipe.



also, what kind of bike is it? to come with a catalytic converter would be strange IMO. are you sure you're not talking about the muffler???
 
#3 ·
maximk said:
But above 3/4 it just dies.
Click to expand...


Please explain.... "it just dies"...



The TM24 can be really picky as far as jetting and current weather conditions. One our 108/TM24 engine, the first settings were a 15 pilot, 160 main. With this jetting we found a decent (could have been better) bottom end but a distinct lean condition up top. With 4th gear topped out plug chops, the plug would come out looking "new". As in no deposits what so ever. We change the plug to a slightly cooler plug that was a bit used (dry black deposits) and after a top end run, came out clean as a whistle. Kind of scarey actually...



We're currently running the same jets as you and found them to be just a touch rich. It runs great with only a slight "burrble" when you crack the throttle wide open. We have our air screw set at 3 turns out from seated.



We're now trying to located a 17.5 pilot and a 165 main. We think this will bring it all together as far as tuning... (I hope... ;))
 
Discussion starter · #4 ·
Like I said we started with a 135 and went on up to 170 but maybe lower would be better. Will give it a shot. My bike is a Sachs MadAss (moped style motorcycle) has a honda style knock-off engine.

Image


if you look closely you can see where the exhaust widens up, for the cat.

So maybe lower than a 135 even? Don't have anything that low so will have to order something.
 
#7 ·
maximk said:
and by it just dies i mean it won't hold rpm at all, complete loss of power. kinda goes in and out, waaaaaaa bbbbbb waaaa bbbbbbbbb wa bbbbb wa bbbbb wa bbbbbbbbbbbbbbbog.
Click to expand...
Rich, looking at that pipe and knowing it's a Chinese 108 (107), wayyyy rich. Try a 120 with a 15 pilot.



For perspective I run 150/17.5 on my built stocker KLX110 with the VM26. A 140 would be better for me even.



TM24 and VM26 take the same type main and pilot.



It's shutting down up top because it's rich on the main.
 
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Discussion starter · #9 ·
Cool, thanks guys. So the exhaust is pretty much dictating the jetting i can run.

Anyone know what the stock jets are in a VM26, i have one sitting around, so i might try to get a jet out of it if its smaller than 135. Otherwise I will order a few smaller ones, and try to get the exhaust opened up this week. Appreciate the input.
 
Discussion starter · #11 ·
So i got the new exhaust. I've been playing with different main jets all week and its pretty much the same deal. What gives. Right now i have a 110 and it still cuts out up top. Seems like with the new exhaust and the lower range of jets i would be seeing some improvements. Could the float level be too low?
 
Discussion starter · #14 ·
Well yet another day wasted screwing with this. Adjusted the needle up and down, seeing no improvement, really starting to think this must be something other than the carb. With every jet from 100-170 we've seen the same symptoms. It come in strong on the low end, then above 3/4 throttle it either completely dies or just comes in and out, but mostly out.

It doesn't seem dependent on RPM, it seems to cut out depending on the load applied. In neutral it may go up to 10k, but in 4th gear it may be closer to 4.5k. May try a new cdi next.



Any thoughts, I'm struggling here?
 
#15 ·
Well there have been threads on the cam timming being advanced and causing the top end to just cut off.....I think fatcat or moose were just talking about this last week.......I know it has been the cause of my problems in the past...also try a different carb just for hell of it and see if it dies on top also... I have had one carb do the exact same thing and then changed it out and whamo the engine ripped...However the carb that I took off works fine on other engines...so there is some thoughts....

Troy
 
Discussion starter · #16 ·
Well go figure, took off the TM24 and swapped in a VM26. Runs pretty good, slight hiccup uptop with the airfilter on, but runs clean with the filter off. Have yet to do a plug chop. I guess I will just run with this, despite the 200 I spent on the TM and the manifold. Such is life. Will probably post that carb in the forsale section but if anyone reading this is interested let me know.



Any ideas on why the TM is not responding to variation of the mainjets. Still the possibility of keeping it if I can figure out what is going on.
 
Discussion starter · #19 ·
Well took the carb apart just for kicks. First thing i noticed was pretty blatant. The jet was pushed upwards about 4mm. here is are some photos which show this better. Will put it back on the bike tomorrow and see if it works this time.

Image


WRONG

Image


RIGHT

Image


WRONG

Image
 
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maximk
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