Teaching an old(er) dog old tricks

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8/2/2018 2:56 PM

Alright, let me begin by saying this is my first two stroke after 20 years of riding and wrenching on old bikes. Bear with me if I’m a little ignorant in dealing with the quirks of a vintage smoker...

So, I recently finished a full restoration of an ‘83 CR125R and have been testing and tuning it. It fires right up and sounds crisp at idle and rev. I drop it in gear and it pulls...weak. When it hits the pipe (like a light switch!) it screams but it doesn’t exactly leap into action. The plug looks good, the carb is clean and tuned and the new clutch isn’t dragging.

I know 2 strokes generally require a certain skill to ride right. Am I just spoiled by the instant torque of 4 strokes? Do I just need to learn how to dance through the gears better to keep it on the pipe? Or is there something else that would cause a bike to sound great and run clean but lack a “hit”?

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8/2/2018 3:30 PM

I"m not specifically familiar with the 83 cr125 but bikes have come a long way from 1983 125 horsepower...makes you really appreciate the talent of the guys that made them fly.....I donot have any vintage 125"s, figured after racing 250 two strokes & 450"s they might be a little underwhelming.....

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8/2/2018 3:57 PM

Unfortunately it sounds like it probably runs exactly how it’s supposed to.

I built an 83 125 also and always questioned if everything was right on the bike or if it was just me. I was 4 in 83 so obviously I never rode this era of bikes to know what a good one should feel like. The only way to tell is to go race against or ride other similar year 125s, or have someone with a lot of time on early/mid 80s 125s ride it and give their feedback.

125s definitely take some serious skill to get around well on. I’d guess you’ve just spent too much time on modern bikes to gauge it and you can’t at all expect it to go anything like a modern 4 stroke. I’m not familiar with Honda’s so maybe there is something you can do to get more hit. As you said....learn to dance. If you can’t dance on a modern 125 you’re going to be clumsy as hell on an old one. That’s why I’ve always kept a modern 2 stroke for a practice bike...keeps my skills up better for the vintage bikes I race a few times a year.

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8/2/2018 10:17 PM

you should do a compression test.

is the cylinder stock or ported?

what pipe is on it?

if it is stock you can have it ported to rev more then increase the compression but it will be harder to ride.

race gas is best and you can run a little more compression with it.

the carb is too small to make big hp. i would also run a 34 if you port it.


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8/5/2018 4:38 AM

The hondas of that area where low power wise without engine work.

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8/5/2018 7:34 AM
Edited Date/Time: 8/5/2018 7:34 AM

My buddy had an '83 CR125 way back then, and it was very difficult to ride. It had absolutely nothing off the bottom or even in the midrange, then hit really hard and screamed on top. 125's in this era made like 25HP, and were hard to keep on the pipe. Unless you are a rather talented rider, 125's absolutely suck to ride around a track. Even good running bikes are "bog-o-matics" unless you know really what you are doing.

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8/5/2018 6:40 PM

Well, aside from the bike’s natural-born weakness or my lack of talent, I suspect there may have been an issue with the clutch hanging up, I tore it down and found that the EBC springs I had in there were a full .050 longer than the stock springs (and way stiffer too). Also discovered that this little sucker wasn’t included with the bike:

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$67 for a .03 cent spring. Of course I bought it because at this point, why stop?

I put a set OEM springs in, double checked that everything went back in properly and buttoned it up. Clutch feels much better, just waiting on my precious metal return spring.

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8/5/2018 6:51 PM

Also, in response to an earlier reply, engine work done:

2nd overbore Wiseco piston, light porting and surfacing on the head, DG pipe and a tuned Mikuni 32 burning 93 octane at 40:1 (Amsoil)

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8/5/2018 10:59 PM

This place usually has the harder to find stuff.
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8/6/2018 4:57 PM

stiff clutch springs won't affect engine performance.

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8/10/2018 2:55 PM

Maybe try replacing the ignition coils on the stator?

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