doughy down low

[CRTAD313]

after some advice to fix a doughy bottom end on a 84 Honda CR125. When i bought the bike it was ridiculous it wouldn't pull out of a corner without FLOGGING the clutch , but started fine. so pulled the carby and reeds. jetting was up to crap had a huge main, float level was wrong, air screw rich and reeds were tired. replaced reeds and jetted standard. which improved things a bit.Have since fully rebuilt motor,dropped the slow jet a size and dropped the needle one clip which  improved it much more as well. It is running a 100% on what it was but I still feel it should have a little bit more off bottom though, it does have a DG exhaust which has done away with the atac valve could this be a factor?I thought maybe the kill switch but it starts easily.

[Lozza]

ATAC is designed to boost bottm end.

[Slakewell]

Tech advise for 84 Honda 125/ Twist wire hard whilst fanning clutch constantly for best results.


Try larger rear sprocket 

[Curly3]

We're all getting a bit doughy down low aren't we.

[smed]

I am running a DG pipe which also looses the atac chamber & DMC muffler on my 85 CR125 as well as a bigger carb off the same year model 250 which i have not even rejetted as it seems to run sweet

84's & 85's run a different bore & stroke to each other though & i am just telling my findings with my bike without the atac,still plenty off the bottom for a 125

As slakewell said gearing,stock is 13-51, I also thought low speed windings but you said it starts ok,also are the ports stock or has it been modified in the past for dirt track where top end is king at the expense of the bottom ,worn carb,my stock carb slide had half the chrome plating worn off

[CRTAD313]

I am running a DG pipe which also looses the atac chamber & DMC muffler on my 85 CR125 as well as a bigger carb off the same year model 250 which i have not even rejetted as it seems to run sweet

84's & 85's run a different bore & stroke to each other though & i am just telling my findings with my bike without the atac,still plenty off the bottom for a 125

As slakewell said gearing,stock is 13-51, I also thought low speed windings but you said it starts ok,also are the ports stock or has it been modified in the past for dirt track where top end is king at the expense of the bottom ,worn carb,my stock carb slide had half the chrome plating worn off

Ports didn't appear  to have been modified and also wondered about the stator but thought it would be hard to start.might have to change gearing, didn't really want to lose top end.

[Lozza]

Does the ATAC a separate bolt on item between the pipe and the cylinder?

[smed]

Yep

[JohnnyO]

It's probably still too rich.. what size pilot are you using and where is the clip on the needle. Over time the needle and needle jet wear and the bike runs richer than when it was new and a worn slide can make them even harder to jet properly.

[CRTAD313]

Running a 65 ,68 is standard and the needle is brand new dropped one clip leaner than standard and air screw 1/4 turn leaner.

[JohnnyO]

That's still a big pilot, i've gone down from a 58 to a 48 in my '89 250. Try about a 55 and drop the needle another clip position and see how that is.

[Lozza]

Anyone wish to sell their redundant ATAC connectors?

Silly question but have you strobed the ignition?

[Nathan S]

Keihin PJ carbs are crap for bottom end power (this is what the 125RE has?). They're basically a methanol or road race carb - the design clearly favours big throttle openings and lots of fuel flow (compared to, say, a PWK). My 93 CR125 was basically untuneable with the PJ - wouldn't idle and had awful low throttle response.
Swapping to a PWK has massively increased the bottom and midrange power, and it starts more easily and idles properly. No loss of top end.

FWIW, I've been finding a lot of my older bikes have required significant leaning off to run properly - it really makes me wonder how these things get to 20++ years of age with such crappy jetting... I'm beginning to suspect that modern fuels are significantly different, or something.
Eg: 88 KX250 went from 52/172 to 45/162 and is still slightly too rich on the pilot.

Anyhow, how many turns out is the idle mixture screw? More than 2 full turns and you should look at a smaller pilot.
Another giveaway of an too large pilot jet, is if the idle speed screw is wound in a long way to get it to idle (and the idle mixture screw doesn't do much).

[JohnnyO]

Nathan the 125RE would've had a round slide Keihin. You're right about the jetting on old bikes, every one i buy is way too rich on the low end, could be a combination of modern fuel, overly rich jetting from the factory and some wear on the needle and emulsion tube.

[Lozza]

Modern fuels are significantly 'lighter' (though they still have higher specific gravities) than old leaded fuel.
The PWK has a major advantage over the PJ and it's not throttle position or the fuel curve.