125-200cc To all 7 ports 125 cylinder experts...

Hi all, I need to ask a question to all who know well the husky 125 engine and in particoular the old 7 ports cylinder....

watching the cylinder bore with the piston at its lowest position, are the piston walls supposed to cover the intake ports for about 3 millimeters ?

I noticed this when I did the top end recently, and I wonder if this is normal as I am getting mad to understand why my bike is so slow ... 2007 wr 125 with cr ignition + fww (with the correct timing) , 0,9 mm squish , new piston , power valves perfectly dialed in , keihin pwk 36 with divider perfectly jetted...

the bike has a very linear powerband, nice torque and great mids with no bog at all ( incredible difference from stock configuration), but the top end feels really weak, it makes revs but it really lacks power ! feels like a strong 80cc , not a 125cc ! Rode a friend 2014 husky 125 ( ktm engine) that felt more like a 250 2 stroke compared to mine ...

Since everything else is dialed in perfectly I wonder if the problem is in the cylinder with the ports that remain partially covered !

Any other hint is well accepted, thank you in advance...

Is your clutch slipping? I know when my rekluse isn't set right it makes lots of noise but doesn't have any top end Cuz the plates are slipping. Just a thought.

what size main and what carb

no definitely the clutch is not slipping... the bike pulls away, just not too quickly...
Carb is a keihin pwk 36 with divider plate: 180 main,40 pilot , nozi needle 3° clip . Its slightly fat on the main, tried a 170 and its crispier but no difference in power...

Maybe the ignition timing is too much advanced? as the bike actually feels very strong on the mids and low end...

Or maybe is it just me too heavy for this thing to go fast (i'm 90 + kgs in riding gear) , but still I tried a 2014 ktm 125 that really flew compared to my old husky...

I am going to go out on a limb here and guess someone replaced your stock cylinder with a WRE/SM 125 cylinder from Europe. Their ports are lowered by almost exactly 3mm. Check the dimension from the top of the deck of the cylinder to the top of the exhaust port. Stock WR/CR 125's are ~30 mm. The WRE/SM cylinder will measure at ~33 mm. All the ports are equally lowered to detune the street legal Euro 125's. The numbers I quoted are not exact but will give you the easy check as the difference is significant.

PS, If you do have the WRE cylinder there is a 7 port cylinder on Ebay for ~$150 that looks to be ok.

Make sure that the power valves are opening fully - try bolt adjustment at bottom of slot
Check compression. Try 38mm mikuni carb again. Could try a fatty pipe .
Its probably just how it is .
I noticed a similar power difference after riding a YZ125 . It felt like my 144 did - more mid.

i have taken out the head to watch inside again and the overlapping between piston and ports is not 3mm , its less, more like 1,5mm .... and the cylinder is named 390/1 so it should be a full power cylinder.. I may add a 1mm base gasket to nullify the the overlapping but I fear that the engine will lose too much torque doing this, and the squish will be too high too...

pv arm is about 3/4 up, because only in this position it mantains the small spring slightly preloaded... maybe its not opening fully, but if i adjust the arm down it will run like crap at low revs ...

I think this engine is just like this... good powerband but not that powerful... maybe it would be a big improvement to get a 5 ports cylinder?

i dont think its carb related because ktms run the 36 keihin and do really fly...

I Don't really like the 5 port cylinder that much its more abrupt but possibly doesn't rev as high or as smooth from what I've experienced
The old 04 7 port motors went really well. It may be an ignition difference

the piston covers the bottom of the transfer ports on the 5 inlet port head also - by about 2mm

I would try to adjust pv arm bolt to the bottom, but if I lower it more than 3/4 the spring wont have any tension on it.... is this normal?

maybe the little spring is weakened and I should replace it, because it will start to put some tension only with the arm bolt almost fully up!

I played a bit with the power valves and the ignition timing: I adjusted the pv arm bolt a little lower than before (its a little higher than middle slot) , and retarded the timing a bit.... I found a little more top end this way , unfortunately with the valve adjusted like this I've also lost some low end torque....

The pv system is very stupid.... you can only have a bike with good torque and no top end, or a bike with good top end and no torque (or even worse with a crappy powerband...) . This is because the actuator arm doesn't have enough throw to fully open the valves from the fully closed position....

I really think you have a problem in the power valve system. These older cylinders with the older power valves were not normally as finicky as what you are describing. I love using the older cylinders for my 165's as they make great, smooth power from bottom to top with not a lot of adjustment needed up on the arm.

Hi. I know it has been a long time since you wrote this, but it can be relevant to others aswell.

In Europe Husqvarna sold a road leagal bike called SM 125 S. It had different setups depending on country, but basically 15-25 HP. The cylinder on this bike looks identical to the one on CR-WR, but it's not. This cylinder sits 3mm lower on the block and they have added the same amount to the top of the cylinder. So port timing is not as agressive.

Not all workshops wordwide know about this model and think all Husqvarna cylinders are the same. So when you replate or exchange cylinders be sure to get the right one back. Or else you will loose power.

Hi, It's been a long time since you last posted. I've been riding a Husky SMS 125 '07 (7 ports cyinder) for the last two years, and I want to prepare the motorbike (mikuni 38, pvl stator, mechanic exhaust valve, etc.) I know that are 144cc available, but they are very expensive moreover are only 5 ports.

I've been planning to prepare the whole engine: file and polish the crankcase, and prepare the cylinder to be like the cr or wr cylinder. But as my mother tongue isn't English (despite I can keep a Conversation, when I hit some technical words I end up lost), could you please tell me the difference between the sms/wre cylinder and the wr/cr one? And what should I do, besides rising 2 or 3mm the intake ports, to make my cylinder perform like a cr/wr one?

Thank you from spain!

I would think a spacer plate under the cylinder then the top machined off to suit the amount of the raise in cylinder height would be the easiest way to do it.

Thanks, I've been searching for kits, and in Italy are some interesting shops selling that stuff, but I still think raising th ports is the best option, as it's cheaper and it gaves the same results.