RM125 CDI - strong kickback

[GGRider01]

I am installing a RM125 CDI in my 300 but the thing kicks like a mule. What would this indicate timing wise? I am running a 2k3 stator with the timing washer in place. Should I remove it and retard or advance timing?

[gasgasman]

Yup. Timing too advanced.

[GGRider01]

Roger that, thank you. I will retard it a millimeter at a time, I guess.

[motopsycho87]

You need to retard it a fair amount, 6-8 degrees to be precise, otherwise you'll burn your reeds. Rm cdi is amazing for low down grunt, but top end suffers badly unless you retard a lot

[GGRider01]

The opposite of what I want. I found pretty quickly that 2 out of the 3 slots on the plate wouldn't line up with the threaded holes with even a little bit of adjustment. I could elongate them, but figured the stock CDI will have to do. The low down grunt has never been exceptional, but neither has it been exceptional on the pipe. A lot of factors at play on my Frankenstein to sort.

[motopsycho87]

If you're finding the bike a bit lacklustre it might be worth looking at the jetting, having the squish clearance sorted (raise the ports to the correct height with gaskets first, I had to use 1.5mm) and overall health, piston, rings, seals etc. The bike rips with any cdi. The RM one massively increases the low and mid, but yes you do have to file the holes out slightly. All depends what you want the bike for. Would suit enduro cross and supercross more than anything else

[GGRider01]

Originally Posted by motopsycho87

If you're finding the bike a bit lacklustre it might be worth looking at the jetting, having the squish clearance sorted (raise the ports to the correct height with gaskets first, I had to use 1.5mm) and overall health, piston, rings, seals etc. The bike rips with any cdi. The RM one massively increases the low and mid, but yes you do have to file the holes out slightly. All depends what you want the bike for. Would suit enduro cross and supercross more than anything else

Exactly my thoughts.

Jakobi brought forward the idea that the 2013 jug on my 2000 bottom end could be throwing port timing out the window. I was so concerned with running as tight a squish as possible without a machinist that I just threw the thinnest gasket on I could. I popped the pipe off, rolled it over to BDC and behold, the piston sits nearly 1mm above the bottom of the exhaust port!

If I'm to measure squish and get it corrected, I'll have to stack some gaskets. Luckily I have two heads, so downtime is a non issue.

With the piston sitting high, I wonder if my compression ratio is through the roof. Piston looked perfect though, so that's one less thing to fret over.

[motopsycho87]

I can't remember what my chamber volume was, but I did have to re machine it twice to stop it pre igniting. Taking a cc out at a time.

[pscook]

Originally Posted by GGRider01

Exactly my thoughts.

Jakobi brought forward the idea that the 2013 jug on my 2000 bottom end could be throwing port timing out the window. I was so concerned with running as tight a squish as possible without a machinist that I just threw the thinnest gasket on I could. I popped the pipe off, rolled it over to BDC and behold, the piston sits nearly 1mm above the bottom of the exhaust port!

If I'm to measure squish and get it corrected, I'll have to stack some gaskets. Luckily I have two heads, so downtime is a non issue.

With the piston sitting high, I wonder if my compression ratio is through the roof. Piston looked perfect though, so that's one less thing to fret over.

FYI, the piston on my 2011 is about 1.2mm above the exhaust port floor, and the squish is 2mm+. Don't sweat it until you measure the squish, these bikes are notorious for having wildly varying gaps. You might be just fine, but again, you might not, but you have to measure first.

[GGRider01]

With the stock CDI, there are no issues. Just not a tremendous amount of power, even with a lot of timing advance. I guess that would indicate a huge squish and a low ratio. I can't find my solder or I'd have measured it already. I'll have to grab some.