Timing and tips on a Stoked Engine.

[crawl9]

Timing and tips on a Stroked Engine.

I have a 2001 RM 125 That I had the Crank Stroked on. Does Anyone know if This Will have an effect on the Igniton Timing of the Bike??(Say I left it in the Stock Setting) Also, does anyone know how to figure Blowdown duration from Degrees of opening from exhaust to the ports?? Also, does anyone have any advice on Tuning This Engine?? I'm trying to learn as I go and do everthing myself. The only thing I haven't done is balance the crank,(didn't have acess to a balancing machine. Any help will be appreciated. I'll post all results I get.
Thanks

PIPE FMF SST
SILENCER FMF SHORTY
V-Force REEDS
Cases Cleared for Crank(increase in Crankcase volume)
Porting- Stock
Stroke 64.5
Bore 54.0
Deck Height .03 above top of cylinder.
Squish Cleareance 1.1mm
Squish Angle 10 Degrees
Exhaust opens at 76 degrees ATDC
Ports at 100 degrees ATDC
ROD Length 100MM
Base of cylinder spaced up .08 overall.

 

[bclapham]

just out of interest crawl, how the hell do you manage to get the big end of the rod to fit inside the cases? i think the usual for these motors is a 4mm longer stroke (pin offet 2mm) but i cant see where the room is for the 5mm offset with your 10mm stroker?

sounds fun all the same, hows itt run???, good luck.:)

ps if it doesnt work out wiseco complete cransk are only $180

 

[mxneagle]

Rich or eric posted a great article on timing a while back. I did a quick search but didn't find it. Please try digging around in this or the advanced tech forum. As for the timing, I wonder if it's the actual position of the piston that is important (ie so many mm's before TDC) which you could calculate to be the same as stock. Or could it be the amount of time it takes for the piston to travel from the ignition point to TDC. My guess is that it's probably much more involved than either of those but trial and error (otherwise known as empirical data to scientists) methods may prove to be the most successful.

 

[crawl9]

I just ran the bike yeasterday for the first time with the stock settings(Jetting, timing,etc.). To get it to idle, I had to run the Idle screw almost all the way in, much farther in the before the stroked crank. It run perty good on the stand,
seems to be loading up a little. Proably the jetting. When I rode it, it was real
sluggish down low. haven't reved high yet. just breaking it in. Does Changeing you Timing Effect your Jetting in anyway? To get the Crank to Fit, I had to cleareance the cases and take some off the bottom of the rod. I also did a search before posting this thread about Timing but couldn't find anything either.

 

[jaguar]

Probably have to trial and error the timing. But first get the jetting correct. Then retard the timing, ride it, advance the timing and ride it, adance/ride, etc. Find good power without the engine running too hot (which too advanced will cause).

 

[crawl9]

I ran the Bike again today. I did the jetting and had to lean everthing up.
Also I tried to retard the timing and the bike ran horrible. I advanced it and it started to run better. Runs good down low but Falls Very,very flat on the middle and on up. I was wodering what the best way to tell if you bikes running too hot or not? I have a temp sensor I can check the outside temp of parts, can you get a reading off outside of pipe to give you a general idea??
Thanks

 

[jaguar]

too hot would be boiling off coolant doing mx.
you might also want to reduce crankcase volume by epoxying where you can (transfer ports, etc). do a search for which typt epoxy is recommended

 

[marcusgunby]

With only a longer stroke im guessing it will always be a tree puller, you need to open up/raise the ports as much as possible to offset this.

 

[RKT]

Crawl.

Not sure how the bike is currently runnig, BUT with a 76 degree power stroke and 24 degrees of blowdown.. I am pretty sure that this bike will have major issues with power delivery.

Are you sure those numbers are right?

Kelsey

 

[jaguar]

Yeah, I'd say that's a bit off.
My KDX200 has exhaust port opening at 96 degrees after TDC (83 when power valve opens), and the transfer intake ports at 120 degrees.

The following is from Eric Gorrs site and may be useful:

Tuning for Specific Powerbands

I've designed the chart shown below, to give you some general guidelines on different powerbands and the changes required to the individual engine components. For specific recommendations on your model bike, refer to the chapters on tuning tips.

Component: Cylinder Head

Low To Midrange: 9.5:1 compression ratio, squish band 60% of bore area

Midrange and High-Rpm: 8:1 compression ratio, 40% squish

Component: Cylinder Ports

Low To Midrange: Exhaust port 90 ATDC, transfer ports 118 ATDC

Midrange and High-Rpm: Exhaust port 84 ATDC, transfer ports 116 ATDC

Component: Reeds

Low To Midrange: Dual-stage or .4mm fiberglass petals.

Compromise: Thick carbon fiber petals

Midrange and High-Rpm: Large area 30-degree valve

Component: Carburetor

Low To Midrange: Smaller diameter or sleeved down carb (26mm for 80cc, 34mm for 125cc, 36mm 250cc)

Midrange and High-Rpm: Larger carb (28mm for 80cc, 38mm for 125cc, 39.5mm 250cc)

Component: Pipe

Low To Midrange: Fatty or Torque

Midrange and High-Rpm: Desert or Rpm

Component: Silencer or Spark arrestor

Low To Midrange: Short, small diameter

Midrange and High-Rpm: Long, large diameter

Component: Ignition Timing Advance timing

Low To Midrange: Stock timing

Midrange and High-Rpm: Retard timing

Component: Flywheel

Low To Midrange: Add weight

Compromise: Stock flywheel

Midrange and High-Rpm: PVL internal flywheel

Component: Fuel

Low To Midrange: Super unleaded 93 octane

Midrange and High-Rpm: Racing fuel 105 octane