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Tuning for stroker crank and hi comp piston

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Installed hot rods 2mm stroker crank, 2008 R piston and kibble white SS valves. Has stage 2 cam and all the ccc mods done like the airbox, pink wire, filter screen, jardine full exhaust system etc.

Feels very weak off the bottom(even weaker than before the crank and piston) and only starts to make power at around 8500rpm (I have a tach).

I've been leaning it out to compensate for the longer stroke and currently have a JD red needle in clip 3, 160 main and 42 pilot. Up at 12-13000rpm it goes pretty well

 

I've heard different things about this but does the timing need to be reset to compensate for the crank? Is there carb slide mods that are needed?

 

It overall feels like it killed the bottom end but I also haven't driven it all winter and spend way to much time on a 300 2 smoker now so it's hard to tell

 

This is my first full out performance motor rebuild

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I'd be looking at cam timing again if you are not making power until 8500rpm. One tooth retarded will make power move up in the rpm range. 

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On 6/19/2017 at 5:25 PM, redhurricane said:

I'd be looking at cam timing again if you are not making power until 8500rpm. One tooth retarded will make power move up in the rpm range. 

it took the tps sensor plug melting on the exhaust for me to realize that when i was tuning the carb it got unplugged and forgotten. i fixed that and it seems better now with more response down low but it still seems kind of gutless. cam timing is right on. maybe its me being used to a 2 stroke now

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You might be able to find some info about the setup you have if you do a search, its worth a try anyway.

I think you should be able to get better results than what your describing, I dont know what your altitude is or average temp but if it was me I would be experimenting with adjusting or jetting alittle richer rather than leaner. I mean if your going to increase CC's and expect an increase in power that almost always means more fuel unless it was way off before you did your stroker modification. Since you have more displacement to work with Im sure the cam timing could be improved for that set up as well as the ignition timing, but neither is easily done.  Did you like the cam before doing the stroker mod, what type of riding do you do?

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Some of it is the difference between the 2T and the 4T, the little 250X will never be as snappy off the bottom as a 300 2T. I will say that my experience with the Stage 2 cam in the 250X has not been good. I bought a 250X from a riding buddy and it had the Stage 2 cam in it when I got it. I hated how it ran, much like a 125 2T, no bottom end, all top. I switched the cam out for the OEM 48 state 250X cam and the bottom end was returned. The guy that I bought the bike from rode it then and liked it enough that he bought it back from me.

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You might be able to find some info about the setup you have if you do a search, its worth a try anyway.
I think you should be able to get better results than what your describing, I dont know what your altitude is or average temp but if it was me I would be experimenting with adjusting or jetting alittle richer rather than leaner. I mean if your going to increase CC's and expect an increase in power that almost always means more fuel unless it was way off before you did your stroker modification. Since you have more displacement to work with Im sure the cam timing could be improved for that set up as well as the ignition timing, but neither is easily done.  Did you like the cam before doing the stroker mod, what type of riding do you do?

I search for everything before starting a post. Couldn't find much.
My altitude is under 1000 and temt is usually around 20-35c.
I was told since the stroke is longer the vacuumed pulse will be stronger and pull more fuel through each circuit. Not sure if that's accurate but it sounds like it might be true. I do mostly woods and trails and I liked it before as it didn't have a lot of grunt so it got traction without spinning and ripped on the open sections. I've driven a stock '13X and the bottom end felt very similar but where it fell on it face at 8000 mine started making real power. I might look at having it dyno tuned at some point becouse I'm terrible at feeling little differences. If I think it's fixed then I think I feel it working better even though it's not sometimes

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Some of it is the difference between the 2T and the 4T, the little 250X will never be as snappy off the bottom as a 300 2T. I will say that my experience with the Stage 2 cam in the 250X has not been good. I bought a 250X from a riding buddy and it had the Stage 2 cam in it when I got it. I hated how it ran, much like a 125 2T, no bottom end, all top. I switched the cam out for the OEM 48 state 250X cam and the bottom end was returned. The guy that I bought the bike from rode it then and liked it enough that he bought it back from me.

Funny enough I actually find the 300 has a smoother bottom end and more controllable power especially when lugged down where the 250 just doesn't have the grunt. The 250 has quite a snappy bottom end

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17 hours ago, CarmanCRF said:


I search for everything before starting a post. Couldn't find much.
My altitude is under 1000 and temt is usually around 20-35c.
I was told since the stroke is longer the vacuumed pulse will be stronger and pull more fuel through each circuit. Not sure if that's accurate but it sounds like it might be true. I do mostly woods and trails and I liked it before as it didn't have a lot of grunt so it got traction without spinning and ripped on the open sections. I've driven a stock '13X and the bottom end felt very similar but where it fell on it face at 8000 mine started making real power. I might look at having it dyno tuned at some point becouse I'm terrible at feeling little differences. If I think it's fixed then I think I feel it working better even though it's not sometimes

Dont know if you saw this yet or not but its got some good info about dialing in or adjusting cam timing.

If you wanted to keep that cam you could probably optimize it with some adjustment, or replace it with a different cam to get more of the low and mid back. Adjusting the ignition timing would probably also help. 

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In theory a Stage 2 cam perhaps not ideal for low-to-mid torque but thinking in your case it shouldn't be as drastic.

 

I'm sure it applies to motorcycle engines as well but in the automotive world,

when you increase displacement (bore, stroke) and keep the same cam lift/duration,

the cam often acts 'smaller' than with the previous displacement, lowering the powerband in the rpm range.

 

More displacement needs to breathe more, meaning a Stage 2 cam may feel like a Stage 1 in a bored/stroked engine.

Setting the valve lash to the maximum clearance specs would also make it 'act' smaller, reducing duration & overlap.

Edited by mlatour
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