is it a 4 stroke thing?(from a 2 stroke guy!)

csdwarf · Mar 3, 2011

Hey, my first bike was a xr 70, my second bike was a ttr 125, third bike, kdx 200, then now i have a ktm 250 exc

my friend also has a ttr 230.

I noticed that 4 strokes seem to have alot more power at idle then 2 strokes, they are able to idle around in gear, my little ttr 125 was geared down some, but i was abe to idle around in 5th gear all day, it never would bog or stall.

why cant 2 strokes do this? because my 250 no dout has way more power everywere then the 125/230, but i can only idle around in 1st, and it doesnt like it, it lugs.

just curious.

thanks!

Matt90GT · Mar 3, 2011

most because of the cam profiles.

You can have a low end, mid top end or a blend of any power band there. Just depends on the cam profile.

It is also not fair to compare a trail bike to a MX bike. Way different power delivery.

cams are very similar to 2 stroke pipes, in that different pipes change the power delivery. Modern Post mid-late 80s 2 strokes all have power valves which help change the timing and compression of the motor creating more low end. Also the pipe shape has a LOT to do with the power delivery on the bike and reeds.

Biggest problem with 2 strokes is that people dont know how to jet them correctly thus load them up on the bottom and lean them out on top. Getting your jetting dialed will help for sure.

Other than that, it is the differences of the motors 2cycle vs 4 cycle. 2 strokes will spin a tire much easier since they have a power stroke every 360 degrees of crank rotation. A 4 stroke only has 1 power stroke every 720 degrees of crank rotation, thus they are termed "smoother" and "better hookup".

Go ride a YZ250F and then a YZ250. Probably the best way to compare a 250cc engine design back to back.

csdwarf · Mar 3, 2011

just out of curiousity, will the 4 stroke motocross bikes, like the 250f's and 450'f idle around like the ttr trail bikes will(like i was explaining)?

because those dont make power(dont pull hard or fast) but have that power at idle.

ive never had a bike worth putting the money into a aftermarket pipe, but how big of difference can one make? for example i would get the gnarly pipe(add tractor like 4 stroke torque to the 2 stroke).

it cant actually do that can it? ive read a few arcticles on how pipes work, so i understand that they do somthing, but how dramatic can the effect me.

a cam seems like it would have much more effect.

thanks!

Matt90GT · Mar 3, 2011

Best example of a 2 stroke that has low end power ~ go ride a TRIALS bike.

If you use a 2 stroke or 4 stroke MX bike for putting at idle, they will over heat. They need airflow through the radiators to cool them.

I dont know anything about your background, but from what you have posted thus far I would say to save your pennies and put that into bike maintenance. you seem to be learning a lot here about just bikes in general and I could only imagine your maintenance skills could use the same amount of education. Invest in a service manual for help.

Again, 2stroke and 4 strokes differ. So yes a pipe can be like a cam, but depending on the application you could notice more difference from a Pipe vs a cam. Like a ford vs chevy you know.

csdwarf · Mar 3, 2011

yeah, im not new to dirtbikes, and ive turned tons of wrench's

rebuild engines from a 1973 bultaco alpina all the way up to a 1960's chevy 283,snowmobiles ect.

im vey mechanically inclinded, but information i have to come look here for, specs ect and also sugestions/oppinions.

i would love to get a trails bike, but locally i have no way to get one except a vintage honda one, i would like to get a gas gas or somthing, but just isnt really an option with my budget.

id be interested in some honest opinions about a wr450 vs a ktm 250exc.

i know this is a 4 stroke forum, but ill ask anyway.

how would my ktm 250 exc do in the slow tight stuff vs a wr 450 (like handlebar tight stuf, not just single track)

thanks!

_JOE_ · Mar 4, 2011

A 250f will not chug along at idle like a ttr. The mx bikes simply don't have enough flywheel mass to keep them spinning at very low rpm. Why is this even an issue? Do you really ride around at idle in 5th gear?

Many would say the KTM 250EXC is a better tight woods bike than a WR.....

csdwarf · Mar 4, 2011

no, i only idle around in 5th never. haha

its just a characteristic i was curious about. so its flywheel weight? that makes sense.

alright

thanks!

_JOE_ · Mar 4, 2011

Flywheel weight helps keep the engine spinning. As mentioned earlier, cam and cylinder setup will also have a huge effect on how well the engine resists stalling. Any engine built to perform in the mid to top end won't lug well. It's one of those give and take situations......Give it more bottom? Take it from the top. My wife's TTR125 quits pulling around the same rpm my old CRF250 started pulling, but you can knock the ttr into gear at idle without the clutch and it'll go. They're just designed to do completely different things, you know?

csdwarf · Mar 4, 2011

yeah, i know exactly what you mean.

my friends looking into a wr450,

would that have the same low end power at dead idle like the ttr's do?

or will it be more like my EXC?

he considers that low end torque, so my exc has no low end torque acording to him

dirt bike dave · Mar 4, 2011

Well, one of my buddies has an '06 WR450, and, sure, it makes decent low end power and will chug at low rpm.

But.....it's heavy for tight woods.

Some guys love big 4 strokes in the woods, but for others, 200 - 300cc 2 strokes are the most fun.

Personally, I like the MX 450's like the YZF, KXF and CRF more than the WR450, because the MX versions are lighter, more powerful and better suspended. They tend to turn and change direction better than the heavier WR.

The WR is a nice mellow trailbike with e-start, so it certainly has its place. My buddy's has been very reliable and low maintenance, too.

Basically, it's a case of different strokes for different folks.

jb_dallas · Mar 4, 2011

CSDwarf

I own a WR426 4 stroke and a KDX220 2 stroke and recently sold my XR400 to a friend. All 3 bikes will chug around as slow as anyone would want to go. Its not about 2 stroke vs 4 stroke, its about the bikes purpose..which gets into the explanations above. A MX 450 4 stroke wasnt designed to chug around..for example.

dirt bike dave · Mar 4, 2011

jb_dallas said:
A MX 450 4 stroke wasnt designed to chug around..for example.

Yep - many of them will overheat if you are doing super technical, nasty stuff. Those high compression, high HP motors really need that air going through the radiator.

Matt90GT · Mar 4, 2011

if you want a fun woods bike get a KTM 200 or 300 woods bike. Enjoy cheap maintenance and lots of fun.

I agree. I like the MX bikes in the woods also, but I dont putt around either. I go as fast as I can so cooling is not an issue there.

jb_dallas · Mar 7, 2011

I rode a YZ400 in the woods for about 1.5 years. I loved the power, but the bike was geared way too tall in first. Also, gearing was spaced too closely. The bike would get hot chugging around in the tight woods, so I geared it down and had a top end of about 40 mph. I got tired of playing the trailizing game, so I sold it and bought the WR 426 and its a little bit heavy, but a good trail bike. With the airbox and exhaust opened up and jetted correctly, the WR426 would give the 400 a run for its money in power.

I agree on the KTM suggestion..I am a minority in my riding group, which are about 80% KTM riders. Ive ridden the 300 EXC..thats one hell of a trail bike with TONS of power everywhere. I was looking for a KTM when I bought my 220. Generally speaking, KTM riders around here seem to be serious riders that ride often, so its hard to find a low hr reasonably priced KTM 300 EXC. The KDX was a very low hr bike and I couldnt pass it up.

2strokerfun · Mar 8, 2011

I think flywheel weight makes a big difference. I built a Kolb Flyer twin-engine ultralight plane years ago. A friend built one too. We both used German-made Solo engines, which are nice compact 22-horse two-stroke engines with 220cc each. His engines came with propeller hubs already on them. Mine didn't, so I had a machinist friend make them for me and when I got them they weighed about 5 pounds each, way beefier and heavier than what was on my friend's engines. At first I was leery, but I noticed how my engines always started easier and ran way smoother than my friends, especially at low taxi rpms. Once you got the props turning with the pull start, they wanted to keep turning.
But you don't want to put 5-pound weights on a MX bike and you really don't want to putt around slowly too much either.

csdwarf · Mar 8, 2011

Yeah, still snow on the ground but i tried the bike out on the road, it goes good, a lot of power but pulls pretty good at lower rpm's through the gears aswell

i might get some flywheel weights, idk we will see once i start to rip.

is it a 4 stroke thing?(from a 2 stroke guy!)

csdwarf

Matt90GT

csdwarf

Matt90GT

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_JOE_

csdwarf

_JOE_

csdwarf

dirt bike dave

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