2 stroke info

[mohadib]

Hello,
So I blew up my old 81 250r and a 98 blaster. These where the first 2 strokes I ever owned. I think I could have avoided blowing them up if I would have had more general info on riding 2 strokes. I ran the blaster WOT for long periods of time, I would gear down and engine break to slow down. I used crappy oil, I used retarded mixes. I let my 250r run lean and coasted in gear with the cluth engaged. etc etc...

So... I would like to make a small video explaning how to properly use a 2 stroke, how they are differient from 4, and include any other 2 stroke info thats good to know. Here is what I have on my list so far:

1. Brief comparisson of 2s and 4s mechanically.
2. Explain how these mechanical diffs show up in real life situations
3. Explain how to ride a two stroke (dont WOT too much, dont engine break)
4. Compare cost and time to maintain
5. Cover 2 stroke gas mixture and differient oils you can use.
6. Explain how to make sure you are not running too lean (plug chops)
7. Cover general pros and cons of both 2 and 4. (Trail riding vs other styles)

Can you guys suggest anything else a newb should know? Or maybe add some information to the points Im going to cover already.

Thanks - Jason

[mohadib]

Hmm, I should also try to cover what a power band is, and why 4 strokes have better power at the bottom. I dont understand that myself quite yet. Someone care to chime in

Does this sound right:

The reason 2 strokes dont have a lot of low end power is due to the expansion chamber sending the sound wave back and the exhaust port timing not being optimal till higher rpms are reached? The expansion chamber creates a much stronger sound wave at higher rpms? Can you get a 2 stoke to hit the powerband in lower rpms by tweaking the expansion chamber? Can someone please shed some light on this? Thanks

[Saul]

Why wouldn't you WOT too much? A properly built and maintained engine, 2-stroke or not should be able to handle WOT easily.

You can bet the desert racers of the 80's on 250R ATC's and 250R TRX platforms went WOT for super long stretches.

[outtaline]

Yeah I hold mine wot all the time in the mud and its never been apart. sometimes it stays wot for 5 minutes or more to get through a pond. Its a 4 poke but that should n't matter yours blew up cause you starved it of fuel

[BOB MARLIN]

If you blew up two bikes, I would have to believe you need to start with a premium grade 2 stroke oil.

[mohadib]

, Im just going on information I got here. I cant actually say WOT blew anything up for me. The blaster was not starved for fuel though, I can say that. Thanks for the input. Got a lot of information now, but still looking for more.

, how often do these racers get their top end rebuilt? Pretty often Im betting, more than the average joe is wanting to do.

[Daddio]

Why wouldn't you WOT too much? A properly built and maintained engine, 2-stroke or not should be able to handle WOT easily.

You can bet the desert racers of the 80's on 250R ATC's and 250R TRX platforms went WOT for super long stretches.

Absolutely! 400 to 1000 miles and I'll bet half of it was WOT.




Have you ever heard of this before?

http://www.macdizzy.com/

[mohadib]

Thanks for the link Daddio. Guess Ill have to pony up and pay to view the forums.

[RodKnockRacing]

2 strokes are all about proper fuel mix and jetting to keep goin for along time

[dcreel]

There is a lot of different reasons why a 2 stroke could lock up or blow up. They all have to do with fuel or air. Or lack thereof. Keep a clean air filter, use a fuel filter to keep crap out of the jets and orifices of your carb. Make sure the jetting is correct. Check your plug, and do plug chops if you haven't to make sure it is right.

WOT for extended time periods will really affect a lean bike by making things leaner. Air leaks will also spell disaster to a 2 stroke.

[Saul]

, how often do these racers get their top end rebuilt? Pretty often Im betting, more than the average joe is wanting to do.

Thats the thing - the average joe probably won't be riding WOT on a daily basis for extended periods of time.

Fact is, if you choose to ride a 2-stroke and ride it HARD then a rebuild once in awhile is common practice. But, if you take care of the engine with good gas/oil mix, proper jetting, checking for air leaks that fresh built 2 stroke will last a LONG time, even being rode HARD by anyone.

Think about it - there are PLENTY of old aircooled 2 strokes STILL to this day being rode and hard - we're talking engines built from 81-84 WITHOUT the benefit of watercooled technology.

Just maintain your engine, get, read, study a manual for your engine and do your best to keep everything within the specs of the manual.

Usually the only thing I would deviate from a shop manual is your oil/gas mixture since todays oils are worlds better then that of the mid-80's.

[Saul]

Hmm, I should also try to cover what a power band is, and why 4 strokes have better power at the bottom. I dont understand that myself quite yet. Someone care to chime in

See - that isn't true at all. A 4 stroke won't have better low end power over a 2 stroke just because it's 4 stroke vs 2 stroke - any engine can be built and tuned to perform at low, mid or top ends of the powerband.

It really isn't a matter of 2 VS 4 stroke.

Thats just a huge myth IMHO.

[mohadib]

Im not trying to have an esoteric discussion about cruse ship motors, 2 stroke disel and what not. Im talking about the 2 strokes we ride. And I have been given every indication that 2 stokes produce less touque at the bottom end than a "comparable" 4 stroke.

Im an average joe. I keep all my wheelers pinned when ever possible. I ride on dirt roads around my house alot, so I can WOT as much I can handle it. I'm not saying WOT is really bad, in fact iM qouting others. What I am trying to do is maximize the joy other 2 stroke riders might have. And a longer running engine feels my heart with joy!

I was also thinking about the numbers daddio posted. 400 to 1000 miles, half the time WOT.
If the rider is averaging 60mph , half at WOT, thats less than 10 hrs of WOT. Im guessing it would take me 60 days to reach that much WOT time. If I could be aware that WOT might fail my stuff earlier, I might be a little more stingy with my WOT time.

This is exactly what I'm looking for. Please keep it coming Thanks!

Anyone care to discuss how power valves change the performance in a 2 stroke?
I get the idea of it I think. BUt Im wondering if this messes up a loop style scavenging engine. Is it harder to get all the exhaust out and get in a new charge? Does having a power valve effect low end torque?

[Saul]

Im not trying to have an esoteric discussion about cruse ship motors, 2 stroke disel and what not. Im talking about the 2 strokes we ride. And I have been given every indication that 2 stokes produce less touque at the bottom end than a "comparable" 4 stroke.

Whats a comparable 4 stroke to the 250R engine then?

Im an average joe. I keep all my wheelers pinned when ever possible. I ride on dirt roads around my house alot, so I can WOT as much I can handle it. I'm not saying WOT is really bad, in fact iM qouting others. What I am trying to do is maximize the joy other 2 stroke riders might have. And a longer running engine feels my heart with joy!

Then when you rebuild that 81R again - take your time to do a leakdown test - properly torque your base and head bolts, run a clean air filter, a high quality premix oil couple with good gas and then jet accordingly. It's just proper maintenance and common sense.

I know you had the 81 apart before you blew it up - did you do all of the above when you put it back together prior to blowing it up?

I was also thinking about the numbers daddio posted. 400 to 1000 miles, half the time WOT.
If the rider is averaging 60mph , half at WOT, thats less than 10 hrs of WOT. Im guessing it would take me 60 days to reach that much WOT time. If I could be aware that WOT might fail my stuff earlier, I might be a little more stingy with my WOT time.

You are spending way too much time worrying about WOT - fact of the matter is a 2-stroke can and will seize up almost anywhere in the powerband if the jetting is off. I've had a ton of people post on the fooler forum about their piston seizing at mid to 3/4 throttle ... moreso then I hear of people blowing em up at WOT.

IMHO it's probably not the best idea to run any 2-stroke at a 'constant' rpm for a long duration - some fluctuation of rpm seems to be needed. WOT, 3/4, 1/2 - it does NOT matter - if that jetting is off you're gunna be rebuilding sooner rather then later.


Just find and download a copy of the 2 stroke tuners handbook if you are really that interested in learning everything there is to know about the ins and outs of the 2-stroke engine. There is enough reading in there to keep you busy for a long time.

Google it.

Good luck in your quest for knowledge.

[mohadib]

Cool ,thank you . I dont really know how one properly compares a 2 stroke and a 4 stroke in terms of tourque output. If it helps I can drag out the links I used to make this assumption. I do understand though random people on the internets are not the last word on anything

It does makes sense to me though that if your exhaust port opens and lets out your charge, *maybe* before its done all the work it can, could possibly lower compression and torque too. It made sense to me that given the way our bikes are tuned, that a certain (higher)RPM range produced better back pressure from our pipes, thus supercharging the cylinder. I'm just putting the fragments together, but it seems logical to me. Maybe someone could fill in the gaps.

My 81r blew up, as stated before, becauase I ran it too lean. I used the carb from a blaster on it and killed it. THis is the kind of stupidity I hope to help others with. So yes, it was my fault. PEBSHB (problem exist between seat and handle bars)

I will focus less on WOT. It was really just going to be a small tip and not the focus of my video. But I do see now how WOT just exaggerates a lean condition. Thanks for setting me straight on that. Really, thanks for the help.