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Old 09-09-2012, 02:44 PM   #31
PistonPants
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Location: Cantwell, AK
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NEVER siezed an engine.

In all my years of riding 2 strokes, I've always kept them stock. Never played with jets, never monkeyed with pipes, ports or armchair tuning. I have never replaced rings (although my DT175 was overdue). I have NEVER seized an engine. Wide open running on beaches and river ice, rock crawling trials pace. Radiator only boils on long long climbs. We're talking about dual sport riding (which we used to call enduro) not race engines. I have found that reliability comes from not 'tuning' and modifying. I humbly suggest just riding and not worrying. The paved sections connecting trails are not freeways. When on the road, don't forget it's a dirt bike.

Have fun,
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Old 09-10-2012, 01:37 AM   #32
FR700
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Quote:
Originally Posted by peter650 View Post
The jets do over lap, but out on the open road, your going to be on your main jet.


* cough *


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Old 09-10-2012, 05:24 PM   #33
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Quote:
Originally Posted by FR700 View Post
* cough *



Unless you really are riding WFO, out on the open road you are gonna be on the needle (and the pilot circuit, but mostly the needle).
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Old 09-10-2012, 08:19 PM   #34
FR700
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Originally Posted by pdxjim View Post
Unless you really are riding WFO, out on the open road you are gonna be on the needle (and the pilot circuit, but mostly the needle).



needle , needle jet

.
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Old 09-15-2012, 06:23 AM   #35
peter650
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In Australia most dirt bikes are geared for 140 to 150klm flat out. On open tar roads most people sit on 120 klms which puts you on the main jet.
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Old 09-17-2012, 08:41 AM   #36
Katze
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The response's to this post are amazing. The motor doesn't care were it's being ridden, as long as it's receiving the correct amount of air-fuel and lubrication it'll run/last forever.

I own a 300exc and dual sport it. I ride the Sheet Iron 300 on it. 20-30 mile sections of pavement and dirt roads with single track. The bike runs perfect.

If the bike is jetted AND GEARED correctly for the riding your gonna do, it will perform perfectly.

Ever here of a KDX200? It's sold as a street bike in Japan. Those guys regularly get 15K miles from a top end and 25-30K miles from a bottom end. Come on guys... this isn't 1967.

To the guy that said he never re-jets his 2 strokes and leaves them stock... be careful. If you go to Colorado or my neck of the woods, we've got some "Thin Air" up here!
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Old 09-17-2012, 10:53 AM   #37
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550SENTA screwed with this post 09-25-2012 at 02:05 PM
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Old 09-23-2012, 08:30 AM   #38
FR700
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Originally Posted by peter650 View Post
In Australia most dirt bikes are geared for 140 to 150klm flat out. On open tar roads most people sit on 120 klms which puts you on the main jet.

*cough*



I live in australia ...


just out of curiosity ... if you are on the main at 120 ... what do you do to get to 140 - 150 ?


... surely it couldn't be open the throttle to raise the needle out of the needle jet to fully expose it





.
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Old 09-23-2012, 07:47 PM   #39
AtomicGeo
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+1

Jet it correctly.

My 2T are plated, and I do use them for dual sport rides (highway and off road). My KX250 geared properly did fine for this 2-day 300 mile ride.

http://advrider.com/forums/showthread.php?t=725130

Quote:
Originally Posted by Katze View Post
The response's to this post are amazing. The motor doesn't care were it's being ridden, as long as it's receiving the correct amount of air-fuel and lubrication it'll run/last forever.

I own a 300exc and dual sport it. I ride the Sheet Iron 300 on it. 20-30 mile sections of pavement and dirt roads with single track. The bike runs perfect.

If the bike is jetted AND GEARED correctly for the riding your gonna do, it will perform perfectly.

Ever here of a KDX200? It's sold as a street bike in Japan. Those guys regularly get 15K miles from a top end and 25-30K miles from a bottom end. Come on guys... this isn't 1967.

To the guy that said he never re-jets his 2 strokes and leaves them stock... be careful. If you go to Colorado or my neck of the woods, we've got some "Thin Air" up here!
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Old 09-23-2012, 09:03 PM   #40
booniebasher
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Quote:
Originally Posted by AtomicXRer View Post
+1

Jet it correctly.

My 2T are plated, and I do use them for dual sport rides (highway and off road). My KX250 geared properly did fine for this 2-day 300 mile ride.

http://advrider.com/forums/showthread.php?t=725130

GEAR IT TALL !!!
makes it more comfortable, otherwise its like your riding a chainsaw, I use one of my 300,s in baja and it worked excellent, everyone had big fourstrokes, i was fine, actually way better off in the dirt, pavement was ok
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Old 09-25-2012, 04:14 AM   #41
peter650
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Quote:
Originally Posted by FR700 View Post
*cough*



I live in australia ...


just out of curiosity ... if you are on the main at 120 ... what do you do to get to 140 - 150 ?


... surely it couldn't be open the throttle to raise the needle out of the needle jet to fully expose it





.
So what your saying, is if your bike is geared for 140, & you are doing 120 your main jet is doing FA
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Old 09-25-2012, 06:36 PM   #42
peter650
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I am just trying to understand this FR700. You got a KTM300EXC max power @8500revs geared for about 145klm = about 17 klm per 1000revs @ 120klm you are at 7000revs but you are not on your main jet. At what revs would you go, onto your main jet? I must of been jetting 2 strokes wrong for the last 30years. Anyway never to old to learn. Cheers Peter
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Old 09-27-2012, 03:18 PM   #43
barryadam
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I get a lot of surge and other unpleasantness on the KX500.
10 miles of pavement is enough for me.

The KDX220R is more civilized on the road. But I wouldn't plan a long pavement ride with it.

Barry
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Old 10-08-2012, 12:27 PM   #44
FOXedupONE
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Did Shenandoah 500 dual sport ride no problem on my plated wr144. Top recorded speed on gps was 68mph. But it and I seemed to prefer 45-55 on the road sections.
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Old 10-09-2012, 11:56 AM   #45
rxcrider
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I had this concern when I picked up a 2005 300 EXC a few years ago. I only found a few people who had actually had a piston seize and they occurred when running at or near WOT and then closing the throttle. Here's why:

The engine and exhaust are hot with little excess fuel and oil like you have at lower RPM. Close the throttle and the engine is still spinning along, but the fuel and air flow just got chopped. Now, when the piston comes down, there isn't a pressurized charge in the crank case to get pushed up the intake ports. This lack of incoming pressure allows the pressure pulse from the expansion chamber to push hot, dry exhaust gas farther back than normal. (go read here http://www.702sportbikes.com/showthread.php?14147-Two-Stroke-Jetting-The-Wet-Oil-Line-Method or google wet line two stroke jetting) Normally, the pulse from the expansion chamber pushes most of the fresh, wet charge back into the cylinder leaving just enough to keep the piston, rings and power valve cool and lubed. When the pressure pulse pushes the fresh charge too far back, hot, dry exhaust gas comes in contact with the pistong and rings at the exhaust port, heating them up and burning off teh oil film. This is when the engine will seize.

The solution I heard that made the most sense was to slow down with WOT engine braking. If you push in the kill putton and twist the throttle to full open, you are pushing a fresh, wet charge through the engine, without burning it. After a couple seconds, you will have filled the expansion chamber with a wet fuel / air mix as well. The next step needs to be done in the correct order to keep from blowing the expansion chamber off the exhaust flange. Doing it backwards won't always lead to a big bang, but it can. Close the throttle, then release the kill switch and the engine will return to life. Then resume riding normally. After being at WOT with the ignition off (where you will observe more engine braking than you are used to from your two stroke) the pressure pulse in the expansion chamber can push the fresh charge as far back as it wants because gas in the expansion chamber is also cool and wet.

The issue is that a perfectly jetted two stroke at WOT won't seize, but when you close the throttle abruptly without reducing the engine speed as quickly, the jetting is no longer perfect because the pressure in the exhaust is much greater than the pressure coming from the crank case.

This can happen as easily in a long sand wash as it can on a road section.

I first learned about this subject when a friend began dual sporting a CR250R. We made him get an FMF Q because the shorty silencer someone had put on it was way too loud. What we didn't realize was that by going to a more restrictive silencer, the pressure pulse would become stronger and he would need richer jetting to accomodate it. Having only dealt with four strokes at that point, I figured a more restrictive exhaust would just make it run a bit richer and the worst that would happen is a fouled plug. I was dead wrong and he seized the piston when he closed the throttle to slow down for a turn on a road section.

EDIT: and I'm now dualsporting a 1999 Husky WR250
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