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New top end on LT500, very boggy
Posted by
ZeroZeroMinusOne
on 05 Jul, 2013 04:20
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My bike has been very boggy with little to no power in the higher rpms. 5th gear has zero power at all. It idles great but doesn't want to blast off. Current jetting is 370 main with stock pilot, motor is stock except for some mystery pipe, air box lid off. Any help would be appreciated.
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It ran this way even before the new topend. I'm new to LTs. I'm hoping a carb tuning issue.
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#2 Reply
Posted by
JayTater
on 05 Jul, 2013 05:03
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Did you try adjusting the clip position on the needle? What's your plug look like? Boggy top end sounds like you could be rich. Does it idle right back down after goosing the throttle, or do you get much "ring-ding-ding" ?
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The needle was on the middle clip, I dropped it down one clip hoping to lean it out a little. When revving from idle the motor revs down normally. 370 is the smallest jet I have right now. Ill check the plug in a bit.
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My bike has been very boggy with little to no power in the higher rpms. 5th gear has zero power at all. It idles great but doesn't want to blast off. Current jetting is 370 main with stock pilot, motor is stock except for some mystery pipe, air box lid off. Any help would be appreciated.
Check the power valve and make sure it is closing at high .
Does the engine sputter at high RPM?
Does the muffler have a spark arrestor incorporated into it?
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Power valve is operating normally.
Engine sputters and wants to shut down at higher rpms.
No spark arrestor in silencer
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Power valve is operating normally.
Engine sputters and wants to shut down at higher rpms.
No spark arrestor in silencer
Give your fuel the "jar" test.
A sputter at high RPM could be jetting or electrical.
I cannot remember when I saw a LT500 with the air box lid removed and a 370 main jet be so rich that it makes the engine miss-fire.
Install a new spark plug.
Disconnect the kill switch.
If that does not help, inspect the inside of the silencer for broken bits that would add restriction to exhaust flow. An over restricted pipe will make engine act like the carburetor is rich.
If the silencer is ok, replace the main jet with a 350 and see if the engine runs any better.
If the 350 main jet does not help any, it is time to start checking ignition components.
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Plug looked kind of lean, a tad gray/brown. Put the airbox on and it ran a little better. I'm thinking its a tuning issue. This stock carb has pretty much had it. The choke lever broke off, I found it sitting on the motor when I got back to home base today (rediculous). Gotta find a decent carb for this thing.
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Bored stock carbs are best, stay away from keihins and lectrons. I would try a 380 390 main with your combo. Stock reeds?
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Yes stock reeds. Ill try the 380-390 jet and report back
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So far I changed the plug and put the air box lid back on and set the needle clip at one below the center clip (second from the bottom) with the 370 main and stock pilot. I runs so much better now but has a hard time idling and has the bog up top which leads me to believe that i need to bump up the pilot jet. Please correct me if I'm wrong.....
One of my riding buddies (major trash talker) just picked up a mint 1988 trx 250r ported and with a high rev pipe, long story short, he got smoked eventhough he was three bikes in front off me when he took off
Too bad my gopro wasnt on at the time.....
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#11 Reply
Posted by
Buckeye513
on 08 Jul, 2013 10:52
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Way to pick on a bike half your size ya big bully!!
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Hhahahahahaha I've been hearing for months how hes going to embarrass me, I tried to explain that the LT has twice the motor of his bike, but I dont think he did too well in math class. He thought his port work was going to make up for the other 250cc
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#13 Reply
Posted by
Buckeye513
on 08 Jul, 2013 11:37
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One of my dads buddies is claiming his 250 is gonna hand my Zilla it's ass when my build is done. Once I get it tuned and dialed in I'm gonna tell him to run it for titles.
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I have heard a properly ported trx250r with a big bore kit can be a handful. Make sure you mount a gopro to your rear grab bar facing backwards. Any idea what kind of mods he has?
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#15 Reply
Posted by
Q2W
on 08 Jul, 2013 12:33
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So far I changed the plug and put the air box lid back on and set the needle clip at one below the center clip (second from the bottom) with the 370 main and stock pilot. I runs so much better now but has a hard time idling and has the bog up top which leads me to believe that i need to bump up the pilot jet. Please correct me if I'm wrong.....
One of my riding buddies (major trash talker) just picked up a mint 1988 trx 250r ported and with a high rev pipe, long story short, he got smoked eventhough he was three bikes in front off me when he took off
Too bad my gopro wasnt on at the time.....
Bumping the pilot up will richen the bike. The pilot will not affect top end - only idle to 1/4 throttle. Putting the air box lid back on, you restricted the air flow. You need to compensate for it on the idle (pilot) circuit. Locate the air/fuel mixture screw. Start your bike, with a flat head, adjust the screw slowly out. This will allow more air into the idle circuit. Back it out until the bike idles like you want it. Also, DO NOT confuse the air screw with the thumb screw - the big one with the phillips and spring on it. That only adjusts your slide which needs to be set at 2.5 to 3 mm. With the airbox boot off, back-off the thumb screw until the side is all the way down, then set the slide height from there.
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#16 Reply
Posted by
Buckeye513
on 08 Jul, 2013 12:40
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Nothing major that I know of. My setup is a 41.5 mikuni, 9" cone k&n filter, vforce v2 reeds, aggressive drag/trail mix port job bored to a 87.5 mm .40 over I believe and a Q v1 pipe. So unless he's only got a 250 chassis with some other power plant I should be just fine oh and he's got about 100lbs on me give or take.
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#17 Reply
Posted by
Motoman991
on 08 Jul, 2013 12:57
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One of my dads buddies is claiming his 250 is gonna hand my Zilla it's ass when my build is done. Once I get it tuned and dialed in I'm gonna tell him to run it for titles.
I want to watch this race.
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He has no chance, I want to watch this race too
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#19 Reply
Posted by
Motoman991
on 08 Jul, 2013 13:36
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LOL I know. He's putting in all that work to that zilla just to give it away.
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#20 Reply
Posted by
Buckeye513
on 08 Jul, 2013 13:38
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Motoman ill be sure my bike shifts and I don't get quad lengthed by a 250 in 1st gear! Lol
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LOL I know. He's putting in all that work to that zilla just to give it away.
Whoa, totally not what I meant......hahaha
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You need a carb rebuild I bet, your slide is most likely worn out like most are. Look at the slide from the filter side of the carb, if the blacks worn off it needs replacing. It will cause an idle issue, also the needle jet and or needle itself can get worn. I'm not talking about the needle and seat, but the needle jet. That and your main is probably a little lean. Your needle clip shouldn't be a clip or 2 more than the the middle position, if it is it has the wrong needle if everything else is tuned right. Your best bet send it to MotorGeek for a 41.5 bore and a rebuild.
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#23 Reply
Posted by
cworobec
on 16 Jul, 2013 01:09
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I put a electron on my bike, it tunes easy and runs bad ass.
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Thanks for the input gents.....I'm going to have to wait a little bit for that rebuild as I have other parts that need replacing at this time. I have a couple of pilot jets to test out, will update this thread when I get the results.
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