Author Topic: New top end on LT500, very boggy (Read 2018 times)

ZeroZeroMinusOne · « **on:** July 05, 2013, 04:20:23 am »

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.

ZeroZeroMinusOne · « **Reply #1 on:** July 05, 2013, 04:30:06 am »

It ran this way even before the new topend. I'm new to LTs. I'm hoping a carb tuning issue.

JayTater · « **Reply #2 on:** July 05, 2013, 05:03:22 am »

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" ?

ZeroZeroMinusOne · « **Reply #3 on:** July 05, 2013, 06:28:00 am »

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.

MotorGeek - Jerry Hall · « **Reply #4 on:** July 05, 2013, 07:37:29 am »

Quote from: ZeroZeroMinusOne on July 05, 2013, 04:20:23 am

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?

ZeroZeroMinusOne · « **Reply #5 on:** July 05, 2013, 08:49:39 am »

Power valve is operating normally.

Engine sputters and wants to shut down at higher rpms.

No spark arrestor in silencer

MotorGeek - Jerry Hall · « **Reply #6 on:** July 05, 2013, 02:09:01 pm »

Quote from: ZeroZeroMinusOne on July 05, 2013, 08:49:39 am

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.

ZeroZeroMinusOne · « **Reply #7 on:** July 05, 2013, 05:45:30 pm »

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.

BadMoonRacing500 · « **Reply #8 on:** July 06, 2013, 01:58:25 am »

Bored stock carbs are best, stay away from keihins and lectrons. I would try a 380 390 main with your combo. Stock reeds?

ZeroZeroMinusOne · « **Reply #9 on:** July 06, 2013, 04:58:35 am »

Yes stock reeds. Ill try the 380-390 jet and report back

ZeroZeroMinusOne · « **Reply #10 on:** July 08, 2013, 08:11:50 am »

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.....

Buckeye513 · « **Reply #11 on:** July 08, 2013, 10:52:04 am »

Way to pick on a bike half your size ya big bully!!

ZeroZeroMinusOne · « **Reply #12 on:** July 08, 2013, 11:30:01 am »

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

Buckeye513 · « **Reply #13 on:** July 08, 2013, 11:37:08 am »

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.

ZeroZeroMinusOne · « **Reply #14 on:** July 08, 2013, 11:50:28 am »

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?

Q2W · « **Reply #15 on:** July 08, 2013, 12:33:41 pm »

Quote from: ZeroZeroMinusOne on July 08, 2013, 08:11:50 am

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.

Buckeye513 · « **Reply #16 on:** July 08, 2013, 12:40:58 pm »

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.

Motoman991 · « **Reply #17 on:** July 08, 2013, 12:57:24 pm »

Quote from: Buckeye513 on July 08, 2013, 11:37:08 am

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.

ZeroZeroMinusOne · « **Reply #18 on:** July 08, 2013, 01:18:52 pm »

He has no chance, I want to watch this race too

Motoman991 · « **Reply #19 on:** July 08, 2013, 01:36:29 pm »

LOL I know. He's putting in all that work to that zilla just to give it away.

Buckeye513 · « **Reply #20 on:** July 08, 2013, 01:38:06 pm »

Motoman ill be sure my bike shifts and I don't get quad lengthed by a 250 in 1st gear! Lol

ZeroZeroMinusOne · « **Reply #21 on:** July 08, 2013, 01:47:37 pm »

Quote from: Motoman991 on July 08, 2013, 01:36:29 pm

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

BadMoonRacing500 · « **Reply #22 on:** July 15, 2013, 10:11:35 pm »

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.

cworobec · « **Reply #23 on:** July 16, 2013, 01:09:45 am »

I put a electron on my bike, it tunes easy and runs bad ass.

ZeroZeroMinusOne · « **Reply #24 on:** July 16, 2013, 06:49:26 am »

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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Author Topic: New top end on LT500, very boggy (Read 2018 times)

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