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TTR125L with Vm24 carb

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I put a bigger carb on my 07 TTR125L and modded the airbox (ripped off the snorkel) but now in 2-4 gears and at mid throttle it kind of cuts out. It like bogs down a little then comes back going back and forth. Does anyone have any idea what this could be? Jets maybe?

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2 hours ago, FSK_Talon3 said:

 

I put a bigger carb on my 07 TTR125L and modded the airbox (ripped off the snorkel) but now in 2-4 gears and at mid throttle it kind of cuts out. It like bogs down a little then comes back going back and forth. Does anyone have any idea what this could be? Jets maybe?

 

A bigger bore can give you more performance, but you can also have too big of a bore.  Too big can cause low intake velocity, and a poor or lean fuel mixture causing the bogging you mentioned. 

It's also possible the bigger bore you installed will work, but the jetting is incorrect for the conditions.

When the motor bogs, can you go ahead and twist the throttle and the motor will clear up and pull good at higher rpm's?

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A bigger bore can give you more performance, but you can also have too big of a bore.  Too big can cause low intake velocity, and a poor or lean fuel mixture causing the bogging you mentioned. 
It's also possible the bigger bore you installed will work, but the jetting is incorrect for the conditions.
When the motor bogs, can you go ahead and twist the throttle and the motor will clear up and pull good at higher rpm's?

Yes. It is just mid throttle. What do you mean bigger boar? Is it bigger boar even if I just swapped the carbs?

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The bore of the carb is where the air goes through.  For example: your bike came with a 20mm diameter bore, and you installed a bigger 24 mm bore carb.  The bigger bore will have a slower velocity of air flowing through the carb at lower rpm's, which can have less negative pressure (vacuum) created at the metering rod and main jet.  Less vacuum will pull less fuel through the main jet, and can cause the bog you have.  At higher rpm's, the negative pressure (vacuum) created is greater, pulling more fuel through the main jet.  You can certainly put a bigger main jet, or move the c-clip down a groove or two on the metering rod to richen the fuel mixture, but then you may be too rich for the lower rpm range.  Depending on what rpm your going to be running, you may have to big of a carb for just playing around on a pit bike.  Bigger ain't always better, just depends what you're trying to accomplish.

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Let me also say that I'm by no means trying to discourage you from the adventure, the thrill, the unknown of trying things. 

When I was young and learning, my scrap pile was larger than most; but I had the best of times learning the do's and donts, and still do at times.  I've got that defective "can't leave it alone gene".  Never a dull moment.

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Make sure you got no air leaks around the new carb for starters, that can cause lean condition and smoke your motor pretty quick. As stated when you have more air you need more fuel. Try going up a couple sizes on the main jet and see what it does.

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So dumb noob question here. I bought the carb of eBay and I'm not sure what jets are in it. Is there a way to tell? I will probably get a couple of face palms.

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Only one :facepalm:so you're good.

The main jet will have a number stamped on it.  Let's say it has the number 150 on it.  The bigger the number, the bigger the jet, and the more fuel it will flow; assuming the bore is not too big and there is enough vacuum at low and mid rpm's to pull more fuel.  If you try a bigger jet, maybe go 2 numbers bigger at a time until the bog goes away.  You can also remove the metering rod, and move the c-clip down one groove at a time until the bog goes away.  Somebody is bound to offer and jet kit with an assortment of jets.  In a pinch, you can use a numbered hand drill set to make your main jet larger.  But if you go to big, you'll have to solder the hole shut, and start over. 

Edited by WALKINGWOUNDED

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Only one :facepalm:so you're good.
The main jet will have a number stamped on it.  Let's say it has the number 150 on it.  The bigger the number, the bigger the jet, and the more fuel it will flow; assuming the bore is not too big and there is enough vacuum at low and mid rpm's to pull more fuel.  If you try a bigger jet, maybe go 2 numbers bigger at a time until the bog goes away.  You can also remove the metering rod, and move the c-clip down one groove at a time until the bog goes away.  Somebody is bound to offer and jet kit with an assortment of jets.  In a pinch, you can use a numbered hand drill set to make your main jet larger.  But if you go to big, you'll have to solder the hole shut, and start over.  Somebody is bound to offer a jet kit with an assortment of jets.

Alright. I will try that. Thanks so much

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The issue sounds like the needle jet, raise and lower the clip to see if it makes any difference.  A VM24 is not too big for a stock bore 125. The question is did the OP buy a real, or knock off VM?  

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The issue sounds like the needle jet, raise and lower the clip to see if it makes any difference.  A VM24 is not too big for a stock bore 125. The question is did the OP buy a real, or knock off VM?  

I got a real Mikuni VM24

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On 5/25/2017 at 5:47 PM, FSK_Talon3 said:


I got a real Mikuni VM24

Then you're golden :)

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So I have a 97.5 main right now. To me that seems low already. Should I try a 96?

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You bike is a four stroke and you bought a 2 stroke carb, that may say Mikuni, but being from ebay may just be a chinese knock off, especially the $35 ones.  But even a real VM24 is going to hard to run right.  The emulsion tube just isn't made for a four stroke.  We could get a VM26 from a YZ80 to get pretty close to run right in our 150's, but not right.  I ended up with a Keihin PD carb from a XR200, and a BBR adapter.  It ran smooth and perfect right off the get go once jetted. I do run a Mikuni VM26 on my CR/XR150 conversion, But it's a Kitaco one with an emulsion tube that is only available from Japan.  With all that said, the KX65 carbs have been a go to carb as of late for both stock and modified motors. My buddy runs them.

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Uh, are you sure it's real?  I have a 190 main in my VM24.  I works very well but I should be running a 185 main.

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Uh, are you sure it's real?  I have a 190 main in my VM24.  I works very well but I should be running a 185 main.

Does it make a enough of a difference that I'm practically at sea level?

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On 6/3/2017 at 7:36 PM, FSK_Talon3 said:


Does it make a enough of a difference that I'm practically at sea level?

I'm only at 800'.

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I was talking to our local engine guru.  He's been doing TTR's even after a lot of us built other bikes.  Anyway, he said the ticket is a Sudco Mikuni flat-side 24.  There is a guy that works there, (I forgot his name . . . Chad maybe) that built a kit for it.  They both tested it, and they rip.  It is $225 ouch.  Then he said the second pick was a PD carb off a XR200, which we used to run back in the day. (2001-2006)  I just picked up another TTR and I'm doing the XR200 carb, since you can pick them up pretty cheap used.  But maybe in a few months, I might swap it over.  But he did say the KX65 carb never ran right for moto, and mainly just used it as a supermoto carb at best.  Since supermoto is topend.

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