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TTR-250 Carb Questions

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I just acquired a 2004 TTR-250. It sat in the PO's garage for two years. PO said it ran OK before then. Bike is pretty clean and has not been abused.

Searched this forum and figured that the carb was gummed up based on all the posts.

The bike starts and runs (high rpm) only with the choke pulled out. Then when the choke is pushed in it dies and won't idle. Sometimes backfires once or twice before stopping. I figured that the pilot jet is clogged. I pull the carb, take the bowl off and it looks pretty clean. I pulled both jets and carb cleanered it real well. Then blew out the passageways with compressed air. Looked clean as a whistle. Drained all the gas out of the tank, took off the petcock and cleaned it too. Air filter element looks like it has just been serviced. Set the pilot screw to 1 1/2 turns out. Reassembled it all back up and it runs identiclally as before. What should I check now? Could the pilot jet still be clogged?

Edited by blimpman
Wrong year

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Pilot jets are pretty tough to clean. They flow such a tiny amount of fuel that the slight speck of buildup can shut the flow down to nearly nothing. You are always safest to replace it, and if it's the stock pilot, put in one size bigger.

These bikes are choked up to make the EPA happy, and they run and start so much better with larger pilots.

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No need really to replace the jet. If you have any index bits anyway. Or run something through it to totally clean it out. Soak and then blow out or use something that fits properly.

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UPDATE...

I missed a small clog in the pilot jet..... dang it....🤣

Running now and just needs some small adjustments. Thanks for all the replies. Great community here. 👍

ttr004.jpg

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I am learning .... slowly...

The engine starts easily and idles perfectly. When starting off in 1st gear, the first 1/8 of throttle causes a hesitation until the RPM picks up. It then runs very well.

I pulled the carb again and went down bought a new pilot jet according to the numbers listed in the sticky. That part is not the same pilot jet that is in the carb. It has a much longer neck such that it sticks out of the carb body and interferes with the plastic baffle. It screws in OK but is too tall.

I cleaned the original pilot jet very well and used a magnifying glass to be sure the orifice was clear end to end.

I have the Pilot screw at 1 1/2 turns out.

Anyone give me something to check or adjust? I think the bike is close.

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I had exactly the same problem with a 2005 ttr 250. Mine was clogged at the port under the fuel screw. A half can of carb cleaner and 100 psi air cleaned it out. I still had a little bog as you describe. I have my fuel screw out about 2.5 turns and it has helped with the bog. Still has just a little bog, but it's not a problem at all. It really takes a long time to warm up to get over the bog after starting. I can take it off choke after about 30 sec after first starting it up and it will idle fine. I'm convinced the carb is clean. Maybe it would take a larger pilot to completely cure it.

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I had exactly the same problem with a 2005 ttr 250. Mine was clogged at the port under the fuel screw. A half can of carb cleaner and 100 psi air cleaned it out. I still had a little bog as you describe. I have my fuel screw out about 2.5 turns and it has helped with the bog. Still has just a little bog, but it's not a problem at all. It really takes a long time to warm up to get over the bog after starting. I can take it off choke after about 30 sec after first starting it up and it will idle fine. I'm convinced the carb is clean. Maybe it would take a larger pilot to completely cure it.

I agree. I would go up a bit on the size. Be sure that the jet is 100% cleaned out. A lot of the time, there is still hardened flabungous (technical term for crap) inside the jet, even though it is somewhat cleaned out and allowing some flow. Or drill it out to a size up with jet index bits.

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According to the jetting info on forum sticky about which size and type of jets to get for a TTR250, the jets listed by part number don't match what is in my bike.

First, the main jet is a small hex head ( not the small round head they describe)

Second, the pilot jet listed is very similar but about 1/3 longer than the one in my bike.

I bought these jets before I took my carb apart thinking I'd just replace them. Can't user either one.

The jets listed in the forum sticky seem to be for a Mikuni VM28 carb. I think mine is a TM28 model. Did Yamaha put different carbs on for different years? Mine is a 2004.

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Like you mentioned it seems pretty close. Be sure that you start with a fresh plug and the highest octane unleaded gas you can get, 90 + octane 92 if possible. The hesitation at 1/8 throttle is common for a cold air cooled bike until it is completely warm which make take up to 10 minutes depending on the temperature. But remember that these bikes are restrcted real bad from the factory. With the stock carb settings they are prone to have these small symptoms. My suggestion is wth clean gas and new plug, start that baby up and get it warm. See if the bike runs a lttle better with the air filter cover removed. You may not be getting enough air. If that helps then move forward to the airbox mod shown in the sticky. The 1 1/2 turns out is a good place to start but you may also not be getting enough gas into the chamber so the bike is looking for gas in the pilot range and just needs to be opened up a little. Back out the fuel screw till it bogs with too much gas and tune it back in until you get a nice throttle response. This bike should run well with the stock parts. And until you want to add a pipe, the air box mod and the header mod in the sticky should help alot. Of course the Jet upgade will work real well but you should be able to get it running better with some small mods. Mine did! Good luck and let us know how it all came out.

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According to the jetting info on forum sticky about which size and type of jets to get for a TTR250, the jets listed by part number don't match what is in my bike.

First, the main jet is a small hex head ( not the small round head they describe)

Second, the pilot jet listed is very similar but about 1/3 longer than the one in my bike.

I bought these jets before I took my carb apart thinking I'd just replace them. Can't user either one.

The jets listed in the forum sticky seem to be for a Mikuni VM28 carb. I think mine is a TM28 model. Did Yamaha put different carbs on for different years? Mine is a 2004.

The TM28 carb is the only carb used on the TTR250, it will accept Mikuni jets, but it's the correct carb.

The pilot jet you want is the VM28/486, a 52.5 or 55. It will fit, I have the same model carb, double-check your part number on the pilot.

The main is a 140 small round main main jet. It will be round, but the one in your carb will probably be a hex head. That's ok, the small round replaces it.

You might want to raise your needle one position, depending on your airbox hole & pipe setup.

The fuel screw is easy once you're jets are sorted out, I screw it in then back out 2 turns, let it warm up completely (10 minutes of riding). Then, turn it in until it starts to die, then back out till the idle is smooth and a nice thump/thump/thump.

Then, set your idle and ride the tar out of it.

I'd really recommend the Pro Circuit T4 for the TTR, it really wakes up the bike and it's not obnoxious at all.

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swingset's advice is correct. I have the 55 pilot and 140 main with a small shim under the needle and it runs great.

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