A forum for owners of Yamaha TTR250 trail and enduro bikes!

OK, updates:

1) Full snorkel is still attached to airbox, just no filter.  Still no air filter, still ETA later this month.  Fuel adjustment knob o-ring is good- I checked when I took it apart and the o-ring does fit snuggly in the aperture.  I also moved the needle clip one ring LOWER than center in an attempt to richen the mix.  All parts on the top of the carb lube'd with powdered graphite to help prevent sticking.

2) I added a fiber washer between the top of the cylindrical slide and the actuator arm to help my carb slide sit further down in the carb assembly... it was only lowering down to about a 1/2 inch above the bottom of the carb and allowing considerable daylight thru.  My suspicion was that i was not able to close throttle and was always getting a 10-20% open condition.  I have a pic, but the board seems to dislike when I post it.

3) After adding this washer, the bike will still start and still absolutely RIP at start-up... so, maybe the slide location wasn't the problem after all.

4) Noteworthy- It will still start and still rip on full choke, but not with the choke OFF (pushed in).  Once I push the choke back in it will drop waaaaay down in revs, chug, lug, backfire in the manifold (I can watch it flex and push back from the engine) and then die.

Everything I have read/watched to this point is telling me that I have a blocked pilot assembly.  I have my doubts, since I have had the carb completely apart twice and sprayed cleaner through every opening.  I do plan to pull the carb once again and go all-out to ensure all paths are unblocked (wire thru holes, ultrasonic, sacrifice a chicken under the full moon, etc...).

Anyone still reading, please take a SWAG at what the issue could be if I am NOT dealing with a blocked passage.  All input welcomed, TYIA!

mossproof wrote:

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Well it certainly sounds lean, too much air or lacking in fuel supply like a blocked pilot - if it will start with choke (enriching the mixture enough to let it fire) then struggles with choke off...

The slide should be virtually shut at zero throttle input. Adjustment is by the throttle-stop screw - knurled screw by the choke plunger. You shouldn't have to put a spacer in somewhere. I normally adjust the slide down until you can't see daylight through, then screw the adjuster clockwise 'till there is just a glimmer of light visible under it. Your pic suggests to me it is still too high.

Don't worry, still reading

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Thanks for sticking with me, mossproof. 

I should have specified - the pic was BEFORE my spacer kludge.  I had been adjusting the throttle-stop screw, but the descent of the slide was halting at the position shown in the pic regardless of the position of the stop screw.  When I had the carb apart off the bike I noticed that I could lower the slide all the way when the arm was not screwed in to the throttle cable rod... but once I aligned the holes in the arm's collar and the throttle cable rod the arm halted descent much higher up and the slide wouldn't bottom out.  The spacer was an attempt to lower the slide closer to bottom when I couldn't figure out what was limiting the range of motion in the slide after attaching the arm to the throttle cable rod.

I have a new suspect- the circular cover of the pilot circuit 'mixer' is held on with two screws and there is a 1-inch squared rubber gasket in there.  I noticed that part of the gasket seemed to be bubbled up (or maybe pinched) last time I pulled the carb off.  I didn't think it was serious until I went and re-read the explanation of what that does, which led me to believe it could be related to the lean condition.  I am going to try the soapy water / bubbles test on this area and see if I'm pulling in air.  I can get the right sized gasket from the local hardware place if needed after the test.

mossproof wrote:

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Any luck?

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Great timing, I just had it on the road about two hours ago.  I was coming back to post updates and to thank you!

This weekend the process was:

-Full tear-down;

-Spray carb cleaner in all passages once all rubber was off the carb;

-Six-hour hot soak in homemade ultrasonic (turkey fryer pot and burner, fish tank bubbler, pad sander strapped to a board for vibration, 50/50 mix of tap water and Zepp degreaser);

-Snaked all passages w/ stripped copper wire;

-Blew out all passages w/ air compressor;

-Rinse and brush-scrub in laundry tub w/ hot water and OxyClean crystals (this dislodged some new gunk I had never seen during the prior attempts);

-Re-assembly w/ a) new, unwrinkled mixer bowl gasket, b) added previously-missing gasket to throttle arm keeper screw, c) new foam air filter and d) replaced cheap eBay throttle cable w/ original.

-One other possible culprit- the rubber washer on the fuel adjustment screw was torn.  It's possible that I damaged it on prior install, or maybe it just gave out.  I obtained a new one from the local hardware and it fitted right up.

I put it back together per the guide on this site, making sure I paid extra attention to the points where the carb anchored to the manifold and airbox.  I would have cranked it over last night but the battery was low so I left it on the charger overnight.  Today I finished dinner, rolled it out in the drive and it ran really well.  It will start on or off the choke, settles into a nice even idle once the choke is off, and revs in and out nicely when throttle is applied.

I think I still may have a bit much air getting in at idle, but it seems like it is in the range that the fuel adjustment screw can deal with.  Definitely nothing drastic like the screaming start-ups before the re-do... it finally feels tune-able.

Funny side note - since I had been using said turkey fryer pot to dye plastic lacrosse heads dark grey and black for several years, any Rit fabric dye that had embedded itself if that pot worked free and turned my aluminum carb a deep black. The good news is that the Rit dye will 90% go bye-bye with a mix of hot tap water and OxyClean crystals. I didn't realize until after the extra hot water/Oxy scrub that I should have been using distilled water and vinegar, but it eventually all came off.  The pot was rinsing clear before I started in with the degreaser, so I guess the heat and degreaser really pull the leftover dye out of any pores in the pot.  Quite the surprise when you pull what is supposed to be a shiny, clean carb out of the pot and it's three times darker than when it went in.

So, thanks again for encouraging me to stay patient and helping trouble-shoot.  I owe you a beer if you're ever around Indianapolis!