XR350 single, good with no air filter

New to me 85 xr350 with single carb, kicks over cold (never hot), bogs down on acceleration. Messed with air screw, removed carb and cleaned. Same problem. Finally, took off air filter and it ran much better. Not great, but could hit acceleration. Lot's of exhaust tho. What's the deal? Should I rip out airbox and put on slip on air filter? Am I rich or lean? I can't tell as I'm just aimlessly turning the screw back and forth. Why is it good with no air filter?

That it runs better with no filter indicates the jetting is too rich. When you take off the filter, the engine gets more air to be able to lean out the rich jetting.

Do you have to use choke to get it to start cold? Able to start cold with no choke is another sign of rich jetting.

Did the bike previously reside at a much different elevation? What elevation did it come from and what is yours?

Be sure the filter isn't over-oiled. Being over-oiled will restrict too much air and cause a rich condition.

When you had the carb apart for cleaning, did you take note of the jet sizes? Did you check its float level setting?

The "fuel screw" only affects the pilot jets range, idle and off idle throttle response to the point where the pilot jet overlaps with the needles starting diameter. Has no effect past that and on up into the main jets range, upper throttle.

Edited by Trailryder42

Buy a box of four new spark plugs and do plug chops. No matter what people say with plug chops and todays gas...hasnt hindered me at all. The plug will tell you. But along with the plugs, youll need some jets. The chops will tell you richer or leaner.

Pod filters are awesome...if youll never see dirt. Filter oil on every filter, whatever you have. But you should have a regular enclosed filter with an airbox.

Youre obviously rich. Did it have an aftermarket exhaust on and then when sold the stocker was put back on? 

Won't start unless at current air screw setting. Choke doesnt matter. Air filter on/off doesn't matter on start up. Bogs down dies at half+ throttle with it on. Tons of power at full throttle with filter off. Smokes a lot out exhaust. I'm so stumped. Feel like it's something simple I'm missing.


Exhaust looks stock. Air boot connecting to carb is a bit folded restricting ~60% flow (due to some mod it looks like on intake boot side is longer).

What color smoke?

It can't be a jet that's fallen out because you said you cleaned the carb, so you'd have noticed it. When you cleaned the carb, did you remove the fuel screw and clean that passage too?

If you want to sort this out, you need to answer the questions put to you.

Take and post pictures of the air boot you're concerned with.

Possibly float level too high making it run too rich.



Edited by Baja Rambler

It will only start with no air filter, petcock off, Idle screw up and get this....twist half throttle. No dice otherwise. When it's running, backfiring like a SOB. Smell of gas. Took off carb again. Jets clear. Float measuring 14.5mm. Same result. Help

"Took off carb again. Jets clear"

But what size were they?

Read back thru this whole thread and answer questions that you haven't yet.

Slow is 50. Main is 148. Carb is Keihin PD 11DAYEI (whatever that means...) This is 1985 XR350 single carb version. No carb detail available online. Cleaned all passages-again. Checked diaphram. All good. The only thing I can think of is that the fuel screw did not appear to have an O-ring. Only the washer. I poked around a bit and didn't see anything. Like I said before, it's still doing the same thing: bogs down to nothing on 1/2-full throttle. it doesn't matter how much I mess around with the fuel screw. The only thing that will make this bike run good, is if I remove the air filter. Is it the onring on fuel screw? Does the main jet have an oring too? I'm at a complete loss...What am I missing?

The fuel screw needs to have the oring on it. If it's there, it's at the very bottom of the hole, once you get the screw, spring and washer out. Use a flash light. It's usually black.

It makes sense that screw adjustment has no effect if the oring is missing.

No oring on the jets.

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