Here is the needle that was in the bike.

This is the current filter.
I added some pipe and silicon tube to move it away from the oval hole of the carb. The issue was still present.

I then taped off a large portion on the filter to see if it was a lean issue, no change.

It was running well with the same filters just a longer runner that cleared the factory battery tray.

https://youtube.com/shorts/eRu1vGn6Ams?feature=share

Here is a link to to a video of it running under wider throttle conditions.

Hard to hear over the wind noise but you can definitely hear the sputter im referring to .

Could it be something like the float, or maybe a spark issue ?
Or could.it really be just the shorter intake tube ? This doesn't make sense to me.tho as many ar running filters directly on the carb.

Your air cleaner is too small.  There is less surface area than a stock flat-panel filter.  The small filter doesn't provide enough air at WOT.  It will cause a rich mixture.

Your spark plug is black.  That indicates a rich mixture.  It's fouled.  You need to replace it.  You need to be sure that the fouled plug doesn't cause misfire.

When you remove the spacer from the top of the slide needle, and you don't replace it with something (like half a spacer or several washers), you set up a condition where the needle can be raised entirely clear of the needle jet.  On this particular carburetor, the slide needle controls fuel flow even at WOT.  You can add more taper to the end of the needle, but raising it completely out of the needle jet will open a flood gate.  You need a few washers on that needle, or half a spacer.

That thing sounds like it's goin grossly rich as soon as the slide goes wide open.  A 155 main jet will not cause that.  I've run jets over #200 with a stock needle and it still runs clean at WOT.  So, you are either smothering the thing with that little air filter, or you are pulling the slide needle completely out of the needle jet.

It's also possible that your main air bleed system is obstructed.  It's a very small jet.  The passage behind the jet could also be plugged, or the emulsion holes in the needle jet could be plugged.

Do a quick & dirty test.  Install a new spark plug and remove your air filter (hose, plastic tube, filter, all of it).  Run it without the air filter.  Get it started and rev up the engine.  Observe the slide while you rev it up in neutral.  Make sure the slide opens all the way.  Then ride the bike.  Does it run OK without that little air filter?  Does it run better or worse?

Hi Mike. This is the size of the filter.on the bike. The photo I showed just had a lot of the area taped off to see if it changed the issue but it didn't. Or at least not in a way that I could notice.
This is the same filter that I had on with the longer intake runner and it was running ok.
I also tried with one of those foam unifilters and it did the same thing.

I agree that it seems to be a rich issue. The spacer was originally on the needle but it was old and brittle (I'm referring to the plastic, brown colored thing that was on the very top of the needle)


Could it also be a spark issue ?  I cleaned up the sparkplug with a little carb cleaner and all the carbon fell straight off.

I'll get a new plug and do the test tomorrow

DragBikeMike wrote on 05/18/23 at 02:45:59:


I have replacement for the needle jet I can put in the carb tomorrow. How is that part removed ?