psychodad

Thanks, two more things to check.

On 7/19/2023 at 4:09 PM, Mech said:

The bigger air passages never block up, nothing that can't be blown out.

I think you should un-tweak the float level first off.  After replacing the needle seat and valve the float level was ~11mm.  I raised it to 13mm per spec (or so I was told).  Will have to get carb in my hand to see if I actually raised or lowered the level in the bowl.  If I lowered it, I'll raise it back up 2mm.

When you had the emulsion tube out did you clear the tiny holes in the side of it ?  Yes, a couple of the holes were plugged.  Soaked in Gunk, all clear now.

If that emulsion tube had a short discharge tube above it that works with the needle to calibrate the flow of fuel and air, are you sure it's still there and the right way up ?  Installed correct.  Only fits one way.

Are you certain the needle is still at the correct clip setting? Are you sure the needle is held in the slide and not able to go up and down ?  Clip only has one (1) position.  Confirmed needle is held in the slide (spring loaded) but will still float side to side as to not bind.

I have heard of problems where someone put an O ring in somewhere on or near that emulsion tube and had similar problems, though I'm unaware of any O rings in there, unless it's to seal the main jet.  There is an 0-ring under the hex on the emulsion tube to seal against the body.  It was so squished when I first removed it I wasn't sure what it was.  Had a hard time trying to decide which one in the kit was correct.  Pretty sure I picked the right one.  Also, did not use any jets from the Shindy kit.  Only float needle, seat, and rubber items.

The passage that emulsion tube is in is designed to hold a measured amount of fuel and if it's full of crud sufficient to change how much it holds it can give a flat spot as you accelerate, but it's fairly minimum.  No crud that I can find.

I'd check the slide is moving freely, and that it's air passages are all clear, and that the carb bowl breathers are correct and clear, and that the airbox and cleaner are all in good order and original.  Slide slides up/down under gravity w/o spring.  Two smallish holes in bottom of slide, both are open. I'm starting to question the airbox condition.  Will elaborate below.  Tried to open the slide by hooking a shop vac up to the inlet and opening the butterfly.  It only opened the slide a 1/3 of the way, but I have a feeling the shop vac doesn't draw enough to fully open the slide.

I'm quite sure than any further cosmetic cleaning with chemicals is not going to cure the problem.  You're probably right.  Not sure the carb is the problem now.

 

First off, thanks for all the comments.  Lots of good ideas.  Full disclosure, I'm not the first one to open the carb.  Someone else cleaned it before me.  Not sure of his level of expertise?  First thing I noticed when I initially looked at the carb, was a coating of dust/dirt on the airbox side of the slide.  I wondered how this carb was recently cleaned and still had a layer of dust on the slide?  Anyone seen this before?  As noted above, I really didn't find anything wrong with the carb other than a couple of plugged holes in the emulsion tube and the badly deteriorated o-ring on the tube.  This is why I was considering soaking the carb in Gunk.  One additional item, when I received the carb the second time after a test ride I found a very thin layer of dust on the carb body under the slide diaphragm.  How does dust get in there???  The diaphragm inside also looked dusty.  Not heavy but a very fine dusting.  I know I previously sprayed that area down with carb cleaner and lightly cleaned the diaphragm.  When I gave him the carb back the first time I told him to check the airbox/filter for leaks.  He said he didn't find any.  I didn't think to ask if the airbox and filter were original.

For the second cleaning I suspended the carb in Gunk with a wire just above the throat bottom to avoid did soaking the throttle shaft/seals.  I was surprised at the clean line the Gunk left on the bottom of the butterfly.  That Gunk is good stuff.  Sprayed everything out with carb cleaner and compressed air again.  I'm in the process of reassembling.

Finally a couple of questions,

1)  There's a hose connection on the carb body just below the diaphragm.  What does that go?  Can it suck unfiltered air?

2)  Where's the fuel filter on a 400 Big Bear.  Is it starving for fuel? Usually there's at least a screen on the petcock.  Didn't see one on the fishe unless it's not replaceable?

If I recall, CV carbs don't like to have their airboxes removed or leaking.  Anything else I should look for?  I still have to get an answer as to what exactly happens when you get above 1/4 throttle.  Not sure if starts missing and blubbers through it or shuts completely down.  Sure would be easier if I had the ATV in my shop......sort of like your wife or daughter trying to describe a problem over the phone.  I have to see or hear it.

To anyone that was able to make it thru this whole post, my hat is off to you.  Sorry for rambling.  

1 hour ago, Gwbarm said:

..... there is a jet down in a hole make sure you get that out, they are usually very stuck.....

Not sure which jet you are referring to??  I removed the welch plug and pulled the air/fuel screw.  There's another brass welch plug between the A/F screw and the bowl.  Are you referring to whatever is under that plug?  I was afraid to pull that plug.  It looks like it has to be in place for the carb to operate and I haven't seen any replacements anywhere.  You can see the brass plug I'm talking about 10 seconds into this video: 

Have a carb off an '07 Big Bear 400 that sat a couple of years, probably more.  Friend asked me to clean it, which I did, soaking the jets and spraying out all of the ports with carb cleaner as best I could.  Replaced o-rings, needle valve & seat, tweeked float level.  Bike starts and idles well but doesn't want to pick up above 1/4 throttle.  That would appear to be in the slide needle range.  Main jet is clean, needle is clean and straight, diaphragm good.  It seems I saw (in a diagram) a port that comes into the slide needle area from the side.  This would be in the carb body between the main jet and the throat of the carb.  I would like to soak the carb in Gunk Carb Cleaner, the gallon paint can with a little basket.  Curious what Mikuni uses for bearings and seals in the throttle shaft.  I'm guessing HDPE or Delrin, or maybe brass; not sure what effect Gunk would have on the polymers.  Has anyone actually soaked a carb in Gunk??  First hand knowledge, please, and what effect, if any, on the carb.  Pulling the throttle shaft out would be a last resort.  Getting the butterfly screws out and staked back in would seem to be a nightmare.

Thanks

Jim

Space, that brings up another point.  Some models have casters you can crank down in case you want to move.  I had to move mine over to get a car in the garage for storage last winter.  The air over hydraulic lift is also handy.  Just things to consider when buying a lift.  But as usual, the options all add price to the unit.

Thanks again for your help.

Many "Thanks" Gwbarm.

Can I bug you for one more piece of data?  What's the stock air screw setting?  Screw was stuck and in the process of working it in & out, I lost count of the initial setting.  I've seen between 1-1/2 turns to as many as 2-1/2 turns out posted online.  I really don't like working on stuff for other people.  I want it to be perfect but perfection is very time consuming.

Careful guys.  You get what you pay for.  Buy something decent, you don't want your quad or bike falling over on you.  I bought one of these a dozen or so years ago.  https://www.atlasautoequipment.com/products/lifts/motorcycle-atv-lifts/atv-lifts/hi-rise-1500

It's Chinese made but heavy and solid.  I bought mine from somewhere else but looks just like that one.

Oops,, it's a 400 Big Bear.

Just rebuilt a 2006 Yamaha Big Bear carb for a friend and would like to double check the float height before I give it back to him  Anyone have a manual they could look it up in or a really good memory. 

Thanks

Jim

As noted, new member checking in to look around.  Mainly interested in troubleshooting ideas and technical information.  Currently rebuilding a carb for a 2006 400 Big Bear for a friend.  Needing the float height, will post request as soon as I find the proper sub-forum.