'07 Big Bear 400 - Anyone actually soak a carb in Gunk?

[psychodad]

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

[Gwbarm]

I have used the paint bucket gunk carb cleaner, probably the best, very caustic, there is a jet down in a hole make sure you get that out, they are usually very stuck, make sure you remove all the rubber parts. What I do with the throttle hook up is leave it sticking out of the cleaner at the top of the bucket.

[psychodad]

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: 

 

[Gwbarm]

No not that one, its under the float bowl next to the main jet, you may already have it out, i was just saying sometimes it not obvious.

 

This is not your carb but it should be similar, down in the hole right between the 2 obvious jets, and you can see the one the video was referring to, my welch plug has already been removed.

[Mech]

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.

When you had the emulsion tube out did you clear the tiny holes in the side of it ?

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 ?

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 ?

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.

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.

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 claer, and that the airbox and cleaner are all in good order and original.

I'm quite sure than any further cosmetic cleaning with chemicals is not going to cure the problem.

 

[Gwbarm]

The Gunk is good stuff, i should have mentioned this earlier, i dont use it that much, because its generally not needed, i only use it when the gas has been in there so long it has turned to tar, and use it on a bike that has been sitting for 20 + years. Generally for a carb that has been in use i just pull all the jets out squirt some carb cleaner in the hole make sure the jet passages are clear and that usually takes care of it, sometimes i may put in an ultrasonic cleaner with simple green or even dish detergent just to jar anything loose and clean up insides a little and take care of trash that may not be visible.

[Mech]

When you say it doesn't want to pick up above 1/4 throttle, how bad is that ?

Is is just a slight hesitancy, or a flat out refusal ?

Also, check the choke plunger is going right back in..

And yeah, you really don't want to be taking the butterfly out. The screws are crimped and the shaft is soft and the threads will munt themselves as the screws come out if you aren't very careful, and if you do get them out, they are mongrels to get back in.

[Gwbarm]

Great Video! I used to watch his videos all the time when he was at Iowa Tech, Shane produced some of best informative how to videos on motorcycle repair i have ever seen. Takes his time explains and shows everything perfectly.

[Mech]

Yeah that is good detailed stuff Gw.  It's easy to forget how much we know and take for granted..

It's a shame there are so many youtubes out there that are full of bad advice..  haha.

[Gwbarm]

Yeah, and bad videos, it hurts my eyes to watch them.

[Mech]

ha..

[psychodad]

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.  

 

                               

[Gwbarm]

I think the hose you are referring to is the hose that hooks to the lower air intake hose: if just left dangling it can suck unfiltered air. Fuel filter is inside the tank attached to the petcock, pull the petcock to clean it.See the grommett on the upper intake hose the vent hoses from final drive hang out there.

 

[psychodad]

Thanks, two more things to check.

[Mech]

I thought you meant you'd set the float height to something other than specs..

There certainly shouldn't be dust getting in there, and it's possible the air that's getting in letting dust in might be part of the problem. They are fussy about the airbox and filter. Gw knows where the breather hoses go.. Check those.

I've heard of people getting the O ring on the emulsion tube in the wrong place and having similar problems, and in some carbs that top discharge tube on top of the emulsion tube can be upside down.

Are you sure the slide's needle holding bits are all correct, and that the washer/spacers on it are in their right places and that the spring is holding it all down properly. In some models the spacers are different thickness and get swapped top for bottom, and the needle is designed to be able to move up and down against the small spring.. Check that.

The symptom, and the throttle range it's in, sounds like it will be the needle adjustment to me.

The other thing is though, how bad it is.. Are you sure it's not misfiring ? Bad plug ?