Bobbywolf

It was actually a new carb, and not used? I tried searching for the seller but no luck. Have a link? Thanks!

No o-rings within the carb were actually replaced. They all looked new, and had a nice amount of 'squish' when sealing up. It did not look like the atv ever ran since the chinese carb was swapped on. It works well enough now, and any grief in the future will result in a mikuni carb kit, going into the factory carb to remove the question marks in the process. Cheers.

By lifting the needle to its top spot (the lowest notch) I was able to get the bike to behave at all throttle levels. I cannot get it to function correctly at any lower needle level, so this will work. It works good, and I doubt it will get any better without finding a replacement mikuni carb. Thanks for the assistance fellas. The forum is badgering me to mark one of you as a solution (gw and Mech were very helpful). Do these mean anything? or are they just throwaway forum flavor BS? Essentially both of you helped me so why would I single someone out? It seems like a disservice to the other. Thanks again gents.

You guys were correct about the throttle cable binding. I have it adjusted now that the butterfly completely closes, and idle is now smooth. Up top is now smooth as well. 1/8 to 1/4 throttle is still a bit rocky. Playing with the needle height is the fix for that I believe. I've never had this much trouble messing with a carb before. I guess it is because it is a bit of a Frankenstein now. Thanks for the assistance guys.

Ok, back to this pig. So I pulled the clean chinese carb back apart, but this time I pulled the factory one apart as well. I compared jet sizes and such, and I stumbled upon something very interesting. The needle sizes are very different, and tapered different. See my picture below. The chinese parts are up top, and the factory parts are below. The emulsion tubes and main jets appear the same, but the needles are vastly different lengths, and taper. I have since installed the emulsion tube, main jet, and needle from the factory carb into the chinese carb, and ran the bike. At first it was still a little lean at idle, but now I have gotten my mixture screw adjustability back. I can now idle, accelerate, and rev at high rpms with no backfiring through the carb. Big step forward. It looks like the long needle was not allowing hardly any fuel through. One issue I have now, is with the idle screw backed all the way out, the bike idles too fast. A little more digging required, but it looks like this junk carb may end up working for me.

I have actually destroyed a carb in the past using an easy out. The flutes pull the extractor into the soft brass, actually making it bigger and more stuck. I then split the carb from the force of the easy out. I was talking to a friend with a milling machine, and he thinks we can get very centered up, and drill out the screw until only the threads remain, and then pick them out. This is likely what I will end up trying. Thanks guys for the thoughts. I am going to be disappointed if I end up with the same symptoms. Is there anything electrical that can manifest itself as a lean condition? Or am I only chasing fuel/air?

You are correct, the needed itself is lifted to the highest position, which means the clip is at the lowest of the 5 slots. My practice when cleaning carbs is to ensure every hole is able to flow carb cleaner in, and out another hole. I then blow compressed air through as well. The pilot jet has no markings. The hole is tiny, and only 1 bristle of my small wire brush fits through it, which is how I cleaned it. The main is 125, which I believe is correct. Great point about choking the carb intake, I'll give that a shot when I put this back together enough to try it. Likely go at it again Sunday. I need to man up and go after that mixture screw in the stock mikuni carb. That is where my best hope lies.

I am working on a basket case for a friend. It is a 98 Big Bear (YFM350FWB). It came with a parts machine which is a 96, which I am coming to find out is VERY different from his machine. Anyway, first thing is first. I checked compression, 150psi. Valves are set correctly, and the engine is in time. I cleaned the carb, and there was some junk in the passages. It is a chinese carb, which I figured from the lack of markings or lettering altogether. The bike runs. It idles ok, but breaks up badly under acceleration. Pulling a new spark plug shows it is running lean. White strap, with no black whatsoever. So I have the carb adjusted with the mixture screw out way too much (about 5 turns), and the diaphragm needle lifted to the top slot. It is still not getting enough fuel (or too much air). It backfires through the carb, and cannot get above idle without carrying on. The carb boot is in good shape, so it isn't pulling any air there. I did test this as well by spraying ether around the boot when running, looking for intake leaks. Anything big I am missing here? I am starting to believe that this chinese carb is the issue. This quad came with the original carb, which I would like to rebuild and use, but the mixture screw is totally stuck, and stripped way down in its recess. Thanks for any assistance.