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Started by Waiex191, May 15, 2020, 10:34:14 PM
Quote from: Pat Conlon on May 20, 2020, 04:02:20 PMThe emulsion tube (aka jet nozzle, needle jet) is held in place by the main jet. The tube slides out thru the top (the bore of the vacuum slides)
Quote from: Waiex191 on May 21, 2020, 08:12:28 AMThanks Pat. The slot cleared the nub nicely, so none of them were buggered. I'll make another tool when it is time to put them back in. I assume you want to send them home with something other than the main jet pulling them in? Is there a shoulder that the tube hits on the way back in?
Quote from: JPaganel on May 21, 2020, 10:31:58 AMQuote from: Waiex191 on May 21, 2020, 08:12:28 AMThanks Pat. The slot cleared the nub nicely, so none of them were buggered. I'll make another tool when it is time to put them back in. I assume you want to send them home with something other than the main jet pulling them in? Is there a shoulder that the tube hits on the way back in?When you put them in, you should be able to push it in with your finger. They aren't pounded in, or anything. They can be difficult to get out because of dirt and varnish, but they should not be difficult to get in, unless something is wrong.
QuoteItem 1: while cleaning out some carbon around the butterfly valve, I noticed that two of the needle valves stick into the bore a little, and two do not. Is that normal?
QuoteThere is the brass tube that sticks out of the carb bottom and seems to go up to the enrichening circuit. On the bottom it sticks into a hole in the bowl. It seems there is a tiny orifice there, a cavity underneath it, which is connected to the interior of the bowl. I'm assuming the fuel slowly bleeds past the orifice to put a slug of fuel around that brass tube, for initial startup. What is a good way to clear this? I couldn't get my safety wire through it. Nor could I blow it out with various solvents or compressed air.
QuoteI am thinking if there is no other good option, I could drill up from the bottom inline with the brass orifice plug, clean out the cavity, and then put a #4 screw or something small there.
QuoteI also wonder if that same problem exists in my GN400 Mikuni carb - I can't seem to get it to kick start when cold, I have to bump it.
Quote from: Pat Conlon on May 24, 2020, 12:42:24 AMThe choke circuit fuel pickup at the bottom of the bowl is commonly plugged. That's where all the sediment and varnish settles. Soak, piano wire, compressed air or ultrasound are your options. Don't drill.*Be careful* if you spray your carb cleaner down that passage the spray will come out the bottom port on the bowl and...HIT YOU RIGHT IN YOUR FUCKING EYE... (don't ask) The tips of idle/fuel mixture screws poke down into the carb throat....as you see....some do, some don't.That's the rub.Unfortunately the threads cut in the carb body on these mixture screws are not precise. They can differentiate 1/8 to 1/4 turn between the 4 carbs. IOW if you screw in these idle mixture screws "until lightly seated" then back these screws out 3 turns, you would think your idle mixture screws would all be the same....but you would be wrong. One carb may be slightly rich, one carb may be slightly lean. Yamaha factory techs never had to worry about these screw threads being imprecise because they set the idle mixture with a 4 channel gas analyzer. (That's what the ports are for on the bottom of your header tubes) Setting an even mixture between the carbs was easy, just watch the gauges. Back to setting your idle mixtures by hand.....Randy at RPM told me about the "Thumb Nail" method of idle mixture adjustment.The key to getting equal air/fuel idle mixtures between all 4 carbs is to: Start the adjustment with all 4 needles in the exact same position. You do this with your thumb nail.When your carbs are off, screw IN the idle mixture screws until the tip pokes into the throat. Now take your thumb nail and feel the protruding tip, now with your other hand turn out the mixture screw until the point where your thumb nail slides off the tip of the mixture screw. *stop* Do all 4 carbs like this....Now all 4 carbs will have the air/fuel mixture screw at the exact same starting position. I have found about 1.0 to 1.5 turns OUT from this position is a good starting point for final tune. To demonstrate my point about the uneven threads, after setting all 4 screws with your thumbnail, they are all even....now turn IN the screws and count the number of turns in until they are "lightly seated".I'll bet you a jelly donut you will get slightly different counts between the carbs. You can write down these differences in your log book, and/or mark them with a felt pen on the caps of the carbs.From the thumbnail test point all carbs are even: If one carb's mixture screw goes IN one full turn until lightly seated that carb is marked 0If one carb's mixture screw goes IN only 3/4 turn....that carb is marked -1/4If one carb's mixture screw goes IN 1 1/4 turns until lightly seated.....that carb is marked +1/4This is just for future reference, down the road, in case you get the number of turns mixed up and have to go back to the starting point with all the needles at the "lightly seated" position, you have the needle position differences recorded. While the carbs are off, use your thumbnail and set those air/fuel idle mixture screws exactly the same between all 4 carbs...as a starting point for fine idle mixture tuning. Thank you Randy.Pat