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-1982 cb750F-
alright here this goes, thanks for help in advance.
I cleaned my carbs. about 3 weeks ago now, and the problems since have just kept coming. as reference; i have quadruple checked i put them back together right (im up to like 6 times of pulling them off now in 3 weeks), and i have brand spanking new gaskets on there, as well as new float needles, also i checked to make sure all my floats float (they do), i have even acquired carburetor chemical dip to dunk my parts in aside from carb. cleaner spray and my q-tips, i just changed the oil 2 days ago, as well as changed all my spark plugs and did a compression check (all great), and i've become exceedingly good at getting a tight seal on all my boots to ensure vacuum, i just put some "engine oil stop leak w/seal conditioner" in for preventive maintenance, and blasted the engine with heavy duty engine cleaner to check for any leaks (none) ok...
1. I cannot get gas to stop profusely flowing out of the carbs. (from the bleed off valves for starters) i do the little hit it with a screw driver technique, and this usually works after some really good whacks, but as soon as i stop riding or sometimes sooner its right back to it; i can't imagine this is normal.
2. when not leaking out of the bleeder valves, they seems to spew gas from somewhere above the bowls on the engine side. i realize this cannot be good at all, but having looked at every square inch of my carbs i have no idea where its coming from (it usually drips off my idle adjust screws)
3. i bought a set of vacuum gauges to work on a friends bike, so i thought i would give it a whirl tuning mine more accurately this time around and turned everything back to factory suggested settings to start from scratch. this is probably one of the better investments I've ever made, and getting everything mellowed out and the same (all four carbs vacuum reading) isn't so bad. problem is, i don't know what the "normal" vacuum reading is suppose to be, my gauges read in "CmHg" and when i got everything to be the same they all read around 05. this is pretty low on the gauge since it goes to 75 but that's what they were all reading the same and sounded good at..... Well i am pretty sure this is not accurate, because i have basically no power in gear now, although it sounds equalized and like it should run great and in neutral you can barely twist the throttle and it jumps in rpm, i can barely get up to 55mph and it bogs out going up hill...
4. i have noticed this for awhile but kind of forgot about it since it never seemed to be an issue. there is a black box mounted up under my battery box that has a black tube that goes nowhere on one side and a clear one that goes nowhere on the other. in the manual (in all its blurry picture goodness) the only thing i could find was a so called "crankcase breather box" either way i have no idea what it is or how to reconnect it. ideas?
5. i know i laid a bunch on you guys in one post, but this has seriously got me bummed, and its the middle of summer and most of my vacation that i took this week is over and i couldn't ride through any of this beautiful weather. If you all can help i'd really appreciate it. Thanks.
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Hi Tangent, Re point 3: It doesn't matter what the vacuum reading is, as long as they are the same. In fact some people just use four u-tubes with liquid in them, and adjust the carbies to get the same height in each tube. You don't have to get an actual vacuum reading.
Re point 4: Two black hoses come up to the front of the air cleaner box to draw off crankcase fumes which are then drawn into the engine. Any moisture goes through the top of the air box and exits via a nipple at the top facing the battery. It goes down a plastic tube to a small tank under the battery. A drain hose off the tank is plugged at the end, but must be removed occasionally, to drain the moisture.
Sorry I can't help with your other queries. Cheers, Rod
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Item #1. Just cleaned my carbs with the same result. Two possiblilties are that something from the tank got through and clogged the shut off needle in the bowl or, as was the case with mine, the small pin that the float swivels on is tarnished and is holding the float open. Take them back apart (again, sucks I know) and take some fine emory paper and polish the float pin. I also put an inline fuel filter in my gas line as the old petcock filter sucks. Good luck.
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Rod, thanks I've got atleast half of that equation set up, ill be reconnecting that box now, I'm sure it benefits the bike in some way.
And WV, do you mean the pins the floats swivel on or the float needles? The pins they swivel on could be a coulprit as they havent been the easiest things to get out either, so that is a possibility. I have an in-line fuel filter, but recently read how important it is that they stay vertical to do their job, and ill admit mine was well not.
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The carbs spewing gas is eather something getting stuck in the needle and seat. the floats push the needle into the seat. If the seating serfaces are not clean or if your Needles have a groove warn into them they will leak. Replacing them with new on allot of the old bikes is needed since they had a rubber tip and it wears a groove in it.
Dont worry about the numbers on that gauge you want them to all match as close as you can get at the 1000 + - 100 rpm.
Your floats need to move easily on the pins you can chack to see if the seats are working this way.
After inspecting or atempted fix.
Put a container to catch gas under the carbs.
Take off one of the bowls.
turn on the gas and once it is flowing out the bottom carefuly push the float up. It should stop pooring gas before you feel like you pushing against the needle. It takes very little pressure to do this. the little plunger on the needle will not be all the way compressed when the gas is shut off.
If you have the brass needles I have heard of people lapping them in allot like valves. I have done this with colgate tooth paste ans a peace of vacuume line. It worked on my SL350. I have not tried it wirh the rubber tiped ones though.
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I was talking about the pins that the float swivels on. Mine were horrible and hard to remove. I polished them with emory paper and it fixed the problem.
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Administrator
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Well the float needles could be worn or the seats could be dirty. Pull the float needles out and check the tips. If they are worn, then they should be replaced. If they are the ones with metal tips, get ones with rubber tips. Also, clean the needle seats.
#2 is probably caused by the fuel level getting too high but I have not seen these carbs so cant be sure.
The ride IS the adventure. The destination is just to get gas!
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the float needles are new, and i've checked for premature corrosion when i last took them off, it could be the seats i suppose, but i suspect that WV is probably spot on with the pins restricting the movement of the floats. I'm going to try the remove the bowl and push the float up thing tomorrow so i'll see for sure; I'm sure your right about #2 though Re-run, it is probably just seeping out where ever it can because they are so full.
Thanks again for the help guys, i'll let you know how it goes after tomorrow.
The float needles are the rubber tipped ones btw.
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well no good news.
i spent some time dipping & cleaning parts of my carbs. again, I also shaved down the pins with my dremel until those things could slide in and out with absolutely no issues at all. I put all back together and reinstalled.
started it up and... leaked immediately. no change at all.
here are the float needles i have on, i bought them sometime in the spring from z1,
http://www.z1enterprises.com/detail.aspx?ID=1964i only rode a couple of times before having this problem, but it rode fine. also the tips of the floats don't seem to have corroded or anything, at least to my eye.
here is a video of the leak when i turn on the gas. (the video is on my photobucket, but doesn't want to play on there atleast for me, but you can download it from there and play it just fine)
http://s18.photobucket.com/albums/b133/gekusei/?action=view¤t=MOV01679.mp4i really don't know where to go from here, on the bench i hooked up fuel with the bowls removed and could push the float up to stop the fuel just fine. I have no idea why its not stopping on its own.
any suggestions will be more help than anything rocking around in my noggin.
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OMG that is a BAD leak..........
If you pull the bowl off does it stop the gas from flowing?
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yeah tell me about it, this is really killing my riding season.
keep in mind that the gaskets and float needles are new too.
you mean if i were to simply remove the bowl while the gas is on does the fuel stop? it shouldn't should it??
i've never tried removing the bowl while installed to test pushing the float up, but i did it on the bench and it stopped fine.
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No
Pull the bowl off turn on the gas and then push the float up and see if the gas stops
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i'll do it while on the bike to see, but i'm not sure what factor could be in place now than with the same test while off the bike. maybe the gas pressure or something? (shot in the freakin dark)
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By pushing up gently on the float it should shut the fuel off. If it does not then the seat valves are not working.
That is the only port that gas should be comming from too.
If it does shut off the flow then check the distance from the float bottom to the carb body. make sure it is set correctly.
Make sure the floats do not have gas in them.
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i understand that, i did that test with them off, but i can see why to do it with them on the bike.
i have msn messenger, exodus-2007@mail.com
unfortunately i do not have a screw driver small enough to get between the starter and the carbs, so i can't remove the last screw without removing them first to get the bowl off, i'm also out of time tonight to wrestle with it. perhaps in the morning, but for now life beckons.
i have plastic floats thought, and i have never understood how the float level is adjusted with them, any insight incase that is the issue?
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I do it both on and off the bike. Off the bike i set the floats to the specs in the book. Then when I put them on the bike I make sure they actualy do stop the flow. If your floats have a small metal tab whear the needle sits you can gently bend it to adjust the float level.
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My roommate has a xs650 and his floats have the metal tab so I've understood how to adjust those, but mine have no metal piece. The whole float is plastic, including where the needle sits.
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If you need and only if it is out of wack you can lightly bend them some to adjust them.
what is the distance from the carb body to the bottom of the float when it just closes the valve but not push in the little plunger? It is discribed in the manual what measurement I am looking for. I think it is 15 or 17 MM.
It is in your book if you need a book we have a PDF of it here on the forum.
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The needles you replaced? did they have the rubber tip? Some did not. Some have a little clip that holds them to the float and some snapped into a clip built into the float.
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The 1982 CB750F has all plastic non-adjustable floats (as described in the workshop manual downloadable from this site). The floats have to be replaced if the 15mm setting is incorrect. When checking, don't compress the spring loaded pin in the end of the float needle.
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