Wont stop leaking gas!!!!!!!!!!!

83 midnight maxim 750... Ive cleaned the carbs 5 times. had the carbs on/off 10 times. The bike will start and run and idle. it actually runs pretty well untill it floods out from overflowing carb/carbs. fills up the airbox and leaks out the boot. and of coarse ive had to change the oil 5 times in 20 miles. Ive put in new needle and seats. that made no difference. I have not synched the carbs due to yics tool. I have hooked up a vacuum guage and they were all good. i have the mixture screws about 3 turns out. Ive adjusted the float levels to 17.5mm from bottoms of floats to gasket mating surface where bowl attaches. (no gasket) I have tried 10 different ways to set the floats just to try to stop the problem. They are at 17.5mm now. im not sure im doing it right. anyway..........my petcock lets out fuel all the time on ON. not free flow but dribbles. I bought a rebuild kit for it but not all the parts were right. so at least it dont leak externally anymore. if you turn to PRI it will drain the tank right out my carbs. I have the tank clean using evapo rust. i have a inline filter(clear and clean). Bike idles okay till the damn thing floods. its worse the more fuel is in the tank. bitch of it is when i use a remote bottle on the bench while off the bike it dont seem to leak. so i think i have it fixed. then start, ride, stop, leak, flood, die, waste money on garage floor. what else can do this other than needles and seats? I had a set of mikuni carbs once overflow all the time. it was caused by plugged vent tubes. but these carbs are different and i dont see a vent. Anyone live in illinois that knows these machines? I need to sell the bike but have to fix it first to get what its worth.

 

you have a problem with your float height ... do a search for the clear tube method

 

You have to still have sticking needle valves or your floats are hanging/sticking. Check you floats for easy movement, make sure you have them it right side up. Search on dressing the needle valves and seats - been covered a few times - good practice to dress the surfaces a bit.

Look at the dry float height setting post - a lot of good pics (and a couple of fuzzy ones I put there )

Also a good idea to verify you float heights with the tube as mentioned

 

I read through the posts on float hieght and seat dressing again. Im almost positive im doing it right. I didnt dress the seats but they are brand new. Although its good advice, it didnt seem to fix his problem, and i believe its the same deal. Ill have to pull them again and do the tube test to be certain i guess. what else could it be besides float adj or needle valves not closing. a fully seated needle valve should be able to handle the pressure of a full gas tank even if you left it on PRI all day. Is there a vent on these carbs? when i adjusted the floats, i set them to 17.5mm dry. then even going further, i made sure they were the same hieght when pressed down to close valve. i even made sure they were the same hanging hieght when holding the carb set right side up. they are all the same. ill check again though. why not try to hit the twenty mark for carb removal and install.

 

I'm pullin mine again this weekend, #2 and #3 keep sticking!!! They will be fine for days then Gas on the floor!!!!

 

did you put in aftermarket needle and seats too?

 

yes they are brand new, i have not dressed them with sand paper but i did use the golf tee trick, on my older honda 3 &4 wheelers the seats always had a small bur on the seat hole, a golf tee would knock the bur off. I need to change my oil again. i have never had this much trouble with needles before!!!! I shoulod have left the old ones in, they did not leak!!!

 

mine didnt seem to leak either. well at least not this much. i can drain my tank on the floor and in the oil if i turn the petcock to prime. what did you set the floats at and how? we have the same problem. ive been trying to fix it fo 6 weeks now. maybe we should have sprung for the oem needles and seats????

 

When dry and filling they can tend to stick. snayke62 everything you said is spot on so I would be looking to be sure my floats swing free.

Try this when you have them off and empty of gas. Turn them upside down and blow into the fuel line - you should be able to tell if they are sealing. As you know something obviously has to be catching or not sealing or you wouldn't have your issues.

There is no vent tube as found on some carbs.

 

thanks bill. I was waiting for the vent answer. Well i guess ill grab a beer, and a philleps screwdriver and take them devils off again. ill take a damn picture this time of them and the adjustments. you would think with the rubber tip needles they would seal very easily. but like to say, it must be getting hung up somwheres. i can remove, teardown, re-assemble and install these things in 30 miutes. give or take 2-6 beers........LOL.

 

You seem pretty knowledgeable but did you put the floats in upside down?
On the hitachi's it is easy to do... I did it. That's not saying much tho haha.

Definitely set the floats via clear tube for sure.

 

Have you checked that the fuel tap (petcock) is not leaking through the vaccum line? This will send fuel straight into #2 inlet port and drain back out through the carbs into the airbox / crankcase.

Worth checking out as it seems you've done all the work you should do on the carbs (and you said the problem didn't happen with a remote tank).

Good luck with it.

 

For what its worth I had the same thing going on with the last set of carbs I did. Drove me crazy. Could not get them to seal no matter where I set the floats. Ended up putting a very tin washer on either side of the floats to shim them into the center of the float pin. Also reset the tang that is used as a open stop so that they could not drop to far down and hang up. Set it so the fuel will flow freely but doesn't let the floats drop to the point the needle cocks in the seat. That took care of the "have to tap it with a screw driver on the first fill issue" and my leak problem. I always test them on the bench before I install them on the engine. Level them out and let them sit with fuel on them for a while. Cuts down on the wasted fuel and time.

 

Excellent Idea - this is a good thing to check before you pull them again!

 

You could spend five bucks and get a lawnmower fuel cut-off.
It won't exactly fix your problem, but will keep you from dumping gas in your oil, or making a big mess on your garage floor while you find the real problem.

Your real problem could be the aftermarket needle and seats.
The float pivot pin AND the inside of the rolled metal of the float need to be polished with ultra fine paper.

 

had the same problem someone told me the floats on my 1985 could become soaked in gas after 2hours or 2 days and let the gas leak out.

 

If they had a hole in them that could be true.

 

wingnut325 good tip, i will check how for they go down. I'll try the washer trick too.

 

Aren't these floats some kind of solid, closed cell plastic foam??
Not hollow?
Chacal !!

 

new find!!! my after market petcock is leaking!!!! I have the carbs off and i'm cleaning, boiling in purple power, then rinse in pine sol!! They are going to be Clean!!!

 

Thats a problem but an unrelated one to the fuel leaking out of your carbs. The floats must stop the fuel flow at the proper level or the bike will run super rich all the time. If the needle valves stop the fuel flow like they should you can have no petcocks and it will not matter. Petcocks are not fuel regulating devices they are just shutoff valves for when the engine is not running. Fix the float level problem first. Then you can still ride while you straighten the petcock issue out.

 

Well. i didnt get a chance to work on it further but read your advice. Im sure the floats are in right. the stopper tang that stops the float from hanging down too far are on the left with the perches towards your body when holding upside down. just like the photo in one of the threads. Ill double check though. I have checked the vacuum hose on the petcock-its dry. as far as the floats hanging too low---what kind of measurement am i looking at? but-its not an anitial fill problem. i had it together last time and they held fuel. the bike ran good. it sat in garage for a week and didnt leak a drop. fired up first push of the button every time and idled. it wasnt until i drove it around and to the gas station and filled up that it started to leak again. i had to take off the fuel line at the filter and kink it closed to make it stop. i am pretty sure there is some pretty good end play between the float brackets and perches. ill shim them centered. I am leaning toward crappy aftermarket parts. but maybe this time around i can get them to work. Ive dabbled with snowmobiles, motorcyles,and quads since i was 12 years old. not saying im an expert but i know the basics. ive never ever had such a hard time with a set of carbs.

 

Yes there are! The HSC32 Hitachi carbs vent the bowls back thru the "air compensator jets" into the airbox boots....that's why overflowing bowls will drain back into the airbox. The later HSC33 Hitachi carbs (700 air-cooled models) use seperate overflow tubes in-between each set of carbs.

The Hitachi's are a closed, solid float. Haven't ever sacrificied a set of Mikuni floats yet, but I would assume that they are similar. NOTE: carb dip solution will eat the floats!

Do NOT set the floats in this manner! Float "height" is a nebulous term since the end points aren't properly defined. Only AFTER setting one carb correctly, via the clear-tube gauge method, can you use that carb's measured "float height" as a basis for preliminary setting of the other carbs (assuming all of the other carbs are equipped with the same type needle and seats)......and again, this "float height" is a PRELIMINARY setting, you still need to measure the fuel levels via the clear-tube gauge method (and adjust as needed) these other three carbs; each one may end up requiring a slightly different float setting to get the desired results:



Float HEIGHT sets the Fuel LEVEL:

- When it comes time to Set the Float Height and thus the Fuel Level within the carb bowls, our advice is to get all the proper tools and fixtures ready, and then bribe someone who knows how to do it to come over and let them do this task for you!

It's not rocket science, but it sure can be a messy, pain-in-the-butt, trial-and-error procedure.......especially if this is going to be your first fuel-level rodeo.


If that's not possible, then read the manual and proceed accordingly. But please take the time to set the fuel levels correctly, not just by the float height measurements, but via the fuel level "sight tube gauge" method-----as the proper fuel level in the bowls is a critical issue in whether the carbs perform properly or not. NOTE that the "float height" measurement is just a "shortcut" method used to try to acquire the correct "fuel level" measurement, as it is the fuel level measurement and specification that must be met in order to insure that the carbs perform properly:

* Fuel levels that are too low results in a lean mixture.
* Fuel levels that are too high results in a rich mixture.


In order to achieve the proper fuel level.....as measured by the "clear tube method" outlined in the service manuals......there obviously will be some particular "float height" that will achieve that FUEL LEVEL. But that actual float height can vary between various carbs due to a number of factors; for example, in the case of the Hitachi carbs, it also depends on which set of float valves and needles were originally installed by Hitachi (we've seen three different types in original carbs) AND which replacement style of needles and seats that you purchased. The factory specified "float height" is for an original carb, using the original float needle seats and valves, which may no longer be available for your bike.



The float height determines what the fuel level within the bowl will be (since the float height determines when the float valve needle assembly "cuts off" fuel flow from the gas tank into the carb bowl), and thus an adjustment to the float height is how you adjust the fuel level. The float height is adjusted by very small amounts of bending the float TANG ARM on the float supporting structure. This tang is the central metal "arm" that contacts and supports----via the little float needle clip - hook (on most models)----the float needle itself. You would bend this tang down (away from the needle) to raise the float height (and thus raise the fuel level in the bowl), or you would bend this tang upward (towards the needle) to lower float height (and this will lower the fuel level in the bowl).


Please note that although you typically are messing around with the float height and adjusting that tang WHILE THE CARBS ARE UPSIDE DOWN----so you can easily access the floats----the descriptive actions such as "downward" and "upward" that you may read about in various manuals are describing such directional movements in relation to the normal orientation of the carbs as on the bike! THIS CAN BE INCREDIBLY CONFUSING WHEN YOU FIRST START PERFORMING THIS ADJUSTMENT PROCESS!!!


Also note that the fuel level check (with the sight tube gauge) must be done with the carbs oriented in the same manner as if they were installed on the bike, meaning perfectly level from side-to-side (you'll want to use a bubble-glass level to make sure they are perfectly level) and completely "vertical". NOTE: the "vertical" orientation confuses some people, as the carbs, when installed on the bike, are actually tilted a bit forward from true vertical in the normal riding position. However, when checking the fuel level with the sight tube gauge, the carbs should be in both a horizontally and vertically level orientation.



Here are some other useful hints, culled from the factory service manual, regarding how to prepare yourself for the correct check of the float height measurement:

- Hold the carb in an upside down position.
- Incline the carb at 60-70-degrees so that the end of the float valve does not hang down as a result of the float weight.
- Measure the distance from the mating surface of the chamber without the gasket in place, to the top of the float.
- NOTE: the float should be just resting on, but not depressing, the spring loaded inlet needle.


Well, okay! Now, although you may not have noticed it immediately, there is a very important and very cryptic passage in the above set of instructions, which is this:

"Measure the distance from the mating surface of the chamber without the gasket in place, to the top of the float."


The "mating surface" is, of course, the bottom of the carb body (where the float bowl gasket would be located) but without the gasket in place.......check. But the next part......the "to the top of the float" bit......well, that's a bit more mysterious, because:

a) of course, as it with the "direction warning" issued earlier, the "top of" the floats, when viewed with the carbs being upside down in your hands (which is the only way to perform such measurements), is actually the physical bottom of the floats!

Told you this would get interesting.......

But that little detail aside, now we have to explore the more challenging part of that statement, which is "what and where, exactly, is the "top" of this bottom of the float?"

This simple question is, unfortunately:

a) ]not[/b] so easy to answer, and.....

b) varies by which carb model you are holding, upside down, in your hands and trying to measure..........



For some models, the information as to exactly WHERE to perform this measurement at the float is either not known, or incredibly confusing.....and the factory service manuals are not much of a help in this regard, what with their tiny, grainy images. It seems as though Yamaha wanted people to focus on the fuel level setting (of course, as that is the end result you're actually shooting for), and figured it wasn't worth the trouble or effort to go over the float-height-measurement procedures necessary to achieve that--------rather, they tell you what fuel level measurement to acquire, and then tell you to just "bend that tang arm" and re-measure the fuel level and just keep going back-and-forth until you get it right! And then do that messy, smelly, spill-gas-all-over-yourself with this trial-and-error procedure three more times.........



Three Blind Carbs: See How It's Done:

Because of all the considerations mentioned previously, and due to the importance of getting this job done once, and done correctly, the procedure that we suggest you follow is to work on achieving the proper FUEL LEVEL in any one carb.......so, install the needle and seat, install the float, fill the bowl with fuel, and measure the fuel level (although the factory gives a rather wide range of acceptable fuel level limits, such as 3mm +/- 1mm----in other words, anywhere from 2mm to 4mm----we feel that you should always strive to get that fuel level right in the center of the range (in the above example, right at 3mm).

You'll do this by very slight bending of that central float tang arm (the one that the needle clip fits over) until you get the measured fuel level (drain and measure a couple of times, to be sure!) that it's correct.


Now, since you know that this one carb fuel level is correct, and if you're using the same float seats and needles in all the other carbs, then simply measure the "float height" of this now known good carb.....and, you can "measure" that height in any way and at any point that you desire, preferably whatever measurement is the most consistent to perform and the easiest to see.......and then that becomes your "float height" for all of the other carbs, too. Just adjust the other float tang arms to achieve that same unique "float height", and you're done!

BUT, I would still fill and measure each individual carb and check the fuel level, just to be sure, before you install them on the bike!


The above may seem like a more time-consuming and "tedious" way of doing things, but it is the only way that we know of to make CERTAIN that your fuel levels are correct........rather than having a "correct" float height.......and as we stated earlier, it is the fuel level that is the end result that you're seeking, not any particular float height (except for the necessary float height needed to get to that proper fuel level, of course!).


The proper FUEL LEVEL is a vastly over-looked, but vitally important part of having your carbs perform properly, as improper fuel levels WILL result in either lean or rich fuel mixtures, and will most likely tempt you to try to "compensate" for such a situation by other, NON-NECESSARY and perhaps COUNTER-PRODUCTIVE changes in other circuits or carb settings, which may affect and degrade other areas of the engine performance. IT IS ALWAYS BEST TO ADDRESS AND SOLVE THE "ROOT" PROBLEMS (or, to put it another way, to FOLLOW PROPER PROCEDURES AND ACHIEVE PROPER SETTINGS) in all of the basic areas.

This method will allow you to actually save time, money, effort, and achieve more accurate, consistent, and reliable results!





Fuel Level Cheat Sheet:


Hitachi all HSC32 series models:

-Fuel level measured via the clear-tube gauge: 3mm +/- 1mm (.12 +/- .04 inches)

 

I did notice one thing that may or may not be pertinent. When using the aftermarket valve needles that are 1 mm longer than stock the tang is much closer to the fulcrum point when the levels are correct. I think this effects the gain on the adjustment meaning a little goes a long way. One way to counteract this is to use the thinner fiber seat gaskets which has the effect of lowering the seat. If you use the copper thick crush gaskets it compounds the longer needle issue and maybe affecting the amount of closure force being applied to the needle during normal static conditions. Just throwing some stuff against the wall so to speak and would like to hear your thoughts.

 

I can see your logic in the longer needles affecting closing pressure. chacal, i understand your post but have only one question----float level via clear tube method spec is 3mm +/- 1mm. at what reference point to compare to- i see somewhere here that it was to the bowl mating surface-is this correct?

 

Check the seats are a real snug fit in the carb bodies. maybe fuel is getting past one of the seats. It happened to me. There is an O-ring lubricant on the market that will SLIGHTLY swell the orings and provide a better seal in this area. These leaks can be a mother%$#*(& to find. You will learn a lot about carbs and fuel systems. Let us know what solves the problem.

 

The reference point for the clear-tube gauge is the bottom of the carb body itself....where the top edge of the bowl "disappears" up into the carb body.

 

I didn't say they weren't vented but that there were no external or dedicated vent tubes. As you point out the vent is actually an air jet not a separate vent. Of course your answer was way more complete than mine

Original question...

Interesting about the floats they are so light it is hard to tell. I have had issues with hollow floats in the past, not fun to find sometimes.

 

okay boys.....i been messing with these carbs for ten hours now. i tried the shim the floats endplay idea. i have polished the seats. i even found a float that was bent and bottoming out. i made damn sure the screen/ o-ring was in and seated correctly when installing the seats. i polished the float axle and inside the float axle housing. the washer that seals the seats are good. every time i connect the carb set to remote tank they leak. i have the clear tubes attached and can watch the fuel migrate to the air jets and out. it is an intermittant issue. one time 1 & 2 will overflow, other times 1 &4, other times 3&1, you get my point. The data has no pattern. i found that a slight tap will make them close. I was able to set the levels indevidually if i tapped constanly until the fuel level equalled out. After i set them and verified good a second time while tapping, i drained and let them fill up without tapping. overflow again. cant say which carb # because its irratic data. If i tap its okay. The seats are NOT leaking betwen the washer because a tap wouldnt fix that. My floats all float good in water. The geometry of the needle valve and float adjustment tang seems good-90 degrees angle when fully closed manually. Ive tried setting all carbs extremely lean with the same results. I went so lean that at one point i had all float valves adjusted closed-no fuel would flow through at all. I left each bowl off whlie i adjustd each one totally seperate flom the rest. My only concern was achieving the correct level using the clear tubes as a reference. I believe ive taken every step in order to safely say i need to get oem needle valves and seats. or at least a set that will that close. I can say that the reason i got new needle valves and seats in the first place was because i opened the carbs to find one needle different than the rest. the diffenrt needle valve would not seat and overflow that carb. the new needle valves i purchased were identical to the different needle that origanally leaked. oh yeah-if i hold the carb set upside down and blow through the inlet hose- the seats stay closed.all i can say is there is a problem with the needle valve sealing in the seats. i cant set the float levels right if tha bastard float valves wont close. jesus. I know where there is another 750 maxim------------think ill have to do a midnight carb swap and play stupid when they ask me whats wrong with their bike. haha not sure what else i can do.

 

It is the float valves, they are such a simple mechanism, almost primitive.
You have got compatable needles & seats? If you hold the float up manualy does it stop the flow? sometiimes this will happen, the lift the float gets from the fuel is not quite enough pressure.
I have had this, like you say you can get them to shut off by tapping the fuel bowl, what I found is the vibration when the engine is running is the same as tapping the bowl & you don't get the problem you have on the bench.

 

Agreed wizard.............before i read this post i said piss on it and installed the carbs after adjusted. The bike runs like a raped ape. its raining here and i had a hard time keeping the rear whell in traction. I only put 2 miles on it. i ve started it several tiimes in the garage. every time fires and idles. no leaks. i leave the airbox drain tube and the crackcase tube disconnected so the gas will go on the groung and not in the oiol. also i can tell right away if the carbs overflow. ive thought ive fixed the problem before only to be disapointed. it will run good for a while then all of a suddon--------leak. i will say that it is running better than before....as of now.

 

I hope yall can see the previous post okay.

 

Sounds like you have it fixed. Just keep an eye on the oil level. If it starts to go up in the window after a couple of rides check the oil for fuel contamination.

 

Well sounds like progress - hopefully you have it cured....

 

I dont know if it made a difference or not, but what i did to dress the float valve seats was take a small, appropriate sized drill bit and twist it by hand into the seats. not to hard but enough to shine up and make the beveled area more noticeable as you look at it. If it leaks again ill have no choice but to buy different float valves. as i mentioned before i did shim the float end play with little tiny washers. this seemed to have no affect and after about to 40th time of assembling and disassembling i got tired of putting them in.

 

Update-----------I took the bike for about 10 miles. Longest trip so far since ive had it. Started and idles good. Runs good, has lots of power. Im actually suprised on the power. I think it needs about two more gears though. Anyway, no flooding yet. The true test will be when i fill the tank with fuel. This bike seems like a nice one. I want to keep it but finances are low. If it dont leak again i will re-paint the engine black. I think ill ask $1200 if it all goes good. Yall think thats reasonable?