i've been searching and searching and no one has a clear answer other then the 3mm fuel level setting. which is a complete waste of time in setting the carbs. that might tell y ou what the fuel level is. which is all fine and dandy, but i don't want to be taking the bowls off OVER AND OVER before i finally acheive that magical fuel level.

IN THE OLD DAYS. THERE WAS ALWAYS A FLOAT SETTING. THIS FUEL LEVEL THING DIDN'T EXIST UNTILL NOW.

so, can anyone give me an answer as to what the float height should be. that's with the carbs upside down. checking the floats at the base of the carb WITHOUT the gasket.

dealer says 18mm WITH the gasket. but your lucky if the bike runs as there won't be enough fuel in the bowl. i've tried 16 as suggested by another post not on this sight. then i've also tried 14.

the local repair shop says he always adjusts the floats level with the base. which takes the floats to about 8 or 9. everytime i go with the level base height i overflow.


IS THERE ANYONE OUT THERE THAT CAN GIVE ME AN EXACT ANSWER SO I CAN GET MY CARBS SET. instead of screwing around trying different things. . it would be greatly appreciated.

The correct "float height" is whatever float height results in the proper fuel level in the bowls.........no two ways around it.

The proper fuel level is actually published in every Yamaha service manual for these bikes, ever since the beginning of time for these bikes. The float height necessary to achieve such fuel level was published in a few early editions of the service manuals, and then dropped, and probably for good reasons (it leads to errors).

The fuel level in the bowl is the actual "goal" you are shooting for. For example, there are no less than three (3)---and probably more---versions of the Hitachi float valve seats and needles available (made by different OEM manufacturers). These needles differ in overall heights, as do the depth of the float valve bores where the needle fits. I will guarantee you that using float valve style "A" will result in a different fuel level in the bowl than when using float valve style "B" if they are both set at the same "float height".

And that's probably why Yamaha stopped publishing "float heights", because they or their carb suppliers were using different types of float valve components as time went on, and thus while the required fuel level never changes (for a given type of carb/engine combo), the float height needed to achieve such a fuel level did change as different components were installed.........

i hear what your saying. but i'm old fashioned and i need a float height. i don't want to screw around with sticking some type of tube in the drain hole. filling it up. then have to drain it. disassemble the carbs. make the adjustment. reassemble and check again. that's A LOT OF WORK.

i want to adjust the float and be done. just like i've been doing for 25 years. the float height specs ALWAYS worked for me. cuz right now. i'm screwing around with things i shouldn't have to be screwing around with if i had the damn specs to begin with. i've taken the carbs apart 10 times now to follow up on everyone's suggestion. and the only thing i can't find is the float height.

maybe if someone has the book that was published back in 1984 where it still had a float height.

the dealer says 18 with the gasket. someone on the internet says 16. the repair shop says level with the base. who's right and who's wrong.

I understand that the proper float height is 17.5 mm, however I am always confused as to where the point of measurement is taken. I have been using the float at the highest point measured with a caliper to the "deck" of the carb body. Of course the carb is upside down. This has worked to get the bike started.

Snowwy, I would recommend that you set one carb to the proper fuel level (via tinkering, draining, etc.) and then measure the float height on that carb, once it's achieving the proper fuel level.

Then you can use that known "good" float height as a basis for setting the other three carbs, using whatever measuring points you used on that first carb.

Then, of course, check the other three to make sure that their fuel levels are okay.


That's about the easiest "shortcut" there is to achieving the proper fuel levels!

Here is the link I was looking for earlier :

xjbikes.com/Forums/vie...eight.html

It's sounds like the tab bending is what's really getting you confused. Try this. Do your clear tube measurement. Note how far one way or the other you are from spec.

Take the float bowl off. Measure from the middle of the float (I think the middle would result in 1-to-1 ratio of wet to dry float height difference) to the to what ever reference point you want on the carb body...like gasket surface. Then take the float off, bend the tang, put the float back on, and compare the difference to your previously measured float height. You want to make the difference equal to the amount you were off with your clear tube measurement.

Then put the bowl back on and find your clear tube measurement. Use gas...not some other fluid. All but one of mine worked with the 17.5mm setting from the gasket surface...but like chacal said...that's not good enough. Remember to keep oriented which way is up or down when you are going from the clear tube spec difference to your dry height difference.

Also, you could try getting one float "right" wet, then measure the float height dry and make the others match. Still double check using the clear tube method...of course!

junkmn wrote:

I understand that the proper float height is 17.5 mm, however I am always confused as to where the point of measurement is taken. I have been using the float at the highest point measured with a caliper to the "deck" of the carb body. Of course the carb is upside down. This has worked to get the bike started.

That height is for the HSC32 (Hitachi) carburetors used on the XJ650 and XJ750. I am the peddler of that value and I obtained it from the "Service Data" section of the old Yamaha fiche which seems to no longer be available.

Since it was just a number in a table there was no information on how to measure it. I've always measured to the bottom of the float at along the plane of the jet needle. I've never had to pull one off and redo it using that method.

You need to make sure that the weight of the floats does not depress the spring plunger in the needle or the measurement will be off. You can achieve that by holding the carburetor bodies at an angle rather than straight up and down.

All the manufacturers went from float levels to fuel heights in the early 80s (so it's not really a new thing). This is about the same time they started capping the mixture screws on street motorcycles. I think prior to that they let motorcycles run a bit rich so precision wasn't an issue. When emissions regulations started to catch them they had to get the mixture on the knife edge where the engine would run well without polluting too much - requiring much more precise measurements.

snowwy66 - you did not include your motorcycle model in your question. If you don't have HSC32 carburetors this information is useless to you. Perhaps you should add motorcycle specifics to your signature.

i don't kow what the carbs are. whatever the book says. they are stock carbs is all i know. 81 xj650

17.5 mm is a bit lean. the dealer says 18 with the gasket and the bike wouldn't run. i went 16 from the base WITHOUT the gasket. that's 15 WITH the gasket. measure at the highest point on BOTH floats. i measure all 8 floats. not just 4. becuase they might get bent OR the tang might not be straight. so one float measures different then the other float.


i lift the float off the needle and tweak the tang with a screwdriver on both sides. then i grab needle nose pliers. and gently grab the little clip on the needle and lift the float and release the pliers. then i measure both floats.

being a retired car mechanic. that is how it's done adjusting the floats on car carburetors. when cars used to have carbs.

anyways, i had a clear tube i was able to screw into the drain hole enough to check fuel level without leakage. looks like i'm about 4mm from the base. so 15 - 16mm is the float height. measured at the base without the gasket to the highest point on the float.

EDIT: I'LL BE A MONKEYS BUTT. i just looked at the manual and just NOW noticed the float setting at 17.5mm +/- .05mm. doesn't say anything about the gasket though.

I used 17.5 to start, but that was a bit low. Went to 17mm float height and got exactly 3mm fuel height.

Quote::

anyways, i had a clear tube i was able to screw into the drain hole enough to check fuel level without leakage.

Ther should be a cast fuel "nipple" on each carb bowl that you insert the clear fuel tube over.....that nipple is where the fuel flows when the drain screw is loosened (you would loosen the drain screw for performing a fuel level check, or just for draining the bowls for winter storage purposes, etc.)

only fuel i get coming out is the drain screw. i never paid attention to that nipple when i had the bowls off. but i'm looking at some pics so i see what your talking about. it might even be plugged for all i know

anyways. i've got 9500 rpm revs now at stand still. 8000 was my max before. wasn't seeing any black smoke on the max revs either. all 8 floats are now set between 17.5 and 18. so we'll take her out and see what she does another day when it's not raining.

don't see my problem being fixed though. but hopefully now i won't have to deal with the carbs anymore.

snowwy66 wrote:

but hopefully now i won't have to deal with the carbs anymore.

HAHAHA...those are famous last words if I ever saw 'em...Your intake and exhaust are bone stock right?

Good to hear you are doing better.

exhaust is stock. the intake is oem replacement. shouldnt' have to take the carbs apart anymore now that i have everything in check. but who knows. once it's ridden. LOL.

sorry, im still confused! Am I supposed to measure like this? If so, my float level was way off! This is with the gasket off