I want to talk float heights

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radare
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Fri Jun 27, 2014 9:54 am

The stock manual, the Haynes manual and even the Chiltons manual all recommend a float height of 6.2 to 8.2mm dry (on bench).

When i set my float heights to this level, they really only can move upward 1/16 to 1/8 of an inch before they hit the body of the carbs. Seems to me that setting them here can't be right.

So I have to ask. Has anyone seen a spec for dry float heights that vary from the common 6.2 to 8.2mm?

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Nelsonmd
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Fri Jun 27, 2014 3:38 pm

I dont' think I have, but when I opened my carbs after the long winter, the floats were around 14mm out. I bumped them back to 7.2, and my wet levels were about 4-6mm below the line. The engine would only idle with the throttle all the way open. I assume that meant too rich, from the fuel level being too high.

Im not sure how they ended up at 14mm, because I adjusted then correctly a few years ago.

Either tonight or tomorrow, I am going to adjust the floats to probably 10mm and see where that leaves me. I am thinking that I might have been running very lean before, and then I overshot it.
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radare
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Fri Jun 27, 2014 6:42 pm

I've checked all of the online manuals and both of the in-print manuals I have at home and they ALL spec the float height at 6.2 to 8.2mm above the gasket surface.

I suspect, Nelson, that someone set yours based on the UK carb specs. They are 11mm to 13mm, but also the BDST28 carbs, whereas we have the BDS26 carbs. Different beasts, but now I'm wondering if you have US carbs on your bike . . . :ponder:

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JohnOfTheJungle
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Wed Oct 08, 2014 9:22 am

Same as a lot of people, my float heights were way "out of spec" at somewhere around 14mm. I adjusted them down to 7mm, and thought the same thing, it just seems too low.

Now of the bike doesn't start (granted I had the entire top end disassembled down to the valve shims, but it's all back together now). Confirmed that fuel is going into the carbs and fuel is in the bowls, checked the plugs though and they're dry, so I'm thinking that the fuel is too low in the bowl for it to get picked up by the enrichment circuit.

Most of the resolutions I'm seeing recommend not even bothering with the dry check and going straight for the wet check. Did you ever resolve this issue Radare? What were the correct dry height settings for you?

As for me? I'm goin WET

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JohnOfTheJungle
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Thu Oct 09, 2014 12:58 pm

Just to note - I did end up wet measuring my floats last night. A little quick background -- I fully disassembled and rebuilt my carbs, bike hasn't run in 5 weeks. Anyway, on my first measurement all of the carbs were showing fuel levels much lower than spec (like 20 mm below the line on the carb bowl).

So, I adjusted the floats (with the carbs still on the bike, but pulling the floats off), but only for carbs 1 & 2 as I wanted to see what affect the adjustments would have before doing 3 & 4. I made several adjustments to 1 & 2 and still couldn't get it to start.

Then I got a hold of long vacuum line and raised my tank up 2-3 feet above the bike on a shelf. I also bypassed the fuel pump and hooked up directly from the tank to the carbs. Opening the tank to prime then caused caused the engine to completely flood, fuel to fill up the cylinders, and fuel to gush out of the carbs. So I pulled the bowls off, made slight adjustments to 1 & 2, and made sure the float was moving freely. At that point I then checked the fuel level for all cylinders - 1, 3 & 4, were all 5mm above the line (too high), 2 was in spec!

I then pulled the plugs, turned the engine over by hand to clear the fuel from the cylinders, reinstalled the plugs, set it to prime and cranked the bike while giving it a little bit of throttle, then BOOM it started up and ran!

So what I think is that although I had set the tank to prime previously and had also cranked the engine, I don't think the carbs were getting filled with fuel to the level they should have. It wasn't until I was able to force more fuel in by raising my tank that I was able to get the carbs filled where they need to be for that initial start.

My problem actually seemed very similar to this guy's, which had no resolution, so I wanted to post it here for reference http://vetxfxg.xjrider.com/viewtopic.php?f=10&t=680

I'll be going back tonight and making small adjustments on all carbs to get fuel level where it needs to be (it's at or slightly above the line for 3 of the carbs). From what I've read it seems that bringing the tang closer (making the gap smaller, it's currently at 5-6mm) allows more fuel in, and moving it farther apart allows less, so I'll be moving them slightly apart, probably by 1-2mm.

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MrJoel
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Sun Oct 12, 2014 8:43 pm

Any measurem nt and comparison between accurate wet method and a true dry method measurement?

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JohnOfTheJungle
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Thu Oct 16, 2014 4:09 pm

I can't say Joel because I have fiddled with mine so much. The last few adjustments I've just left the carbs on the bike and taken the floats out and adjusted the gap between the tang and the part of the float that it's connected to.

As was indicated in an earlier thread -- I've set that gap on mine to about 6mm and that seems to be getting me close to spec on the wet measurement.

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zoli2750
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Fri Oct 17, 2014 3:19 pm

When carbs are now down on bank I have the opportunity to investigate and try to understand the rout of fuel inside the carb bowl.

It will help me to understand the importance of fuel level / float height, maybe it might help others too.

This are two same metering tools of fuel in bowl just in other terms and other parameters.

Interpoleting the hights of fuel level to the inner life of the bowl - in my case 3-5 mm above the line - I received this picture:


Image
1. We have two value to be measured for better view, the pilot jet's positon since it sits inside in its tube in 19mm from the lower end of the tube.

Image

2. The carburator positioned approximatly in a 10 degree form horizontal level when on assembled on engine.
Unfortunately I don't have the hands and the precise tools to measure the exact level position on the carb on and without centerstand. I can measure - I would rather say I can calculate - levels with trigonometrical angle calculation, which gave me an approximate 10 degree.

Image

So let's look what I can translate from the measured levels:

The lower fuel height, the 3mm corresponds to the psoition of the pilot jet in the tube.

It means that when the fuel float level is under the predefined 3mm value, the engine is predeterminated to run lean on idle because the fuel level is under the jet, the engine struggels to pick up enough fuel to run evenly.

When the fuel level is above the 5mm, the fuel level reaches both the pilot air and main air jet's air holes inside the jet housing, the engine will struggle to suck enough air for the proper air-fuel mixture both on idle and after throttle open.

As my english is not so fluent as I would like it, I borrow a more eloquent passage from a colleauge posted on an other forum:

http://www.thumpertalk.com/topic/116575 ... t&p=842620

"the float working like a toilet bowl, but there's a little more to the story because the fuel in the bowl is constantly sloshing & bouncing around as you ride, which makes it more difficult to maintain a certain level as opposed to a toilet which is stationary. Fuel delivery depends on the differential of pressure between the venturi and float bowl, which is vented to the outside world. The air pressure in the venturi decreases as air flows through it (intake stroke) and because the float bowl is vented to the outside world which is at a higher pressure, it causes fuel to be pushed through a jet and into the venturi. The amount of fuel going into the venturi through the jet depends on the size of the jet and the pressure difference. If the float level is too high, then it may block certain air passages that allows the carb to depressurize and if this happens, the carb will momentarily deliver too much fuel causing your engine to bog, especially over rough terrain, jumps, etc. If float level is too low, then the engine will obviously starve for fuel and momentarily run lean.

The trick of the matter is finding the balance point to maintain enough fuel in the bowl so the engine doesn't starve for fuel while also making sure there's not too much fuel in the bowl that might block necessary air passages and it all has to be built into a small enough package to compliment the rest of the bike, which will be bouncing, sliding and thrashing about under normal operation."


Actually a very precise float height is not needed it is just enough to set the fuel level inside the given measurents, between 3-5mm on a european bike.

I think it's the better to have it on the middle, beacuse one can't set the same precise level on a bike.

Actually the factory service manual doesn't mention a centerstand in the float measurement and adjustment section, since it is not mentioned one could interpret that fact as the measurement should be performed not on centerstand but on both wheels down, bike supported with garage jack on one side for positioning the carbs vertical.

I have chacked the degree with a smartphone app, it conveyed the same 10 degree.
The centerstand actually does not defers the value. It is 10 degree on centerstand and on two wheels, so it is doesn't matter when one measures the fuel level on or without centerstand.


It's free to confirm or denie my beginner person's reasoning
:)

regards

zoli

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radare
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Tue Jun 27, 2017 9:55 pm

I'm going to reach into the ground, pull the old dead corpse of this thread up and give it mouth to mouth. Yes folks, I'm back to float heights again. And I call bullshit on the manual and its 6-8mm value for bench setting float heights. It's not right.

Tonight I spent hours and hours very carefully setting the fuel level (wet) on my Scrambler. My target was 5mm below the line on the float bowl (spec is 4 to 6mm below the line for US models). With the fuel level set exactly (or as nealry as humanly possible given the meniscus of gasoline) at 5mm and confirmed on all four carbs, I decided to pull the bowls and see what the float heights were.

Without surprise, none were in the 6-8mm range that is specified in the manual. They were all in the 11-12mm range.

It many not yet be definitive but I'm going to start saying NO to the 6-8mm spec and instead, recommending an 10-12mm spec instead.

And dont' look away just yet; there will be a graphic coming soon to illustrate the point :prob:

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cafe_bill
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Wed Jun 28, 2017 11:42 am

radare wrote:
Tue Jun 27, 2017 9:55 pm
Without surprise, none were in the 6-8mm range that is specified in the manual. They were all in the 11-12mm range.

It many not yet be definitive but I'm going to start saying NO to the 6-8mm spec and instead, recommending an 10-12mm spec instead.
Really interesting...

My Seca has been parked for several years and I recently pulled the carbs all apart, ran the parts through the ultrasonic cleaner, reassembled with new gaskets and such and set the floats according to the factory manual's dry instructions. In previous rebuilds (I've owned my Seca since it was new in '92) I've always taken the time to set them wet. This is the first time I've got lazy and only set them dry.

The bike wouldn't even start. Since it acted like no fuel, I opened up each drain and found nearly no fuel in any of them. At that point I was disgusted, pulled the bike off the lift table and put it in the corner until it learns to behave... And went to work on my Buell for awhile.

Now it seems I need to open the bowls, give them some more height and go back to wet measurement... Sigh.
Bill
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