Honda-SOHC
Other Stuff => Tricks & Tips => Topic started by: Nurse Julie on August 23, 2020, 04:25:27 PM
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HOW TO SET CARB FLOAT HEIGHTS.
I thought it may be useful to add this to our hints and tips section for others to refer to.
Setting float heights can be tricky if its your 1st time, so here is a little pictorial explanation.
The aim is to set the float height at the correct level as per the manual of your particular SOHC/4, as measured from the top of the float to the flat face of the float bowl join of the carb body, with the float valve needle being fully extended in the open position.
1. Stand the carbs up fully vertical or lay the carbs down horizontal with the floats dangling down and not compressing the float valve needle. By standing them up you are allowing the floats to dangle with no downward pressure pushing the float valve needle closed. The float valve needle must be in the fully extended open position at all times throughout the process to get the final correct level of the float. I always have the carbs standing up vertical, it works well for me.
[attachimg=1]
2. Ensure the float brass arm is not bent or twisted. Do this by laying the floats on a flat surface to make sure both ends are touching the surface and there is no bend or twist in the arm. Bend the arms gently to straighten if necessary. If the arm is straight and level, the final measurement of the float height can be done on just one of the two floats per carb.
3. Become familiar with the float ‘tang’. This is the little tab that you adjust up or down to set the float heights.
[attachimg=2]
4. Ensure you have very free movement of the float when it is held in position in the posts by the pin. The holding pin needs to allow free movement of the float. If the pin feels too tight to allow free movement, check the pin for straightness and polish with some Solvol or similar to gain free movement. If you need new pins, you can by a length of 2mm brass rod from ebay etc for very little money to cut new ones from.
5. Know what float level height your carbs should be set at, depending on model (look in Haynes or the workshop Manual).
6. Use a measure of some type. I always use a vernier but an old credit card cut out into a U shape at the correct measurement does the job as well.
7. With the tang only just touching the needle and not depressing it at all, adjust the tang. It may have to be an adjustment up or down on the tang depending on your starting point. The adjustment needed may be miniscule in either direction. I find a small thin flat blade screwdriver is ideal for getting down in the gap of the tang to lever it up a fraction (lowering the float height) but I usually remove the floats completely to push down on the tang (increasing the float height).
[attachimg=3]
8. Now measure between the top of the float and the body of the carb where the bowl joins, ensuring the float pin is not being compressed at all. Keep repeating this procedure until you achieve the correct float height.
In this 1st photo you can clearly see the float needle is fully extended and the tang is only just touching but not depressing the needle.
In the 2nd photo, you can see where the measurement is taken, once again, showing the needle fully extended open.
[attachimg=4]
[attachimg=5]
9. Check, check and check again before re assembling the carbs and fitting to bike.
Here is the link to Bryans ' How to bench sync' your carbs.
http://www.sohc.co.uk/index.php/topic,17769.0.html
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Thanks Julie,
That's a really clear guide.
Out of interest has anyone got an idea what the fuel level should be when everything is correctly set up?
I only ask because after many, many hours of fiddling with (and swearing at) the carbs on mine I've finally got the bike to start and tickover well (so far) without incessant incontinence and when set at the right float height the fuel level sits at pretty much exactly the level of the carb bowl joint and I wondered if this is correct compared to a good running bike.
Cheers,
Andy
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I have never checked the level myself but I understand the fuel sits 3-4mm below the level of the top of the carb bowl.
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Thanks Julie,
I wonder if that may be a part of the problem with my carbs as the floats are set correctly but give fuel level pretty much on the joint.
When I first fill the carbs they sometimes overflow a bit but a quick shake of the bike and it stops and the bike starts up and runs fine and leaks stop.
I have fitted replacement float needles so maybe they are a bit different to the originals so I wondered what was 'normal' for fuel level.
Cheers,
Andy
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Hi All,
Just set the float height on my first carburetor - my float shape is curved at the top and flat at the bottom. I set my vernier gauge to 21 mm with quite a bit of trial and error to get it just right removing the float to make the adjustments - interestingly this coincided visually with the float bottom being dead horizontal i.e. parallel to he carburetor body. I was a bit concerned that the float valve would drop out but with the bottom clip in place this prevents it from doing so.
That will do me for tonight I'll sort the other 3 out next week before I build up the tops and assemble them into the mounting plate. Not sure what Carbs are in NJ's pics but mine does not have the rubber fuel pipes with a T piece. It just has one fuel pipe feed with interconnects between the remaining pairs.
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The carbs that I used for the photos are Keihin 069a's from a CB 550/4 . The principal of setting the float levels is the same for all the models I mentioned, even though the carbs may differ slightly in design.
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You can get a copy of the original Honda gauge for just over a tenner now. Ebay item 221394726969
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Great guide, just what is needed to keep these bikes running, the more clear guides the better they save that hard learned knowledge. We (I) could have been doing things wrong for years without knowing it !
Cheers
Dennis
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Thanks for the guide Julie.
Bryan, thanks for the heads-up re: the float gauge, I have just placed my order on ebay. I have a gauge I made myself but a claibrated one I can use on a few bikes is a better idea.
I have to take the carbs off the 400/4 yet again as they have begun to flood again, this time from the float bowl joints!The originals are the Keyster kit o-rings.
I purchased a set of Julie's viton o-rings a few weeks ago so I'll fit these and hope it cures it. I would like to sell the bike before summer is out and once it is fully run-in.
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A few of my buddies in USA use this nifty little measure, they buy them from ebay USA.
[attachimg=1]
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I used an aluminium rule to do mine. Just put the end edge flat on the carb joint face and look at 90 degrees along the base of the float to get the float height right. Worked a treat. No leaks.
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I used an aluminium rule to do mine. Just put the end edge flat on the carb joint face and look at 90 degrees along the base of the float to get the float height right. Worked a treat. No leaks.
I was going to do that until I realised that the scale did not start at the edge of my ruler!
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I find a vernier just perfect for the job
[attachimg=1]
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I have always used a vernier too - a ready made adjustable float heaight tool!
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Really useful guide, thank you Julie👍👍
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I find a vernier just perfect for the job
(Attachment Link)
that makes it much easier but tell trigg to stand by
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You can cut one yourself out of an old credit card or whatever card.
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I used a Vernier Gauge courtesy of Aldi that I bought from the Man aisle about 5 years ago - I finally got to use it for something useful.
Humans & their Gadgets eh.lol
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Absolutely brilliant advice. Any chance that we could have a “How to folder” in the forum and any advice that passes the peer review can be moved into said folder. This will help those of us that never did an honest apprenticeship need some good advice in a ready access folder. No advice on beer drinking required, cheers.
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Hi Julie
The carbs you illustrated aren't from a CB400F are they? I know I'm tired or getting drowsy from fumes but my floats at least appear to be the other way up to the ones you show, I've got a flat surface....they also seem to rest at an angle...my carbs are much cleaner now btw :o
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Hi Julie
The carbs you illustrated aren't from a CB400F are they? I know I'm tired or getting drowsy from fumes but my floats at least appear to be the other way up to the ones you show, I've got a flat surface....they also seem to rest at an angle...my carbs are much cleaner now btw :o
No George, they were 500 or 550 carbs, not 400. If you have set the floats correctly, as in my guide, the floats shouldn't sit at an angle. With the float tang just touching but not depressing the float needle, they actually sit almost spot on horizontally with the mating face of the carb body where you take the measurement from.
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Thanks for this Julie, a bit of a relief, I should have left things alone today, starting something when you're tired isn't helpful! ;)