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Thread: Floats and needle valves

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    Floats and needle valves

    Hi! Earlier this year I had a problem with gas seeping out of one of the overflow pipes on the float lid of my BT7 Tricarb. I replaced the needle valves, which were a bit worn and the problem disappeared. I did however experience some rough running so I went ahead and adjusted the floats. It proved difficult to get a correct distance between the lid and the float and when I finally managed the angle of the metal bracket did not seem right, and the needle on one carb occasionally got stuck because of this. I ordered the newer all plastic floats hoping that they would fix the issue, but when I installed them I noticed that they would not allow the needle valves to open. In fact they kept the spring loaded plunger on the needle partly depressed even when they were in their lowest position (see pics). I am beginning to suspect that I installed the incorrect needle valves and that they are too long, which would explain all the issues. Has anyone experienced this problem and does anyone have the correct dimensions (length) of the float needle for the HS4?
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    Re: Floats and needle valves

    As seen on this pic the valve actually sits above (or below when in the car) the float axle/pin, and that does not seem correct to me.
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    Yoda dklawson's Avatar
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    Re: Floats and needle valves

    If you chose the all plastic floats, the valve is adjusted by increasing or decreasing the number of fiber washers between the valve body and the bowl lid.

    During the past couple of years someone on this board brought to my attention that regardless of what the factory spec is for setting the float height, the functional adjustment is to fully engage the choke (lowering the jets) and adjusting the float level until the fuel is just below the height of the lowered jet. (Remove the vacuum chamber and mixture needle to see this).
    Doug L.
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    Re: Floats and needle valves

    Thank you - I have seen the posts on adjusting the needle valves with washers when using the fully plastic floats. My problem is that there are no washers and the needle valve still sits too high, so adding washers would just make the problem worse. The needle is fully closed and the float cannot move. I also have the plastic floats with the metal hinge, but I need to bend it to an awkward angle to adjust the float because the valve sits so high.

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    Re: Floats and needle valves

    I'm not an expert with plastic floats in fact I have never used them. And I don't dispute Doug L's approach to getting an accurate float adjustment but, It sounds to me that you have a misalignment issue and not so much a height issue. Even though float levels may have optimum settings they also have a fairly wide range of operation. If you engine was running alittle rough after your initial install I believe it was because the needle valve wasn't closing tightly enough and it was leaking past and flooding or over fueling the engine. If it was starving the engine from not enough fuel then the engine would have poor acceleration and even bucking.
    If the float is set too high on initial setting then the bouancy of the float rising to the top of the camber is not enough to put enough pressure on the needle valve to keep it closed. Reset your float to specification and ensure that there is no binding what so ever in its travel. A safe bet would be even set the float a smidgen lower that specification and ensure that in its rise that it can close the needle valve. If the float is too low then the car will drive with poor acceleration or even bucking. In that case, raise the float a smidgen. After you get it back together and the car is running pretty well then take it for a run, push in the clutch, shut off the engine, pull to the side of the road and pull your spark plugs to read them and see that they are burning with a good mixture. Sorry that my typing time and I didn't see you last post.
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    Re: Floats and needle valves

    I meant to mention in my last post that you can still get the HS series floats with the bendable metal tab. They are available in the new plastic that is more resistant to ethanol. They are black instead of white. I bought mine from BP Northwest. See link below.

    http://www.bpnorthwest.com/carbureto...nitrophyl.html
    Doug L.
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    Re: Floats and needle valves

    My Preference would be:

    Get rid of plastic floats and the needle valves, Go to the metal floats and Crosse jets.


    With Crosse jets the second generation are better than the first, both need cleaning with acetone before installation.
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    Re: Floats and needle valves

    Quote Originally Posted by dklawson View Post
    I meant to mention in my last post that you can still get the HS series floats with the bendable metal tab. They are available in the new plastic that is more resistant to ethanol. They are black instead of white. I bought mine from BP Northwest. See link below.

    www.bpnorthwest.com/carburetor-float-su-hs2-hs4-hs6-type-nitrophyl.html
    Good to know, I haven't had my carbs apart for near 10 years. I might need those floats one of these days. Thanks.
    Metal floats are still my preference. I have never used Grosse Jets. Don't know anything about them.
    About TV Shows-
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    Re: Floats and needle valves

    Thanks - I may have to do that, I still have the nylon floats with metal hinge. But it is a bit strange that when I use all original parts they just don't fit at all, the float shuts the needle valve even in its "fully open" position. I noted that there are different parts numbers for the original needle valves for different carbs (at least on the US Moss website), but the Grose valves are the same for all SU carbs used on Big Healeys.

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    Re: Floats and needle valves

    Best to contact Joe Curto. He knows about the problem and has a solution involving modifying the lids.

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    Re: Floats and needle valves

    I have not come across metal floats for the HS series carbs. I thought they were not used after the earlier H series carbs.

    You will either love the Grose Jets or hate them. If you choose to use them, spray them through with carb cleaner, rattle them a bit, then spray more carb cleaner through. They are shipped with a thin protective goo on them to keep the steel balls from corroding. If you fail to rinse that coating off you are very likely to have problems with them.

    I have had Grose Jets fail open and fail closed. I no longer use them. I choose to use the 0.096" orifice Viton tipped float valves instead. To each his own.

    In general the only difference on HS2 through HS6 float valves is the orifice size and the tip material. Presumably the Grose Jets have a flow area equal to or larger than the largest traditional float valve. Therefore, one size of Grose Jet fits all.
    Doug L.
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    '67 Triumph GT6 Mk1

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    Re: Floats and needle valves

    Thank you British_Recovery for providing Joe Curto's name. He has a number of tutorials on YouTube, one of which deals with SU float lids. There are apparently two versions of the HS4 lid, one older (that I apparently have) where the needle valve sits a bit higher (when turned upside down) than on the newer ones. The metal hinges on the float also look a bit different. On the older type it is flat whereas it has a "Z" shape bend on the newer ones. the all nylon floats only fits the newer lids. I will either have to try to rebend the hinges on my old floats to make them work better or modify the new all plastic ones by filing down the plastic a couple of millimeters. Will keep you posted.

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    Re: Floats and needle valves

    According to Tom Bryant, Joe Curto doesn't recommend Grose jets. They both prefer the viton-tipped brass float needle valves.
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    Re: Floats and needle valves

    After some further trial and error I think I have found out what is going on. A PO had replaced one of the floats with the newer type with the "Z" shape bend. This does not work with the older type HS4 Lid, it is not possible to get the geometry right no matter how you adjust the steel hinge, so it was prone to leaking and the float level was not right. I have decided to bite the bullet and have ordered new float lid assemblys (with floats and needles) from SU. I could have kept the two with the correct type floats, but I want to avoid having a mix of new and old, that would inevitably cause problems next time something needs to be done to the carbs.

    I take this opportunity to share a workshop tip I once learned from my late father. When you need to put in a screw where there is limited access (such as the float lid screws on the tricarb closest to the air filters) we all know how easy it is to drop the screw and having to look for it under the car or, worse, somewhere in the engine bay. I wind a thin, stiff steel wire (preferrably stainless as it slides better) one turn tight around the screw, below the washer, and bend the wire upwards so I can steer the screw into the hole by holding the wire. While still holding the wire I turn the screw a few turns with a screwdriver until it sets, but don't tighten it. I then pull the thread loose from the screw before I tighten it.

    I assume that many of you already know this, but for those who don't you may find it useful.

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