Hi Guys
I am taking a guess here that the question has arisen due to flooding?
I had a run in with a Spit a few weeks ago, petrol pouring out of the rear
carb car new to owner.
Fit a pair of new needles and floats, the floats were not a pair and as they
are reasonably cheap here we decided to remove the risk of a sinking float.
Still fuel poured out, so having had a problem before with the seal around
the thread that secures the float valve, I taped these with ptfe tape, yep
fuel still leaked out! Time to get technical, got a low pressure gauge and
measured the fuel pressure, 5 to 6 PSI. Looked for literature and found that
SU's like 2 PSI so suggest to owner shell out for pressure regulator, he
looked at the price and asked if I could think of any other way. As it
happened I could, shorten the spring in the pump. (The pump works by the
lever pulling the diaphragm down and filling the pump with fuel and then
releasing the tension as the cam turns and the spring pushes the diaphragm
up therefore the spring is what provides the pressure, when the flow is shut
off and the pressure rises the spring is overpowered and the diaphragm is
held down until the float level falls and allows fuel to flow again.) So we
set about cutting the spring, this is a very crude way of reducing the
spring rate by reducing its free length, we took a quarter at a time and
eventually got to 2.5 PSI which as I have not had a return visit from the
owner I guess was low enough. I have checked out several other cars with
"NEW" fuel pumps and found that they all run in the 5 to 6 PSI range but
some carbs seem to hold it back whilst others don't even when the float
level is correct, though on 2 of the cars I have looked at there were signs
of staining on the float chamber lids so these are probably running on the
limit.
I too have found that exact fuel levels are not too critical it just means
that the mixture jet will not be at the same height on both carbs.
Hope this helps
Graham.
----- Original Message -----
From: "Randall" <tr3driver@ca.rr.com>
To: "'Paul Dorsey'" <dorpaul@negia.net>; "'list Triumph'"
<triumphs@autox.team.net>
Sent: Friday, November 30, 2007 9:20 PM
Subject: Re: [TR] setting the float level on a SU H6
>> When setting the float level on the SU H6 carb, the manual
>> says to pass a
>> 7/16" rod between the float level aluminum forked lever and
>> the inverted lid.
>> However, when this is done does this mean the needle
>> completely shuts off
>> (with the mimicing of fuel by one's breath). Or does it
>> mean, 'that at
>> 7/16"ths the fuel level just begins to stop' or other?
>
> Paul, I don't actually think it's all that critical. Small errors in
> float
> level don't seem to cause a problem.
>
> But I take it to mean that the valve should be closed (unable to blow
> through it), with the fork dragging on the rod (on both sides).
>
> Randall
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