Does anyone know what the correct float level should be for the sand cast (probably reproduction) H8
carbs fitted to a '53 XK120?
I have them set at about one inch, which seems a bit low, but it still belches a bit of raw gas out of
the top of the main jet after shut-down, even at room temperature (having run the engine for only a minute or two). It only does this occasionally but often enough to be concerned about. It will even happen with fuel feed line disconnected (no pressure). Owner says he uses non-ethanol gasoline.
Floats, needles and seats are all new, genuine SU.
Any help appreciated.
Patrick
Okaaay. Then does anyone know where I might find Grose-jets for these carburetors?
The part number for the SU needle and seat is WZX 1091 so I’m looking for the Grose-jet equivalent.
Thanks as always.
Patrick
Try Tony, at SNG Barratt.
I called Barratt today and spoke with Frank.
He said they had nothing available except for Strombergs.
Maybe I’ll try again and ask for Tony.
Thanks for the advice.
How about Joe Curto, he deals with every SU carb ever made.
Is there a reason you want Grose jets? I tried them years ago and 2 out of 3 of them leaked. I have since read many posts from people having the same problems with them. The original type needle and seat works fine.
Well, duh:,I plumb forgot that!
Joe will have the answer.
Hello Rob,
The gasket kits (his own brand), floats and needle valve kits (genuine SU) came from Joe.
After assembly, I still have fuel, occasionally, spilling over main jets and into carb throat.
In the course of trying to correct this, I asked Joe if he was a fan of Grose-jets and his reply
was a terse “NO!” So I did not actually ask if he had them available; I just assumed he did not.
By the way, the O in my username is for O’Reilly.
Fuel spilling occasionally sounds like intermittent needle valve seating when closed is expected. That can be due to fuel pressure too high. If fuel pressure is too high, a running engine parked can vibrate the seating open occasionally. The various combinations of needle valve styles and materials give mixed results when facing high fuel pressure.
Another element to check is the fuel level in the float chamber, which is described by 1956 SU Workshop Manual, p.A.4, “the standard level is 3/8 in. (10 mm) below the level of the rectangular facing known as the jet bridge”. N.B., this is lower than some other publications say, my experience is the SU-specified level works better than higher settings…
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So in theory we’re related, going back to the original Raelleagh in the 11th century.
I also have read that the meniscus level should be down somewhere below the top of the jet, but didn’t have a reference.
The SU pump only puts out about 4 psi or so. Some aftermarket pumps put out a lot more.
Hello All,
My reason for wanting Grose-jets is that I cannot get these H8s to stop OCCASIONALLY flooding.
I just replaced gland washers on the main jets which were leaking externally and likely the
reason the car came to me. That is, hard starting after sitting for a few weeks.
When I removed the air cleaners, I noticed a pool of gasoline in the recess upstream of the bridge on
the front carb.
I then ordered floats and needle valves (genuine SU from Joe Curto) and replaced them.
I still OCCASIONALLY get a bit of fuel (maybe a teaspoon, sometimes more, sometimes less;
difficult to measure) from EITHER carburetor. Fuel is rising up out of the main jet and spilling into the throat of the carburetor. This happens at room temperature. Float levels are such that I can see the gas just below (~1/4 inch) the top of the jet, with the dashpot and piston removed.
Early on I suspected that the pressure might be too high, unseating the needle valve. It measured
approximately 4 psi, fluctuating slightly with the pulses of the electric fuel pump. I installed a pressure regulator and brought it down to 2 psi.The occasional flooding continued. And I was NOT able to induce the flooding by cranking the pressure back UP.
Most recently, I have removed both float chamber lids, reattached the feed line and suspended them high enough to watch them. Holding the float levers closed with rubber bands (yes; this is jury-rigged)
I can see gasoline dripping from the valves at times. Not always; not both at the same time (yet). If I open one or the other briefly and let it close again (with the help of the rubber band) it may or may not drip again.
In other words, the observed leakage is about as random as it is when all is assembled for running.
Therefore, I decided to try Grose-jets. Over the roughly 50 years that I’ve been at this, I’ve used them
a few times on “problem” cars. I realize that a stray drop or two should not be a problem but I don’t like the idea of several ounces (?) of raw fuel eventually making its way into the oilpan. Ironically, the needle valves in the carbs when it came to me were Grose-jets or some other brand with a “dual ball” construction. I was unable to blow through them. I don’t know how it ran at all. The car was driven here; no performance complaints.
So far I have not found a source for appropriate Grose-jets. I could not find any identification on the ones I removed. I’ll continue my search.
Sorry for the long post but I wanted to provide as much information as possible.
Thanks for your interest and assistance.
Patrick O’Reilly
Hello Patrick, excellent details to help sort further. Always being a little skeptical, maybe a little more consideration on pressure issues is worthwhile. Your description above indicates you understand that gasoline is pushed by the pressure in the line in excess of the air pressure. There is no pulling of gasoline.
The SU Workshop Manual lists an LCS pump as having a maximum output lift of 48 inches, 1.22 m. That means the output pressure maximum is approximately ( 750 kg per cubic meter x 9.8 meters per second squared x 1.22 meters = 9000 newtons per square meter) which is 1.3 pounds per square inch. These pumps for SU carbs are quite low compared to many modern fuel pumps.
In my experience, pressure reduction device like the Mr. Gasket 1-6 psi pressure regulator sold by Holley have not worked in these applications. The pressure regulator experience I found included no reduction, intermittent reduction function, and appearance of correct reduction overcome by the pulse mechanism in the LCS operation. The only satisfactory solution I have found is to use a correct low pressure LCS pump from Burlen SU and no pressure reduction regulator. And even so, the fuel pump location matters, these needle seats have a 1-2 psi sensitivity for closing and can be jarred open by engine vibration at idle (car may run fine on the road since fuel consumption is ongoing at higher rate).
In older cars with high-mounted fuel pumps, people have even resorted to having a fuel return line from near the carbs to the tank to solve this vexxing problem.
Maybe these thoughts will not help find your solution, but at least they can be in your mind to consider.
Something is not making sense to me. Patrick, do you have the SU LCS pump or something else?
With the pump off, the fuel stops flowing, in fact it should flow backwards a little bit. The level in the jet and the bowl should be the same, 3/8" below the throat, and there should be no pressure in the line to add more fuel.
There must be something else in your system causing high bowl levels.
How about clogged filters in the tank, pump, and carb bowl inlets?
We talked about SU pump pressure in 2013 and I wrote this:
The Mark V Service Manual gives a test for the flow rate of
the SU LCS pump, the same one specified for all our XKs.
‘‘From a supply tank located 33 inches below the pump, the
pump should be able to produce a suction lift to push the
fuel up to discharge into another tank or bucket located 48
inches above the pump, at a flow rate of 12.5 Imperial
gallons per hour.’’
That works out to be right around 1 US quart or 2 pints per
minute or a bit less than 1 liter per minute.
So one could calculate the head pressure in 81 inches of
fuel, which has a specific gravity of about .75, and so a
column of gas 1’’ x 1’’ x 81 inches high would weigh about
2.3 lbs.
So the head pressure is about 2.3 pounds per square inch,
and thus the pump has to do somewhat more than that to
maintain that flow rate under those conditions.
Of course our carbs aren’t 81 inches above our tank, so at a
pressure of 2.3 psi it can easily keep up with our needs.
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Well I finally sourced a pair of Grose-jets from Moss and that seems to have done the trick.
Many delays along the way but so far, so good.
Thanks again to all.
Patrick