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View Full Version : SU float bowl....measuring the height?



karls59tr
11-03-2012, 04:42 PM
The new Grose jets have white plastic jet that has a tiny plunger on top. When I insert the 7/16 drill bit between the Tang and the top I assume the little plunger should be compressed when I take the measurement. Correct?

titanic
11-03-2012, 05:19 PM
I don't think so. The fork should shut off the gas when it first contacts the plunger.
Berry

bobhustead
11-03-2012, 05:50 PM
not familiar with grose jets. no instructions in package?
Bob

SkinnedKnuckles
11-03-2012, 06:31 PM
Oh great - another iteration of the Grose jets. White plastic? Besides that, measure the height with jet in the "off" position - upside down with the floats holding it closed.

dklawson
11-03-2012, 06:57 PM
+1 for what Brent said. Measure the height with the bowl lid upside down so the float is pressing against the valve.

Also repeating Brent's comments... White Plastic? They were bad enough before. To each his own.

TR3driver
11-03-2012, 06:57 PM
Interesting, they must have redesigned them. The older ones had a brass body with a chrome steel ball to contact the fork. Maybe they got it right this time (even though they are still trying to solve a non-problem IMO).

I would try to blow through the jet, and compress the plunger far enough to stop the flow of air.

karls59tr
11-03-2012, 09:49 PM
I should clarify. I believe I'm mistaken about the fuel bowl jets being Grose jets. The float bowl jets I am referring to came in a rebuild kit that I ordered from the UK. I had them left over from an SU rebuild I had done previously. I must have put them in a Grose jet marked packet. Sorry for the confusion. The jet I mentioned is a 6 sided brass unit with the moveable internal part being a cylindrical piece with 4 ridges. It is made out of what I assume is plastic. There is a tiny plunger on the end that contacts the tang.

LexTR3
11-04-2012, 09:31 AM
The brass fuel bowl jets I have gotten from Moss and TRF have never let me down. I think the needle portion of the jet was modified in recent memory to replace the small metal tip with some form of plastic so it wouldn't wear as quickly.

dklawson
11-04-2012, 10:14 AM
I think the needle portion of the jet was modified in recent memory to replace the small metal tip with some form of plastic so it wouldn't wear as quickly.

Most of the ones I have seen like that have Viton tips. They work very well.

LexTR3
11-04-2012, 11:43 AM
Doug,

I should have written "viton." Thanks.

titanic
11-04-2012, 01:04 PM
Getting back to the original question about setting the float heighth with the plunger compressed. I remember the topic was discussed on the BBS site (MGA, H4 carbs), it was determined that if the float heighth was set with the plunger, the fuel level in the jet would be way below spec. because the plunger is not compressed in use unless the fuel pressure is way beyond the normal spec.
Berry

TR3driver
11-04-2012, 01:30 PM
because the plunger is not compressed in use unless the fuel pressure is way beyond the normal spec.

What good is a spring that never gets compressed?

Besides, in an SU, the float won't exert enough pressure to hold the valve closed if the pressure is even slightly beyond normal spec.

KVH
11-04-2012, 01:44 PM
I'm never clear on the theory of the bowls and the jets.

The jet shuts off the gas flow when the float is adjusted correctly so that just the "right amount" of gas lies in the bowl? Is that correct? Some sort of gravity and venturi theory?

And if the jets or bowls have any debris, the jets will stick and gas will leak out the vent holes?

How is the volume from the fuel pump handled?

It always puzzles me that the camshaft continually operates the pump with constant motion, but the floats can somehow manage just the right amount of fuel.

titanic
11-04-2012, 04:17 PM
Randall-I came away from the discussion that the spring is used to dampen vibration cause by the engine. It was calculated (FWIW)that 8-10lbs pressure would be needed to fully compress the spring. Someone attached lit. from Burlen on setting float level. It showed an hs carb and spring loaded float needle. The instruction stated that the level be set with just the weight of the float on the needle, not with the spring compressed. I have wondered about which was the correct way to set the float level, but the discussion answered my question.
KVH-The float&needle valve is used to maintain the fuel level in the jet about 1/8"-1/4" from the top. It works exactly like the float assembly in a toilet. If the jet sticks in the open position, fuel will go out the over flow tube and or into the carb throat,sometimes even into the crankcase. If you have used the priming lever on the fuel pump, you will notice that the resistance stops when the float bowls are full because the pressure in the delivery line holds the fuel pump diagragm down against the pressure of the diaphagm spring, preventing it from sucking gas from the tank. That is probably a foggy description, but it is paraphrased from the shop manual.
Berry