Author Topic: Quadrajet part number 7029282  (Read 570 times)

Offline kavesh

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Quadrajet part number 7029282
« on: October 10, 2019, 11:02:26 AM »
Hi, I recently overhauled my quadrajet which is mated to a Holden 308 V8 motor.

Motor is idling reasonably well. However, when I removed the vacuum advance hose from the carb I noticed that there was traces of fuel in it. It was wet with fuel. I have looked through the carb and that port through the float bowl and base plate leads to the intake and does not come in contact with fuel, unless the carb is dumping fuel into the intake. i don't believe that it is running rich either as my plugs suggest that if anything I may be a little lean
I must admit that I did not notice this in the past but I am pretty sure that fuel should not be there.
Has anyone experienced this before and can assist me with a fix please.
Thanks in advance
Kavesh

Offline Cliff Ruggles

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Re: Quadrajet part number 7029282
« Reply #1 on: October 12, 2019, 04:12:37 AM »
Unlikely it's got a leak path between the fuel bowl and that port. 

I'd put a might-vac pump on it, fill the bowl with fuel and see if you can pull any into the pump.  If not it's not coming from the carburetor fuel bowl.......Cliff

Offline kavesh

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Re: Quadrajet part number 7029282
« Reply #2 on: October 12, 2019, 11:22:11 AM »
Thanks for the reply Cliff.
I do not have a vac pump so cannot perform that test.
What I have established is that the port does down into the intake. I followed the holes through the carb to determine this.

Would a high float level cause more fuel to be dumped into the intake? My float is set at 5mm measured at the toe end of the float.

Offline hiy_po

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Re: Quadrajet part number 7029282
« Reply #3 on: October 13, 2019, 06:21:31 AM »
I am new to this site as well so just my 2 cents. Think you should be at about 7.5mm so maybe tad high. One thing I notice when mine is high is fuel in the purge line that goes down to charcoal canister. Maybe check that hose for fuel as well.

Umm ignore that just googled your part number and it looks earlier than mine so no charcoal canister but I think they were set lower again than the newer ones so maybe drop it about 3mm measured where you mentioned from end of float.
« Last Edit: October 13, 2019, 06:44:46 AM by hiy_po »

Offline kavesh

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Re: Quadrajet part number 7029282
« Reply #4 on: November 19, 2019, 10:17:48 AM »
Just an update, I have lowered my float level from 5mm to 10mm.
When I took the vehicle for a drive I found that it now has a hesitation when the accelerator is depressed, this was not an issue before with the float at 5mm.
I had a look at my plugs and it suggests that it is on the lean side as its light brown in colour.
There is no fuel at the vacuum advance port as well.
Do you think the hesitation is due to the float level. My carb spec says float should be at 11.9mm on a stock motor which is what mine is.
My jet size is 71 with primary rods 45 B.
I have 76 jets which I am tempted to try with the float left at 10mm. Opinions?
Please assist with advice here.

Offline Chris_Oz

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Re: Quadrajet part number 7029282
« Reply #5 on: December 11, 2019, 06:35:03 PM »
Hi,

I am also in Au and am just learning the Joys of tuning a Qjet.

71 to 76 jet change is HUGE, that is a 24% increase in effective jet size on cruise and a 17% increase when on the thin end of the needle.

Try to keep changes UNDER 10% or you will get lost. Do you have any smaller needles, a .042 would give you a 8% increase.

The float should be right at 10mm, if you didn't have the hesitation before, the high float level may have been hiding it as it dumped fuel down the throats.

Your carb should have APT, have you adjusted it? Did you reset it back to factory after you rebuilt it?
What Piston spring are you using? If the spring is too weak or you have low vacuum, it can cause a hesitation until the secondaries start feeding it.

Do you have Cliffs Book?


Offline Cliff Ruggles

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Re: Quadrajet part number 7029282
« Reply #6 on: December 12, 2019, 03:48:03 AM »
What size are the main airbleeds in the airhorn and main casting?  On the Chevy carbs built for US engines in that period they were nearly 1/8".

Up until 1969 the Chevy units used very small MAB's just under .050".

Fuel delivery to the engine is effected much more by the MAB sizes than by which jets and metering rods are used.

Float level also effects fuel delivery as does the size of the fuel inlet seat.  Very few kits have the correct N/S assembly in them so the smaller hole lowers the fuel level some even with the correct float height.

I would use a .135" N/S assembly and set the float to 1/4" (.250") and leave that alone.  We do NOT tune these carburetors by moving the float height it is done by using the correct parts, settings, then jets/metering rods/PP spring to get the engine running correctly in all areas.......Cliff