Nozzle Drip on Stock 454 Engine

[Roger3]

Trying to solve nozzle drip on 71 corvette, stock 454 LS-5, 365hp, with 65,000 original miles. When I bought the car (I'm second owner) it didn't have original carb. Owner had problems many years ago and a local shop replaced it for him.

I bought car after it sat up about 8 years. I replaced gas tank, fuel filter, and rebuilt the carb that's on it (17054917). It ran okay but always had a slight nozzle drip out of passenger side only.

Idle has to be down around 600 RPM or less for minimum nozzle drip. If I increase idle to 650rpm by opening butterflies with idle screw, nozzle drip gets worse.
Timing at 18-deg BTDC
15" Vacuum
Idle adjustment screws are backed out 4 turns
Idle channel restrictor 0.052"
Idle tube 0.035"
Idle Bypass Air Holes 0.140"

What should I adjust (channel restrictor diameter, idle tube diameter, idle bypass air holes, or something else) to get it to completely stop having nozzle drip and idle at around 650rpm?

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A few years ago I bought a quadrajet 7041204, freshly rebuilt. When installed it had very bad nozzle drip. I sent it back to guy I bought it from (twice). He supposedly made some adjustments but each time I put it back on the nozzles were still dripping badly. I put in on the shelf but would like to get it corrected so I can use it. It runs good except at idle. I haven't checked the size of the idle channel restriction orifices, or the idle tubes, but the air bypass holes are 0.090", much smaller than on the carb discussed above. Should my first step be to enlarge the idle bypass air holes?

Open for any suggestions.

Thanks,

Roger



What should be my first step.



Which carb should Measuring the air bypass Nozzle drip with 17054917 carb has gotten worse over the last couple years. This week I took it apart and removed the idle tubes and idle restriction orifices to make sure the passages were clean. They were clean. I reinstalled them and can get the nozzle drip to stop if the engine is idling about 580rpm. Too low for normal driving and for the AC at idle.

[omaha]

I am not sure about that particular carb but check the size of the idle airbleeds, use the recommendations in Cliff's book if necessary. too large of an airbleed makes it hard to get the required fuel that you may need. Seems like too much advance at idle maybe just a little. Are you tuning the idle with a vacuum gauge? If not you should. The channel restriction and the idle tube size seem ok. (maybe slightly small on the idle tube) You may want to open up the idle discharge holes (where the needles stick through) just a bit.  NOW, if you pull a small vacuum line and leave it off while setting the idle, see if this will help with the nozzle drip. This should allow you to close up the plates a bit and still keep the same rpm. (a similar effect to idle bypass). the larger the vacuum hose, the more the effect would be. this should give  you some idea if you may need more bypass. (you could pinch down a larger vacuum line kind of like an adjustable bypass, with a set of vice grips or a small clamp). It would seem that .140 hole would be large enough but maybe not.

[77cruiser]

What's the float level set at? How about fuel pressure? Is the vac. advance hooked to manifold or ported vacuum?

[Roger3]

Omaha,

I am using Cliff's book and making small changes one at a time so I don't drill any holes too big. I'm going to focus on the carb that should be on the car (7041204). I was trying to get the other carb to work first since it could be the test unit in case I make a mistake.

I'm going to take the 7041204 carb apart this evening to see what size the holes and orifices are.

I did try to adjust it with one of the vacuum ports open. It made the idle slightly worse, more erratic and died.

The only way I can get it too idle right now is with the butterflies open too much. If I slowly close them the idle drops and the engines dies.

I'll back timing down to 14deg and see if that helps but I tried it at several different settings.

77 Cruiser,

Float level is set at 3/8".

Fuel pressure is 5-psi. Engines has a stock AC Delco fuel pump with return line.

I don't have the vacuum advance hooked up. I disconnected it, along with all the other vacuum lines to make sure no vacuum leaks were a concern. It should idle without nozzle drip, without vacuum advance correct?

Thanks for the help.

Roger

[77cruiser]

I don't have the vacuum advance hooked up. I disconnected it, along with all the other vacuum lines to make sure no vacuum leaks were a concern. It should idle without nozzle drip, without vacuum advance correct?

Thanks for the help.

Roger

Well maybe but if more timing will allow you to close the throttle more it might eliminate the drip. But sounds too like you might need more fuel.

[Roger3]

I took the 7041204 carb apart last night. The carb was very clean inside. Jets and rods are correct according to my spec sheets for a 71 corvette. Here's the size of bleeds:

Idle Channel Restriction .049
Idle Tubes .035
Idle Air Bypass .099 (this is much smaller than other carb 0.140) Cliff Recipe doesn't give a number for this
Idle Mixture Screw Hole Opening .079
Air Bleed Bushing in Air Horn .041 (this is much smaller than the other carb .073) Cliff Recipe 1 says .050 to .052

Any recommendations on what to change first (idle air bypass or air bleed bushing or something else)?

I ordered a few parts from Cliff (idle tubes and idle channel restrictions). When they come in I'll put it back together and update the results.

Roger

[Cliff Ruggles]

A stock 7041204 carburetor would have the large main airbleeds in the airhorn and in the main casting.  If they are clear down at .041", someone has altered the carburetor, or it is commercially "remanufactured"......Cliff

[Roger3]

Cliff so what changes should I start with?

[Cliff Ruggles]

Might want to try setting the carb up to factory specs for idle tube, down channel and idle bypass air.

If someone has reduced the MAB's to smaller than .118" then make sure you are using the correct jets/metering rods for the changes.

I would also install our orange PP spring for the BBC application......Cliff

[Roger3]

Cliff,

I ordered the idle tubes and restriction orifice from you with the carb listed.

Where can I find the size the orifices should be? I checked all the books I have (GM service manuals, quadrajet books, etc) and can't find that information.

Thanks,

Roger

[Cliff Ruggles]

What are the sizes for the upper and lower idle airbleeds?.....Cliff