Cliff's Quadrajet Parts and Rebuild Kits
General Category => Quadrajet Carb Talk and Tips => Topic started by: jbh7052 on August 07, 2018, 06:35:12 PM
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Hey Mr. Ruggles! Want to start with saying thanks for your help in the past. You, your kit and your book helped me fine tune a quad for a small block chevy in my jeep! Still running great! Now, I just purchased a standard kit from you and it will go on a stock 350 in a 1972 c30. Gear ratio is 4:10 and tire size is 235-85-16. I have a 1992 700R4 tranny. Any advice on initial setup of the carb? 7042210
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Set the float to factory specs, and make sure the power piston hanger arms are level and exactly even. They used an APT system in the baseplate in that model so very important that the metering rods aren't hanging in the jets are different heights.
The 700-R4 will require a TV cable hook up. Not sure if there is enough material far enough from center on that carb to make it happen. You may need to add a piece to the linkage for correct geometry/operation of the cable......Cliff
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Thanks for the input sir! I have the tv system in place already before the carb rebuild. I will check everything you mentioned and am thankful for your advice. I will get it rebuilt this weekend and post results.
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I have the carb apart now and soaking in cleaner. To gain access to the apt do I just take out the aluminum plug in the base plate?
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Yes. Then you may have to use some heat to get the screw to turn.
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Thanks 77cruiser!
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Got the Transmission done and back in the 72! Carb rebuilt with cliffs kit. Started and idled first thing! However I was unable to get the APT screw to break loose....maybe I am a little chicken to get mean with it. Anyway, after discovering the throttle cable was a 1 1/2 in short of full travel and got the tv cable adjusted for good line pressure to the fresh 700R4 I am on the road. Again this is a stock 350 in a 1972 C-30 with 4:10 gears so it aint no race car! truck weighs 5,500lbs so she is a little beefy! Seams to be a little sluggish for in town driving but it cruises at 70mph with minimal throttle! Timing is set to 8 deg before TDC with HEI dist and a vacuum advance attached to ported vacuum source front right of carb just above throttle plates. Do I understand Cliffs book correctly that the APT only helps with part throttle or cruise applications? The gas mileage in town is hideous which I believe the APT will help with correct or will it only help with the steady throttle position?
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With a C-30 truck and 4.10 gears I wouldn't expect great fuel economy in the city for stop and start driving. It still should be decent when everything is tuned correctly.
I owned a 1970 GMC 3/4 ton truck many years ago with a stock 350 and 4.10 gears. I ran 7.50-16" tires on it. The engine was rebuilt back to stock with a GM 350/300hp camshaft. It did pretty good for fuel economy for what it was. Averaged around 11-12mpg's and a little better at 14-15mpg's on the highway cruising around 65-70mph........Cliff
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Well sounds like I am not far off then! Thanks for the advice and another great rebuild! It has a little hot start issue. I am gonna bump the float down a little off the factory setting and see if it improves. Thanks again!
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I'd set the float at 1/4" and look elsewhere for the hot start issues......Cliff
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Pulling the airborne off today and setting the float level to 1/4. Does a spacer help enough with heat transfer to help alleviate some of the hot start symptoms? If so what height? Anything other than a thin plate will render the divorced choke useless right?
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It would help if it was plastic or wood. What is the fuel pressure?
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Not sure on fuel pressure. Factory style AC Delco pump. I will get a gauge and check that as well. Thanks for the help!
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The factory 1/4" thick gasket is plenty of insulation from the heat of the intake. Spacers make using the divorced choke a lesson in humility and I doubt if that's what the issue is anyhow.
Did you pressure test the casting during the rebuild to make sure the bottom plugs aren't leaking?....Cliff
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No sir I did not pressure test. However I marine tex the locations illustrated in your book. Sorry for the delay in my response...came down with strep and didn't feel like wrenchen on it. I set the float to just over 1/4 in from top of casting and plan on checking fuel pressure this week. Funny thing is my other quadrjet that you helped me build for specifically for my jeep has the same hot start. I must be doing the same thing wrong twice 🤔 Both are great starting and great running carbs. I will post what I find after fuel pressure test.
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well I think I found the problem. I bought a summit racing fuel pressure gauge......it reads 11psi!!! not sure how accurate the gauge is because I have never had a fuel pressure gauge before. I am running a new AC Delco stock fuel pump. so is it better to install a regulator or invest in a different pump?
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11 PSI is pretty high for any carburetor. The later fuel pumps used higher pressure and often you'll see very float settings for certain carburetor numbers. I prefer to get the fuel pressure down to around 6-7 psi vs running the float nearly on the bottom of the bowl......Cliff
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got the fuel pressure down to around 4.5. I used a summit fuel pressure gauge and regulator. Regulator adjusts from 4.5 to 9.5 and i adjusted it all the way down. However, still have hot start problem after it has sat for 20 minutes or so. The gauge will actually rise roughly a pound after turning the engine off and it sits for a few minutes. After a couple minutes the pressure will drop to zero fairly quick. New clear fuel filter installed just before the regulator and obvious the pump is allowing the fuel to drain back to the tank because the filter is almost empty. i know that has nothing to do with the issue i have but just stating things i observed. Guess next step would be to remove the air horn and set the float a little lower??? Maybe pressure check the bottom plugs like i should have during the rebuild!! :(
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4.5 psi is a little low, I'd set it at 5.5 to 6 psi as fuel pressure does effect the level of fuel in the bowl during operation.
Pressure check the bottom plugs, sounds like you are getting a leak into the intake after shut-down if it acts flooded/difficult to start after 20-30 minutes of sitting......Cliff
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pressure checked the plugs and did have a small leak. Didn't seem to be to bad but the carb was not hot like it would be after operation. drilled, taped plugged and epoxied and had to order a choke pull off. as soon as i get that from your team i will give it a good try again. thanks so much!!
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Got the choke pull off installed. Drill tap and marine tex the threads fixed the hot start! However, during the process something changed! I now have a stumble at steady throttle. The only thing I changed while in the carb for the main well plug leak was to change the plastic retainer that hold the power piston in place. I had left the original in when I rebuilt it but since I was there I decided to go ahead and put the new one in. It was super hard to get in place. The power piston moves up and down freely by using my finger but would that cause the stumble of it was not moving easily? Again it didn't do this before I replaced the choke pull off and the small plastic retainer on the power piston.
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Check the power piston hanger arms, make sure they are exactly level and even. Most likely the hanger is bent down on one or both sides, see this all the time......Cliff