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post #1 of 10 (permalink) Old 07-08-2011, 10:32 PM Thread Starter
 
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Edelbrock Tuning

I am having a hard time dialing in my edelbrock 800 cfm on my 455. I seem to have it set when the car is in park where i can manually rev the throttle and all is well. When I put the car in gear and attempt to give the engine gas the carb feels like it is stumbling out of the gate. When in drive the car is definantly not getting the right F/A ratio. It seems to be not getting the right amount of gas untill the throttle is wide open. I have adjusted the F/A ratio screws and the fast idle linkage a little confused at this point on what to do next any ideas, oh yeah the carb is manual choke.....as always thanks for the help.

65 LeMans, 455,TH400, Edelbrock preformer Intake&Carb, K&N Filter, Custom Headers & Dual Exhaust W/ H pipe, 15in ralley wheels...... More to come.
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post #2 of 10 (permalink) Old 07-09-2011, 02:43 AM
 
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How new is the carb or when was the last time it was rebuilt?

I ask because my Edelbrock 800 gave me fits until I rebuilt it.

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post #3 of 10 (permalink) Old 07-09-2011, 05:57 AM
 
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Originally Posted by SDGoat619 View Post
I am having a hard time dialing in my edelbrock 800 cfm on my 455. I seem to have it set when the car is in park where i can manually rev the throttle and all is well. When I put the car in gear and attempt to give the engine gas the carb feels like it is stumbling out of the gate. When in drive the car is definantly not getting the right F/A ratio. It seems to be not getting the right amount of gas untill the throttle is wide open. I have adjusted the F/A ratio screws and the fast idle linkage a little confused at this point on what to do next any ideas, oh yeah the carb is manual choke.....as always thanks for the help.
do you think its getting too much gas or not enough? diagnosing carb problems is a process of determining where the problem occurs. you said it idles ok. that eliminates f/a screws since they only effect the idle circuit. you said its ok at wot. that eliminates main jets. what we are left with are things like the accelerator pump, float levels.
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post #4 of 10 (permalink) Old 07-09-2011, 11:10 AM Thread Starter
 
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After doing some more research on edelbrocks website I think my problem is that I need to figure out my fuel pressure. I think that it is struggling under load. Which the tech said could be fuel pressure.

http://www.edelbrock.com/automotive_...ech_vids.shtml

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65 LeMans, 455,TH400, Edelbrock preformer Intake&Carb, K&N Filter, Custom Headers & Dual Exhaust W/ H pipe, 15in ralley wheels...... More to come.
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post #5 of 10 (permalink) Old 07-09-2011, 11:14 AM Thread Starter
 
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Should fuel pressure be between 6-8 psi

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post #6 of 10 (permalink) Old 07-09-2011, 05:01 PM
 
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Yes most carbureted engines should run around 7psi

And here we are.

Doesn't matter what carb you chose, they all need to be dialed in to each engine and its quarks. Once you get carb and distributor set right for your engine it should run like a Swiss watch.

I understand why people get holley and edelbrock carb, as a 800 cfm Qjunk are hard to come by and the reman's are a bit pricey. I still love the Qjet. The way they idle and run. That feel of the secondaries coming in is great. Get that timed to the down shift and look out.

Is this a rebuilt engine and/or has it ran well since the rebuild and/or before the edelbrock?
To tight of rocker arms can cause this trouble too.

Freethinker hit the main trouble.

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post #7 of 10 (permalink) Old 07-09-2011, 09:36 PM Thread Starter
 
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I think that it is running lean my idle seems fine but while under load is seems to struggle. Before i put the 800 on i had a 600 and it ran fine. The only problem that i had was the acc pump was clogged. Now I have upgraded to the 800 and it ran fine out of the gate lots of pressure out of the acc pump and i was happy. Now the pressure out of the acc pump seem to be less which is why I am leaning to a fuel line pressure issue. I did get the 800 used and it was in terrific condition, couldnt ask for more 1yr old(not on a daily driver) and it only cost me 150. i need to get an inline fuel pressure gauge to find out what psi I am at.

65 LeMans, 455,TH400, Edelbrock preformer Intake&Carb, K&N Filter, Custom Headers & Dual Exhaust W/ H pipe, 15in ralley wheels...... More to come.
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post #8 of 10 (permalink) Old 10-06-2011, 05:20 PM
 
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Your primary jets and/or metering rods may need to be changed. At wot if everything seems ok then secondary jets are ok but perhaps the cruise step on the meter rod is too big. Calibration kit is like 60 bucks and provides many different setups. Also comes with springs to adjust full opening of the primary jets. Nice thing is meter rods and springs can be changed in less than 5 min and jets in less than 20
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post #9 of 10 (permalink) Old 10-07-2011, 05:50 PM Thread Starter
 
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What size jets should I start with on the primaries.

65 LeMans, 455,TH400, Edelbrock preformer Intake&Carb, K&N Filter, Custom Headers & Dual Exhaust W/ H pipe, 15in ralley wheels...... More to come.
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post #10 of 10 (permalink) Old 10-08-2011, 11:04 AM
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Jets/rods aren't going to have much if anything to do with an initial 'bog' --- neither is fuel pressure. That's going to be all accelerator pump and also the secondary air valve opening rate on a QJet. Some folks think that lightening up the tension spring on the secondaries and hogging out the relief port on the pull off (or disabling it completely) is the "hot tip" for QJets --- it ain't. You do want those secondaries to come "on line" as quickly as the engine can tolerate, but no faster. Having those big 'ol barn doors snap open instantaneously, before the air flow is there to activate the secondary metering circuits, is no bueno. There's not an accelerator pump in the world big enough to deliver enough fuel to support that --- you'd need a leprechaun riding along on the intake next to the carb, ready to dump in a bucket 'o fuel in order to be able to do that

Get yourself a copy of the Cliff Ruggles book on QJets and study it. It's all there and it all makes sense, and it works.

It's a process, Grasshopper ---- tune the accelerator pump and secondary air-valve controls to eliminate the bog, then tune the primary rods/jets and the secondary rods + rod hanger to get the fuel mixture right under load (best done on a chassis dyno), then repeat --- as many times as necessary until everything is humming along in harmony.

There are only two reasons to care at all about fuel pressure: you want "enough" so that the fuel bowl in the carburetor stays at a constant level as much as possible, but not "so much" that it forces the needle off the seat and overflows the fuel bowl. Those are the only two boundaries that matter. As long as you're staying between those two limits, varying fuel pressure by several psi isn't going to make one bit of difference to the motor.

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