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Old 09-02-2008, 08:45 AM
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popping at top end

Hey
I just installed a Crete 350 all new parts...the timing is between 11-12 degrees. when i get into 3rd gear or get on it there is a popping sound. it doesn't do this when there is no load on the motor...just when i am pushing it...I think my advance is out of whack...

can someone tell me how to adjust the advance...it is a vacuum advance and i never played with on so i do not know where it belongs...

Also i have an eld. 650 carb. I am not able to get this thing to run clean...it seems to be running very rich...i am not sure which of the two screws is air / gas...can anyone tell me how far they should be adjusted or how to adjust the carb...it seems to run no matter what i do with it.
thanks
Les

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Old 09-02-2008, 11:17 AM
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I would set the timing to 12 degrees before top dead center with the vacuum advance removed and plugged. Lock the distributor down, then connect the vacuum advance to a full time manifold vacuum source.
Next the carb adjustment screws control the idle, one is not air and the other fuel, they adjust the air/fuel mixture at idle on both sides. Use a vacuum gauge to set the idle, adjust one side at a time until it reaches it`s highest idle, then set the other side the same way.
Have you checked to make sure the mechanical advance works? this is under the rotor button, check to make sure it moves freely. If all checks out okay and it still pops then I would say you have a very weak ignition, which could be the coil, the module or the pickup coil. You can buy a cheap spark tester at any autoparts store. If the spark is yellow it`s weak.
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Old 09-02-2008, 11:30 AM
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hey
I can set the timing, thats not an issue...I have the vacuum line hooked into the port from the carb. I know there is a allen key adjustment inside the Cap...I have a HEI Dist. and it is new...how do i go about checking a weak ignition with that Cap. I am new about motors!

To set the idle are you talking about RPM...I have the motor at 600RPM...and then it drops of course when i go into gear...

I am a metal man...not an engine guy so I need all the help i can get.
Thanks
Les
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Old 09-02-2008, 12:02 PM
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Quote:
Originally Posted by seafoam56
Hey
I just installed a Crete 350 all new parts...the timing is between 11-12 degrees. when i get into 3rd gear or get on it there is a popping sound. it doesn't do this when there is no load on the motor...just when i am pushing it...I think my advance is out of whack...

can someone tell me how to adjust the advance...it is a vacuum advance and i never played with on so i do not know where it belongs...

Also i have an eld. 650 carb. I am not able to get this thing to run clean...it seems to be running very rich...i am not sure which of the two screws is air / gas...can anyone tell me how far they should be adjusted or how to adjust the carb...it seems to run no matter what i do with it.
thanks
Les
Lets start with the carb. The only external adjustment you have is the idle circuit. Main metering and power is controlled by steps on a metering rod that is inserted thru the main jet. You can see two small sheetmetal covers held in place by a screw one on either side of the primary venturi. This cover is over the metering system. The metering rod is lifted by a spring applying pressure under a piston. The piston is exposed to manifold pressure (vacuum). When the vacuum is high, the piston is pulled down against the spring, this coincides with a closed throttle position, this pulls the largest diameter of the metering rod into the jet making the jet size smaller. As the throttle is opened the manifold vacuum reduces permitting the spring to raise the piston which lifts the metering rod. The rod is tapered or stepped so when it moves upward it has a smaller diameter in the jet which makes the jet bigger resulting in a richer mixture.

Things that you can adjust:

1) Is spring force, this controls the timing of the metering rods movements compared to the available manifold vacuum.

2) Metering rod diameters, larger diameters result in a smaller jet, small diameters result in a larger jet, as the metering rod acts as an obstruction inside a jet. Edlebrock sells tuning kits go to their web site, contact their tech rep to discuss what you've got. These carbs tend to be on the rich side, which means they have smallish metering rods. You'll need to know your cam, vehicle weight and gearing, transmission type and converter stall before talking to them.


Ignition, the problem you have could be ignition. There's more to ignition than the base setting. You need to know when and where the vacuum advance comes in to play and how much advance it generates got given amounts of manifold vacuum. Some engines like vacuum advance from a continuous manifold source usually on the carb. Others like the vacuum advance run off a timed port on the carb such that there is no vacuum advance on idle. Similarly the mechanical advance has a rate and amount determined by springs working against a weight to set the speed or rate at which the advance comes in. Also, the advance cam has a stop that determines the maximum amount of advance.

It is as easy to have too much advance as too little. Many rodders don't realize that the base advance is combined with vacuum and the mechanical at various points. Pushing up the base setting can quickly over-advance the timing up on the top end. The trick is finding how much advance the engine wants at various RPMs Some rules of thumb are:

1) Hot cams want more base advance than mild cams, this is because the mixture is low on density and high on exhaust contamination so it burns slowly, the engine runs better with more base advance to give more burn time. But the engine has a high density mixture with little or no exhaust contamination from the mid thru high RPMS and doesn't need so much total advance, the extra degrees put in at idle need to be removed from the motions of the mechanical advance, so that total advance doesn't become over-advanced.

2) Vacuum advance is intended to provide extra advance in cruise when road speed is high but engine revolutions are low. In this situation the throttle is close to closed therefore mixture density is low. As with the above description, when density in the cylinder is low, the burn speed is slow, therefore more advance is required to get sufficient burn time. This is a great aid to midrange torque and fuel economy. The vacuum advance needs to be adjustable for the cam. Again a large cam results in low vacuum, so the vacuum can for this needs a softer control spring so that it actuates further on less vacuum that it would with a mild cam. Adjustable vacuum cans are available that either use replacement springs (GM style) or use a screw to increase or decrease spring force (Accel, MSD, Moroso style).

These are the things you need to lean about to get the engine tuned. It's not a small task and is complicated and time consuming to do without a air fuel ratio meter, a dyno, and some ignition instruments like a Sun machine that can simulate the engine for the ignition. Not impossible to do, but needs you to understand what's going on so you can isolate phenomena as to cause and effect relationships.

Bogie
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Old 09-02-2008, 12:26 PM
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284I/296E Duration .507I/.510E Lift Rough Idle 2500+ Stall Converter Needed

that is the size of my cam...I have a 750 Carb and not a 650...I did read up on the metering rods when i got the engine...

I know of the two screws on the front of the Carb. i was told that i back one in at a time till it closes with the engine running...and turn it back to where the engine runs smooth and do that to the other side...

does that make sense.
Les
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Old 09-02-2008, 01:23 PM
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Quote:
Originally Posted by seafoam56
284I/296E Duration .507I/.510E Lift Rough Idle 2500+ Stall Converter Needed

that is the size of my cam...I have a 750 Carb and not a 650...I did read up on the metering rods when i got the engine...

I know of the two screws on the front of the Carb. i was told that i back one in at a time till it closes with the engine running...and turn it back to where the engine runs smooth and do that to the other side...

does that make sense.
Les
Those are the idle fuel quantity screws, they will affect idle quality and some of the transition circuit. After that, their influence goes away as those two circuits depend upon manifold vacuum which diminishes as the throttle opens. As the throttle opens, pressure in the manifold begins to move toward atmospheric, while air velocity thru the venturi increases. This causes a local vacuum to form within the venturi. This then draws fuel from the main metering circuit to be introduced by the boost venturis to the passing air stream.

With the carb off the engine and upside down, you should see the needle tips of the idle screws projecting in a hole just under the throttle when its in the idle closed position. Adjacent and above the idle holes should be the transition slots. The bottom of the slot should be about equal to the top of the throttle plate when the throttle is closed at the idle position. As the throttle is opened air trying to get around the throttle plate will develop a local vacuum that will draw fuel from the transition slot. At this point there is still insufficient air flow thru the venturi for main metering to start flowing. The transition slot covers a problem that old pre 1950ish carburetors had of having a flat spot just off idle.

Main metering turn on and overall all mixture ratio is controlled by fuel level and main jet size which in the Edlebrock Carter and the Q jet is variable by the size of the jet and the metering rod; with the Holley the main jet is a fixed size and the power jet is a separately valved circuit rather than the smallest restriction on the metering rod. The other effects on main metering are the air correction jets and the emulsion tubes. These are there to break up the fuel flow in main metering with air bubbles. Without this feature, main metering gets richer and richer as airflow thru the venturi increases with engine speed to a point where it can 't be controlled. The air correction jets and emulsion tubes work to put bubbles into the fuel flow, the faster the air rams into the intake the more bubbles form, by controlling the correction jet size and the number and size of holes in the emulsion tubes the designer can control top end over richness, often referred to as the rich hook. This however is an area of tuning the average rodder is well advised to stay out of. Most production carbs come with fixed correction jets and pressed in emulsion tubes, messing with them usually messes the carb up and getting replacement parts is nye-on impossible. some models of Holleys and Demon carbs do allow you play here by offering repacement screw in parts.

Bogie
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Old 09-02-2008, 01:38 PM
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Bogie
are you able to but in a nut shell how to adjust the carb...are you saying I have to change the rods...I always heard Eld. Carbs were easy to get around...also how do you know how to adjust the air/fuel nuts.
thanks
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Old 09-02-2008, 03:23 PM
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I have two questions for you ...first is this popping thru the carb and is it rhythmic? ..And lastly have you done any cam work to this motor recently??
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Old 09-03-2008, 06:29 AM
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I believe it is coming through the Carb. once i put a load on the engine. This is a new Crete motor so it has been all redone.
Thanks
Les
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Old 09-03-2008, 07:32 AM
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The one part of my question still needs and answer ...is this a rhythmic popping ...(one after another and same duration of time between the pops)?
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Old 09-03-2008, 07:44 AM
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I would say yes....it sounds like pop corn...very close together and stops when i let off the pedal.
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Old 09-03-2008, 07:59 AM
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re: popping at top end

I think you have 2 different problems.
1. the carb is probably rich because the edelbrock carbs are can't have over 4-5 lbs of fuel pressure, i would tryto get the pressure set to 4lbs before trying to tune it or you will waste your time. Also those carbs usually will work right out of the box, the only tuning would be minor , if you have a major problem tuning is not the answer.

2. the popping sounds like the ignition timing is off somehow, the vacuum advance should be hooked to manifold vacuum and would not affect the timing under load with your foot in it. Double check your plug wires and make sure the distributor is stabbed right. Even though it shows 12 degrees timing maybe its not .... are the timing marks on the timing cover or aftermarket bolt on?
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Old 09-03-2008, 08:01 AM
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Well I hate to say it but it sounds like you may be loosing a cam! I've had 4 go in my time ...all started with that rhythmic popping thru the carb at high RPM. And if I continued to drive the vehicle the popping would start at lower and lower RPMs. Another question for you, did you break in this engine per manufacturers spec.s? You might want to check the oil for any debris. Good Luck ...I hope I'm wrong! *G*
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Old 09-03-2008, 08:09 AM
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re: popping at top end

11echo has a good point. How many miles do you have on the motor? did you have to adjust the lifters at all? maybe a rocker adj nut came loose. If all else fails pull the valve covers and look for some rockers that aren't moving like the rest.
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Old 09-03-2008, 08:14 AM
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hey
i did break the engine in as the spec...and I changed the oil and it was very clean...

I will have to check the fuel pressure...to see what i have...the timing numbers are marked right on the balancer...in bold numbers...

i had this engine in and i had it running great...no sounds, no popping...and then i blew my trans...put a new trans in and i guess when i through the engine back in the advance must have gotten out of whack and i am trying to figure out how to adjust that...that is where i am confused...

the carb issue, i have never gotten it to not run rich....its really rich right now...ughhh
Les
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