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Discussion Starter · #1 · (Edited)
The car/engine (specs are at the end of this post) bogs down under load. Specifically, when I give it gas, the engine initially responds normally, but then bogs down/stumbles. Then, I give it a bit more gas. Again, the engine initially responds normally, but then bogs down. The engine runs fine idling and when I give it gas with the trans in neutral. The car has a brand new Edelbrock 1406 carb and new Edelbrock 1721 mechanical fuel pump. I watched the trouble shooting video on the DVD that came with the carb. The tech in the video said to check for problems with the fuel line, without any detail behind that statement.

Maybe, the problem is the way I plumbed the fuel line. The steel fuel line comes out of the frame right next to the fuel pump. I installed a brass elbow on the "in" fitting on the fuel pump, pointing right at the where the steel fuel line comes out of the frame. There is about a 20 degree bend in the rubber fuel line which connects the fuel pump to the steel fuel line. Could that bend in the rubber fuel line be the problem? On the "out" fitting of the fuel pump, there is another brass elbow pointing north to the carb. There are no tight turns in that segment. The only way to avoid having a bend in the rubber fuel line would be to take apart the fuel pump to make the "in" fitting point directly at the fuel line.

Another possible problem is the fuel. The car was in storage for 5+ years. I siphoned out as much of the old gas as I could, but think there might have been a gallon of the old gas left. I added 10 gallons of fresh 87 octane gas, as per the GM specs for this engine.

Specs: 1965 Chevelle 300, GM Universal 350 (not modified), Edelbrock Performer EPS intake, stock points distributor, ignition timing idling with vacuum advance disconnected and plugged - 10 degrees before TDC, manual transmission (M20), no a/c.


713848
 

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Secondaries opening too soon under load ????
 

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Well I can tell you that a 1406 Eddy carb is jetted pretty lean and that bog might be from the sec side when the sir valve opens too soon, the fix is to put an air valve off a 750 in there and open the squirter nozzles up to a .035, I tested 3 of the Eddy's at the track a couple of weeks ago.
 

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One (of many) possibilities is 'gunk' from the old gas tank has contaminated/fouled your carb.

If a tank has 'sat' for a long time the inside of the tank corrodes, Also, 'old' gas leaves a 'film' of nasty gunk on the interior surfaces. Particles (some so fine they pass thru the filter) slough off and foul up just about everything.

Some folks clean/flush 'old' gas tanks. Because a new one (Spectra; a Canadian Co) costs about $200, I recommend replacement to ELIMINATE the problem. Replace the 'sock' and the sender while you're there. They are not expensive and reduce the risks of re-work.

After you are sure your carb is clean (you may need to give it a thorough cleaning), try running the car from an 'external' gas source (a can connected directly to the fuel pump). If she runs fine? Voila. You have some fuel line flushing to do (if not replacement) and address the tank.

'Out of the box' that carb should have run fine. It may need some tuning to optimize overall performance.

You do have the dwell set properly? Vacuum advance connected to the manifold vacuum port?

Pete
 

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Try to set your timing with the engine revved north or 3000rpm's so that you're accounting for your distributor's mechanical advance. My 350 is happy with a lot of timing, I have my total timing set at about 36 degrees and it's all in at 3200ish rpm's. IIRC this put my base timing at idle more like 14 or 15 degrees. So based off of your base timing you might need to advance it a few more degrees. Without enough timing, my 350 behaved the same way.
 

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Like bry66 said, check for total 'all in' timing with the vacuum advance connected. Your problem might be the vacuum advance not working. I don't think the fuel lines are the problem but I would not use those 90 degree brass fittings either. They are very restrictive. Your slight bends in the rubber hoses are fine and will not cause a problem.
 

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Discussion Starter · #7 ·
One (of many) possibilities is 'gunk' from the old gas tank has contaminated/fouled your carb.

If a tank has 'sat' for a long time the inside of the tank corrodes, Also, 'old' gas leaves a 'film' of nasty gunk on the interior surfaces. Particles (some so fine they pass thru the filter) slough off and foul up just about everything.

Some folks clean/flush 'old' gas tanks. Because a new one (Spectra; a Canadian Co) costs about $200, I recommend replacement to ELIMINATE the problem. Replace the 'sock' and the sender while you're there. They are not expensive and reduce the risks of re-work.

After you are sure your carb is clean (you may need to give it a thorough cleaning), try running the car from an 'external' gas source (a can connected directly to the fuel pump). If she runs fine? Voila. You have some fuel line flushing to do (if not replacement) and address the tank.

'Out of the box' that carb should have run fine. It may need some tuning to optimize overall performance.

You do have the dwell set properly? Vacuum advance connected to the manifold vacuum port?

Pete
The old gas problem is the one that concerns me. I wish I had done more about that. I tried to research the issue, but apparently did not try hard enough. Yesterday, I talked with the carburetor expert at Edelbrock. He thought the plumbing was okay, but was concerned about the old gas issue. His recommendation is to drive the car to see if the problem works itself out.
 

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The old gas problem is the one that concerns me. I wish I had done more about that. I tried to research the issue, but apparently did not try hard enough. Yesterday, I talked with the carburetor expert at Edelbrock. He thought the plumbing was okay, but was concerned about the old gas issue. His recommendation is to drive the car to see if the problem works itself out.
It's not likely your gas since it runs and idles fine. It is a problem while under load which in my experience is going to be either fuel or air or timing (I know that doesn't leave much else). Vacuum advance is not likely the culprit since it is not present under load (low vacuum condition). You should rule it out though. Never assume. Here is what I would do...

1) Disconnect the vacuum advance and plug the port on your carburetor. Check your initial and total timing. Just be sure the initial is somewhere around 8-12 degrees and that you can rev the engine and see it advance to a ballpark of 32-35 degrees at 3000 rpm. You can fine tune it later for peak performance. Leave the vacuum advance disconnected for the time being and eliminate it from the equation.

2) Look at your carburetor closely, fully actuate the throttle linkage and ensure your choke plate (if it has one) is connected and not flopping around. It should be full open on a warm engine.

3) Not familiar with your particular carburetor, but I would inspect the secondary throttle plate as well and ensure it is closed, does not flop around, opens and closes without binding under spring tension (push on it with your finger), actuate the throttle linkage and ensure the secondary remains closed; Finally, adjust the secondary throttle plate to open a little later (i.e. keep them closed a little longer under WOT...you'll have to look up the instructions on that).

4) Ensure you have no obvious exhaust restrictions (plugged cat, rat nest in your muffler, etc...). There is a test you can perform with a vacuum gauge that goes something like this... With the car running in park/neutral, Connect vacuum gauge to manifold vacuum (note the reading at idle), raise the RPM to about 2000 or 2500 and watch the gauge. Initially the reading may be slightly different than your idle reading but the key here is that if you have an exhaust restriction, the vacuum will slowly drop off as you hold the rpms steady at 2000-2500.

5) If all of these are good, then I would start looking at fuel delivery. I good be wrong in my very first statement. You could have a clogged filter, check/replace it to be sure. Too little fuel and I think you would be getting a lean back fire through the carb under load. Too much fuel and you should be seeing black smoke out the tail pipe. Again, not familiar with your carburetor (not even a carb expert) so someone else will have to chime in. Carbs can get weird on you.


I've had engine "bog" caused by every one of these items. Good luck and please be sure you close out your thread (with the solution) when you find the problem.

-Kevin
 

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If you simply mean your connection to the pump, I do not disagree.

If (huge IF) the problem is fuel contamination, running the engine from the existing tank is not something I would continue to do.

My recommendation:

Replace the fuel filter.

Go back and check the dwell. If the dwell is 'off', correct it, and re-set the timing.

Check the fuel pump outlet pressure. Too little, or too much, MAY produce your symptoms. Too much is the wrong pump. Too little could be a defective pump or some fuel line restriction(s) 'upstream' of the pump.

To help locate the problem:

Connect a longer 'hose' from an 'external' gas can to the inlet of the pump. See what that does. It may not help, but it's cheap and can't hurt. If the car runs fine from an external source, the problem is 'upstream' of the fuel pump (fuel, and/or something clogged). Concentrate there.

I won't say contaminated gas IS the problem, but because the car sat for so long, it MAY be.

Just trying to be helpful.

Pete
 

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So where is the fuel filter?
 

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what you have there is a very lean carb. 1406 is known for that. it's running on the accelerator pump till the shot runs out, then it's lean bog city. I've had very poor results tuning these carbs for issues like this. This is the reason why I don't run them. There's others here that think they're the greatest thing since sliced bread. I go by my own experience as noted.

You can try stiffer step-up springs, larger jets or smaller metering rods.
 
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the 1406 comes with the yellow step up spring this is wrong, get yourself a calibration kit for the 1406 and stick a silver spring in it and go from there. u may have to go down on your metering rods , jeff swisher u need to chime in
 

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what you have there is a very lean carb. 1406 is known for that. it's running on the accelerator pump till the shot runs out, then it's lean bog city. I've had very poor results tuning these carbs for issues like this. This is the reason why I don't run them. There's others here that think they're the greatest thing since sliced bread. I go by my own experience as noted.

You can try stiffer step-up springs, larger jets or smaller metering rods.
Or do what I did, take the stock squirter and open the tubes up to a .035 hole. My 1406 ran great at the track a couple of weeks ago with no bogs or hesitations. For me the float level on those carbs all need to be set right and no more than 5.5 psi pressure also with an Eddy carb.
 
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