Fuel Mileage Drop... - Page 3 - Chevelle Tech
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post #31 of 48 (permalink) Old Nov 26th, 18, 8:42 PM Thread Starter
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Re: Fuel Mileage Drop...

Okay. I pulled all the spark plugs out and they look great. Still gapped at where I set them when I put them in a while back. I started it up and let it warm up. Then I checked the timing. It appeared to be maybe 1 off, so I adjusted it a little bit. Then I adjusted the idle mixture a little bit. When I took it for a drive, it was okay for about a mile - then it started running like crap. I brought it home and put the timing back where it was, and set the carburetor back to where it was also. I took it for another drive and it was still running like crap.

So, I pulled the carburetor off and took it apart. I just figured I would change the power valve, and put new gaskets in. Well, when I pulled the screws out of the base plate, 3 of the holes have pulled threads. Now I have to try and find a 12-24 heli coil kit, which no one around here seems to carry. I do have a crappy Holley 1850 that has been in the shed for years that I can throw on temporarily, but I know it is going to suck to drive it with that on there.

The other option I have is to source a used Edelbrock 750 locally and try that. The problem is that the last time I had one of those on the car, it would run out of steam about half way through second gear. I don't know what was causing it, but I suspect that it was running out of fuel. I would rather find an Edelbrock AVS Thunder 800, but even the used ones seem to be high priced.

I checked my cap and rotor - they look fine. When I say it was running like crap, it basically had no power and was popping through the exhaust (like a misfire). I will probably go back through the spark plugs and make sure that I didn't crack one putting it back in. I will also check the plug wires to make sure that they look okay.

I hate dealing with something like this - it just kind of ruins my week (especially since it is my daily driver).

1971 Malibu, factory buckets/full gauges/console, 377 roller cammed small block, Turbo 400, 3.42 10 bolt posi (Buick), - All your base are belong to us.
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post #32 of 48 (permalink) Old Nov 26th, 18, 10:02 PM
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Re: Fuel Mileage Drop...

If it ran ok before the work check firing order 18236572
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post #33 of 48 (permalink) Old Nov 26th, 18, 10:06 PM Thread Starter
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Re: Fuel Mileage Drop...

Quote:
Originally Posted by 1967 chevelle malibu View Post
If it ran ok before the work check firing order 18236572
I did one cylinder at a time, so the firing order is correct. It would start and idle just fine - no misfires. I just located an Edelbrock 1411 750 CFM carburetor for $80 locally that was removed about 3 weeks ago. Hopefully I can just bolt it on and go. We'll see how it does.

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post #34 of 48 (permalink) Old Nov 27th, 18, 2:38 PM
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What timing curve are you running?
Vacuum advance?
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post #35 of 48 (permalink) Old Nov 27th, 18, 3:11 PM Thread Starter
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Re: Fuel Mileage Drop...

I picked up another carburetor today to get me by until I can repair the threads on the Speed Demon. Once I got it home, I decided I would double check the spark plugs. Well, I discovered that the number 6 plug wire was broken. I got the plug wires rectified, and I am waiting on some sealant to set up before I start it up with the new carburetor. Unfortunately, I now have to source an air cleaner stud - the one I bought from O'Reilly is too short. I will update on how it runs (if it runs at all).

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post #36 of 48 (permalink) Old Nov 27th, 18, 3:15 PM
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Re: Fuel Mileage Drop...

1/4-20 all thread is what I use for the studs.
I usually get it in 4 foot or longer lengths.. good stuff to have around.

If your recent edelbrock carb score runs rich try swapping front and rear jets. move front to rear etc.


I have a used 800AVS and I never stuck it on a car yet.
When i got it the needle and seats were DIRTY!! guy had all kinds of issues with it ..that I feel was the only issue


I like the AFB style myself.
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post #37 of 48 (permalink) Old Nov 27th, 18, 3:28 PM Thread Starter
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Re: Fuel Mileage Drop...

Quote:
Originally Posted by jeff swisher View Post
1/4-20 all thread is what I use for the studs.
I usually get it in 4 foot or longer lengths.. good stuff to have around.

If your recent edelbrock carb score runs rich try swapping front and rear jets. move front to rear etc.


I have a used 800AVS and I never stuck it on a car yet.
When i got it the needle and seats were DIRTY!! guy had all kinds of issues with it ..that I feel was the only issue


I like the AFB style myself.
The stud I got was just too short. I had an Edelbrock 750 in the past, but it would always run out of steam 1/2 - 3/4 of the way through second gear. I was using a mechanical fuel pump and that may have contributed to it. I now run an Edelbrock QuietFlo electric pump that is preset at 6 PSI, so it should be perfect for the Edelbrock. I really wanted to get a Thunder AVS 800, but no one ever sells them cheap around here (I got the 750 for $80). We'll see how it does.
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post #38 of 48 (permalink) Old Nov 27th, 18, 3:35 PM
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Re: Fuel Mileage Drop...

yea 80 is not bad at all.
I have not had any of them run out of steam on me yet.
I think you nailed it on running out of fuel.

I stuck an 800 performer series on an 11:1 compression 396" that has [email protected] .050 cam and ran to 7000 rpm, that carb wanted a lot more jet.
It had the same jetting as the 750 I had.
Man it popped and carried on until I jetted it way up and installed 65-37 rods in it.

Ran great then.
That was years ago and just this year I installed a tunnel-ram on that 396 and 2 600 edelbrocks.
HUGE difference in power everywhere.
Actually had the owner shaking from the adrenaline rush.

Carbs are fun.
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post #39 of 48 (permalink) Old Nov 27th, 18, 9:46 PM Thread Starter
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Re: Fuel Mileage Drop...

I finally got it up and running today. It had a hesitation off idle while sitting in the driveway, so I adjusted the accelerator pump setting - no hesitation. I took it out for a drive and all of my power was there (stupid spark plug wire). It pulled all the way to 6,000 RPM in first and second without missing a beat. The only issue I am having is that when I come to a stop, the engine does not want to drop down to my idle speed (750 RPM). I have to blip the throttle and then it will come down.

So, I let it run the carburetor empty in the driveway, then I checked the throttle linkage and movement - it seems to be fine. It was doing the same thing with the Speed Demon. I am wondering if it is possible that my mechanical advance mechanism in the distributor is not full retracting. I had the cap and rotor off yesterday while checking things out and I moved the weights by hand and released them - they seemed to snap back okay. I may have to open it back up and move the mechanism slowly back and forth to see if I can feel any drag or hangups.

But, as far as the Edelbrock carburetor goes, it seems to be running just fine. I may even notice better mileage if I can keep my foot out of it.
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post #40 of 48 (permalink) Old Nov 27th, 18, 9:53 PM
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Re: Fuel Mileage Drop...

Brian, I think I have some 12-24 heli coils. You up for a trip to the NW valley?

or this, if you have Prime these would be there Thursday.



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post #41 of 48 (permalink) Old Nov 27th, 18, 9:56 PM Thread Starter
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Re: Fuel Mileage Drop...

Quote:
Originally Posted by Tom Mobley View Post
Brian, I think I have some 12-24 heli coils. You up for a trip to the NW valley?

or this, if you have Prime these would be there Thursday.
https://www.amazon.com/Thread-Kits-1...4+helicoil+kit
I appreciate the offer, Tom, but I ordered a kit off of eBay, along with an extra pack of the coils. Coming from Colorado, so it should be here in a couple of days. In fact, the kit I ordered is the exact same one - only it was about $2 cheaper on eBay. All of the threads for the bowl screws look okay - it's just the base plate threads in the body that are messed up. Who knows - by the time I get it fixed, I may decide to stick with the Edelbrock (especially if my mileage improves).

1971 Malibu, factory buckets/full gauges/console, 377 roller cammed small block, Turbo 400, 3.42 10 bolt posi (Buick), - All your base are belong to us.
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post #42 of 48 (permalink) Old Nov 28th, 18, 3:57 AM
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Re: Fuel Mileage Drop...

Brian,
If you are going to stick with the AFB [ a wise move ], it would pay to check the transfer slot position [ because you had an off idle flat spot ]. Looking at the cam duration & engine size, you might have too much slot exposed at idle. 0.040" is ok, a bit less is better, over 040 is too much. If over 040, bypass air is needed by drilling the pri t/blades, starting with a 3/32" hole in each. Because of the flat spot & now also the additional air, you should increase the IFR 0.002". This does NOT richen the idle, it richens off idle where the flat spot was. Also check float level is correct, 7/16".
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post #43 of 48 (permalink) Old Nov 28th, 18, 11:58 AM Thread Starter
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Re: Fuel Mileage Drop...

Quote:
Originally Posted by Gtogeoff View Post
Brian,
If you are going to stick with the AFB [ a wise move ], it would pay to check the transfer slot position [ because you had an off idle flat spot ]. Looking at the cam duration & engine size, you might have too much slot exposed at idle. 0.040" is ok, a bit less is better, over 040 is too much. If over 040, bypass air is needed by drilling the pri t/blades, starting with a 3/32" hole in each. Because of the flat spot & now also the additional air, you should increase the IFR 0.002". This does NOT richen the idle, it richens off idle where the flat spot was. Also check float level is correct, 7/16".
Once I adjusted the accelerator pump rod position, the flat spot seems to have gone away. The way it was adjusted when I got it, the throttle would have to move at least 1/8" before fuel would squirt - now it squirts as soon as it starts to move.

1971 Malibu, factory buckets/full gauges/console, 377 roller cammed small block, Turbo 400, 3.42 10 bolt posi (Buick), - All your base are belong to us.
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post #44 of 48 (permalink) Old Nov 28th, 18, 3:51 PM Thread Starter
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Re: Fuel Mileage Drop...

I looked at the advance mechanism in the distributor today and it seems to be just fine. It move smoothly and returns back to where it should. So, now I have to figure out why it won't return completely to idle after I come to a stop. I do not have the choke wired up, but I am wondering if something on the choke mechanism could cause it to hang up. If so, I will just remove the choke components completely.

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post #45 of 48 (permalink) Old Nov 28th, 18, 7:11 PM
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Re: Fuel Mileage Drop...

Is there play in the throttle shaft, is the return spring strong enough? Worn throttle bodies can cause the plates to hang up.
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