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Topic: Fuel problem 2

in Forum: C3 Fuel, Emission Control, and Exhaust Systems


Fuel problem 2

Posted: 8/21/05 7:20am Message 1 of 6
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Roseland, NJ - USA
Joined: 12/4/2003
Posts: 966
Vette(s): 1974, 454 with 4 on the floor, matching numbers.

In my original post (fuel problems), you guys came up with great suggestions. After checking things out, I've discovered some old problem are back, and my fuel problem is still here.

After replacing my plugs & wires for the third time in 1500 miles (burned boots) I noticed that I'm running lean (plug tips were white) which is causing other problems. 2 suggestions have been made by 2 different peole. One says that I can make adjustments on my Q-jet via 2 screws in front of carb. The other suggest that I need to replace the needles, or other related parts, and that the 2 screws are to adjust the idle.  My question is this: Who's right ? And If I can adjust the carb via the screws, which way do I turn them ? As you can see I'm not a mechanic, and trying to learn. Funny, I seem to remember knowing more in the 60's, and not having all these problems with my BB 65 GTO clone. Must be old age creeping up, or just the fact that it's a Vette, and I know squat about them. I'm about ready to cash in, buy a brand new toy (no Vette) where everything works,  has factory warranty, and call it a day.       




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Fuel problem 2

Posted: 8/21/05 9:11am Message 2 of 6
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BINGHAMTON, NY - USA
Joined: 7/19/2003
Posts: 3808
Vette(s): ......
The 2 screws in front of the carb,are for your mixture,air to fuel ratio,that is if you are running a quadra-jet carb,I don't know anything about Holleys if that is what is on your 454.In my opinion working on these old Vettes is the best part of owning one.Any body can take a new one to the dealer for repairs,I do all my own work on mine,except for machine work,I.E. bearing pressing ,stuff like that,there is a machine shop just down the road from my house,as long as I dont need work done in a hurry,all I have to do is drop the stuff off at the shop,along with the neccessary new parts to be replaced ,and he charges me next to nothing for the work.Working on your own car is great,hang in there,we will talk you through it,I've got to get out to the garage and finish up the work I've been doing on mine,I finally got around to pulling off the old intake manifold,and putting on a Edelbrock Performer,I rebuilt the Q-Jet a couple of months ago.


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Fuel problem 2

Posted: 8/21/05 12:45pm Message 3 of 6
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Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
Hang in there, buddy!!
The two screws at the front/bottom are mixture screws, but are only for the idle mixture, and have nothing to do with fuel after that. They only control it up to about 1000-1200 rpm.
The best way to adjust them is with a vaccuum gauge hooked up to manifold vac. Turn the screws (one at a time) in until the engine starts to stumble slightly, and then turn it out untill it starts to stumble again. From that point, screw it in ,and watch the vac. gauge. When you see the highest reading on the gauge, stop, and do the same procedure on the other screw. It will take a couple of times doing this to get the idle mixture right, so plan on taking a few minutes to do this.

In order to richen the main mixture, you will have to disassemble the carb, and change the primary jets, and needles. The secondary "jets" are not changable, but the needles are. They fit onto the top side of the secondary butterfly/choke plate, and move up/down with the plate to control the amount of fuel for the sec. side of the carb.

Just because the plugs are white, doesn't mean it's runnin' lean. The plugs should be white, with just a touch of tan/gray color. You might be using a plug that is too hot(temp. range) for your engine. You could try a cooler plug, and see how that works out.

Don't give up just yet! We'll help figure it out with you!


Joel Adams
C3VR Lifetime Member #56    

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Fuel problem 2

Posted: 8/21/05 6:43pm Message 4 of 6
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East Hanover, NJ - USA
Joined: 9/25/2004
Posts: 525
Vette(s): '68 Black Conv. Matching 327/300 4 Spd. P/S, P/B, P/W, Tele, A/C

Cookie,

Loose the headers..............

Install cooler plugs..............

Use the factory wire looms..

Anthony




Fuel problem 2

Posted: 8/21/05 10:13pm Message 5 of 6
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sonoma, CA - USA
Joined: 8/9/2002
Posts: 784
Vette(s): 72 LT-1 AC coupe,69 l-36 coupe
the tip of the spark plug doesn't always tell you the whole story unless you really have a problem, I.E. oil consumesion, rich fuel mixture, the tip design, extended or not, and heat range make a difference, to get a good reading and the car seems to be running OK the plugs should have maybe 5-6 hundred mile on them, when looking for the color look past the tip down inside towards the base of the center electrode for the correct color with a magnafying glass.
    Ron is right, what the hell would we do if we didn't work on our cars, its kinda like sex, working on these classics is like foreplay, and you don't rush it, and getting off by driving them is the end result.   


Fuel problem 2

Posted: 8/22/05 5:28am Message 6 of 6
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Roseland, NJ - USA
Joined: 12/4/2003
Posts: 966
Vette(s): 1974, 454 with 4 on the floor, matching numbers.

Thanks guys, just getting frustrated trying to fix the same problem. Since my burned wires are due to having headers, I followed the suggestion of a person who has the exact engine/header set-up as I do, Accel shorty plugs/extreme wires. 

As for the carb, it's been rebuilt, I'll get it done again and hope for the best.  




in Forum: C3 Fuel, Emission Control, and Exhaust Systems


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