stock 350 getting about 8 miles a gallon?! - Team Camaro Tech
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post #1 of 15 (permalink) Old Nov 9th, 01, 06:12 PM Thread Starter
Join Date: May 2000
Location: Fremont, CA USA
Posts: 17

Hi all. I have a 67 and I just spent the last 2 years putting every cent I have into fixing this car. I put a Goodwrench 350 in it (God I wish I had looked for a better engine BEFORE I spent so much on it) and all new bushings, shocks, springs, clutch, etc. I have a saginaw 4 speed (if anyone in the bay area puts in 5 or 6 speeds, please e-mail me) and the rear end is stock. My main question is, why in heavens name am I only getting 8 miles a gallon?!?! I was told I should be getting more like 15 mpg, and I'm not sure exactly why. I'm pretty sure my carb has something to do with it, cause I purchased a holley 750 when I was planning on building the engine up, but I am still using it on my stock 295 hp Goodwrench. Another question is, I have puddles of oil under the car, but the engine is brand new and I can't see any visible leaks. The starter has a lot of oil on it and seems to be under the leak. Is there a common spot back there that leaks on these engines? Any help would really be appreciated.

Thank you
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post #2 of 15 (permalink) Old Nov 9th, 01, 07:49 PM
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Just as a reference, I put a rebuilt 350 (4 bolt main, long block) in my '72 3/4 GMC 4X4 which cost me $850.00. I am getting 12.5 mpg average with this. I would think that you should definitely be getting better mpg.

67 BB RS, M22
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post #3 of 15 (permalink) Old Nov 10th, 01, 12:33 AM
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check your manifold, but I'm guessing it's at the negative terminal right above your fuel pump, that's where mine leaked, and I mean the thing pissed oil. a 750 is way too much carb, I have an RV cam in my goodwrench (which I really recommend) and it still runs rich on a 600cfm performer.
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post #4 of 15 (permalink) Old Nov 10th, 01, 02:55 AM
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How do your plugs look? The Holley has alot of adjustability and there are some good reference books available as well as their website and tech line. I suspect you will see an over-rich condition. Starting points can be fuel pressure, float level and the health of the power valve. Tell us more as you dig into this. I get about 14 with a fairly stout 355 so it is feasible.

Rick Dorion
69 RS Conv,355,M20,4.10's and I don't worry about stone chips.
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post #5 of 15 (permalink) Old Nov 10th, 01, 04:52 AM
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are you sure your leaking oil and not tranny fluid, or power steering fluid? yes i too thing that thar carb is too big. a sure way to tell would be to swap on a friends for a while, just to see if it helps. are you sure you don't have a leak in the fuel system? if you have a crappy fuel line some of your gas will leak out, but probabally only when you have the fuel pump running.
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post #6 of 15 (permalink) Old Nov 10th, 01, 06:13 AM
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As for gas mileage, you should definitely be getting better mileage than that unless you have 4.56 gears or something. With my built 400sb 2.73 rear gears, and a 600 double pumper, I get around 15-16 mpg on the highway. Like was previously said, the 750 cfm carb is probably a little big for that engine, but if you are patient, you should be able to tune it to work fairly well. Take a look at your plugs. I would bet that they are black from too much fuel. Adjust your floats to where the fuel level is just below the sight plugs. Adjust your idle mixture screws to where you get the highest manifold vacuum reading (you'll need a vacuum gauge). If the plugs are still black, go down two sizes on the main jets, readjust your idle mixture screws and drive around some more. If your plugs are still black and you are still getting horrible gas mileage, you will probably want to start changing some other things on the carb. The jetting that Holleys come with (in my experience) is pretty close and you shouldn't stray very far from it. Don't be afraid to try something else. Just make sure that you know how to put it back if it doesn't work. Also, get yourself a good Holley tuning book. I just got one from Summit for $12. They aren't much and they are well worth the money.

As for the oil leak. First, make sure that it is oil and not transmission fluid. I would look at the valve cover gaskets, rear of the intake gaskets, and maybe the rear main seal. Good Luck
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post #7 of 15 (permalink) Old Nov 10th, 01, 06:17 AM Thread Starter
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Location: Fremont, CA USA
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Well, I haven't gotten a chance to check the plugs, but I know it's not the tranny cause there is no oil on it, and it's not the fuel lines or pump. I just put a holley fuel pump and new hoses for that in. I want to switch the minfold and the carb with a smaller carb, the only problem is all my friends drive rice rockets or 4th gens. I will have to save up a bit for the parts, but if I can get out of work today or tomorrow, I'm going to shoot over to the Goodguys show and see what deal I can get. Another thing I just thought of, and this MIGHT be related, is that the engine seems to top out at 4500 rpm or so. It won't go above that and at every rpm it sounds 1000 higher than what it really is. when I'm just cruising, it hears like I should change, but it's only at 2000 rpm or lower. This is a big problem and I really appreciate any help you can offer.

Thank you,
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post #8 of 15 (permalink) Old Nov 10th, 01, 06:43 AM
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Go to the Good Guys and find a performer and a Qjet. There usually are a bunch there cheap. If you don't find one I have a spare I will sell you cheap.

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post #9 of 15 (permalink) Old Nov 10th, 01, 02:30 PM
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In my opinion, the 750 can be made to get reasonable economy, but you cant beat a q-jet, especially on a mild engine. Are you running the 750 on a stock iron intake (with an adapter)? What is your timing set at? What kind of distributor? How many rpms at highway speed? How much vaccuum at idle? You should have around 19"-20" vaccuum. Are you running vaccuum advance (you should be). What kind of exhaust system? Which tranny?
The oil leak is probably your valve is way too common with smallblocks.

375hp 78 Chevy truck
77 Chevy Nova
95 Chevy Lumina 3.4L
and building a 78 Nova
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post #10 of 15 (permalink) Old Nov 10th, 01, 08:29 PM
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All the carb answers are worth checking.a customer brought her car to me complaining of 'horrible' gas mileage.Problem? Dragging brake caliper.Just a thought.
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post #11 of 15 (permalink) Old Nov 11th, 01, 12:47 PM
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A 750cfm 3310-2 Holley vacuum secondary carb should be jetted from Holley to feed the 375hp/396 so prob. is very rich.

My stock L-48 350 always got about 16/17mpg until I started romping on it. The only thing I did to it was change to the 350hp/327 hydraulic cam. (M-20 and 3.31's). pdq67

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post #12 of 15 (permalink) Old Nov 11th, 01, 02:07 PM Thread Starter
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Well, my intake manifold is an old beat up edelbrock and I definately need to change it soon. I also am using a crappy points distributor that needs to be changed and I have an HEI from delco sitting in my garage that is going in. Am I correct in assuming that most of you believe the problem lies solely in the carb? As far as the timing goes, and vaccum stuff, I have no idea. I am not great at tuning and thus I have tons of problems like this. I am taking it to a friends shop on Tuesday to hook it up to a gas analyzer and he is going to show me how to tune the carb right. What timing should I ask him to do for me? I know I have a lot of questions, so thank you for any answers. The only other thing I'm worried about is the rpm problem. I am running a saginaw 4 speed and go about 70 at 3000 rpm in fourth. I think that is fine, but it seems like the engine is running at 4000. It tops out at 4500 rpm which I believe is way too low for this engine. Thank you all again.

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post #13 of 15 (permalink) Old Nov 11th, 01, 02:16 PM
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Also look at the gear ratios on your saginaw ...If you have a 4 spd that comes from a 6 cyl car , you are going to be running higher rpms in the lower gears ... This, along with the big carb ( what rear-end are you running ) can all combine to get you high rpms and low speed ... also make sure clutch is not slipping and brakes are properly adjusted
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post #14 of 15 (permalink) Old Nov 11th, 01, 02:34 PM
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What are your driving habits? Can you go a full tank without opening the secondaries? How much idling time (tuning etc.) does your car get per tank? See where I'm coming from? Fill the tank and get on the freeway at 60-65mph for a half tank or more and then fill it up and check your mileage. Also be sure your speedo is right because that will have an adverse effect as well. If you're still dis-satisfied then it's tune up time, carb, timing, plugs (plug gap) and even the air cleaner. Also look at where you buy gas, it could have an effect.

"The '69, the '96 & the club"
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post #15 of 15 (permalink) Old Sep 3rd, 05, 06:59 AM
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Re: stock 350 getting about 8 miles a gallon?!

The Holley is a shame to waste, but needs to be elsewhere, I dont agree that a rooster is the best carb in the world. I do think it's small primaries make idle overload and such much less of a problem. If you know how to adjust one, and this can be fun, go to it.

A stock manifold, if it a 4 barrel with no adaptor, ought to be fine. If it is, odds are its for a spreadbore. A CFM of anything ove 600 is a waste on a stock, low compression motor. A stock spreadbore deseves a spreadbore carb, not an adaptor plate? Is your Holley a spreadbore? They do make some and so do others. Roosters are not the only ones.

The gas mileage you are getting is nutty, had a 74 350 in a Nova with the same kind of problems, yet it was a two barrel. Factory stock smog and emission controls and a two barrel. Had a newly built 350 with Edelbrock manifold and 1406 carb (650) that did 14-16 in a ONE TON VAN consistently. I got 10 or better towing a fully loaded trailer at 70-75 miles an hour. It's all in the basic setup.

Two things come to mind beyond selling the Holley. Ignition and proper venting of the motor to make sure you dont have a bunch of pressure blowing oil out. Stock distributor makes me wonder about the oil leak. Check stock gasket under distributor? Lots of folks leave them (dist hold down) a little loose because they have tuning problems and wish to move distributor easily. DONT?? Breathing of the motor makes me think about valve cover leak in the back near the starter.

Have a 450 Holley working great on a basicly stock 283 in a pickup truck. Had similar problems with that one when I first put this together cause my oldest son just had to buy another carb that I didnt recommend. I installed it and turned my back on his troubles. I soon won that debate. Gave That Holley away.

HEI is not a cure-all. It does make things simple. If you go that route, make it a good quality, new product. Make sure it has higher capacity module and coil installed and do not skimp on this. The GM original, a used one at that, may well give you good service at simple driving, but performance when you decide to test your rig, will let you down. May seem better than what you had, but the right way will astound you with the difference.

Someone mentioned plugs. The differences in spark plugs may seem minor, but having the right ones are a must. Only you know what you did but the engine must have come with recommendations. The plugs will be different depending on basic setup. Depends on pollution controls and such. Carburation has to be in tune with this and compression. What kind of compression did you purchase?

Just one last little thing. Did you get the choke setup right? Electric? Try running it without the choke plate ever closing? May be fun to start, but may answer the adjustment and gas wasting question immediately.

lastly, I think you did purchase a good engine product, but all manufaturers have lemons. if you cant make lemonade out of this one, I would complain loudly and find some satisfaction.
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