For the most part, the 350 in my Laurentian runs very well. No lag at all, good response etc. However I do have two minor issues. 1-fuel consumption. I haven't tracked it yet, but I have used half a tank in about 90 miles. That equates to about 11 miles per imperial gallon with mostly hwy driving. That seems a bit excessive. My gearing is something like 2.80:1 as far as I know and my trans is a THM350. Should I look at smaller jets for the carb? I hate to sacrifice driveability. I'm running about 12 degrees advanced timing. The vacuum advance is working. I don't notice any black smoke on acceleration either. Also, on heavy stopping, the car will often stall. She'll start right up. Slow stopping is fine. Would this be a float issue or do I need one of those plunger stops for the throttle return?
I am running a 600 cfm Performer on my 350 in the LeMans, TH350, 2.73 rear end and Todd my mileage is about the same as your's. I can watch the gauge go down on trips to cruise ins. Cost me $25 to go Saturday night from East York to Etobicoke and back. I have leaned this puppy out so far it whistles. Recommended fuel is 91 ocatane minimum too and I assume same for you.
I have been reading my manual and it suggests resetting the choke and changing metering rods or jets or both. Highway acceleration is very good but the City trips are brutal on fuel consumption. I am reluctant to start messing with the carb, I was going to get new plugs and wires this week and see if that helps.
Can you imagine that we are running similar sbc passenger car engines, just think how our Big Block buddies must be doing. Now that I think about Dad always had to stop half way for gas when we went to the cottage in our family 350 Lemans back in the day.
I suggest that your idle is set too low, that's why you are stalling. I have mine set just above stall, shutters sometimes but never quits.
I'm with you-afraid to mess with the carb as it runs well otherwise. Mine has a manual choke which I prefer anyway. Now that I think about it I remember my dad saying his only got about 10mpg. Of course back then 10 bucks filled it.. I turned my idle up and it still stalled on heavy braking. Carl- I'm not sure of the # but it's a dual feed, vacuum secondary universal Holley 600. Carb was brand new (thanks to Carl!)
sounds like the one/both bowl levels might be too high, spilling fuel out the vent tube. you can check the float level, with the engine running, remove the sight plug on the side of the bowl, fuel should barely trickle out. idle mixture is easy enough, adjust the idle speed to about 700 rpm, slowly turn one mixture screw in, about a 1/4 turn at a time till the engine just starts to stumble/idle rough, turn the screw back out a 1/2 turn. repeat other side. readjust idle speed with car in gear. if you have a vacuum guage, adjust till you get your highest vac reading. i've always found holleys to be almost right on the money right out of the box. your mileage does sound a bit low, i've had my 800 holley, 454, 3.73s only around this area, probably roughly the same mileage.
Tough to beat a well running Quadrajet on all counts. The one on my L-69 would flow up to 800 cfm when demanded to yet the primaries were misers like driving around on a dualjet. I want one back on my car!
Hey Todd, place your order for a Quadrjet with Astro-Jet, he is sourcing one for me...he knows people. If you get him the original Rochester number he may find it or get something that works. Probably a $300 to $400 deal with a re-build. You can search the web for the part number. I would think your # is something like 7029272.
Tough to beat a well running Quadrajet on all counts. The one on my L-69 would flow up to 800 cfm when demanded to yet the primaries were misers like driving around on a dualjet. I want one back on my car!
I've said it before and I'll say it again, the Q-Jet is the best all around carb ever invented. Whoever the Rochester engineers are who came up with it should be in at least the GM, if not the automotive Hall of Fame. If you did nothing else but went to the track and were running full throttle all the time, I would say yes, get a Holley double pumper but for all around street use, you can't beat the mighty Q. They are so good that many other manufacturers sourced them to put on their engines, including Ford for the mighty 429CJ in 70-71. Properly jetted, they can return very good fuel economy while cruising around on the primaries but the big secondaries are there when you need them. Plus there is nothing like the moaning sound of a quadra-jet when it's going full out.
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Hillar
1970 LS4 (eventually an LS5) Laurentian 2dr hdtp -and a bunch of other muscle cars...
I have found the answer to my poor mileage problem. I usually drive the LeMans to cruise ins and follow 65 Camino there and back. With 65 Camino it doesn't matter if he's driving his 400 HP Mustang or 200 HP El Camino he never gets out of second gear, so that means I never get into high gear. Putt Putt Putt we go. Probably carboning up my car too.
For the past two days I have been using the Lemans as my driver as Cadillac is in for service. I have commuted to work, gone out for dinner and taken in a cruise in. I have driven the car like I usually drive, maybe a little harder too and lo and behold one eighth of a tank of gas, like 3 gallons max.
I know 65 Camino posted "hypermiling" topic but to me he is a "Miling N00b"!
Why would you never get out of 2nd gear? Left to it's own devices, any THM will shift into 3rd gear by about 25-30 mph. Were you deliberately holding it in 2nd? Why would 65 Camino drive around in 2nd gear? That night we all went to Applewood, surely you weren't driving in 2nd gear on the way back?
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Hillar
1970 LS4 (eventually an LS5) Laurentian 2dr hdtp -and a bunch of other muscle cars...
Why would you never get out of 2nd gear? Left to it's own devices, any THM will shift into 3rd gear by about 25-30 mph. Were you deliberately holding it in 2nd? Why would 65 Camino drive around in 2nd gear? That night we all went to Applewood, surely you weren't driving in 2nd gear on the way back?
I was leading that night !
You members of the Ontario Bar take everything so literal, LOL, it's a joke!!!!
A properly setup Q-jet IS the best carb, bar none! But..... can you tune them? I cannot, but i can tune a holley. There is a guy who is the Q-jet expert, he can make a q-jet run the same number or better than any prepped holley AND get better mileage.
The Q-jet guru?
Cliff Ruggles.
He is a pontiac nut too!
http://www.cliffshighperformance.com/
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'74 ventura with a P455. Runs 11.98's in the quarter so far, shooting for low 11's.
1980 chev pickup, 6'' lift and 36'' iroks, 10k winch, soon to have a pontiac 400 under the hood.
Thanks for the tips guys. I'll run the Holley for now and tweak it a bit. Don't I need one of those large adapters to run a Q-jet on an Edelbrock intake?
The Performer Intake should accept a Quadrajet, I believe the manifold is able to take a spreadbore or squarebore. My intake is a Bowtie ZZ4 which is the LT-1 replacement and it is almost identical to a Performer. I had a Quadrjet on it before going to the Edelbrock carb. Having said all of this I like my Edelbrock carb too, it really hauls on the highway when the secondaries come on and you downshift the tranny, sounds like it is sucking the hood in too. I agree with BILTIT, once a Q-jet goes wrong it's wrong!
I was able to change out most tune up parts on my engine. New plugs, new Rotor, new Distributor cap. Wires are on back order. The result was that I was able to take 3/4 of a turn out of the idle mixture screws and lean it out even more. I was amazed that those pieces made such a difference. So I was way too rich. Car is running way better, took it out to Ajax Canadian Tire cruise last night a good 30 minute 401 run. It was purring and only used about a quarter tank. We drove at about 60 to 70 mph except just nearing Don Valley cutoff to head into Toronto I blasted the doors in on 65 camino and his Dad and tipped 100 mph.....bad boy, I feel so bad, just think of the wasted gasoline.
That's great! I'm hoping I can achieve similar results. Our cars probably weigh about the same. I remember my dad's 77 LeMans with a 350 4bbl (stock however) got very good gas mileage. Todd
i was thinking on changing my two barrel to my q-jet and intake from my 305. Im not really looking for more power(its a 283 in a 19 ft. long car, how fast can i go!) but i did like the q-jet and i miss that four barrel sound. Would it be worth it or do you guys think keeping it it orig. would be the way to go as far as gas millage and looks.
I think you are probably good with the 2bbl. They are about 490 cfm anyway and you are driving it in low speed conditions. To get a good sound you can switch to open element air cleaner, there is a 2bbl to 4bbl opening adaptor that lets you run those open air cleaners. I may have the part lying around. I got it at Karbelt years ago. I used it before on 2bbl and you get the same sound as a 4bbl when you mash it.
