Holley or Quadrajet
Thread Starter
Instructor
Joined: Dec 2008
Posts: 147
Likes: 16
From: GA
Holley or Quadrajet
I have a 70 L46 350/350hp. I am having trouble getting it to Idle. It runs great at 1500 and up but starts to choke up below that. I started adjusting the valves and figured out it had solid lifters so I gapped them at .020???? Timing is set to 36 deg at 3000rpm and dwell is 30. I think it is the carburator and want to know if I should rebuild it or one of my old holleys I have sitting around. A 4150 list 3310 (750cfm vac sec auto choke) or a 4150 list 4777 650cfm man choke dbl pump).
Comments please..
Thx
Buddy
Comments please..
Thx
Buddy
Drifting
Joined: Sep 1999
Posts: 1,970
Likes: 91
I have a 70 L46 350/350hp. I am having trouble getting it to Idle. It runs great at 1500 and up but starts to choke up below that. I started adjusting the valves and figured out it had solid lifters so I gapped them at .020???? Timing is set to 36 deg at 3000rpm and dwell is 30. I think it is the carburator and want to know if I should rebuild it or one of my old holleys I have sitting around. A 4150 list 3310 (750cfm vac sec auto choke) or a 4150 list 4777 650cfm man choke dbl pump).
Comments please..
Thx
Buddy
Comments please..
Thx
Buddy
Racer
Joined: Sep 1999
Posts: 336
Likes: 0
From: Scott AFB IL
Coke or Pepsi ?
Q-Jets are finiky to set up, but once dialed in, they hold for years without adjusting. Hollys are easier to dial in, but need attention a little more often, so the question is, are you going to try the rebuild or are you going to pay someone? I would suggest spend the money, drop the Q-jet off, and pick it up when done.
If you want the experience, get a kit for the holley and try it. Not impossible, just need a lot of patience. There are a lot of screws, springs, etc. Keep small tubs or ziploc bags handy and label them. I would think the 650 would be enough for your 350 application. Unless your've been in the motor of course. (cam, bore, etc.)
I agree with Dennis, I think you have hydraulic lifters. Also, I thought the clearance should be 0.60, better get a book and see if I'm wrong, that might be part of your problem. Too little clearance and no passing of gas(es). I hate when that happens.
If you want the experience, get a kit for the holley and try it. Not impossible, just need a lot of patience. There are a lot of screws, springs, etc. Keep small tubs or ziploc bags handy and label them. I would think the 650 would be enough for your 350 application. Unless your've been in the motor of course. (cam, bore, etc.)
I agree with Dennis, I think you have hydraulic lifters. Also, I thought the clearance should be 0.60, better get a book and see if I'm wrong, that might be part of your problem. Too little clearance and no passing of gas(es). I hate when that happens.
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
L46 has hydraulic lifters. There should be no clearance. Buy a Chassis Service Manual (official factory are the best), or do a search on the forum for information about adjusting valves. You need to tighten the valves to zero lash, then tighten the nut down ½ to one full turn (depends on the source of the instructions) either works, but there are logical reasons for doing it either way.
Unless your old Holley is a spread bore model, you can't put it on the intake manifold. Your best bet it to dial the Q-jet in. Set up properly your engine should run like a top. Learnn exactly what you have, check that the basics adjusted correctly.
Unless your old Holley is a spread bore model, you can't put it on the intake manifold. Your best bet it to dial the Q-jet in. Set up properly your engine should run like a top. Learnn exactly what you have, check that the basics adjusted correctly.
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Burning Brakes
Joined: Oct 2001
Posts: 911
Likes: 5
From: TN
70 350/350
The 4777 Holley will not fit on your 70 350/350 without an adapter plate to convert from the QJet's intake design since the 4777 is a square bore type.
With an adapter you will need to check the hood clearance.
I am using a 4777 Holley 650 on my 1970 since I installed a ZZ crate engine many years ago. The aluminum intake on my ZZ crate engine is similiar to the LT-1 intake and is a square bore. If it could of been used I would of stuck with my Holley 6210 double pumper 650 spread bore.
With an adapter you will need to check the hood clearance.
I am using a 4777 Holley 650 on my 1970 since I installed a ZZ crate engine many years ago. The aluminum intake on my ZZ crate engine is similiar to the LT-1 intake and is a square bore. If it could of been used I would of stuck with my Holley 6210 double pumper 650 spread bore.
Thread Starter
Instructor
Joined: Dec 2008
Posts: 147
Likes: 16
From: GA
My L46 should of had hydraulic lifters but I assume some one has been in it. I don't know what they did so I have no idea what the gap should be on the rockers??? Thinking it was a hydraulic I adjusted the valves to zero lash then added a 1/4 turn. The motor spun like a top with zero compression, this is why I think it has been changed to a solid lift cam.
Any comments on what the gap should be????
It has a rebuilt q-jet that was a 1975 model. I am thinking the metering rods springs are too stiff since a higher hp motor like mine will create less vacuum and the metering rods are not pulling into the jets. This also may explain why my idle adjust screws have no effect.
Am I correct????
Any comments on what the gap should be????
It has a rebuilt q-jet that was a 1975 model. I am thinking the metering rods springs are too stiff since a higher hp motor like mine will create less vacuum and the metering rods are not pulling into the jets. This also may explain why my idle adjust screws have no effect.
Am I correct????
Drifting
Joined: Sep 1999
Posts: 1,970
Likes: 91
My L46 should of had hydraulic lifters but I assume some one has been in it. I don't know what they did so I have no idea what the gap should be on the rockers??? Thinking it was a hydraulic I adjusted the valves to zero lash then added a 1/4 turn. The motor spun like a top with zero compression, this is why I think it has been changed to a solid lift cam.
Any comments on what the gap should be????
It has a rebuilt q-jet that was a 1975 model. I am thinking the metering rods springs are too stiff since a higher hp motor like mine will create less vacuum and the metering rods are not pulling into the jets. This also may explain why my idle adjust screws have no effect.
Am I correct????
Any comments on what the gap should be????
It has a rebuilt q-jet that was a 1975 model. I am thinking the metering rods springs are too stiff since a higher hp motor like mine will create less vacuum and the metering rods are not pulling into the jets. This also may explain why my idle adjust screws have no effect.
Am I correct????
Drifting
Joined: Aug 2008
Posts: 1,381
Likes: 11
1) What method did you use to adjust the valves?
2) The factory metering rods, spring, and jets will usually still work fine even on an engine that's been mildly modified. What is the manifold vacuum at idle? If it is a steady 12" or more, the calibration in your q-jet should be ok. The rods, spring and jets do not control the idle. There is a completely separate circuit for this. Get the engine to idle as low as you can and look down into the primary bores - you should see no gas. Gas dripping from the nozzles will cause what you describe.
2) The factory metering rods, spring, and jets will usually still work fine even on an engine that's been mildly modified. What is the manifold vacuum at idle? If it is a steady 12" or more, the calibration in your q-jet should be ok. The rods, spring and jets do not control the idle. There is a completely separate circuit for this. Get the engine to idle as low as you can and look down into the primary bores - you should see no gas. Gas dripping from the nozzles will cause what you describe.
Melting Slicks
Joined: Jun 2002
Posts: 2,842
Likes: 99
From: Orrtanna Pa.
Even if you had a hydraulic cam with the lifters set loose it should idle . You'd hear some clacking noise from the rockers, but it should idle. Timing sounds fine too. I would try spraying carb cleaner around the intake, and carb throttle shaft to check for leaks.
If I remember right my 327 pulled about 20 inches vacuum idling with the 350 horse cam. and it was Cadillac smooth too.
If I remember right my 327 pulled about 20 inches vacuum idling with the 350 horse cam. and it was Cadillac smooth too.
Last edited by The Money Pit; Jan 28, 2009 at 04:37 PM.
Thread Starter
Instructor
Joined: Dec 2008
Posts: 147
Likes: 16
From: GA
I removed the Carb and found where someone had used the thin gasket under the thick gasket. It had the heat passage in the gasket which over hung the manifold and left a small area open. The Idle is better now but still not good and no response from the idle screws. While idling I looked down in the primaries and did not see dripping but I did see gas accumulating and running around on the top of the butterfly valves.
Is this normal??? Any more suggestions???
Thx
Buddy
Is this normal??? Any more suggestions???
Thx
Buddy
Drifting
Joined: Aug 2008
Posts: 1,381
Likes: 11
That is not normal and it is why the mixture screws do not respond. They control the fuel at idle and it comes from below the throttle plates. So if you are adding fuel ABOVE the throttle plates, as you describe, it idles off that instead. This can be caused by a few different things. A sticking needle and seat (not likely), a float that is set too high (maybe), or most likely from having the throttle open too far and allowing the engine to run off of the main metering system.
A couple more questions:
1)Do you have a vacuum gauge? If so, hook it to read manifold vacuum (if you don't have one get one they're cheap). If you have less than 12" or if the needle fluctuates your cam may be too big for the idle circuit in the carb or it may just be plugged with crap. Is it he original carb?
2)What RPM does it idle at?
3) Again - what method did you use to set the valves?
A couple more questions:
1)Do you have a vacuum gauge? If so, hook it to read manifold vacuum (if you don't have one get one they're cheap). If you have less than 12" or if the needle fluctuates your cam may be too big for the idle circuit in the carb or it may just be plugged with crap. Is it he original carb?
2)What RPM does it idle at?
3) Again - what method did you use to set the valves?
Thread Starter
Instructor
Joined: Dec 2008
Posts: 147
Likes: 16
From: GA
Assuming they are solid lifters, I set the Gap at .020 cold. 2 things make me think it is solid, 1. adjusting the valve anywhere past zero lash opens the valve, 2. It has screw in studs and guide plates which I do not think are stock.
I used TDC and 180 deg out to set the Valves. I was just trying to get it close until I got the Idle correct. Is it that important to do the intake almost closed, adjust the exh, blah blah blah etc... to adjust the valves initially?? It will sorta Idle at 550 and when I try to set it higher it jumps up to 1500 or so. It is not the orig carb because i see a 2000 rebuild sticker and the #17059286 says it is a 1979 auto carb. By the way, I have a 4 speed.
Thanx for helping,
Buddy
I used TDC and 180 deg out to set the Valves. I was just trying to get it close until I got the Idle correct. Is it that important to do the intake almost closed, adjust the exh, blah blah blah etc... to adjust the valves initially?? It will sorta Idle at 550 and when I try to set it higher it jumps up to 1500 or so. It is not the orig carb because i see a 2000 rebuild sticker and the #17059286 says it is a 1979 auto carb. By the way, I have a 4 speed.
Thanx for helping,
Buddy
Racer
Joined: Apr 2006
Posts: 340
Likes: 0
From: Warrensburg MO
Even with hydraulics, the lifters won't compress with oil in them, and your valves will open instead of the lifter collapsing.
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
is the qjet a carter or a rochester? i had similar problems (including the fuel leak) on my carter q jet. the ethenol in gas had rotted the fuel bowl. got an old rochester from my engine builder for $35 that he just pulled out of his junk pile, and bolted it on. runs great now. he said the carters are pos.
Thread Starter
Instructor
Joined: Dec 2008
Posts: 147
Likes: 16
From: GA
How do I know if my lifters are solid or hydraulic? I dont think it matters too much right now because the car runs smooth over 1500 and has great response.
I will do a Vac test today and post it.
Thx
buddy
I will do a Vac test today and post it.
Thx
buddy
Thread Starter
Instructor
Joined: Dec 2008
Posts: 147
Likes: 16
From: GA
OK, motor cold, cranked it with a vac gauge on the manifold. It will only idle roughly for a minute until it loads up and quits. Vacuum was unstable but around 5 or less on the gauge at about 550 rpm. Should I warm the motor first??? Runs the same hot or cold.
I guess at this point I need to figure out whether I have solid or hyd lifters and correctly adjust the valves. What procedure do you recommend and how do I determine for sure the lifter type?
Thx
Buddy
I guess at this point I need to figure out whether I have solid or hyd lifters and correctly adjust the valves. What procedure do you recommend and how do I determine for sure the lifter type?
Thx
Buddy