I have a 71 GS 455 . It ran 13 flat for 12 years with a 118 cam, performer intake Fred Catlin Q-Jet, Stinger S-4 Hooker headers 3:73 gears and anyone could drive it. It was slowing down soI rebuilt it, ported the heads unshrouded the valves, took off .o2o installed a TA290 08H cam & kit notched pistons, took .o2o off the block ,fel pro gasket im guessing 10.25 , adjustible pushrods stock rockers TA super comp headers and a 3000 converter. The car SCREAMS, runs cool, and has great oil pressure but it wont idle Its ideling through the carb not the idle circit {I dont want to drill out the idle ports on this carb} I have cut 3coils from the primary spring, I hooked up my vaccume advance and welded beads on my advance weights so it idles at aprox 26 degrees{1300 rpm} and jumps to 34 total almost instantly. But in town its a 2 footer that dies often and you hafta turn back the timing to get it to start when its warmed up {EMBARASSING] So can I make a Q-Jet work or should I buy a Demon and single plane, if so which ones do you recomend? Or is my ignition the problem? Any input would be appreciated. thanks
I have the same trouble with my 413 cam. Not as bad as you. I can get it to idle but not on the idle circuit on my 850 Edelbrock q-jet or the 800 q-jet from my old motor. I have drilled a 3/32 inch hole in each plate and it is better. I am also wondering about enlarging the idle circuit to .093. Hoping to talk to a local carb guru this weekend. It did get better with the 3/32 holes. I have about 9-10 inches of vacuumn but I think it should pull 13. Intial timing is 22* 34* all in at 2000. This is not the first time this problem has been discussed but have not had anyone come up with the answer.
Big Cam, Wont Idle Thanks Doug, I dug up a Q-jet off a 73 455. I dont feel so bad about drilling. In Nov 02 Car Craft they rebuilt a Q-Jet for a 66 401 with a "Mild Cam" They drilled the idle tubes to .039 inch they said you could go from .031 to .049 and they said to be careful cause to much would (sour driveability). I may try this and the holes in the plates. I've got nothing to loose. I'm only running 7 lbs of vacuum, but I think the plates being open lowers the vacuum? My Chevy friends say I need a Holly or Demon to idle with that much duration. What do you all think? Thanks Lin
cam position? Guys, Did you degree the cams here, and where did you install them? (Intake lobe centerline) It is absolutely fundimetal that you check any new cam, when it goes in the motor, for lift, duration, centerline on both the intake and exhaust, and the installed intake centerline..(relative position of the camshaft, in relation to the crankshaft) With the 08H, I run it at 106*, and have absolutely no problem getting it to idle at 600 rpm, in gear, with a any carb/intake combo. Even with a tight converter, and the most troublesome carb to get to meter at idle with reduced manifold vacuum.. and that carb is the 1000 Thermoquad. many.. many un-nessisary holes have been drilled in the primary butterflies of these carbs. I used to idle my 308 equipped race car, with a 1000 TQ, at 800 rpm with that monster cam, and a loose converter, and that does required a .062 hole in the primary butterflies.. but that cam is 268/274 duration, on a 108 centerline.. way bigger than what we are talking about with these hoter street cams Have 3 cars in the shop right now, and have built many motors with this cam. But it is what I consider the "max overlap" cam for a street motor, at 19-20*.. But every one has the cam in at 106*, runs around 20-25* of intial timing and seals up well. Any error, in the position of the cam in the engine, valve and manifold vacuum sealing, carb cleanliness and function, timing advance (both initial, total, and the fact that all the mechanical advance comes back out of the distributor at the base idle), in park or neutral, are critical. The most common issue here is the cam being installed either retarded, or with not enough advance.. Advancing the 08H 6* gets the intake valve closed soon enough, to allow the engine to make vacuum, at low rpm. And it is very unlikley that advancing the cam 4* on the chain, got you 4* of actual advance.. Cams vary.. I have had to skip a tooth to advance the cam in the past, and then had to go back and install the rollmaster set on the retart marks, to get it where it needed to be.. nothing wrong with doing this, the engine has no idea of the postion of the timing chain, all it cares about is that intake valve is closing at the right time. Typically, to advance a cam 4-6 degrees, I end up on the 8* advance marks, but there is no pattern here, and I have to check each and every one. This is the main reason for degreeing the cam. The next most common problem is that the distributor has too light of springs on it, so it does not get all the mechanical advance out of it, at the curb idle in park.. and when you drop it into gear, it naturally slows the engine down, which causes the distributor to then go back to it's actual intial timing setting, which then causes the engine to slow down more.. and die.. it's a domino effect. Checking this is simple.. Start it up and warm it up.. disconnect the vacuum advance if your running it.. then hold the timing light to show the mark (any mark for that matter that shows up lined up to the timing tab) and then rev the motor up, and watch it move the mark up toward the water pump, release the throttle, and the mark has to then return to it's original position. Then, with the carb idle screw, slow the motor down to as low as it will run, while your watching that timing mark.. (easier to do with 2 people).. if the mark drops toward the ground, as the engine slows down, then the mechanical advance is not getting all the way back out of it. It's late, and this is just a quick check proceedure, we can get into the specifics of how much timing to run at a later date.. but I want both of you guys to go and check this... Typically, the advance curve of the points type delco distributor (with points or converted) has to start around 1100 rpm, and will be all in by 2800-3400 rpm, depending on the particular advance mechanism parts your working with. This is just fine. If you have it "all in" by 2000-2500, I would be willing to bet that distrib is in the advance curve all the time, and when the motor is running above, say..800 rpm.. when it drops below that when you put it into gear, then the mechanical advance drops out, and the engine dies. Running your vacuum advance from a manifold source, also contributes to this issue.. same deal, only it's dropping the vacuum advance out of it when the motor slows down, instead of the mechanical.. often times, this can be a combination of both.. This is the number one reason that a car drops more than 200 rpm, from park to drive.. just had a car in the other day, that idled at 1100 in park, and then 600 in gear, and this was exactly the problem. Easy to see and diagnoise if you know to look for it. Always run your vacuum advance from a ported source (meaning the throttle has to be open to expose the port to vacuum). The sole purpose of the vacuum advance is to add a little timing to the motor, to improve both part throttle performance, and fuel economy, at light throttle settings. Using it for anything else, typically causes problems with a combo with a larger cam. Small cam motors can typically get away with all kinds of little errors.. Also, get a vacuum reading from a good source (base of the carb).. that 08H cam cam will idle at 10-12 inches.. at 750 rpm.. the 413 will have 12-14 inches. If your running around 20-25* of true initial, and the distrib is functioning properly, but your vacuum reading is below the numbers I gave above, then a dozen Krispy-Kreams says that the cam does not have enough advance at it's installed position, and the intake valve is closing to late. Of course, any type of vacuum leak (at the valve seats, intake, carb base, or a hose, or other vacuum run device) will show the same symptoms.. if in doubt, plug every vacuum port. That should get you started. JW
Big Cam, Wont Idle Thanks Jim I borrowed a degree wheel, stared at it like an idiot and somehow determined 4* was straight up, my timing set only has 3 choices, if I got a different set and put it in 6* advanced would that work {I assume TA's new set isnt 4*off} You were right about my timing, I replaced the weights I'd welded with stock but left the heavier springs I got it to idle 13* 1100rpm but im not getting the total advance I should, and when its Idling it starts loading up, when you rev it back up the advance kicks in and takes forever to settle back to 13* & 1100 all of the time smelling eye watering rich. You hit on another thing I was in denial about, with my heads shaved .020+ over the years and block decked .020 and TA .062 intake gaskets I almost couldnt get the intake bolts started and the front and back have huge gaps the seals were loose in there so I filled em with RTV {Im a Redneck what can I say} I know I should have my intake shaved but they want to know how much & what angle, I dont know! and this is my first shot at the internet. Would TA's .015" or a stock gasket help? Im thinkin my intake is sealing and im still running a steady 7lbs vacuum inbetween it trying to die and the advance sending it the other way. I really appreciate you taking the time to respond, I think im seeing daylight at the end of the tunnel. Thanks: Lin
Lin, My advise is to get a set of the TA .032 gaskets, and then have the intake sides cut by a local machine shop, till those bolt holes line up nearly perfectly. I would venture a guess that if you could get the intake bolts in with the .062 gaskets, then the .032's will take care of most of it, you may just have to trim another 20 or 30 thou off the intake.. While it is my prefered method to use the .062's and cut the intake flange of the heads to line everything back up, I don't think that is real practical for you at this point. I am a little leary of the .015's or a stock valley pan, while I know guys are running this stuff and getting away with it.. there is just too much silicone involved in that deal for me to be comforable, and if you had seen the places I have seen that stuff end up, you would understand my concerns. But let's tackle one thing at a time.. I don't think the intake is your biggest problem, here.. let's get that distributor working properly, get 20-25* of true initial, with another 10-15* of mechanical advance in the thing (shoot for a total of 34*) and go from there. After you get that all squared away, then the next thing to do is to tackel the cam degreeing, and the intake fit, all in one shot. Once your sure of the cam position and intake sealing, then we can talk about the carb, but right now, with 7" of vacuum, we need to address these items first. Let me know if you have any specific questions, and just as soon as I can, we will be going thru cam degreeing on the board here, as part of the dyno project we are doing, and I will do it both with the heads off, and the heads on.. JW
Jim, Thanks so much for taking the time to address this. My builder set the 413 up at 106* I have my initial timing at 22* and 34* in at 2200 rpm. Not running the vacuumn advance since I set the initial at 22*. Will set it back up when I make sure the vacuumn limit is set lower. Actually mine idles just fine at 950-1000 rpm in neutral and drops to 800 in gear. The problem for me is it is not running on the idle circuits and the idle adjust has no effect becuase it is running on the primary's. Can live with it but you cannot really dial in a q-jet without all systems doing their job. I am working on changing back to my Postons manifold instead of SP-1 (tired of dealing with the clearance problem) and using the .030 two piece gaskets instead of the one piece. Lin. Will let you know what works for me. And results of my testing. Should start checking things this week.
Big cam wont idle Thanks Jim I put my welded weights back on added metal until it idles at aprox 22* and hits total of 34* at 2600rpm and doesnt climb and returns to 22* quickly when you let off, its idling rough at 800rpm and only pulling 5lbs of vacumme anymore rpm and the advance kicks in but then it pulls 7lbs. Thanks to the converter putting it in gear doesnt change much. But it still doesnt idle dependably Im sort of guessing on the 22* at idle cause I just have a standard timing light and a 30* mark. The welding and grinding on the weights is a pain and seems rigged, how do the pros shorten the timing curve? It is at least kindof idling at a reasonable rpm so im at least making progress Thanks again for your time. Lin
Low Vaccume This looks different I hope this is under Big cam wont idle After 3 sets of advance weights and 2new timing lights before I found one that worked right, my car idles at 22* and advances to 34* at 2500rpm but tops out at 36* total at 3000 before I narrow it more, Ive heard with a stinger S4, 36* is what you want. All advance is out at idle 1000 in N 900 in gear It is idling on its own but you want to hold your foot over the gas petal,vaccume on the carb is 5lbs steady, vaccume on the intake {goes to the tranny} is a unsteady 7lbs {do you think my pushrods are set to tight?} I ordered a TA timing chain and thiner intake gaskets in hopes my cam is to retarded or my intake isnt sealing {family still wont ride in it} While I have my intake off anyone know how to cut the pendilum in a performer to give it more upper rpm? p.s. im getting my timing out of untouched MrGasket advance weights the bushing and the heaviest springs {wierd huh} if I could get it to idle slower I could run the lighter springs, its hard to work on timing when your car barely idles! Thanks everyone ive learned more on this websight in a week than I have tinkering with this car for the last 23 years. Yes this is my first car and will be with me till death do us part! Thanks again Lin 71 GS 455
Retared Cam I posted a question under Wet Behind the Ears "Big Cam Wont Idle" my car idled rough and pulled 5 to 7 lbs vaccum, thinking I needed to advance the cam (TA 290-08H) to 106 center to close the Intake valve sooner for more vaccum. I checked the cam the way it was 4 degrees advance on a 3 keyway sprocket my figures were 21 at .050 opening, 37 at .050 closing, max lift at 98 degrees. I put on my new T/Chain and gears at 8 degrees advanced and got the exact same reading, so I put it straight up and got 13 at .050 opening, 45 at .050 closing, max lift at 106 degrees exactly what I wanted. Unless I goofed up, I was way to advanced would that cause idle and vaccum problems like being to retarded? I double and tripple checked myself so it has to be right the results just weren't what I expected. Thanks Lin
Lin, Thanks for letting me know what worked for you. I have a little less cam than you (TA 413) and am only pulling 9 to 11 inches of vacuumn. My engine builder swears he set it up at 106 degrees. Also my distiributor curve is pretty close. I am going to mod the distributor a little more today. Need to have a few degrees less in in both the mechanical and vacuumn advance and put in a stiff pair of springs just to double check that it is pulling our all the mechanical at idle (it did drop two degrees when I checked at 600 rpm.) What rpm is your idle set at? Mine will idle at 900 rpm and have no stall problems but still on the off idle circuits on the carb.
I havent got it running yet I just took my intake in to be shaved today {my car got back burnered for haying season} Im having trouble believing 6*A is straight up on the t/gears so I am degeeing the stock cam in a spare 455 to see if my results are similar before I button it up{if I can find cam specs on a 1974 stock 455 cam} Before I pulled it apart I got the timing to stay put at idle 22* 1000rpm and top at 36*at 2800rpm Ihave a converter so putting it in gear drops it to 900{still through the primaries} and Idles on its own but verry rough and frequently dies. I hope degreeing the cam and sealing the intake gives me more vacume then Im going to experiment with another Q-Jet that wont break my heart if I screw it up. When i get her going ill let you know the results. Thanks Lin
You might try a set of Rhoades (sp?) lifters, while degreeing the cam is obviously the big picture, every little bit of vacuum gained helps. These have been around quite a while and always seemed to help me gain a little edge when trying to get a thunder stick to idle.
Eddie, I have used the Rhoades in my sisters Mustang. Judging from what Jim has said I should not need them. Mine drives fine just trying to get that last bit of tune correct. Weekender is going to give me a hand when he gets his O2 sensor back and see what the mix curve looks like. Thanks for the reply. Like your avitar looks just like my X clone.
