I have a 72 GS 455 that I cannot get to idle correctly. I know it has a small cam but I do not have the info on it. The rest of the engine seems stock except for the point replacement electronic ignition. The idle has to be set high enough that the ported vacuum has vacuum at idle. A recurring problem is when you put the car in drive @ even 950 rpm it wants to die after a couple of seconds. I checked the timing and have set the mixture screws to peak vacuum. The choke and high idle work fine. The timing is set at 8 BTDC with a total at 32. The idle has to be set high enough to where the ported vacuum has vacuum. I did change some things which help stable the idle. The port that had the EGR valve vacuum hose attached to it has vacuum at idle. When I pulled the hose off the EGR valve closed, I plugged the carb port and the idle was much better. I also moved the dist adv vacuum hose to a full vacuum port. The car will now idle in gear with a drop in RPM of about 350. I did not have any other vacuum leak other than the EGR valve being open at idle when it was hooked up. I know this is not correct way to get an idle but I could use some ideas for a better fix. I did see a Q-jet carb with a custom mixture screw in the middle of the original ones (dead center), was this drilled for air adjustment? It was for a 454. I would really appreciate any and all help. Thank you Nelson
Check yout actual ignition timing (disconnect vac. advance) with a timing light, both in neutral and in gear. Then report back, it should remain the same in both situatiions.
Try Bumping The Timing Up To 12 At Idle, Just For Troubleshooting. Also Look Down The Primaries For Fuel Dripping Out Of The Nozzles At Idle. A Good Indicator Or Proper Throttle Setting Is To Remove The Carb, Turn It Upside Down, And See How Much Of The Transfer Slot Is Exposed At Idle. The Transfer Slot Should Just Barely Be Exposed By The Throttle Blades At Idle. If Not Your Idle Transfer Circuits May Be Blocked Or May Need To Be Enlarged. Last But Not Least,*** Is There Fresh Gas In This Car?? Good Luck
Your primary throttle blades are open too much. If they are open to where you are getting vacuum at the ported connection, then you aren't running on the idle system of the carburetor, but on the mains. What is the Q-jet number currently on the car. There are differences between small block and big block carburetors, most notably in the idle system capacity. If you have a small block Q-jet on a big block, that might be part of the problem.
Ok, I will try to answer all the questions. The carb is a 7042240 and it is not dripping fuel at idle. It is a Calif car and does have the EGR valve. I did check the timing both in gear and at idle, it did not change. Next I set the timing @ 12 when at idle @850 rpm, It really likes the advance timing. I used my adjustable timing light to get the total which was 43, with vacuum advance plugged. It totals out @ 1800 RPM. I adjusted the idle screws for a total vacuum of 18 inches. The carb now has ported vacuum at idle like it should. I left the EGR valve plugged. The car now idles in gear and am able to even turn the AC on without it dying, this was all done with car at operating temp. It starts fine and you can even hit the gas then shut it off without it dieseling. It sounds better at idle and drives very good, I just worry about having that much total timing. Which base gasket is correct? What would cause these issues? Could someone installed the cam with not enough advance? Thank you to all for the help and info. Nelson
Have you read larrys power timing thread. If not I will tell you your missing out on more power :3gears:
It is possible, with the cam you are running that the engine needs a quicker advance, with more initial. This is typical of aftermarket cams. especially with the factory compression. 18.5" at idle is actually pretty good, so I do not think that the cam is much more of anything much above stock. You might try using weaker advance springs, with less total, limited at the dist. The factory used VERY slow mechanical advances, and faster vacuum advance with EGR. Try this: adjust the intila timing to about 2-3 deg above factory settings, and try driving the vehicle. If it pings, disconnect the vacuum advance. If it now drives fine, there is too much vacuum advance. We'll go from there. While messing with the dist, make sure that both advance mechanisms work. Ray
OK, so you have the engine running well, but the total (without vacuum advance is 43*). That is too high. The answer is to limit the amount of mechanical advance. Right now, if your timing numbers are accurate, you have 43-12, or 31* of mechanical advance. There is a pin that rides in a slot under the advance weights in the distributor. That is what limits the advance. Take a look and see if there is a bushing on the pin. If there isn't, you can add one and limit the mechanical advance that way. If there is already a bushing the only way to limit the advance would be to disassemble the distributor and weld up part of the slot. Then file the slot to give you less mechanical advance. 20* of mechanical advance is a good number to shoot for. Then you can run 12* initial and 32* total, or 14, 34, or 16, 36 etc. Again, if you numbers are correct, all your advance being in a 1800 RPM means that you will need to limit the vacuum advance also. You will need to limit the advance in the canister to 8-10* tops. All the info and pictures on how to do this is in the Power Timing thread.
Good to see you are making progress! Try setting the idle mixture screws for highest vacuum with the car in gear and wheels blocked. keep the vacuum advance disconnected while you do this as well.
Actually, if setting the idle mixture, using park instead of drive will make adjustments, especially if the convertor stalls at a low rpm. Using a tach also makes adjustents as well, especially if the gauge is damped. Go for maximum rpm, then adjust for a 10 rpm drop per screw. With your cam, it might be wise to go for the maximum rpm and leave it there. Engine rpm will affect the idle mixture, especially if the cam affects the idle drastically. Make sure that the timing, advances and idle speed are close to factory settings before continuing, as all will have an effect on the mixture. Let us know...
I pulled the dist and made a stop for the vacuum advance. Also I found something that I could use for a stop bushing for the weights so I would not have to wait on a kit. I have the idle down around 850 and 600 in gear. This is much better than it has ever been. It likes the timing advance and no way can I get it like this with the timing at 6-8 degrees. I will check out how the drivability is today and check with the AC on also. Thanks Nelson
I enjoyed reading your thread for the step by step, and all the good help you've recv'd from Larry, etc.. I'm wondering if I never experienced this due to No EGR/Air Pump on my 1971 (also Fremont Calif. built). o No:
Hey Rick, That could be as I have left the egr valve without vacuum for now. When I get more time I will look into the way it is supposed to hook up. I was reading about your car and noticed you found your build sheet above the gas tank. That is where I found the one for my Calf built 71 BB convertible. I found the build sheet for my calf built 72 GS under the original carpet, you just never know where these sheets will turn up. I took her for a drive tonight and drivability is 100% better, especially with the AC on. Thanks to all for the help Nelson
