I need your help. I replaced my 430 with a slightly modified 455 and the idle speed seems excessive to me. Engine runs great, starts great, but runs a higher idle speed than I want. Currently idles about 1100, I can get it to idle nicely around 800, but that struggles to stay alive when placed in drive, let alone run when the AC is turned on. So 1100 in neutral, about 800 in drive and 700 with AC on in drive, any lower and it will stall. Car runs great, instant power, pulls hard, just concerned about the idle, since it makes an aggressive thunk when placing in gear. I have heard this maybe normal when shift kit install in trans? Now all this seems to correspond with the TA catalog for the cam characteristics, so I am not sure there is anything I can do as this maybe the best I can get, but thought I would ask here. Here is my setup with pics of the setup as well. Appreciate any advice. 76 455 block bored .30 over Forged Pistons, 9.5:1 TA Aluminum Stage 1 SE heads (non ported) Edelbrock Performer Intake TA 290-94H cam (Average Idle 1000 in Park, 750 in Gear according to TA) Stock 67 430 exhaust manifolds 67 Carb 7027240 - used to maintain stock SP control 67 rocker shaft and arms 2 1/2" dual exhaust 67 ST400 transmission (with ST300 converter) Thanks Clyde
Clyde, lots of initial timing helps a lot here. 20* or so, or locked out timing. The torque converter also affects Park to Drive RPM drop. Are you sure you are getting high stall at idle?
Clyde, that Quadrajet would need idle circuit modifications to be able to idle correctly. You are probably having to turn up the idle speed to help, which opens the primary blades so the primary system starts to drip fuel and it will load up. The idle tube restrictions need to be enlarged, and the down channel restrictions for starters. It may also need some additional bypass air for the 455 set up.
I did use the smallest bushing the in distributor, if remember correctly I ended up on 34 total and 18 initial due to the bushing setting mechanical to 16. Mark I did have to turn up the idle to get to where it is. I did order Ruggles book and look to try and modify it but afraid of messing up the carb. I do have another carb of a 73 455 AT to mess with and a second 67 carb to get the front shaft out of. Any suggestions on what size to open up the passages in that carb?
The 7027240 had .030 idle tube restrictions and .052 down channel. With that cam and engine set up, I would recommend .035-.036 on idle tube and .055 on dcr. Go to .090 on the idle mixture screw holes, you may need to cut a coil and half from the tension spring. That should help you set idle where the carb will idle through the idle circuits, and not have to increase throttle opening. We have new idle tubes and down channel restrictions if you need any. We can size them before we ship if you request. Our website has instruction page for pulling idle tubes, and Cliff's book does as well.
I don't know much about qjets, if it was a Jolley or eddy I would riches the mixture this can help the shift rpm drop. I would also modify the butterflit's with a small by hole to lethe a little more air through without getting into the transition circuit. X2 on more base timing, check your timing at the 800 in gear I bet you loose a few degrees
Yes, another thing that causes a big drop in RPM when shifting into gear. Light springs can let the weights add timing and flop around at idle speeds. Drop it in gear, the converter pulls the RPM down and the timing retards leading to more drop and stalls. In general, you don't want the advance curve to start until the engine is above idle speeds.
So I picked up a carb from Mark at quadrajetpower. 73 Qjet and he modified to the engine specs. I have sent it back once for readjustment, but I am still having the same issue, so I want to run my issue across here to see if its something I can tweak. So replace the 67 carb with 73 and starts up fine, warm it up and set the idle to about 1000 and adjust the mixture to get it about 16 in max on the vacuum gauge. Not sure if it matters but I was getting 20 with the smaller carb. Timing is set at 34 total, 20 initial, seems to really like the initial to smooth out the idle. Timing was not changed from where it has been set with the previous carb. Vacuum advance modified to allow only 10 degrees. Car runs great, drops to 700-750 in park, 700 with ac on doesn't drop like it does on the other carb. Runs good, feels like it pulls better. Now here is the issue, I shut the car off, doesn't matter how long to wait to start it, fires right up but will only idle now at 500 rpm, I can work the throttle a few times and eventually it works its way up to 1100 (sometimes takes a minute sometime longer to comeback) and holds steady. Again seems to idle to fast, I cant lower the rpm as the idle screw is all the way out to so no more adjustment. Turn off and restart, the process repeats, if I don't pump the throttle it will stay slugging along at 500 rpm never regains the lost rpm,, if I readjust the carb at this point back to 1000 rpm and readjust the mixture screws if needed, first pump of the throttle, it is off an idling high again, this time at 1400-1500 rpm. If I place the 67 carb back on this all goes away and runs like it did before, idle rock steady, 20 in vacuum, drops to 700 in gear, and 60 with ac, just runs rich. That were I at with this thing, I am just at a loss on what to try next, I really think its in the carb, and hate to send it back, but right now I am feeling I bought something I cant use. Its really difficult to drive the car this way, stopped to get gas and restarted to the low idle and kept stalling in gear until I can get the idle to comeback. Clyde
Multiple times, replace base gasket multiple time, not vacuum leaks with original carb. This one does have a high pitch squeal like its sucking air, but that is coming from the primary opening in the air horn. Just assumed it is due to the modifications.
I had one few months ago I got from a local Qjet builder (customer supplied), was fighting the same issue idle was all over the place and inconsistent also, it also whistled something fierce dicked around with it for hours, finally pulled one of my carbs of the shelf and all was well, I didn't go digging in the other Carb for a cause, just sold him the one I had, moral of the story is something hokey was going on with it
Wanted to update this thread, been a few months broke a pinion gear and been off the road for awhile. Now that rear is back in the car I got to working on it again. Its running now but not so sure I am 100% on it but it does run. What I did was move the vacuum advance from manifold to ported. This allowed the idle to come down in range, but I needed to up the timing to allow it to idle right. I originally set it at 20 initial and used a small bushing to max mechanical advance to 34. Before you ask all this was done with the heaviest springs installed I the distributor. Some wide open testing showed pinging at WOT. I backed it off to 16 initial and 30 total and car runs without pinging. Adjusted the electric choke and car starts now but still needs to warm a few minutes so it doesn't stall out, this was not an issue when set at 20 initial, and no hard starting was experienced. So where is it today, well if I go out to run on the weekend (sitting all week), starts good,, as to turn a few turns to fill the carb, but on push on the carb to set the choke and a pump or two after first crank fires right up. Starts at 1300 rpm and rises to 1500 on choke. wait one minute slightly depress and chock steps down a notch and runs around 12-1300 rpm. Another minute or two I will depress and let the choke come off. This is where it gets flakey. It will drop to an idle somewhere from 550-700 which is way too low, especially since I set the idle speed to 1000 rpm when hot. If I drop it in gear it will stall, if I wait another minute or two and stab the throttle here and there eventually it will idle faster as set. If I put it in gear and go not problem, put back in park returns to 1000 rpm. Now car is at operating temp at this point. I shut car off, wait a few seconds and restart, we are back playing with the low idle problem. If I drive the car this problem seems to go away, but it may start idling 100-200 rpm higher. Carb still has the annoying whistle, for the most part its running but still annoying with the lack or idle stability and the air cleaner stud only allowing one threads use.
