340 camshaft question, yea another one.
After installing the XE 274 I didn't have any idle control with the mixture screws.
I'd have to measure the hole size as I don't remember but it's .015 of the slot exposed. Yes I am running a pcv. The spark plugs are light tan.
I had FBO recurve the distributor to fit the cam and they recommend to use manifold vacuum. I have a sheet on how it was set up is where I got the numbers from Don.
With the magnum heads it has a 1.6 rocker ratio so the cam has a little more lift, it that makes any difference.
I have decided to replace the converter and freshen up the engine.
Would this be a case where a set of Rhoda's lifters would help?
There it is again..... mixture control.
Are you saying you had no mixture control after the holes went in?
or before? I'm betting before. Your tuner was on the right track, it just never got finished.
I know replacing the TC with a higher stall will help. But the root cause is still there.
As to Rhoads, there is a fello here, that puts them in everything he owns, and loves them. I don't and I can't see a need for them in your combo.I have run 3 performance cams, including the 292/508/108 and never had an issue. I suppose that bad boy-292 could have taken advantage of the Rhoads, on account of the bottom was a little soggy; but I had a clutch and gears so it was not that awful.
I still believe you need more T-port exposure. .015 is waaay not enough. The slots should be a little taller than wide, the mixture screws should be out about 2 turns, the secondaries closed up tight,and the initial timing whatever it takes in the range of 14 to18 degrees to achieve an idle down around 700/750 in neutral and or 650ish in gear. I am not a fan of the holes in the throttle blades, preferring instead to crack the secondaries if the engine wants more air; as the 274cam will.
Some carbs (like your Edelbrock)don't like the secondaries cracked very far until they start producing a tiny hesitation. A little more pump-shot can cure that. But if not, then a combination of less secondary cracking and some thru-hole air is the answer. I prefer to maintain some idle speed adjustability with secondary cracking, cuz once the T-port sync is working really nicely, I don't like to mess with it. So then the only way to adjust the idle speed is with timing or bypass air; and taking off the carb everytime to adjust the hole size gets to be a PITA.
So to that end, I would still recommend to close up those holes and start over cuz I think they are too big right now; you need more Transfer exposure.
So to recap; T-port sync,idle timing, and idle air bypass.And in your case the TC. Getting these four optimized will cure your woes, and the 274 can stay; it's a great cam for a combo like yours, namely;high compression and tight-quench.A 2800TC will really wake it up. Some here on FABO have had great success with higher stalls in custom TCs.
Parting shot; When I was first learning about the T-port sync back in 99, I was on my own. And I happened to start with the 292/508/108 cam so I had a lot of learning to do. I had been a boat mechanic at one time, and I remembered how little 2-cycle outboards are tuned. The porting on those is set up to cruise around 3200 to 3600 on account of that's how fast the props need to turn. Well as you can imagine when you throttle them down, that porting idles pretty raunchy. You could never troll them like that. To tame the idle on those ,they start to retard the timing,a lot. And they always have idle by-pass holes thru the blades. So I remembered all that. And I thought, if it works for them, it should work for that 292.
But where to start?
Well I had been running this beast for a while so I sorta had a baseline. I would have to learn from empiracle data. I picked some arbitrary settings and dialed it in.But what bypass air should I select? Well, I tee'd into the PCV line and installed a restrictor orifice in that new Tee. Then I adjusted the orifice size until the idle speed seemed reasonable. Then the roadtest. There were a lot of roadtests . Eventually I got things dialed in pretty close. I kindof kept records and I could see the progression towards success. The adjustable bypass air helped me a lot. When I was finally happy, I translated that hole size to twin holes and punched them thru the blades. And got rid of that Tee. More roadtests. Eventually I figured out that I could crack the secondaries a bit and get rid of some hole size. But I also figured out that if the secondary cracking got to be too big, it gave me tip-in issues. So I pulled off that 750DP split it open and saw that with just a bit of modding I could deliver some idle fuel into the secondary holes. So I drilled some tiny holes and PRESTO! I had 4 corner idle . Of course it was back to the drawing board on the primary side :( Eventually, I had a set-up that took throttle without tip in sags, idled rumpidy-rumpidy. Idled slow enough that with 4.30s people could walk alongside the car, with me perhaps slipping the clutch now and then. My goal had been accomplished!
So what did I learn?
Well, the T-port sync is job #1, followed very closely with initial timing, and idle air bypass. These three set the stage for a make or break idle. And with an automatic, the stall can be big factor too. With my Holley,it took transfers a little taller than wide, and the 292 liked an awful lot of initial timing. and an awful lot of bypass air.I was uncomfortable giving it the timing that it wanted, and so was the starter. The mini-starter seemed to cure that, but I was still uncomfortable. See; an automatic with a 2800 stall doesn't have this issue. You can crank in a ton of timing and make the engine happy, cuz it is never loaded very hard bellow it's stall. But A stick car is often asked to pull down low. And if I gave it the idle-timing it wanted then it got to be real jumpy down there. It took me a long time to figure out that the jumpiness was not fuel, but rather timing. I finally bought and installed a dash-mounted dial-back timing gizmo, and that is how I figured it out. What I discovered was that at 4 miles per hour, the engine pulled pretty smoothly with timing down to 5* advance. It just didn't have enough torque down at 650 rpm to pull itself on anything but level pavement, and even then it might take a bit of slippage to continue. But I had discovered the secret. First, the jumpiness was not fuel. And secondly; idle-timing and pulling-timing are not the same. Or rather the timing that the engine wants at idle in neutral, is not the same timing that it wants when it's in gear! So My unwillingness to give her 25* in neutral at 750 had been well founded.
So it was back to the drawing board. The T-port sync was established, so I just had bypass air and timing. Back into the PCV line went the Tee. So I cranked the timing back, and adjusted the bypass, and more roadtests. Now I had the adjustable Timing control so I could try timings on the fly! Soon I had an idle timing worked out, and that just left the bypass air.Which by now was not a big deal, cuz I had the 4-corner idle. Soon she was running like a top.
Now I gotta tell you, During this period, I also had to keep adjusting the Power-timing, as the initial was jumping around. And the rate of advance also had to keep up. And of course the idle vacuum was changing so I was swapping PVs, and MJs too. So there was a lot of learning going on and a lot of tuning. And not every change I made was in the right direction. So there were times I was backtracking to the last known-to-be-good setting, and off I went in a new direction.So the point I am getting to, is that zeroing in on the tune, was, for me , a real time consuming passion.Dozens of hours and thousands of miles and months in duration.
Bottom line was, a little taller than wide, 14 to 18 degrees, and whatever bypass required, and make sure all the air going in has at least some fuel in it, so that the overall AFR is a tad rich. Every cam after that followed the same guidline, with minor changes.
Automatics can run a little more idle-timing and; the higher the stall, the more idle-timing it can take. There is a point of too much idle timing. The trick is not to force the engine to take timing but rather,to meet it's needs.
Yeah I know, another flipping novel from AJ...............:)