I thought I would get some input before I get into some more tuning. Fun eh? Its a fresh 340 stock (3.55 4 speed) except '68 4 speed cam and Edelbrock RPM intake. I'm running around 15 deg initial timing with Mancini orange box and distributor. Vacuum is only around 9 inches for some reason but it runs well around town but I would say sluggish with heavy throttle. I did lean it a little with a rod change when it was on the test stand (#13 stage 1 leaner cruise/leaner power). Luckily I have an old Innovate LM1 AFR meter. Right now I get around 14.2 idle, 12.7-13.4 cruise, it will dip to low 12s under light throttle if I'm cruising at a low rpm. If I'm cruising at say 3500 rpm and with light to mid throttle it goes lean 14-15 AFR right away. There is no hesitation or bog symptoms. Where to start? I'm thinking to go a bit leaner cruise/light throttle but I'm not sure what to do about the lean condition. Increase pump shot and see what happens? If you have seen my other post I need a heat insulating carb spacer before I do anymore tuning.
Tuning an Edelbrock 650AVS on a stock 340
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What's the static compression ratio?
9.75
I'm assuming then that it has the early two eyebrow pistons with positive deck height.
I would put the vacuum gauge on it and pull in some more initial timing while watching the gauge. That's a quick way to tell if it needs more timing.
The heads have nail head valves and a small mill down to 63cc. I can try more timing again although I don't think that helped. I am having an issue (I'm full of them trying to get this car on the road) where I set idle at 700 rpm and then by the time the engine warms up its 1500 rpm. This has happened multiple times so there is something going on....maybe to do with a fuel vaporization issue.
Whose version of that cam do you have? Oregon?
Yep . I might get another gauge. It is old
Ok. That cam is pretty much spot on to what the factory was. I think it's minus ONE degree of duration on one side. That's as close as anybody's got it as far as I know.
It should idle like a stock 340:
Grind #2120
221/227 @ .050”, 276/286 adv, .438”/.456” lift, 114 sep
Per the 68 Plymouth service manual, the factory specs are:
276/284 dur, .444"/.453" lift
Int op = 26° BTC
Int cl = 70° ABC
Exh op = 78° BBC
Exh cl = 26° ATC
Naw, they had a slight lope. Not much, but it didn't sound like the auto camshaft. There was a noticeable difference. Still very mild though. That's a really good copy though. They did a nice job on it.
They say they copied it from a supposed factory original. There is a very mild lope. I got my new vacuum gauge and a carb spacer so let the tuning begin. Hopefully I can get it sorted before the snow flies.
They did. @krazykuda Karl and one other member made it happen, so you can thank them. They sent them an original, they mapped it and put the grind in stock. That's the kinda support we need in this hobby.
Yeah, 9"Hg of vacuum is way too low for that cam & squeeze, We had 9"Hg w/9.7:1 & a MP 292°/.508" PurpleShaft with the original tight LSA, He got frustrated fussing w/the advance & locked it out @34°. It had 11"Hg at idle(~950rpm) locked out. I'm not recommending You lock Your's out, just letting You know what idle vacuum was possible with that much larger cam, which I measured @248°@.050" tappet lift.
*EDIT* ; This was a 340 Six Barrel in a '70 AAR 'cuda, 1&5/8" headers.
Agree, 9" of vac is too low. You need to find out why. Could be the cam itself, faulty in some way. Wrong cam put in box?
I would imagine with the low vac that the pri t/blades are cranked open too far exposing too much T-slot. Would also cause unstable idle. I would also expect that the met rod pistons are not staying DOWN at idle, causing more A/F instability.
The key is finding out why vac is so low & remedying that.
Acc pump shot. I have been working on these carbs since the 70s. Have yet to find an engine that needed the pump rod to be in any other hole other than the outer hole. That is because of the superior metering design.
I would imagine with the low vac that the pri t/blades are cranked open too far exposing too much T-slot. Would also cause unstable idle. I would also expect that the met rod pistons are not staying DOWN at idle, causing more A/F instability.
The key is finding out why vac is so low & remedying that.
Acc pump shot. I have been working on these carbs since the 70s. Have yet to find an engine that needed the pump rod to be in any other hole other than the outer hole. That is because of the superior metering design.
I checked the vacuum with a new gauge and its the same. Also the idle speed picks up when its hot. I think that there is likely a vacuum leak. I'm going to sort that out before I do any tuning. I also have a new Edelbrock carb heat insulator to install.
I installed the Edelbrock insulator and took it for drive to warm it up. I also managed to break my ancient PCV valve 
I noticed the AFRs were different...richer at cruise and tip in. I took the car home and measured 12 in vacuum which is an improvement. Perhaps the carb was leaking at the base. Also, the idle rpm stayed stable which is a change. I sprayed the remainder of the throttle body cleaner and then some WD40 around the intake but didn't find anything. I advanced the timing and got around 15 in vacuum. You can't see past 10 deg on the cover so I have no idea what the timing is although I would say more than 15 degrees.
I noticed the AFRs were different...richer at cruise and tip in. I took the car home and measured 12 in vacuum which is an improvement. Perhaps the carb was leaking at the base. Also, the idle rpm stayed stable which is a change. I sprayed the remainder of the throttle body cleaner and then some WD40 around the intake but didn't find anything. I advanced the timing and got around 15 in vacuum. You can't see past 10 deg on the cover so I have no idea what the timing is although I would say more than 15 degrees.
I installed the Edelbrock insulator and took it for drive to warm it up. I also managed to break my ancient PCV valve
Use a Dial Back timing light.
Set your timing light to the degrees of advance you want, then flash the mark on the front vibration damper to line up 0 at Top Dead Center.
Then you will know how much advance you have.
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It’s broke so I just have a simple gun. I did mark the balancer for 15 degrees though.. will check it tomorrow and I have a piston stop on order.
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Had great luck with an Edelbrock 650 AVS II, on a stock build 360 with the stock grind 340 cam.
Dropped it on, ran perfect right out of the box, just some minor turns on the low speed idle screws and was all dialed in > 12° BTDC timing.
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Dropped it on, ran perfect right out of the box, just some minor turns on the low speed idle screws and was all dialed in > 12° BTDC timing.
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The engine runs with the most vacuum and idle speed with the 15 degree damper mark at the timing cover 10 BTDC....that's 25 degrees initial!. Maybe my damper TDC mark is off. I'll double check that in a day or two.
Nope it’s good
That's likely correct.
I’ll likely dial it back to 20 it was fighting the starter hot) but I’ll have 40 total then.
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