Whether it has been to many years and I have forgotten something, Or I have a problem I have missed, I am having problems getting my 327 to run right. The engine is a stock spec 327, with 461 heads with 2.02/1.6 valves, an L79 Cam, a c4b intake, and an off the shelf Holley 600, in a 4200 pound 59 Elcamino, with a 4 speed, and 3.54 gears. It has always idled Rich, and I am trying to clean it up so I can put the engine in my Dads 65 C10.. Currently I have the distributor set with 30 degrees mechanical advance, and approximately 14 degrees of vacuum advance, on manifold vacuum. Initial timing is at 4 degrees, idle at 950. It has a pertronix ignitor in it, with a Mallory coil. The carburetor has .090 holes drilled in the throttle plates, 64 jets, and a 5.5 power valve. with these settings, it seems to run the cleanest at idle, and has the best throttle response at the bottom, but seems a little sluggish up top, and when I accelerate from cruise on the highway (about 2800rpm) I get a backfire out of the carburetor.. My plans are to limit the vacuum advance to 10. (per my 1966 Chilton L79 distributor specs)and unsure on the Carb. Prior to the power valve change, It had 13 inches of vacuum at idle, now it is back up to 15. What recommendations do guys have? jet change and same powervalve? 6.5 Powervalve and same jets? (66 were factory installed) before I put in the 5.5 P.v., this thing would make may eyes water at idle.
My SBC setting initial timing is 12 to 14 BTDC total 35 to 40 total with vacuum advance set to Manifold vacuum.No hole in butterfly. You spec are for different fuel.
as far as the rich idle, yeah going to smaller jets on the primary would be a good place to start. Is the carb mechanical secondary's or vacuum? If vacuum you can change the settings as to when they open up. As far as the backfire while cruising, that seems to be a timing issue. If the advance adjustments dont work, might need to acctually look at the pertronix and mallory parts themselves, they might not be keeping up properly. I know I have had hit and miss luck with both companies and its one of the reasons I have put most of the old cars in the garage back to points.
4* initial is way too low for a performance build. I would first dial in more initial, try 10-14 degrees with the vacuum advance disconnected. This will give you a bump in idle rpm, which you can then back off with the curb screw. 950 sounds high for that combo , I'd shoot more for 750 with 10-14* of initial. If you need that much idle rpm to keep it happy taking off from a light with a manual trans, you're masking other problems. You've got the right idea with running your vacuum advance to manifold vacuum, but you want to limit it to 10* via a Crane limiter plate or by fabbing your own. You want the added advance at idle full manifold vacuum provides to really help clean up your idle mix and provide a strong idle. Then limit your mechanical advance so you're seeing 34-38* at 3500rpm with the correct stop bushing and set the curve by changing out advance springs to see what your engine likes best. I'd start with 2 medium weight springs, as you have a relatively small engine pulling around a heavy car. This will be a little experimentation to see what your engine likes best. I don't know much about the Ignitor distributors, but I would imagine they operate pretty similar to the MSD setups with the interchangeable mechanical advance stop bushings? All said and done you'll likely end up with the same total advance, but you've moved the curve around which sounds like just what your engine wants. Make sure to get your timing curve squared away before touching the carb (apart from adjusting curb idle and mixture screws). Now let's look at the carb. I'm assuming this is a vacuum secondary carb? With your combo, you should not need holes in the throttle blades. That's typically what guys with huge cams need to do to prevent opening of the throttle butterflies so much that the transfer slot is overly exposed and you start drawing idle fuel from the primaries. I'd bet you've had to add more fuel via your mixture screws to compensate for the added air introduced by the drilled holes. I had a problem with getting enough air at idle with the big cam I run, but on my carb I was able to adjust the secondary butterfly stop to add a little more air. Your powervalve number should be half of your idle vacuum in gear. So at 13" of idle vacuum, you'd go with the 6.5. This is Holley's advice and it's always worked well on my rigs, but you may hear differing opinions on this. Your lean pop through the carb is likely in your accelerator pump circuit. Make sure the arm is adjusted so there is almost an instant flow from the squirters when you tap the throttle. Holley says there should be .015 of clearance with the throttle closed. So set the arm so that a .015 feeler gauge will slide in and out with just a little resistance. You should see the pump arm move just a hair without delivering fuel via the squirters. Then you can experiment with pump cams to see what your engine likes best. This is almost all trial and error, but it sounds like your engine wants more pump shot sooner. Holley sells pump cam kits that will get you where you want to be. Also take a look at the squirter. Pull it out and check the number stamped into the side of it. You might want to try sizing that up to the next size and see how it likes that. All these parts are cheap, so it's worth experimenting. The 600 is a little small for your setup, so its base configuration and components likely need stepping up to work best with your combo.
I would tend to agree with SDLuck. I have never drilled holes in the butterflies, and I am at altitude of 5300 ft. I also don't use the ported vacuum, rather constant vacuum. I like to see it all in by 2500rpm, with total advance around 38 degrees, on 91 Octane. I have built and ran your exact combinations by the way, with no issues. Bob
On my 327 with similar build I had similar problems that cured when I threw my new pertronix distrib in the garbage. It kept sporadically popping at high RPM, pretty rich at an idle. I stuck a MSD in there and it has been night and day different. For reference its 327, .060, comp 280H, holley 650, performer intake, ported camel hump 1.94s... I had it dyno tuned with the pertronix and they used 80 rear, 70 primary, w/6.5 pv. 15 degrees at idle and 38 total I believe is what I set the MSD at and used the light and quick springs.
I think your ignition timing needs to be changed. I run my 327/375 Rochester injected engine at 17 degrees initial, 36 degrees total, all in at 2500 RPM.......mechanical advance, no vacuum. Been running it this way for over 30 years.....with the first generation Pertronix ignition. Runs straight up to 6800 RPM without issues. Those early heads like a lot of timing advance, but with good fuel, not E10 corn gas. Then fix your carb. to function properly.
Fix the backfire on acceleration first. If you can find someone with an ignition scope, have him check the ignition system. Specifically you want to know what kind of available secondary voltage you have. The great thing about a scope in the right hands is that it only takes a minute or two to verify the health of your ignition system.
Thanks for the advice so far. The pertronix is a new unit just installed Saturday, which is a HUGE improvement over the previous distributors I have had in it. The holes in the throttle blades were drilled before I discovered my previous distributor was excessively worn. I have new throttle blades and a 6.5 power valve on hand to put the Carburetor back to baseline. I have a vacuum advance limiter on order, to get the vacuum advance pulled back to 10. The distributor is otherwise specced out to a 1966 Corvette l79 unit, with 30 degrees of mechanical advance, and the 10 degrees of manifold vacuum. With 4 degrees initial timing and the advance plugged in I should have 14 degrees advance at idle, and 34 total mechanical in by 4,000 RPM. If I go above 4 degrees initial it doesn't like to Start hot, and diesels. I will continue to mess with this and report back . My last 327 was identical, down to the same intake manifold, and ran perfect with standard, off the shelf parts I have fought this for so long I'm about ready to just replace the old Cam and go with a shorter duration modern grind, so Dad doesnt have to fight this. I have a 383 going together for this later this year so I can do it all over again, with a crossram for added enjoyment.
Timing should all be set without vacuum Advance .Had tdc been verified. Sent from my SM-J737T using The H.A.M.B. mobile app
4 BTDC seems pretty light, but did you set/reset the floats? I bought a “rebuilt and ready to run “ Holley 780, long time ago, put it on and couldn’t adjust the mixture screws. Ran pretty rich idling. Really didn’t know squat about carburetors then (not much better now either) buddy came by and immediately knew what the issue was, lowered the float in the primary bowl and got me all fixed up.
Timing set, 4 degrees BTDC, with vacuum advance plugged off. reconnecting the vacuum advance yields( at this point) 14 degrees additional advance, to soon be limited back to 10
Plug the line to the distributor, get out your timing light, set the timing to 12 degress BTDC, then reconnect the vacuum line, slam the hood and have fun. That will clean it right up, THEN put the undrilled throttle blades in it and your going to be fine. Understand?
Try driving it for test purposes with the vacuum advance disconnected and the port plugged. See if it backfires. It can be tricky to adjust vacuum advance, everything else has to be tuned up, dialed in, and squared away or it will not seem to work correctly. Most OHV V8 cruise very happily with 50+ degrees of ignition advance on flat ground highway. If it won't, it indicates a tuning defect. The next thing is your manifold vacuum is pretty low at idle. This isn't a "bad" thing, it's a performance engine issue. But if it's only 13" at idle then you want to get a better handle on what it is at cruise, on flat ground on the highway. A 5.5" "should" be OK, but maybe not. Measure vacuum when driving around, especially flat ground cruise. If the power valve is open, even a little bit, when cruising it will run absolutely pig rich and foul everything out and bugger your jetting selection and the rest of it.
READ THIS... Mr Sinister knows his stuff! I would add, the Pertronix advance limiters are junk. They are too bendy and change every time you bang into them. I would put a new Holley 650 on it. It worked perfect right out of the box on my 327.
If you decide to upgrade the carb, I've got a brand new Edelbrock AVS 650 with their chrome fuel line I'll make you a good deal on. It's got maybe 100 miles on it. I bought it to try as a "fuel economy carb" on my 55 and didn't really notice an improvement in mpg, but man did it idle and cruise sweet. Their annular boosters are legit.
Thanks for the offer, but not in the cards for me, I'm broke. I'm going to fight this bastard, which is identical in every way to another engine I ran, which ran perfect until the block cracked.
an update for anyone interested. It turns out this is not an L79 cam, but another one on the list from the old P.A.W. days, that my buddy ordered by mistake. (Free Cam is a Free Cam Right.) 1t is 222/[email protected], .436 lift, 108 LSA. I baselined the Holley back to stock, with 64 jets, and have the timing set at 6 degrees initial, 30 degrees Mechanical(36 total) pulling 14 degrees of vacuum advance on manifold vacuum. I added Hotter plugs and new wires, and while i was at it put my 1.52 Comp cams rockers on it, which it liked a lot, and it is now running better than ever, with 15 inches vacuum at idle. It is a little rich still at idle, and is on the transition circuit a bit, which I will get to, but doesnt smell near as bad as it used to, and will with this cam anyways. Good enough to drive and have fun.
I would remove the vacuum advance and screw the points base to the distributor frame. Now set the initial to around 16-22, next set mechanical, have it start advancing timing at 1000 rpm. Now have it all the way in by 3000 rpm.. Find what it likes. You can also adjust timing, rate of advance, octane and thermostat..
Diablo, Calif. looks to be around 4,000 feet. Not high altitude, but most stock carburetors run a little bit or even a lot of bit on the rich side of things for safety. You can almost always safely jet down a fair bit in a stock configuration. If jetting is too lean, the engine will "surge" or misfire on steady flat ground cruise. Want to use stock heat range spark plugs to get a baseline. The remedy for fouled plugs is to adjust the carburetor fuel "curve", not try to burn off excessive carbon with hotter plugs. Also want to avoid hot spots in combustion chamber. "Too hot" plugs can cause engine damage. Where you want to be really, really careful about being too lean is when engine is under load, power, and acceleration. Think of what happens to an acetylene torch flame when the O2 is cracked open.
To get to this point. Removed worn points distributor, replaced with dual point, replaced with HEI. Removed HEI replaced with Mallory unilite Rebuilt, recurved stock distributor, installed pertronix unit, adjusted vacuum and mechanical advance until engine was happy tried a 5.5, and back to a 6.5 power valve, jetted down to 64 from 65s, tried various sized holes in the throttle blades until to lean, replaced blades with new ones, verified float adjustment, verified fuel pressure, ran with and without PCV valve, front and rear ports, replaced plugs. replaced plug wires because I had a set, replaced and readjusted valves because I had a set of 1.52 ratio rockers. I have run this engine from 4 to 16 degrees initial timing, with light and by ear, with and without vacuum advance, ported and manifold vacuum. I have done all the steps, with all components, in every configuration. I tried a 500 edelbrock, and a 750 Edelbrock carburetor as well. I have come back to these setting 3 times by process of elimination. This is where it is happy. Go figure.
Wow, I got exhausted just reading that.. I would put that stock points distributor back in with a good set of Accel points and condenser.. Set the dwell to 28 making sure there is no mechanical advance raising the timing. Before installing the stock distributor, I would remove the vacuum advance and screw down the movable plate to the distributors frame.. This will keep the points stable. This is very important with the points system.. Next remove the wire from the points to the negative coil terminal and replace it with the exact same gauge wire. I've seen the wire strands brake down inside the insolation, due to the vacuum advance constantly moving with the vacuum changes . The ohm meter will read continuity due to the couple good strands but that wire wouldn't carry an amp through it.. Best to check electrical continuity with a 12 volt light tail light socket with both hi and low beams together and solder a ground wire to the socket. This will test the wire with load against it.. Once you get it running, set the timing to what the car likes. You will need more initial without the vacuum advance. Usually 18 to 20 does it. What's nice is the timing never goes too low and the engine doesn't have to recover from this.. Make sure the starter doesn't fight during starting and make sure there is NO full throttle ping or run on when shut off. I wouldn't do anything else until the distributor is ironed out. Trying to trouble shoot more then one thing at a time can make it impossible to find the issue or as in most cases, issues..
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