Guest Anonymous Posted October 27, 2000 Share Posted October 27, 2000 l28 engine, heavily built with high compression NisMo pistons. Triple webers, stock distributor with electronic ignition and mechanical advance. Vacum advance was removed because there is no provision on the webers for it (?!?!) It pings under full throttle at low rpm(Below about 4k rpm). Why? I've been slowly retarding the timing to no apparent benefit. The timing marks say it's at 5deg retarded initial advance(ie. 5deg AFTER TDC). I don't have a timing light and don't really care what the actual timing is. I am assuming that the distributor is off by a tooth or 2, I can't imagine an engine running period with the initial advance retarded so much? All I know to do is to keep retarding it until the pining either stops or it starts running bad. It has a monster cam, header, and sky high compression. Does vacum advance retard or advance the timing with vacum? Where does the vacum signal come from? My thinking is that if vacum retards timing and signal comes from intake manifold, then lacking vacum advance would increase advance. But some guys at work tell me vacum advance advances timing with more vacum. Can you tell I know jack about carbs and mechanical timing? If that is true, then vacum advance would have your timing advanced at idle, and decrease advance as engine load increased, which seems backwards to me, no? I hate this mechanical fuel/ignition stuff, can't wait to get a real engine in it! Someone please enlighten me. The only way I know to stop pining is to lower boost a little bit It runs like a bat out of hell from 4-8k rpm, and runs fine under 4k rpm unless you give it too much throttle, then it pings. Yes I use 92 or 93 octane gas. Should I try some sorta octane booster? If that works, am I relegated to using octane booster continously? Does octane booster stuff really work? ------------------ Morgan http://z31.com/~morgan/s30 http://carfiche.com Quote Link to comment Share on other sites More sharing options...
Mikelly Posted October 27, 2000 Share Posted October 27, 2000 I'd look at the distributor... Sounds like you a re a took or two off... you could always play with the plug wire rotation and see if that solves it, and that would confirm being a tooth or so off... However, are you noticing any high tempuratures when this happens? You might have an internal problem somewhere in that motor... Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted October 27, 2000 Share Posted October 27, 2000 Any kinda idea what your compression ratio might be? If its to high, then yeah octane boost would probably be in order. Retarding the timing usually causes the engine to run a little hotter. Thats the way they used to do smog control on old cars, was to plug off the vacuum advance and set the timing retarded half of what it was stock. Made it burn hotter and less CO's supposedly. A lot of the old timer hotroders would say advance the timing for optimum performance until it has trouble starting (a initial hesitation before it turns over) and then back it off a bit. (some of the hardcore guys would just put a switch between one of the primary coil wires, turn the starter over to get it going, then switch on the coil) That was back in the day of tune by ear, which I've done but don't prescribe to these days. If your compression ratio is under 10, or 10.5 you probably can get away without octane boost by just continuing to retard the timing. You do lose a little performance, but its better than losing an engine to detonation. My .05 worth probably .02 at least.. Lone Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted October 27, 2000 Share Posted October 27, 2000 Engine runs cool, not even a remote problem with overheating. 4 core radiator and a fan shroud. I was told the compression is around 9.5:1. It runs perfectly fine except for the pinging at low rpm. Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted October 28, 2000 Share Posted October 28, 2000 Morgan: typically a vaccuum advance unit is just that, with vaccuum it advances your timing, without vaccuum it has no effect and you have only mechanical and initial timing acting (ie. your intial of currently 5BTDC and whatever total your dizzy will bring in mechanically). have you checked out your dizzy to see that it's not 'locked' into full advance? (can't see how it is if you can 'see' 5d BTDC)sounds like you have as you say two much advance for lower rpm use which would correspond to when a weight/spring setup would not yet have full mechanical coming on.....any chance they locked it in at max timing with no mechanical/spring/weight advance?? The norm for low rpm/load pinging on a sbc would be someone with a two large vaccuum can. let us know what you find, have you taken in a timing curve on the engine? ie. rpm/timing gun so you KNOW what the curve is? many assume curves are fine and often they are too large and detonating which they don't always notice or too small and they're missing BIG power.....best IMO to find out what you have first or it's hard to know what else you're affecting, Quote Link to comment Share on other sites More sharing options...
John Scott Posted October 28, 2000 Share Posted October 28, 2000 Morgan, vacuum advance is like it sounds. It runs the engine at more advanced timing to achieve better economy under no load conditions. On a high performance application, I usually run a distributor w/o the vacuum and just rely on the mechanical. The vacuum advance shouldn't have any effect at WOT conditions. If its out of calibration it usually causes a part throttle pinging. Anyway, your pinging might be due to carbon build up on the pistons which create hot spots and predetonate. Your car is under a more severe load at low rpms, especially with a big cam. Also, a too lean fuel curve can cause pinging. I don't know squat about Webers, but if they come in progressively this might be a cause. Whenever I've had a distributor in even a tooth off, it runs like crap throughout the whole range, if it will even start. With the motor off rotate the engine by hand until your timing marks are aligned. See if the rotor is pointing to the #1 terminal on the cap. (If its not on the compression stroke it will be 180 degrees off. If so make another complete revolution of the engine, then confirm rotor position. A tooth off will be way out of the vicinity of the #1 terminal. If it is off, then either Mike's suggestion of rewiring cap accordingly, or just pull it and install it correctly. Not the distrib? Then I'd try one of the fuel additives that are supossed to remove carbon deposits and get your timing back up to where it should be. If nothing else works, then try an octane booster. I hate the stuff and makes a mess of the plugs! Another thought, if the vacuum advance was disconnected, how was it done? Just unpluged? If its like a Mallory, removing the arm from the vacuum canister that's inside the distributor will cause the distributor plate to move around causing eratic timing. This would be evident by using a timing light and seeing fluctuations in the timing while remaining at the same throttle position. I wouldn't set the timing by the hard to start rule. The best way is whatever gives you the best performance w/o predetonating. The max advance rule doesn't hold true in all engines. This can be confirmed with your favorite accelerometer. JS [This message has been edited by John Scott (edited October 27, 2000).] [This message has been edited by John Scott (edited October 28, 2000).] Quote Link to comment Share on other sites More sharing options...
Drax240z Posted October 28, 2000 Share Posted October 28, 2000 Morgan, if you decide that the problem is not to do with your ignition, and is instead something weber related, try contacting ZR8ED on this site, or zcar.com. You can probably dig up his email address with a search here. He's had lots of sucess with his triple setup, and has helped a ton of people with jetting webers. ------------------ "THE STREETS WILL FLOW WITH THE OIL OF THE NON-BELIEVERS" Drax240z 1972 240z - L28TURBO transplant on the way! http://members.xoom.com/r_lewis/datsun.html Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted October 29, 2000 Share Posted October 29, 2000 There shouldn't be any carbon build up with under 10k miles on the engine. I hope not anyhow. But I check. I check the vacum advance plate dealie too... The advance diaphram and everything is off of the distributor. ------------------ Morgan http://z31.com/~morgan/s30 http://carfiche.com Quote Link to comment Share on other sites More sharing options...
John Scott Posted October 29, 2000 Share Posted October 29, 2000 Probably right about no carbon build up with that few of miles. If the vacuum diaphram is off, whats holding the plate in place? There should be some kind of linkage that connected the diaphram to the plate. I'd have to see the dist. for sure, but something needs to retain/ limit the movement that the vacuum advance used. I know my dist is different, but I disconnected the vacuum line and left the diaphram on the dist. If I were to remove the canister and linkage the plate would be free to move and throw timing way off. JS Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted October 29, 2000 Share Posted October 29, 2000 Morgan, I think its time for you care about what your actual timing is. I'd pick up a timing light and check it. If the the timing checks out then I'd look into those carbs. Glenn [This message has been edited by Glenn Richelsoph (edited October 29, 2000).] Quote Link to comment Share on other sites More sharing options...
Mikelly Posted October 30, 2000 Share Posted October 30, 2000 I ran 10:1 compression on a L6 2.8 motor and 12 degrees of advance at idle for 3 years without trouble on 92-93 octane. You should be able to just fine with 9.5:1! I agree with Glen, as you need to pick up a timing light to find out what the deal is. Interesting problem... Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted November 2, 2000 Share Posted November 2, 2000 I'm concerned about your timing maps too, and I also think you need to check timing. I run between 15 and 20 deg of advance with my Webers with no problems but my distributor is mechanical advance only. I'm more suspicious of your Weber setup. I think if timing was your problem you would have isolated something with all your adjustments. I know it took me a while to get my carbs jetted and synched correctly, and I at first mistook my problems for ignition also. My car ran like crap at low rpm and take off at first. A few simple checks- -Check for intake leaks. -Use a carb air flow meter to make sure each barrel is flowing the same. -Pull plug wires from the spark plugs one at a time with engine running. Engine rpm should drop identically for each plug wire pulled. -Check out the linkages on each carb. They must be adjusted to all the same length and at the same angle. THIS ONE IS IMPORTANT. This can cause the carbs to open at slightly different speeds which will kill you when trying to accelerate at low rpms. -You may have to play with jetting some, but I don't think you're ready for that yet unless your jets are way off. Once you get those carbs running right, you may decide you have a "real engine" in it. My car runs like a scalded dog and the Webers sound awesome at full throttle. Good luck. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted November 2, 2000 Share Posted November 2, 2000 Well. I said screw it and told myself I was gonna retard the timing until it quit pinging or quit running, whichever came first. Got home, turned it down a bit and went for a spin. Repeat. Repeat. Repeat. Damn this thing is retarding a lot and still running fine(Minus low rpm pinging)! Repeat. And finally, with the distributor retarded about 1 cm off the scale, it quit pinging. I swear I retarded the timing 10-15 deg easily. Anyone know how many degrees each tick mark is on a l6 distributor? It will pull smoothly and without complaining from 1500rpm in anything but 5th, and from idle in 1st easily. How many teeth are on the distributor? It's gotta be at least 1 tooth off, if not 2 or 3. It scares me to think about how much of a !@#$%^& the guy I bought the car from was. To date we have: Distributor incorrectly installed and timing advanced ~10-15 too far. Flaky light wiring that works sometimes. Leaky rear main seal. All electrical connections he made were crimped(stereo, ignition, gimp A/C system) instead of soldered or at least crimped with nice weatherproof connectors. Hot wire for fuel pump($10 wal mart cad plated POS pump) is spliced into ignition switched hot wire on steering column with a crimp connector. Wire ran under center console, under hatch carpet, through a hole that had a rubber plug in it(thus crimping wire badly against body) and is crimped onto the fuel pump underneath the car. Wal-mart window washer pump zip tied onto inspection lid, and connectors cripmed together. Door speakers screwed onto outside of door panels. Front wheel bearings so loose it took over 5 full turns to torque them down properly. Gimp A/C lines zip tied to brake lines. More stuff that I can't remember because it's well past my bedtime. What a moron. ------------------ Morgan http://z31.com/~morgan/s30 http://carfiche.com [This message has been edited by John Scott (edited November 04, 2000).] Quote Link to comment Share on other sites More sharing options...
Drax240z Posted November 2, 2000 Share Posted November 2, 2000 Yikes Morgan! I'm glad you got that car before we saw one less Z car in the world, sounds like the guy was a disaster waiting for a place to happen! Just remember that you got a sweet deal out of it. ------------------ "Gimme Fuel, Gimme Fire, Gimme that which I desire" -Metallica Drax240z 1972 240z - L28TURBO transplant on the way! http://members.xoom.com/r_lewis/datsun.html Quote Link to comment Share on other sites More sharing options...
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