Guest Anonymous Posted November 7, 2000 Share Posted November 7, 2000 Sounds like you need a spark plug cleaner, they do sell them. I would leave the gap alone, I like a little over gap like 48 to 50 because I'm running a Crane Hi-6. Get a compression gauge and check your compression. Any of them lower than 130 put two table spoons of oil in there and recheck. If the compression comes up its leaking past the rings. If it stays the same check your valve adjustment. If still low you need valve job. When you say fouled, what does the spark plug look like? Does it burn oil or smoke? If it does smoke when? You have to be running very rich to carbon foul a plug, you will see dark black smoke coming from the tail pipe. If that is the case you need to rebuild your carbs. Good luck, post what you find. Quote Link to comment Share on other sites More sharing options...
jeromio Posted November 7, 2000 Author Share Posted November 7, 2000 So, I have a low mileage junk yard L28 with dual SUs that ran very nicely for about 6 months with a rebuilt P79 head. Then I inadvertently put some stale gas in it (you may have seen these posts over at zcar.com). I have since drained and cleaned the fuel tank and the bowls, fiddled with the carbs, replaced the wires, cap and rotor (car has the Crane electronic upgrade) and the fuel filter several times. It already had a newe Accel coil. I have gone thru about 60 spark plugs. I have tried gapping them tighter (the NGKs come 44 and I tried 32 - have lately settled on 40 which is the lowest setting of the wire guage I have). They keep fouling! And it's very random. It'll run fine, then after a day or a week it'll cough and sputter. When I check it it may be one fouled plug, or it may be 3. One time it was 5. Number one is the most robust - I've only replaced it twice. I'm running 93 octane and occasionally put some fuel system cleaner in the tank (mostly out of desperation). I've leaned the carbs out - I get some pinging on hard acceleration and much backfiring on downshifts. What would cause some plugs to foul and not others? When it's more than one plug, it's almost always been one from each carb (such as 3 & 4). I bought one of those cheesy mechanical "Spark Strength" testers and all 6 seemed very strong - if anything number 1 was weaker, even though that's the one that fouls the least often. What causes fouling? I know that too much fuel will do it, but what else? What should I be looking at? I'm getting like 8 miles to the plug here and it really sucks! I'd appreciate any ideas any of you may have... Thanks. Quote Link to comment Share on other sites More sharing options...
jeromio Posted November 7, 2000 Author Share Posted November 7, 2000 I did a compression check - all 150 or higher. The shop did a valve job on the head when they did the rebuild. It does smoke a little - but not very much. I do suspect the carbs need to be rebuilt. It's just that I want to put a turbo L28 in it and it sucks to invest in something that's gonna get replaced. The fouled plugs are black and sooty - too much fuel. It's strange - like maybe things are running well and then a glob of crap shoots out and only affects one or 2 cylinders. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted November 9, 2000 Share Posted November 9, 2000 Do you have the early or late su's? Flat tops or round? What year is your car? Do you have trans fluid in the tops of the carb pistons? Quote Link to comment Share on other sites More sharing options...
jeromio Posted November 10, 2000 Author Share Posted November 10, 2000 71 round tops 50/50 trans oil and MarvelousMystery (lighter than trans) L28 F54/P79 engine. ShortBlock has about 70K miles on it. P79 was rebuilt about 4000 mile ago. I have the timing set to just below max vacuum (using a vacuum guage on the front carb). It's advanced to about 15 degrees if you go by the marks (the accuracy of which I question). I have the vac advance pulling from the cross over tube. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted November 11, 2000 Share Posted November 11, 2000 I would guess you have the standard fuel pump,only use the mech. fuel pump not and or elect. Try dialing the carbs as lean as possable at idle. The floats could be set to high, bend the flaot tab a little so as there is less fuel and test. Take the carb piston out and inspect the needle, it could be rubbing or bent. I have heard of some good how to rebuild su site's but I do not know where they are, try Z car club web site. I have three Webers on my ride, a long time ago I had su's and they are the easiest carbs to rebuild. Most of the time I could just play with the settings to get them to work good. Do you have the Crane Hi-6? If you do get thier coil a 91 or 92. I found thier coils work best with thier systems. I would advance the timing until it pings and back off a little and stick with the ported vacuum to the dist. Quote Link to comment Share on other sites More sharing options...
Guest scca Posted November 11, 2000 Share Posted November 11, 2000 pinging: i dont think thats from the carbs, 15 may be too much initial. check total . you should have MAX 36 degrees use a variable timing lite. i generally removed the vacuum advance and relied on the mechanical only. but as long as its working correctly that fine. (as long as the cam is stock) Fouling:? sounds like oil problem not a mixture problem. it takes a lot for a SU to get rich enough to foul a plug where it wont clean up onits own. as for plugs you might want to try using a BP5ES or BPR5ES. this is a hotter plug than a 6 and will help burn off everything more. ------------------ Mike mike@fonebooth.com http://www.fonebooth.com/brakes.html raceparts and brake upgrades. Quote Link to comment Share on other sites More sharing options...
jeromio Posted November 11, 2000 Author Share Posted November 11, 2000 I have the cheapo electric, noisy-ass purolator pump. I fear fiddling with the carbs too much because then I'll just end up completely disassembling them. The pinging I chalk up to the lean mixture. Actually, the other day I boldly tweaked the screws a sconch and now there is no ping at all. The advance works, I've tested it. When it's running well, it runs beautifully. I've been on the same set of plugs now for a week. Seemed like one was fouled a few days ago - much backfiring and complaining and lack of power. I was pissed so I jut ragged it - drove it at 5-6K for 5 minutes. And it cleared up. I looked for some hotter NGKs a few months ago and wasn't able to find any. I haven't tried any of the "real" parts stores yet though (the ones that close at 5pm and aren't open weekends). I guess realistically it'll be a year before I can put the turbo motor in (not only do I have to find the motor, I have to find the money). So, maybe I should just bite the bullet and rebuild these carbs. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted November 12, 2000 Share Posted November 12, 2000 Get the mechanical fuel pump, it will work alot better. I don't think the P79 has a place for one, so you will need to make one or get another head. Like a P90,P90a or N42. You will need a P90 anyways for your turbo motor and keep your bottom end. Then put all your turbo stuff on when you are ready. Quote Link to comment Share on other sites More sharing options...
jeromio Posted November 30, 2000 Author Share Posted November 30, 2000 Just by way of an update - the car has been running fine. It has started to gag twice in the past month. Both times I just got ill with it and ran it at high RPMs for 5 or so minutes. Cleared up. I have a spare set of plugs in the rear "tool chest" and haven't had to use them yet. So, my theory is that there was still some residual crap in the tank or the lines or where ever. And now it has finally (hopefully?) burned itself out. It runs great. I'm still leaning towards delaying my rear suspension parts purchase/rebuild and buying the L28turbo. The bouncy crunchy is sucky, but it'd be a great project rebuilding the taht motor for transplant in the spring. Anyone have any estimates for cost outlay on parts for a mild L28 turbo rebuild (bearings, seals, headwork?)? They want $400 for the complete engine minus the ECU. There's a guy on zcar.com who has turbo ecus for $80 - is that fair? Plus I should be able to get some money for the currnet engine at some point... Quote Link to comment Share on other sites More sharing options...
Drax240z Posted November 30, 2000 Share Posted November 30, 2000 Lets see, I got my turbo engine for $200. Took a bit of talking to the wreckers to get them down there though. -Head cleaning, rebuild, surface plane, valve job, new valve seals, etc... $300 -Timing chain kit (don't use nissan, $$$, I went with sealed power) $95 -Nissan Rings, main bearings, rod bearings, rear main seal, head gasket, manifold gasket were about $300 total. I got a good deal from a guy that used to work for nissan. -ECU - I sold a turbo ECU AND AFM for around $80 together... But $80 for one isn't out to lunch if its for sure working. Check out my turbo info page at: http://members.home.net/drax77/newpage.html then click on the turbo buildup article... ------------------ "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 http://members.home.net/drax77/newpage.html Quote Link to comment Share on other sites More sharing options...
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