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Post by mrrubburn on Jan 26, 2016 16:00:35 GMT -5
My 1994 subaru J10 FWD with carburator is sometimes missfiring. I changed distributor, spark plugs, leads, condensers, coil, removed the carburator and cleaned all the gunk out. It idles great, power is there and timing is spot on! I set it to 3 BTDC because I had the head skimmed and our fuel here sucks. It misfires mostly when it is at operating temperature. Sometimes when i floor it and let the engine idle down (not engine braking), it stalls or almost, not always thou, sometimes the engine slows down normally. I noticed that sometimes when it is idling @ 850 rpm and tap the throttle to the floor, I hear a BIG SINGLE KNOCK before it responds (Probably pre-ignition from the sudden fuel burst into the cylinder) but after that its all good through out the rest of the revving. Did a compression test and showed 152 psi on all three cylinders, so thats good. When it happens, it does it on all gears, with load or no load even if engine braking, it just missfires, sometimes it stops immediately, other times it keeps doing it for a while... What could be....? The only thing I can think is left to do, is pull down the fuel tank and clean it.... Please help
Thanks in advance MrRubburn
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Post by coondog on Feb 1, 2016 15:48:33 GMT -5
First off, I've never messed with a carb'ed justy, but I do have a lot of experience with tuning carburetors, and tuning carbureted engines.
One rule of thumb I use with carburetors, that others might disagree with is, to keep them running optimal, I tune with the weather. I.E. for me its april 1 and october 1.
I can't recall the ignition timing spec for the justy off the top of my head, but 3BTDC is pretty damn low, even for shitty gas. I do a lot of carb tunes on V8 setups, and I never run that low because of the performance loss it major. Some engines like different igniton timing specs, but my base line would be 8BTDC and adjust from there. If you really do in fact have crappy gas, 8BTDC might be a little high for 87 octane, but I've never had detonation using 8BTDC on 87 octane. With your timing set that low, you probably have low manifold vacuum, causing the carb to lose a lot of the scavenging effect.
Since air density is reduced when the engine is warm, I would definitely be looking into my tune to find out where the problem lies.
I would up the timing, and use a vacuum gauge to set the carb up to where it has the highest vacuum reading at idle, and make fine adjustments from there.
Hope this helps, Connor.
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Post by mrrubburn on Dec 30, 2016 5:28:17 GMT -5
Thanks for all your help man Although the timing wasn t actually that bad because factory timing is 5 btdc, I managed to find the source of the problem, which was the wire going from the breaker to the coil. It was very close to the housing of the distributor causing it to leak spark to earth, and when it heats up it gets worse because everything expands. I highly recommend that when someone is suspecting the condenser or breaker or want to change them, check this wire first. The breaker wire and the condenser wire connect to the same black holder on the dizzy between the housing and the cap, it has screw and holds the wires with a square nut on the bottom. Check that first because you might not need to change you breaker or condenser. I tried it myself by installing my oldest previously swapped out condenser and breaker which both looked horrible and points badly worn, and when set correctly it ran like a dream, even with fouled plugs! Right now Im actually setting my carb mixture, leaning it half of a quarter turn each time until I get a brown plug. Im doing about 40 mpg so its already looking good! MrRubburn
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Post by certimafied on Jan 6, 2017 19:58:52 GMT -5
Alright I'm going through some running issues with my carb'd 88 right now. Here's my two cent (experience):
Diesels on shut off: clogged fuel return.
Misfires occasionally (my vac advance is disconnected and diaphragms blown):
Dirt/grit in dizzy And/or Ignition coil positive and/or negative posts have continuity to coil case "shorting out"
My recent misfiring, more sputtering at certain RPM, Alternator way way way over charging I mean 17v at idle almost 20v with rpm.
Not saying this is what you have going on but a few a things to look at real quick. Good luck!
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