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| How to remedy a stubborn misfire https://slantsix.org/forum/viewtopic.php?t=59754 |
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| Author: | davidrad [ Thu Jun 09, 2016 2:47 pm ] |
| Post subject: | How to remedy a stubborn misfire |
Hi guys, My recently acquired a 70 Swinger that is basically a barn find plus some surface and trunk rust and an eaten interior. The 225 fired right up after 20 years of sitting. It did take some priming and a temporary ballast resistor jumper. It has a miss on at least one cylinder. Below is what I've done so far to remedy the miss. I have the curb idle screw bottomed out to keep it running well while idling in gear. No load idle and fast idle are both high. Plugs gapped at .035 Wires points gapped at .020 condenser syphoned old fuel put in new ethanol free fuel with lead treatment and seafoam Oil change & Filter, royal purple with seafoam additive valve adjustment while hot and running. .010 & .020 rebuilt Holley 1920 Carb, it wasn't horrid no varnish, just sticky alternator ballast resistor Air cleaner PCV The timing is probably about 35 degrees advanced but that's where it runs best at. The timing marks don't jump around and is pretty constant. I haven't checked the balancer to see if the timing mark is lying, but since I did it by timing light and sound at this point I'd be happy with running correctly rather than being on the marks. New Clear Fuel filter so that I could see the amount of rust I was sucking in. (yuck) Compression tested while cold without WOT. 135 in the front three going down to 115 by #6. What have I missed? I haven't done the coil yet, that's probably a tonight thing. Any help is appreciated, I'm running out of ideas. |
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| Author: | Joshie225 [ Thu Jun 09, 2016 3:11 pm ] |
| Post subject: | |
Have you run a compression test? It's pretty common on engines that have sat for this long to have stuck rings and/or valves which don't seal well. It's also possible that the timing chain jumped a tooth throwing off the cam timing and necessitating the carburetor adjustments you've applied to keep it running. You can pull the distributor cap and roll the engine back and forth by hand to get an idea of the slop in the timing chain. Don't rule out a vacuum leak or a bad idle circuit in the carburetor either. |
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| Author: | davidrad [ Sat Jun 11, 2016 2:15 pm ] |
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I had read on one of these posts that if my compression was above 90 my timing chain probably hadn't slipped a tooth. Can someone verify this for me? |
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| Author: | slantzilla [ Sat Jun 11, 2016 10:44 pm ] |
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Have you checked for vacuum leaks? With it running spray carb cleaner around where the intake meets the head. It is very possible the gasket has deteriorated. It is also possible your carb is junk. As for your timing chain, a jumped chain will normally cause poor performance, but usually will not drop cylinders. |
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| Author: | Jase [ Sat Jun 18, 2016 11:58 pm ] |
| Post subject: | Re: How to remedy a stubborn misfire |
Quote: What have I missed? I haven't done the coil yet, that's probably a tonight thing. Any help is appreciated, I'm running out of ideas. |
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| Author: | Doctor Dodge [ Sun Jun 19, 2016 8:11 am ] |
| Post subject: | Re: How to remedy a stubborn misfire |
Quote: Hi guys, ...
My guess is the miss-fire is likely caused by the Holley carb. It may have a plugged or partially plugged idle circuit.rebuilt Holley 1920 Carb, it wasn't horrid no varnish, just sticky... One test, look down the carb and find the 2 brass air bleeds. Take a pen tip and plug the larger hole air bleed... while the engine is running. See if doing that helps smooth-out & stabilize the idle. DD |
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