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Posted By Discussion Topic: 59AB Spark Plugs too lean? How to correct?     len47merc 12-20-2015 @ 10:50 AM reply profile send p.m. Senior Posts: 1165 Joined: Oct 2013 Gents - have a look at the attached pic of plugs with about 3,500 miles on them since new. These are left to right from cylinders 4, 6 & 7 respectively. In pulling them today (reference other thread concerning 'low rpm/high load miss') the plugs for cylinders 2, 3, 5 & 8 all are a medium gray, the gaps are consistent at .025" and quite frankly they are clean as a pin. The remaining plugs - 1 (not pictured), 4, 6 & 7 also are found to be at .025" and very clean but the color for these is as shown in the photo - a bit more on the light brown side. These 4 (3 in the pic) are fed as I recall by the driver's side carburetor barrel. What conclusions might you all have about this and what if any corrective actions may be required/would you take? I validated the jets in the carb upon install with a pin gauge and found them to be consistent and correct. EDIT - apologies about the 90 degree rotation on the pic. Orientation was correct on the hard drive. Weird. Steve This message was edited by len47merc on 12-20-15 @ 1:19 PM ford38v8 12-20-2015 @ 11:42 AM reply profile send p.m. Senior Posts: 2736 Joined: Oct 2009 Len, The carb jets are best adjusted while the engine is fully warmed up and running. Open/close them individually to run best, while readjusting the idle to the same 500 RPMs. You can also go by the highest steady vacuum. Either way, be sure your vacuum wiper doesn't leak. Alan len47merc 12-20-2015 @ 12:00 PM reply profile send p.m. Senior Posts: 1165 Joined: Oct 2013 Thanks Alan - is it your opinion the driver's side barrel has the screw turned in too far causing it to run too lean throughout the rpm range? I previously set idle at 450 rpm and adjusted the mixture screws using my vacuum gauge but have not re-validated the settings from ~3,500 miles back. From the pic does it appear to be so lean as to be concerning? In your humble opinion could this also be related to the 'miss' I've referenced under the separate thread today (I doubt it but thought I'd ask anyway)? Appreciate your thoughts here - Steve This message was edited by len47merc on 12-20-15 @ 1:16 PM ken ct. 12-20-2015 @ 1:38 PM reply profile send p.m. Senior Posts: 1513 Joined: Jan 2010 Len, IMO the greyish plugs are slightly on the lean side.Should be more on the coffee w/milk color. Try setting @ 7/8 to 1 1/8 turn out and clean plugs or install new ones and rd. test again. OMO.. ken ct. oldford2 12-20-2015 @ 2:33 PM reply profile send p.m. Member Posts: 275 Joined: Oct 2009 Now wait a minute...If you are talking about the idle screw jets remember that they only control the idle. For most of your running the mixture is controlled by the main jets and the power valve when accelerating or under load. So, the idle jets have little effect on the color of your spark plugs. as Ken would say....OMO John This message was edited by oldford2 on 12-20-15 @ 2:34 PM len47merc 12-20-2015 @ 3:02 PM reply profile send p.m. Senior Posts: 1165 Joined: Oct 2013 ken & oldford2 - thanks for your replies. This is what I have been struggling with, that being that my experience tells me the idle mixture screws only control the idle and not also the mixture @ speed/rpm; however, the fact that 4 plugs, as ken reinforces, are running lean, tells me that something is ever-so-slightly amiss with the carburetor's driver's side barrel and I am wondering if the idle mixture screw for that side could cause the lean appearance of those plugs. Note again I gauge pinned the jets when I installed them and found them to be consistent and correct, so the only thing I can think of is the idle mixture screw on the driver's side (which was found to be turned in slightly more than the passenger side) is causing what appears to be a lean condition, even though the screws are understood to only control the idle mixture. Thoughts? Steve This message was edited by len47merc on 12-20-15 @ 3:02 PM ken ct. 12-20-2015 @ 3:53 PM reply profile send p.m. Senior Posts: 1513 Joined: Jan 2010 Len what did the jets mike out at (size). They do contribute a small amount of fuel in the running down the road speed even though the MJ's are supplying most of the fuel. ken ct. len47merc 12-21-2015 @ 5:59 AM reply profile send p.m. Senior Posts: 1165 Joined: Oct 2013 Ken - both jets were marked 50 and and also pinned at 50. Car has ran and idled great since install and initial set-up. As noted earlier I did find the driver's side mixture screw was turned in ~1/4 turn further than the passenger side (car was idling very well at 450 rpm and ran great through the rpm range). I pulled out my old spark plug color charts and confirmed the color of the 2, 3, 5 & 8 cylinders are about as close to optimum as one can get. Cylinders 1,4,6 & 7 are burning lean per this same reference chart so, given I know the jets are consistent, your comment Ken that the mixture screws do contribute fuel throughout the rpm range is the only thing I can figure is causing this condition. Given the driver side was found to be scr*w*d in ~1/4 turn further than the passenger side, and those corresponding cylinders are burning lean, at this point I have to assume this is the root cause. Installing a new set of plugs today and resetting the mixture screws with a vacuum gauge (confirmed windshield wiper motor is holding vacuum last eve) - will be focused on what the optimum setting is compared to where I found it and also see if the driver's side was scr*w*d in a bit too far. Will see if the new plugs and mixture settings address both the low rpm/high load miss noted under the other thread and as well balances the burn on those cylinders. Any and all additional thoughts appreciated - Steve TomO 12-21-2015 @ 8:12 AM reply profile send p.m. Senior Posts: 7243 Joined: Oct 2009 Steve, the light brown color of your plugs looks normal to me. I would have to see the plugs from the other side of the carburetor to see the difference that you are seeing. A lean mixture would lead to an overheating condition of the plugs, white color and blisters. The idle mixture screws only control the mixture at idle and just above idle. The slight difference in fuel mixture between the 2 sides of the carburetor can be accounted for by slight differences in the nozzle bar components, or contamination in the nozzle bars or the accelerator pump discharge nozzle. To help determine if your problem is fuel delivery or ignition, next time it happens, try pulling out the choke a little at a time. If that improves the performance, your mixture is too lean. If it has no effect, your problem is ignition related. To set your mixture screws: Set the idle speed to 425-450 RPM Lightly seat the screw and back out 1 1/4 turns Connect your vacuum gauge and adjust each idle screw in the same direction 1/8 of a turn, check the vacuum gauge and note if the vacuum increased. If it decreased, turn the idle screws back to the starting point plus 1/8 of a turn and recheck the vacuum. By turning the screws the same amount each time, you prevent the problem of one side being adjusted rich to compensate for the other side being lean. Tom len47merc 12-21-2015 @ 12:14 PM reply profile send p.m. Senior Posts: 1165 Joined: Oct 2013 Good Tom thanks. Greatly appreciate the diagnostic processes here. Trying to go down the most logical, efficient and cost effective sequence here - this helps immensely. From memory Tom I recall your saying the NAPA FA54 is the proper equivalent for the 1GA-12300 called for on my '47. Please correct me if I am wrong - going to go test drive the car shortly with new plugs, adjusted carb and validated fuel pressure. If low rpm/high load miss is still there after this and your suggested tests going to the condenser next assuming the results support the same. Thanks again Tom - Steve

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