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| Engine swilling fuel; 13.7mpg https://slantsix.org/forum/viewtopic.php?f=19&t=62799 |
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| Author: | wjajr [ Tue Sep 04, 2018 1:37 pm ] |
| Post subject: | Engine swilling fuel; 13.7mpg |
225ci, bored +40, Oregon cam grind 346, center line 99*, 9.6:1 compression, oversized valves, ported head, Clifford 4v intake, and shorty headers, 2600 stall converter, 3.55:1 suregrip 8 3/4 rear. 3000 rpm = 60 mph, 2000 rpm = 40 mph I have several problems that have got me puzzled. Engine always runs in rich zone on A/F mixture gauge except when under WOT. Front three plugs read rich, back three read lean. New NGK UR5 I suspected Holley 0-8007 secondary idle air was excessive causing rear three to look or read lean. Primary idle mixture screws out about 1.75 to 2 turns produced highest and steady vacuum at idle in park, ~13Hg Main jet = 53, PCV valve MV781 which I think is a standard Motor product number purchased around 2008. Base timing +14*, timing mark steady, no floating around. Engine idles smoothly at 900 rpm in park, and 750 rpm in drive. Changes made last night to above in quest for better drivability, and fuel economy. Removed carb, made sure very little light showed past secondary throttle butterflies by adjusting their stop in an attempt to reduce idle air. Checked secondary vacuum diaphragm which opens secondary throttle plates, no holes found. Reinstalled Carb, once bowls filled with fuel, she fired right up, on high idle around 1250 rpm, kicked down to 800 rpm in park, smooth idle, vacuum ~14Hg Down jetted to 51 (this is out of the box jetting for 0-80070, made sure just a square of transmission slot was showing below throttle plates. Turned in primary idle mixture screws 1 to 1.25 turns out for highest vacuum ~14Hg at 850 rpm in park. When rubber cap was removed from vacuum tap on intake at base of carb idle increased about 100 rpm to install vacuum gauge. Drove car into town a 30 miles round trip 75% at 40/45 mph, the rest slow in town 25 to 35 mph. Read # 2 & 5 plugs once home: 2 looked a little lighter, and 5 looked a bit darker. A/F gauge read rich most of the time Went on second test drive, this time I removed rubber cap from vacuum tap at base of carb to intake to let in additional idle air. Drove well, would dip into lean condition with slight throttle opening while approaching a hill, and PV would kick in sending A/F mixture into rich. #2 plug looks a lot lighter, #5 showing a bit of tan on porcelain. Now those two plugs look like they could have come from the same engine… I seams that there needs to be less fuel, or more air passing through the carb. Would the wrong PCV valve cause this? A hose connects between valve cover air intake and air cleaner into space between filter and carb a low pressure area. PCV looks shinny clean, sort of rattles, and is controlled by an internal spring. I’m wondering if this is the wrong valve, disallowing enough air to pass through cab to lean out mixture. I’ll order or pick up a new one for 1967 slant. It looks as if these valves changed in some way once charcoal canisters were installed. Should I step down two more jet sizes to say 49? Other than being a pig, this engine is running very nicely with 900 miles on it. Not getting real hot while idling. It dose heat soak, but always starts easily and cools down in a half minute or so once running. |
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| Author: | Jase [ Wed Sep 05, 2018 8:56 am ] |
| Post subject: | Re: Engine swilling fuel; 13.7mpg |
Sounds like you are headed in the right direction. This is the same carb as was on the car before? The cam and compression change may have upset the idle and transition circuits, which are what the engine runs on most of the time when cruising.. What about the power valve? It seems it is opening too soon, as it should be opening when needed, and bringing Air-Fuel ratios back into balance as the airflow increases. . . Can you isolate the carb to run on the primary side only to reduce variables? |
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| Author: | wjajr [ Wed Sep 05, 2018 10:23 am ] |
| Post subject: | Re: Engine swilling fuel; 13.7mpg |
Power valve is 5.0. I just picked up a 6.5 this morning which it needs now that I have a lot more vacuum than before rebuild. 5.0 comes on line a little late which may be a small component of a slight flat spot. Before rebuild I only had around 8 to 9 inches Hg at 1000 rpm idle. Now up to 13 -14 Hg at 800 rpm. I'm beginning to think someone may have messed with air bleeds before I got the car. This car was built as a drag queen in early 90's and raced four seasons at Englishtown NJ. |
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| Author: | wjajr [ Thu Sep 06, 2018 12:39 pm ] |
| Post subject: | Re: Engine swilling fuel; 13.7mpg |
I popped in that 6.5 PV yesterday, flat spot almost gone, it's only slightly noticeable with light footed slow throttle openings. One can see A/F gauge dip into lean and flip to rich as soon as PV opens. I may have to adjust accelerator pump to dump a larger volume of fuel quicker, and not last as long. It's time for a fill-up, and tomorrow I may change out the 51 jets to #50 and if that won't lean out A/F reading I'll drop in #49 jets. With engine idling in park, exhaust has very little smell, a big improvement over the stink that engine made before its rebuild. Just for the record, idle mixture screws are out 1 1/2 turns. |
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| Author: | and739 [ Thu Sep 06, 2018 2:02 pm ] |
| Post subject: | Re: Engine swilling fuel; 13.7mpg |
Glad to hear you're making progress, wjajr. Thank you for documenting your work. I'm sure this may prove beneficial to me and others doing similar tuning. |
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| Author: | wjajr [ Fri Sep 14, 2018 8:22 am ] |
| Post subject: | Re: Engine swilling fuel; 13.7mpg |
This high fuel consumption has me baffled. A/F gauge reads same as before rebuild, and with four bad valves and a lot of cylinder wear I was getting 18 mpg. Engine idles nicely with twice the vacuum (13.5 Hg) before rebuild, and pulls around 18Hg at 3000 rpm. |
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| Author: | Dart270 [ Fri Sep 14, 2018 10:07 am ] |
| Post subject: | Re: Engine swilling fuel; 13.7mpg |
New motor will have worse mileage due to friction, but that seems excessive. Have you verified that the vac advance is working properly? Lou |
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