My '67 L79 is running pretty well, but it burns gas at a ridiculous rate...probably around 6-8 mpg. I recently pulled all the plugs and they all looked great, except for #8. Picture is below. I'm guessing potentially a stuck or burnt valve here, or potentially oil leaking into the combustion chamber. Doesn't seem to be the exhaust valve, as the rag test at the exhaust pipes does not point to any suction. Either way, this plug is black, crusty and not what one should see, especially considering there's less than 1000 miles on this plug. I just had shoulder surgery, which is a long recovery, so I won't be pulling heads or wrenching anytime soon. I'd like to find an honest, trustworthy shop that could diagnose and do the repairs. The 4 speed also likely needs a rebuild, as I have to double-clutch to shift into 4th to avoid grinding. I live about 2 hours west of Denver, CO, but am open to anywhere within a reasonable distance from here. I would likely ship the car if it's further than Denver, though. I've had bad experiences in the past with another car, so I'm really looking for a rock solid shop that has an impeccable track record of satisfaction. Thank you for your suggestions!
Recommendation for Engine Work
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Re: Recommendation for Engine Work
Anthony
Welcome to NCRS Tech Board!
In addition to plugs/timing questions already requested:
Engine (cam) mods? Idle speed? Ignition wire - is plug getting spark? Dwell?
Compression / leak down test results?
Carburetor mods? Last rebuild on carb? Jets sizes?
Pull engine oil dipstick - any gasoline smell?
Exhaust color (if any)?
DaveJudging Chairman Mid-Way USA (Kansas) Chapter- Top
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Re: Recommendation for Engine Work
Anthony
Welcome to NCRS Tech Board!
In addition to plugs/timing questions already requested:
Engine (cam) mods? Idle speed? Ignition wire - is plug getting spark? Dwell?
Compression / leak down test results?
Carburetor mods? Last rebuild on carb? Jets sizes?
Pull engine oil dipstick - any gasoline smell?
Exhaust color (if any)?
Dave
In addition:
- Type of plug wires (solid core, resistance, spiral core)?
- Resistance (ohms) measured on #8 compared to others?
- Is the choke opening fully?
- Does the heat riser valve open fully? It may be best to wire it open.
- Rear end ratio? If it has a low rear end gear, getting single digit mileage is possible during short trips.Mark Edmondson
Dallas, Texas
Texas Chapter
1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top- Top
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Re: Recommendation for Engine Work
Plugs are NGK XR5s
I was using the timing method described in the tuneup section of the shop manual.- Top
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Re: Recommendation for Engine Work
Anthony
Welcome to NCRS Tech Board!
In addition to plugs/timing questions already requested:
Engine (cam) mods? Idle speed? Ignition wire - is plug getting spark? Dwell?
--Cam is the stock L79 cam; idle speed is around 800 rpm; ignition wires are brand new; dwell is set per the shop manual; I cannot check the spark to the plug right now due to my shoulder surgery, as it's definitely a 2-hand job to pull the #8 plug.
Compression / leak down test results?
-See above. Unfortunately, I cannot do one right now due to being down one hand for another month/6 weeks.
Carburetor mods? Last rebuild on carb? Jets sizes?
-The carb is a stock, date coded 3810, rebuilt by Eric at Vintage Musclecar Parts
Pull engine oil dipstick - any gasoline smell?
-Good idea. I'll do that, as I can manage that with one hand!
Exhaust color (if any)?
-No color here of any note.
Dave
Thank you; my answers are embedded in the quote above.- Top
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Re: Recommendation for Engine Work
In addition:
- Type of plug wires (solid core, resistance, spiral core)?
-https://www.rockauto.com/en/moreinfo.php?pk=643774&cc=1321377&pt=7224&jsn=9
- Resistance (ohms) measured on #8 compared to others?
-Wires are brand new so I did not do this; the plug was fouling even before I changed the wires
- Is the choke opening fully?
-Yes
- Does the heat riser valve open fully? It may be best to wire it open.
-I have not checked this; what happens if it doesn't?
- Rear end ratio? If it has a low rear end gear, getting single digit mileage is possible during short trips.
-This should be stock for the car; 3.55:1 IIRC- Top
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Re: Recommendation for Engine Work
Anthony,
Suggest you contact the Rocky Mountain Chapter for Colorado recommendations.
RMC can be found on the NCRS contacts page https://www.ncrs.org/contact/index.php scroll down until you find the Rocky Mountain Chapter.
Gary
....NCRS Texas Chapter
https://www.ncrstexas.org/
https://www.facebook.com/profile.php?id=61565408483631- Top
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Re: Recommendation for Engine Work
Anthony
If all other plugs look OK, then you have an issue with a single cylinder. Purchase (or make) a spark plug tester - image below (Amazon, etc). Just pull the plug wire in question, insert the tester tool, clip it on a good ground, and have someone crank your motor. You should get a strong spark, if not, check connection/boots.
If good spark, then a compression / leak-down test is in order.
Sort out this fouling issue before tackling fuel mileage concerns.
Dave
KDT2757-2.jpgJudging Chairman Mid-Way USA (Kansas) Chapter- Top
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Re: Recommendation for Engine Work
The car has suppression core cables. These are delicate and their resistance can increase with handling, bending, heat and age. Cable resistance can vary greatly out of the box, so it's a good practice to check each cable's resistance before installation. This is worth checking, although you say the fouling precedes installing them.
A heat riser not opening fully can cause a variety of problems including poor mileage. Though not likely the cause of a single plug fouling.Mark Edmondson
Dallas, Texas
Texas Chapter
1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top- Top
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