Recommendation for Engine Work

[Anthony N.]

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!

[Owen L.]

Re: Recommendation for Engine Work

Would you post a couple pics of the other plugs?

What is the brand and heat range on the plugs?

What timing method are you using?

[David H.]

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

[Mark E.]

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.

[Anthony N.]

Re: Recommendation for Engine Work

Would you post a couple pics of the other plugs?

What is the brand and heat range on the plugs?

What timing method are you using?

I didn't take pictures of the other plugs, but they were that nice brown/tan color.

Plugs are NGK XR5s

I was using the timing method described in the tuneup section of the shop manual.

[Anthony N.]

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

Hi David,

Thank you; my answers are embedded in the quote above.

[Anthony N.]

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

Hi Mark, thanks for the reply; my answers are embedded in the quote.

[Gary C.]

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
....

[David H.]

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.jpg

[Mark E.]

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.