2F Compression test and Plug diagnosis (1 Viewer)

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Duke

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Joined
Aug 28, 2010
Threads
14
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139
Location
San Diego, CA
I've been contemplating having my head done on my '40 as I've been having a puff of smoke on hot starts and it smokes for about 20 seconds after idling for more than 5 minutes.

So, I redid my compression test from a few months ago as the tester line was cracked and old (friends). Bought my own and went to work this morning on it.

Results are as follows:

Cyl Dry Wet
1 149 150
2 148 150
3 150 152
4 145 145
5 145 145
6 155 155

Looks good and I'm assuming that my pistons/rings are doing their job.

My concerns are the appearance of my spark plugs. They have about 3000 miles on them and my feeling is that it's running lean and cold? The first photo (taken with my iphone so sorry for the quality) is of all six in order. The second shows cylinder 1 on the left and 2 on the right, the other four have the same appearance. I would appreciate some feedback from the many experts here on the forum along with some suggestions.

I did a rebuild on the carburetor about 3k miles ago. Pulled it completely apart and soaked it in carb dip. I purchased a Keyster kit and re-assembled in the order it was take apart. It's run wonderfully since then. I did take it in to a guy with a dyno shop in Tacoma, WA (Bill's) and he "tuned" the carb for me based on the dyno/emmisions reading. I'm not an expert in the terminology so forgive me if I have something wrong in my vernacular. I'm learning.

The dyno guy said it was running lean and I needed to get a larger primary jet. So, I pullled off the top of the carb, pulled the primary and it was (hard to read) a 121 or 124. I replaced it with a 144 and noticed an increase in responsiveness immediately. Went back to have it retuned and was told "it was better, but still was running lean". We left it at that and I drove it thru the fall and Christmas daily.

I am running Penn 20-50W oil in it and have been changing it every 1000 miles since I purchased the vehicle. It had been sitting for 12 years prior to me purchasing it and I believe it was driven hard by the PO in preparation to sell it. As such my feeling is that the valve guides were damaged as they were not using a high zinc oil in it prior to parking it, nor did they change the oil prior to starting it up and selling it to me.

I am changing the oil again today and can say that it now has very little discoloration. It is getting progressively cleaner and will probably drive it 1500 to 2000 miles on this oil change.

Lastly, I run 92 octane fuel in it. My timing is set right at the BB and I adjusted the valves per OEM spec when I first got it. Runs like a Singer Sewing Machine. I am pulling a consistent 19" of vacuum at 660 rpm idle. I've replaced the plugs and gapped them to .033 inch.

Thanks to all and I look forward to your counsel :)

best.....
Ken
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Like your dyno guy said....you're still lean. And it looks like you're running some cheap, ethanol loaded gas. Get yourself some ethanol treatment, 1970's motors were not designed for this garbage.
 
Could any of the fouling be a result of the oil burning on hot starts or do you think this is fuel related only? What do you recommend for fuel treatment? Octane booster or??? By the way I purchase my gas from Shell
 
I'm rebuilding an 81 2F and bought an engine from a guy in Portland. He says he only put 2,000 miles or so on it before deciding to swap it for a 350. It has sat for the last 1 1/2 years while I've been working on other parts of the rebuild. Finally got everything hooked up this weekend and it cranks over but refuses to start. I've checked and double checked my timing to make sure it is set correctly. New plugs, new wires, new DUI dist and so on. I've put a little fresh oil in each of the cylinders because it sat so long and am ready to do a compression test. I can't warm up the engine first because it won't start so my question is what are considered good compression numbers on a cold engine? Thanks. :cheers:
 
The F/2F/3F engines were designed to run any excuse for gasoline that you pour into them.


It does look a bit lean. and it does look like you have gotten some pre-ignition (from the melted and slashed deposits on the plugs).


Mark...
 
Sounds like valve guides are worn.I would not worry about it with those numbers. What carb do you run?
 
I just pulled my 12/78 carb apart a little bit last week and I'm pretty sure these are the stock jet sizes for that build date:

Primary main: 1.36mm
Secondary main: 1.71mm
Primary slow: 0.75mm
Secondary slow: 0.80mm

I haven't pulled the power jet yet, but I think the primary main along with the power jet will be your two primary sources to look at for whether you're running rich or lean. Obviously the secondaries have a part in it as well, but I would check those first. Sounds like bumping up to the 1.44mm on your primary main was a good idea.

I don't know much about octane and how that affects engine performance, but I have come to the understanding that you want to use higher octane for higher compression engines, which a 2F is not. I have read here on MUD some other things about octane, you might want to research and make sure you're running the correct octane fuel. Maybe using an 86 or 88 octane will help a bit? My '77 doesn't seem to care much about 10% ethanol gas, which is standard here. That may or may not have an effect on what you're experiencing.
 

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