Well...I've driven the car about 100 miles now...the poor idle/stumbling/missing is still there. At times it seems like it's gone...but it still returns. Frustrating...I decided to do the ATF down the carb today after a quick retest of the low cylinders...1 and 5. Original compression test was 85 and 95 respectively...now they're 60 and 105! Not good.
Decided to repeat #1 with some oil in the cylinder (wet compr. test)...used the oil/straw/finger method...it came up to 65...repeated with a little more oil (wasn't sure I got enough in) and it came up to almost 70. So I poured a quart of ATF slowly down the the carb...back and forth down the width of the throat while increasing idle. What a white smoke show in my yard and neighbors too. Did it at a good time though...everyone was at work. Took it for a good long ride afterwards...still, no change.
Is it time to take the valve cover off and try to tap the valves? If so, what should I actually do?
Thanks, Bob
Its normal to get a small increase during a wet test, you have proven that you don't have a simple ringl issue. The wet test doesn't completely eliminate the possibility of deeper scores in the bore. 65sporty is right, you most likely have a valve issue.
I recently learned of this test, I have never tried it myself. A running compression test. You would remove the schrader valve from your compression tester hose, and while cranking for compression, watch the gauge closely. Supposedly if the valve guides are worn allowing the valve to seat intermittently... you would see a variety of readings. The needle on the gauge is going to move fast, IDK if I am ready to fully endorse this test.
What you really should do is a cylinder leakage test. A leak down tester at HF is $45 and you need a small compressor with a tank to use it.
The hose has no schrader valve, so dont mix it up with your compression tester hose. The process with this tool is to bring the cylinder to TDC compression, Zero the gauge (turn the regulator knob until the leak% is zero on the right gauge) to compensate for any leaks in the tool (air leak at the fitting doesn't matter after you zero). Attach the gauge to the hose already installed in the SP hole. The % of leakage is of some concern specs vary, but 20% and up definitely warrants looking for where it leaks from. You need to disconnect the PCV from the valve cover(prevent false diagnostics) and listen at the carb for air escaping (intake valve) the tail pipe (exhaust valve). Some air will naturally get past the pistons, but if you have no air leaks in other areas and lots from the oil fill cap(rings, scored cylinders, etc). Someone will probably point out air could bubble through the cooling system, I have to say if you ever see that... you have a major crack or severe head gasket failure which will require a machine shop.
The point of the leak down test is to find combustion chamber leaks. If the engine rotates when you attach the tool, you will have to disconnect and reset the engine. Your distributor rotor can be used to help you find TDC for the cylinder in question. It usually takes several tries for the first one, if you use a tool to hold the crankshaft, you will most likely damage yourself and/or your car... there is lots of leverage working against you when you give 100 psi to a cylinder on compression. This leak will show where the issue exactly is coming from, or if it passes the test as acceptable leakage, it show your problem is outside of the combustion chamber... like a push rod or cam lobe. That is why I recommend it before you do any teardown. You can plan your work better once you know where the issue is and your compression is bad enough you
might see the problem at teardown, but if you don't you will thank me because you will still know exactly where to focus to find it.
If you don't have and can't rent the tools needed, you could pay a shop to do the diagnostic for you. $100-$200 worth of small compressor and gauge would be about the same as I would expect the diagnostic to cost. You will most likely need the services of a good machine shop for this repair... so I wouldn't get excited and disable the car until you have a complete plan.
I am relieved with some caution but now it's time to drive it. Although the carb. is rebuilt now, the single air/fuel mixture screw in back still does not make any sense. Screwing it all the way in does not choke off engine idle. Engine runs the best when it's screwed all the way in. I noticed in the rebuild directions there is a procedure to drill out the two plugs down in front, although there are no springs and screws in the kit. This is where I'm use to adjusting fuel/air mixtures. Initially, I was surprised to see those holes plugged with no adjustment screws in there. Anyone have any insight on this?
