Compression and Vacuum From Way Up Here

[Dizzy]

@Solace in Solitude Carb is properly capped at the port. Still concerned about smoke. The primary main nozzle must be responsible for the gas in the upper part of the carb. The compression numbers are not current, but they were low. The vac number seems good. The fuel pump is new.

You mentioned DUI. I'm still semi-electronic ignition. However, I probably should check for dwell on the new dissy, because it could cool my spark if the points are off. The U-groove Denso's from SOR are gapped closer than 2F spec (they have a different geometry).

 

[Solace in Solitude]

So... it seems like you are really only concerned with the smoke and the low compression numbers.

If your timing is set properly, your plugs cleaned and properly gapped, your distributor cap and rotor in good shape, your points (I don’t know what you mean by semi-electronic) in good shape and properly gapped, vacuum leaks are fixed, valves are properly adjusted, fuel mixture is properly adjusted, carb is clean and properly adjusted, choke is properly opening, you’ve done about all I can think of... anything else, to improve performance, would probably require a mod ... like DUI.

I would re-test dry, then wet, the compression (be sure engine is at operating temperature, the choke is fully open and the throttle is wide open). There are instructions here —>Compression test 2f confused

Use the “altitude” procedures, provided earlier by @4Cruisers, to determine your altitude factors.

the difference between the dry and wet numbers is the improvement in how well the rings seal, after squirting oil into the plug holes. The more improvement, wet, the worse your rings are.

You could also do a leak down test, but I wouldn’t bother unless you really plan to spend money rebuilding the engine.

“A compression test uses the engine turning to generate the compression in the cylinder for the compression stroke, in which both intake and exhaust valves are closed. A leak down test uses a set of gauges and pressurizes the cylinder with air and measures how much of that air is escaping.”.

there’s good info here —> Did a leak down test on my 2F

I think you said the PCV is new... are you sure it’s installed correctly? It’s a one-way valve and should ventilate (let air out of) the crankcase.

Is there oil accumulating in your air cleaner?

try adding Marvel Mystery Oil to your oil and see if it helps with the smoke... I don’t have a real feel for how much smoke you’re seeing.

There are people on MUD who have run for years, with very little compression and a lotta smoke... @JohnnyC comes to mind. Maybe he’ll see this and chime in.

nite!

 

[Dizzy]

By semi-electronic, I actually meant, 'semi-transistorized.' Meaning points, but the use of an igniter and OE coil.

Some of my concerns are carb related. Like the '75 has an Auxiliary Accelerator Pump, and I don't know if it is really a benefit at altitude, but is the go-to for some on Mud. Also the power valve, it was originally controlled by the VSV, and I might be rich at deceleration when vac is high, but the throttle is closed?

I'm not sure a PCV can be installed incorrectly, one end is significantly larger than the other. The air cleaner tube isn't getting any oil from the valve cover, but it might take more than the first tank of gas to show something like that.

Is it possible that the rings are sludged up and the use of Marvel Mystery oil will help them seal?

 

[Solace in Solitude]

Re: “Is it possible that the rings are sludged up and the use of Marvel Mystery oil will help them seal?” Read this comparison of Marvel and Seafoam —> Marvel Mystery Oil Vs. Seafoam: The Detailed Comparison- CAR FROM JAPAN


The PCV valve is one-way, it ventilated the crankcase TO the intake manifold, under the DS of the carb. If installed backwards, it won’t work. Read the middle column —>Repair Guides

Re: “Some of my concerns are carb related. Like the '75 has an Auxiliary Accelerator Pump, and I don't know if it is really a benefit at altitude, but is the go-to for some on Mud. Also the power valve, it was originally controlled by the VSV, and I might be rich at deceleration when vac is high, but the throttle is closed?”. I’ll leave these questions for experts, like Mark (@65swb45).

 

[Dizzy]

Old Dry / New for Today Dry numbers:
(1) 97 / 103 (psi)
(2) 102 / 105
(3) 92 / 96
(4) 87 / 100
(5) 95 / 97
(6) 95 / 100

Last week, I adjusted valves. Yesterday night I gave each cylinder a minor flooding with Marvel Mystery Oil, let it sit for the night, and put half of the bottle into the crankcase. Then I just barely got it up to temperature this morning, pulled the plugs and measured compression numbers. I was satisfied, so I didn't do wet numbers. Then I brought the coolant back up to temp, pulled the plugs, cleaned them (number 2 was shiny, but cylinder number 4 was smoldering but the plug was clean). I also pumped more Marvel into the cylinders, thinking that it must have helped the rings(?), because my new dry numbers were higher than my old wet numbers. The bottle of the stuff claims increased compression, but I'm pretty sure that the website does not. Many of the cylinder's valves were not significantly altered from spec, aside from #4, and fixing that one got me the compression high enough to be within the 10% spec range. I didn't see an increase of vacuum significantly as a result of the MMO, but rather the valve adjustment.

So, I'm thinking that I might need a valve job, or that the valve seals are leaking at periods of cooling down, or deceleration. I'll need a valve spring compression tool. Is there anything that I can fabricate to do it with the head on? If the seals are inexpensive, I'd try it without pulling the head and doing a full head rebuild. Maybe the valve guides are worn too, and that is causing the slight oil burn, in which case I'll have to scrape head gasket, drain coolant, etc.

Aside from the puff of smoke, I'm probably in good shape. I'll check the valves again in the relatively near future. So, if at 7,000' above sea level (divide by a factor of .8106). The (dome piston) 2F should have about this much compression at sea level, today.
(1) 127 psi.
(2) 129
(3) 118
(4) 123
(5) 120
(6) 123
(The difference between #2 and #3 is 11psi, less than 10% of either the low total or the high total)

 

[Dizzy]

I put back in the old Autolite 65 plugs that were gapped to 1mm. I did it primarily for lack of knowledge of gapping the U-groove denso.

I changed the oil. The 2F was smoking quite a bit, and I suspected that the oil had lost viscosity. A drop from the dipstick would run thru a white paper towel. It seemed that a drop from my other truck would stay as a drop, then disperse thru the towel. After about a gallon or so of gas, I gave up on the half quart of marvel mystery in the crank case. The drain plug was full of sludge; and when I replaced the oil filter the other day, I took tin snips to it for inspection - with nothing noteworthy. However, I also suspect that pressure in the gas tank was forcing gas thru the bowl because it always looks kinda wet in the primary barrel, which would probably destroy the motor oil as it is drawn thru the cylinder with the engine off. On a hot summer day, I could hear the pressure relief, it sounded like the first day I tried to play my trombone. I drilled a strategic hole in the OEM gas cap to hopefully deal with what might be a bad fuel vapor check valve.

Then I installed a high mileage dyno oil 10W-40 from O'Reilley, plus 2 regular quarts that I had in the shed. Today, I saw no smoke, zero, out of the exhaust both at cold startup, and at deceleration. It is supposed to have more detergents, and a swelling effect on old seals. When I first started this engine back in April, the exhaust was clear, so I'm hoping that there is enough left of the oil control rings, and the valve stem seals that the engine is good to go, so long as the crank case isn't full of anything unusual.

 

[Dizzy]

Update.

Plugs stay relatively clean, and look about right. Valve stem seals did the trick more than anything else. I didn't pull the head, so I know that there are chunks of baked on oil on the valves, saw it with the intake off. Running Techron 88 octane, dino oil, nothing else.

The 2F runs strong, but maybe the carb secondary needs checking, throttle pedal was maxed out for that one section of freeway that is a steep hill with an extra lane - happened back in the day with my '73 hardtop 40 with F and OEM (counterweight) carb too.

The last ten gallons of suburban pavement driving, I got 12 mpg. Pulled into the driveway this evening, and found about thirteen inches of vacuum on a hot motor, hot air cleaner assembly. Idle seemed lower than it did in the winter, and nice and smooth. This motor is still getting the shakedown.

I was under the impression that a decent 2F would get 12 to 18 mpg, but mine has low vac and compression and is gasping for a fuel charge of mass, not volume, and, it did 12 mpg over an overzealous residential speed bump program.

What are your thoughts?

 

[4Cruisers]

Update.

Plugs stay relatively clean, and look about right. Valve stem seals did the trick more than anything else. I didn't pull the head, so I know that there are chunks of baked on oil on the valves, saw it with the intake off. Running Techron 88 octane, dino oil, nothing else.

The 2F runs strong, but maybe the carb secondary needs checking, throttle pedal was maxed out for that one section of freeway that is a steep hill with an extra lane - happened back in the day with my '73 hardtop 40 with F and OEM (counterweight) carb too.

The last ten gallons of suburban pavement driving, I got 12 mpg. Pulled into the driveway this evening, and found about thirteen inches of vacuum on a hot motor, hot air cleaner assembly. Idle seemed lower than it did in the winter, and nice and smooth. This motor is still getting the shakedown.

I was under the impression that a decent 2F would get 12 to 18 mpg, but mine has low vac and compression and is gasping for a fuel charge of mass, not volume, and, it did 12 mpg over an overzealous residential speed bump program.

What are your thoughts?

I think you should stay away from La Bajada hill .

 

[Dizzy]

I think you should stay away from La Bajada hill .

 

[SteveH]

Vacuum can change with barometric pressure, so you will show better engine vacuum on a nice sunny day. I have found that bad valve stem seals are the #1 reasons for gunky oil ash buildup on spark plugs. My FJ40 has rarely done better than 12 mpg, in 30 years of driving. I once got something like 18 when I drove 55 mph for 100 miles.

My EFI conversion resulted in even worse mileage (more like 10.5 city), but considerably better seat-of-the-pants performance.

 

[Dizzy]

@SteveH What size tires get 10.5 mpg? What is your idle rpm?

I'm running 4.11s, on 215/75/R15.

 

[SteveH]

33x9.5s, 4.11 gears, 900 is idle rpm (AFI TBI setup - hard to get it set lower without screwing up other settings). I do adjust my MPG for the tire size (I add 7.5% to the MPG figure. I still get crummy mileage, but I don't drive the truck enough to matter.

 

[Dizzy]

I have this hypothesis that injection sprays the walls of the intake, and it takes the motor pumping faster to scavenge the gasoline. I once saw a Sniper video where fuel droplets ricocheted off the bottom of the FJ intake manifold, and back out, spotting the top of the butterfly. I'm a carb person at 600 or less rpm, but fuel injection conversion makes more sense for what I'm doing, particularly in regard to mountain driving.

I'd give your rig better than 7.5% for MPG, based on circumference. My 215s have a pretty accurate speedo reading, based on the residential monitor sign. 33s are 14.2% greater in circumference than a 235/75, which is on the 29" side.

 

[SteveH]

You are probably right on the tires and value. At one point, when the speedometer indicated 60 mph, the radar-speed sign would show 66, which is 10%. My speedometer was fairly accurate when I ran 235-75-15s. So, the truth is out there somewhere - there is error in both factory speedometers and radar speed signs. I would think a GPS might be pretty accurate over a short distance, so I could try that.