Compression and Vacuum From Way Up Here (1 Viewer)

[Dizzy]

My 2F came to me with little history, besides knowing that the crank turns. I bought some Bosch tools at the auto store and tried them out today. I'm at 6,800' above sea level. I probably have used about ten gallons of gas since the engine was installed.
Compression:
#1=97 (wet=100)
#2=102 (wet=103) carbon and/or shiny plug
#3=92 (wet=92)
#4=87 (wet=88) carbon and/or shiny plug
#5=95 (wet=102) carbon and/or shiny plug
#6=95 (wet=102)

I read a steady 13 or 14 in. of Hg on the vacuum gauge, and I'm a bit advanced beyond the ball bearing to account for altitude.

For about the last seven gallons of gas, I have noticed significant smoke at startup, only after the engine cools completely, and at deceleration. I haven't adjusted the valves after I first fired up the motor, but I realize that I need to at least recheck them.

I'm thinking that the motor will probably need a valve job, based on the slight puff of smoke alone. I'm also thinking that the vacuum is about 21 in. of Hg for an altitude-corrected vac number, and that the lowest dry compression number is about 107psi (on cylinder #4) and that the highest dry is 126 (on cylinder #2). But, I'm currently looking for a trusted source for altitude conversion.

Aside from checking the valves, what is next for the 2F to improve its performance?

 

[71FJ40]

Im at 8200 and consistently get 140+ compression numbers

Adjust valves, check for vacuum leaks, make sure manifolds are tight

Miles? which carb? which distributor?
Check HAC
Check for which jets are in carb

 

[Dizzy]

@71FJ40
?miles
'75 Federal Spec OE carb, no high altitude jets.
new Non-USA vac advance distributor with octane selector on OE igniter coil.

 

[71FJ40]

What smog equipment if any?
Do you have a leakdown tester?
Pic of engine bay?

Just drove through there last week - could have swung by to get a 2nd set of eyes on things

 

[Dizzy]

Well, I consider the stock carb smog equipment, in that the ported vac is designed for the VSV, rather than the Non-US distributor. There is no VSV. I have Aussie headers, torqued to spec, and they fit. The intake manifold can probably be sealed up better from the bottom, but the crack only appears on the inside, the outside (bottom) shows no vulnerability, but I need to fab up a thick plate (I'm thinking cast aluminum about 5/16"). There is no air injection system. I have no heat riser in the stock air cleaner. The PCV valve is fresh and OEM - it appears to be working right. The carb has been properly capped at the EGR inlet tube. The Auxiliary Accelerator Pump is connected to the manifold, as is the power valve. The charcoal canister vents to atmosphere.

I don't have a leakdown tester.

I don't have current pics of the engine bay. But you would see a new City Racer brake booster.

There is a 1mm hole drilled in the primary throttle plate, opposite of the progression holes for altitude compensation at idle and the slow speed circuit. Three of the plugs appear clean, no indications of lean, fouling, or oil leak, but they are also a week or so old.

 

[4Cruisers]

Here's a table for adjusting for altitude - for compression testing:

 

[Mace]

Did you do the compression test with the butterflies open?

 

[4Cruisers]

Here's a table for vacuum loss at altitude:

 

[Dizzy]

Did you do the compression test with the butterflies open?

Well, I used a brick and a rock on the gas pedal. The return spring was removed. The secondary was probably closed, choke open.

 

[Dizzy]

Alright, so using @4Cruisers provided chart numbers for vac, I get different results than what I got yesterday. The numbers should be about 22% less than the sea-level reading.

However, today I had a chance to work on it more. I pulled the valve cover and checked clearances. Cylinder #4 intake had little to no clearance. I did the valves just prior to the install, using some web-sourced numbers for a cold motor. At that time there were a few which seemed really, really out of wack. However, I wonder if debris falling in when hand-turned it caused the valves to not close properly after I got the motor installed and running? Basically, all of them, today, were a bit tight, except for the #4 intake valve which was beyond tight.

(above, the 2F when I got it; it probably took a bath with rainwater before that)

So, after the warm-valve-adjust today, I got an elevated idle rpm, and at least another inch of Hg on the vac test. It was fun watching the needle go up after the coolant recovered full heat. Also, I saw less smoke out of the tailpipe. However, I still have to guess that I'm burning a little bit of oil - but I guess that it won't slow the truck down too much, unless, I pull it for a full swap or rebuild.

The non-USA vac advance distributor is below, but it is not hooked up, yet. Also, I'm having a hard time getting an adjustment from the octane selector, is the clear cap supposed to remove a certain way. BTW, I hate to say it, but these Yazaki cables have more measured resistance than the CarQuest ones that they replaced which were attached to some externally rusty Autolite plugs that came with the engine.

 

[Solace in Solitude]

Is the idle mixture adjusted correctly?

What color smoke? Only on startup, when engine is cold?

Different colors mean different things

Good here

Diagnose Exhaust Smoke

 

[4Cruisers]

The clear plastic cap at the octane selector simply screws off (CCW looking at the cap from the firewall). For adjustment, see Post #2 here:

Distributor Vacuum Advance Adjustment

All, I have a question on Vacuum advance adjustment. I have a distributor in my 72 LC (Mnf. in 10/71). Not sure if it is the correct one. Here is a picture from another post. Is the dial located on the opposite side of the vacuum hose the adjustment for the advance?? What should that be...

forum.ih8mud.com

 

[Dizzy]

Is the idle mixture adjusted correctly?

What color smoke? Only on startup, when engine is cold?

Different colors mean different things

Good here

Diagnose Exhaust Smoke

It doesn't smell like toast, or sweet. The color is kinda blue / white?

The idle mixture is approximately correct, however, it seems that the idle circuit isn't playing a big role on this carb, in that closing the idle mix screw completely just barely stalls the truck - I'm clearly somewhat dependent on the slow speed circuit. The same was the case on my Nissan pickup with a Weber (jet selection didn't help because the throttle blade had to provide more air). On that project, the hole drilled in the throttle blade, opposite the progression holes, allowed me to get the idle mix screw back down to specification, so that I was only idling on the idle circuit (there is no air up here). I've checked the Nissan using an exhaust sniffer, and I have no problems with throttle response. In other words, if you lean out the idle mix to get a greater throttle blade opening (for additional air) then you burn lean when you transition to the main circuit by accelerating quickly. The plugs suggest that the engine is getting enough air, and that I'm either burning oil in some cylinders, misfiring, or fouling.

 

[Dizzy]

@4Cruisers What compression and vac numbers do you get on your fired-up rigs, over there on the big volcano?

 

[4Cruisers]

@4Cruisers What compression and vac numbers do you get on your fired-up rigs, over there on the big volcano?

15.2 inches Hg, which I think is good for 7,240 feet. Dry compression numbers on the '76 2F in my '71 FJ40, after warm valve adjustment (not adjusted for altitude):

#1 110 psi
#2 110 psi
#3 114 psi
#4 109 psi
#5 114 psi
#6 115 psi

This is for an engine that hasn't been run for more than a few minutes since ~2002.

 

[SteveH]

I have never seen over 125 on a 2F (many I have tested) at 7000' elevation. A 2F that had 20K on it (years ago) registered 118-119 across the board. I shaved .030 off my 2F head ('78) and still barely get 120 psi. These numbers are not adjusted for elevation and are dry.

YMMV.

 

[MoCoNative]

This discussion all makes me feel better about my 106-110 PSI on a 73 1F and about 15 in/Hg in my garage at 6800 feet.

You should be able to get the idle circuit to work. I'd guess plates are open too much. It takes a delicate tango of adjusting idle speed via throttle plates, idle screw and the timing. Start at factory 7 BTDC with that distributor, they have a pretty aggressive advance curve. I found with an aggressive advance curve, I could leave my base at 7 and still get good power at elevation. I'm running a modified vac advance 2F dist, opened up the advance stopper and swapped some springs. 10 to 11 degrees is where I usually ran my timing for years. Hooking up the vac advance will help, but you don't have the port to do that.

The octane selector just lets you advance or retard the timing on the side of the road with moving the distributor. Neat feature, but I found I never really had to adjust it.

 

[Dizzy]

Is there supposed to be any vac gain (percentage) by capping the PCV?

Is there a FSM compression or vac number that is a minimum? I know the '75 has domed pistons and a different head than the later 2F.

My primary bore looks kinda wet, and gas resides in that pesky hole for the EGR. It passes the flashlight test at idle, but I wonder why the main nozzle is so messy?

 

[Solace in Solitude]

I’m a little lost on your concerns, after everyone’s’ suggestions.

Are you still concerned by tailpipe smoke?

What is your current vacuum and compression numbers?

This link speaks to PCV and it’s vacuum relationship... I don’t know if it will answer your questions.
—> Positive Crankcase Ventilation (PCV)

You said, “The non-USA vac advance distributor is below, but it is not hooked up, yet.”. If the vac advance is still not drawing vacuum from the carb, is the carb port capped?

IIRC vacuum is recommended to be 15-20.

IIRC compression is recommended to be >113, but @Mark W said “I consider 120 the minimal acceptable. You want to see even compression inall cylinders. No variance greater than about 10%.”

The “No variance greater than 10%” is, IMHO, more important than the “120”.

@Poser offers good valve lash adjustment instructions in post #11, here —>2F compression

What do you mean that the “main nozzle is so messy”?

If you mean “oily”, before my rebuild, I had zero smoke out the tailpipe, but there was so much blow-by that the valve cover would become a bit pressurized. When I removed the valve cover vent hose, from the air cleaner, it looked like a chimney. If fact, the pressure once blew my oil filler cap off, in the middle of nowhere. I tethered the new cap, to prevent losing it.

That much blow-by causes oil pooling inside the air cleaner. Too much oil can cause it to drain back into the carb... it can be messy.

I know a failed oem fuel pump diaphragm can dump fuel into the crankcase oil... I doubt a failed pump will allow oil into the fuel delivery... but, I’m not sure. Anyone?

You mentioned a “crack” in the bottom of the intake manifold (IM)... my 40 came with an IM, with a big bugger weld across the bottom of the IM, under the carb. I replaced the IM because I suspected it was causing vacuum loss... it may have. But, I eventually found my oem dissy vacuum advance was a yuge vacuum leak. I had zero power above 6k’ and poor performance the rest of the time.

I replaced my oem dissy with a Toyota-geared, vacuum advance DUI and had Mark rebuild my spare Aisin carb, adding performance improvements.

The DUI (and it’s associated ~12*BTDC timing and .050” plug gaps) and Mark’s carb magic were the two most productive performance improvements I’ve made.

I can now (if need be) cruise at 75, with 31x10.50R15 KM2 tires. I prefer not to driver her that fast, but it’s easy to pass on 2-lane highways now.

I hope some of this helps.

 

[Mark W]

I just happened to be at the computer when the notification popped up that I had been tagged in this conversation. Not following this thread at all. Anyway, Toyota FSM shows the nominal cranking pressure on a fresh 2F is 149 psi and minimal acceptable is 113 psi. I expect to see 165 psi from a good fresh engine. I have seen 185 psi from a hot rodded 2Fs with cut heads or late model F head swaps, but that obviously is not stock. As mentioned in the quote above 120 psi is the the minimum that I consider "ok". These number are based on more 2Fs than I can even pretend to remember, over about 25 years now.


Mark...