Zero vacuum at idle. Need help.

[misterpepper]

I'm trying to resurrect a '69 with a 1F motor and cannot get it to run well. I'm getting zero vacuum at idle, as measured from the port at the base of the carb, and have very poor throttle response off idle. Anything more than just very gentle use of the throttle causes it to want to stall out. With the engine well warmed up it gets a little better, but nothing that I would consider safe to drive.

The carburetor I currently have on it is a trollhole-style amazon special, but I have also tried a genuine trollhole that was on it previously but needed a lot of going through to clean and verify that everything was working. I followed PinHead's videos on youtube and had everything working pretty well except for the power valve being a little sticky. But I've also tried a '69-'71 2bbl genuine Aisin carb set up according to the Haynes manual for all of the adjustment screws. Nothing runs well but at least with the two later style carbs I can get them to idle off choke.

I have rebuilt the mechanical fuel pump and fuel stays pretty close to exactly halfway in the sight window.

I have verified timing with two different timing lights. Both have the timing pointer at the top edge of the BB, so roughly 8 degrees advanced compared to the stock 7. My altitude is ~2700ft, desert climate.

I have verified that spark is good for all cylinders with at least 3/8" spark according to my cheapo spark gauge.

Compression is 75/125/122/118/122/122. A little low for cylinder #1, but I would think it could still be made to run okay. I did a motor flush and an oil change but the numbers didn't improve.

I've tried two different sets of spark plugs and wires and two different ignition coils. (I'm blessed to have a second FJ40 to borrow parts from but the other 40 is even further from finished than this one.)

The distributor is a mechanical advance and appears to be functioning correctly, according to the timing light.

I suspect there is a vacuum leak somewhere, but I just can't find it. It would need to be a pretty severe vacuum leak to have show zero vacuum at idle according to the vacuum gauge, right? I've sprayed everywhere on the top side of the engine with both carb cleaner and starter fluid trying to find the leak.

The PCV valve is a new, Toyota valve, along with the grommet. I do get strong vacuum at the hose between the PCV and the carb riser. If I disconnect the hose from the top of the PCV with the engine running the engine dies immediately. If I plug the hose with my thumb I can feel a strong vacuum from the carb riser, but the vacuum gauge still reads zero until I rev the engine a little. Once I have the engine revved throttle response improves dramatically.

I have adjusted all the valves and the seals for the valve cover, the base gasket and all 4 screw gaskets, are new and don't appear to be leaking.

This did originally have a vacuum-assist transfer case but has been converted to 3-on-the-floor with a floor shift transfer case. I'm not sure where vacuum would have come from originally to power the transfer case but I assume it would have come from one of the three ports that I can see plugged on the intake manifold.

I suspect the truck does have a rear main seal leak. Could that be a significant source of vacuum leak? Not sure how I could verify that without taking the transmission off. Is there an easier way to identify a vacuum leak away from the head? Unfortunately I don't have access to a smoke machine, but if that's the only way I'll get one.

I suspect whatever my issue is will be easy to fix, but I am having a heck of a time trying to identify it. I'm open to suggestions. I've been beating my head against the wall at this for over a month now. I still need to try searching for the vacuum leak using an unlit propane torch but previously the backfiring made that a little scary. I have things tuned as well as possible (lean drop method, idle in the 650 range but not terribly steady) given the circumstances so it's probably safe enough to do now.

Does this sound like a carb issue to you, a vacuum leak issue, or something else entirely? Please help.

 

[charliemeyer007]

Put a big hemostat on the brake booster hose if it has one. You got a vacuum 4x4 unit? Isolate it.

 

[Skreddy]

The port that you are using is likely a ported vacuum source. It’s above the throttle blades and won’t see any vacuum when at idle. True 0 vacuum would mean the engine isn’t sucking air at all.

Are you still points ignition? What’s the dwell set at?

Oil leaks don’t matter for vacuum leaks (rear main seal) as that’s not on the induction side of things.

I’d unhook and plug/cap every vacuum port to start. Get it running then start adding each component to see if one makes a difference. How old is the gas?

 

[misterpepper]

Put a big hemostat on the brake booster hose if it has one. You got a vacuum 4x4 unit? Isolate it.

No brake booster. Vacuum 4x4 has been removed, mostly by the PO but I did remove the lingering hoses along the dash. Nothing that was hooked to anything engine related. Not sure where they were hooked to originally and if the PO capped things correctly. I can't find anything not capped within the engine bay and I doubt an opening at the transfer case would cause a vacuum leak at the engine, would it?

The port that you are using is likely a ported vacuum source. It’s above the throttle blades and won’t see any vacuum when at idle. True 0 vacuum would mean the engine isn’t sucking air at all.

Good to know. It is above the throttle blades. Where should I be measuring from while adjusting the carb? There is a small port on the intake manifold but nothing else I can see. Very little vacuum related within the engine bay.

Not a points ignition. Cap and rotor. Gas is mostly new but there was some old gas in there before. Probably 70/30 new to old.

 

[mrboatman]

Use the port on the intake manifold

 

[JohnnyC]

As usual… to help you…. pictures would help us a lot

Got to help us take some of the guessing out

 

[Skreddy]

No brake booster. Vacuum 4x4 has been removed, mostly by the PO but I did remove the lingering hoses along the dash. Nothing that was hooked to anything engine related. Not sure where they were hooked to originally and if the PO capped things correctly. I can't find anything not capped within the engine bay and I doubt an opening at the transfer case would cause a vacuum leak at the engine, would it?


Good to know. It is above the throttle blades. Where should I be measuring from while adjusting the carb? There is a small port on the intake manifold but nothing else I can see. Very little vacuum related within the engine bay.

Not a points ignition. Cap and rotor. Gas is mostly new but there was some old gas in there before. Probably 70/30 new to old.

As said, port on the intake. With not many vacuum sources, basically your only potential for leaks is where each intake runner meets the head, carb to intake, any ports or plugs on the intake, or a crack in the manifold itself (usually where it and exhaust are bolted together). Those Amazon carbs are either ok out of the box, or need work immediately. I run one on my 60 and it was really bad before going through it.

That 75 psi could be indicating a bad valve or something but further diagnosis, like a leak down test would be needed.

For the distributor, it’s either a points type or an electronic type. If it’s original, it’s going to be points and likely vacuum retard, not advance.

As said, pics would help greatly.

 

[pb4ugo]

You mentioned you have vacuum at the pcv valve and it stalls when disconnected, so you obviously have vacuum. Maybe try the vacuum gauge on another engine to confirm it works. If its okay maybe find another good vacuum source on the engine for the gauge. Follow @Skreddy post on capping vacuum sources.

 

[misterpepper]

Here are some pictures.

The port at the base of the carb that is currently capped is the one I was using to test vacuum.

Another picture of the carb. This is the amazon special, but it is essentially the same as the trollhole carb that was on this engine when I got it. I needed a few parts off the trollhole to hook this one up, but I can swap back easily. I've only been inside this one far enough to verify that the machining is flat on both mating surfaces of the upper castings and that the power valve moves freely. The idle solenoid is working correctly (kills the engine when unplugged) and I get a strong squirt of fuel when the accelerator linkage is pressed.

I've also tried this carb. History unknown and not recently rebuilt. At one point I did have the engine running with this carb but idle was only ~350rpm and I didn't have a compatible throttle cable, so my focus has been on getting one of the other carbs running.

Here is the distributor, coil and wiring. Notice anything wrong here? Resistor checks out (1.5ohms iirc) and I've replaced some dodgy wires. Is this the incorrect distributor for this engine? If so, blame the PO. I do have a couple other vacuum (retard?) distributors handy, but I've never swapped a distributor before.

 

[charliemeyer007]

I have run a Delco since I got my 72 in 82. It came that way with a 2 BBL Rochester carb. Anyway the Delco finally wore out so I bought the chinesium one from Amoron $150. The points bent in like a week, but the real delco ones fit and so did the cap/rotator. Runs great - I like the straight mechanical advance. The only vacuum thing on my rig is the gauge.

 

[Pighead]

I have verified timing with two different timing lights. Both have the timing pointer at the top edge of the BB, so roughly 8 degrees advanced compared to the stock 7. My altitude is ~2700ft, desert climate.

Some engines like a bit more timing advance than what the book says...

 

[Skreddy]

This is your points. The may need a little cleaning with a file or some 220 sandpaper folded over so both sides are “sandy”. Just a half dozen passes should clean them up. Maybe hit that rotor tip too.

 

[misterpepper]

So, good and bad today.

I connected my vacuum gauge to the port on the intake manifold and I can see that I am getting vacuum. More while the choke is off, but I assume that is to be expected. It's difficult to tell exactly how much vacuum I am getting because...

Now I'm not getting any spark.

I lightly cleaned the points as well as the rotor tip with some 2000 grit sandpaper and when I put things back together it now won't fire up at all. I can sometimes get the tiniest hint of a spark, but nowhere near enough to fire up. And yes, I've checked several times to see if I can figure out what went wrong. Maybe the distributor was only just barely holding on. Maybe something else got fried. Tomorrow I guess I get to learn how to swap a distributor.

 

[charliemeyer007]

Take the plugs out. Remove the valve cover. Rotate the engine to tdc #1 compression (valves will be loose). The rotor should be pointing at spark plug hole #4. Loosen clamp on dizzy, as you pull out the dizzy the rotor will move. Place new dizzy in hole, put rotor in same place as the one you pull out was. Push dizzy in, rotor should move to point at the same place the old one was when you started. Tighten clamp. Make sure the oil pump was engage.

Watch some vids first.

 

[JohnnyC]

The port that’s in the manifold near the carb is not manifold vac

Unless you remove and put a fitting to give you direct vacuum

OR on mine I took it off and removed the fibers/filler and cleaned it out in order to give me direct vacuum

 

[misterpepper]

I cleaned up and tested/adjusted one of my original toyota points style vacuum distributors but when I went to stab it in I found that the PO had welded two distributor clamps together to make a clamp thick enough for the Delco mechanical advance distributor that was in there before. I can't really see anything wrong with the Delco distributor. I did try a different cap+rotor on it with no luck. But it will be nice to be back closer to stock. Tomorrow I'll see if I can find a distributor clamp locally or maybe just cut the weld and separate off one of the modified clamps.

 

[diesellibrarian]

You sanded the points, but are they gapped correctly? Hard to tell from the pic but it looks like the block is sitting on the lobe of the distributor shaft and the points appear to be closed.

Does your timing light have a dwell meter? If so, what does it tell you?

 

[diesellibrarian]

 

[misterpepper]

My timing light does not have a dwell function but the distributor that was in there when I started this thread, the Delco, was still opening the points when I removed it. I did gap the Toyota distributor correctly (0.018") before installing it. The Toyota distributor is a vacuum retard so I have it connected to the port on the intake manifold that evidently has some sort of wadding inside. With the Toyota distributor in and connected to manifold vacuum I am running again, but the engine is still running very rough and wants to stall out rather than accelerate.

I am getting around 13-14 inches of vacuum at the manifold, so my "zero vacuum" issues were just operator error from testing at the wrong port. The fact that the vacuum is so low suggests that I still have some tuning to do. I'm going to rig up a gravity fed temporary fuel tank with brand new fuel to eliminate bad gas as the culprit and try tuning the carb again.

 

[JohnnyC]

if its vac retard.... just disconnect the vac line and run mechanical of the dizzy

where r u getting the manifold vac from.... did you add a bung?