Collapsed Rings? Bad idle..

[rocksy]

Good evening folks,

Posting here because I much prefer this format to the Facebook group format.

I recently obtained an 83 manual dlx with 130kish miles on it. Extremely clean example. When I purchased it, the head was removed as it had blown a head gasket due to an overheating event. The head was warped over 20 thou, so I took the head off of my parts care and reassembled everything via the petros head gasket method. Head and block were within half thou of the tolerance from the FSM.

When I went to start it up after reassembly, it would not idle at all. The carb had been sitting for 1-2 years since the car was parked, so I replaced it with the known good carb from my parts car.

It will now start, and it will idle, but the idle surges very heavily. I don't have a tach but it is surging between what I estimate to be 3k rpm and then dropping to the point where it almost dies before surging back up to 3k rpm again.

I am scared to let it idle for too long like this, but I also cannot let it do so as my neighbors have become very upset with me as it sounds like I am intentionally revving the engine when it idles.

I am hoping to get the idle corrected, but for the brief (less than one minute) that I have let it idle, I am noticing some smoke coming from the intake/carb area. I am also hearing a strange high-ish pitched whine when the engine is at the high point of this idle cycle. I am curious if this is symptomatic of excessive crankcase pressure. Does this sound like a possibility to those more experienced than I? I am hoping the engine was not overheated so bad that the rings collapsed. The cylinder walls looked really good and nothing was obviously wrong turning everything over by hand with the head removed.

As far as the bad idle, where would you start? Is it possible that bad gas is causing this? I suspect gas is 2ish years old. I am hesitant to touch any of the idle adjustment on the carb, but if that's the place to start I will study that section of the FSM. Could my distributor gear be off by a tooth? I can't time it until it's idling at least somewhat normally.

Then comes the question of the smoke and strange whine. Am I being excessively paranoid about the possibility of collapsed/worn rings? Really hoping the engine doesn't need a full rebuild. The head gasket post mentions that the engine may initially smoke from weird places as assembly lube burns off of various surfaces. I wonder if I just haven't given it enough time to idle. I suppose I could rule this out with a compression test?

[Paul]

The compression test should provide useful information on how well the head gasket replacement went, in addition to the condition of the rings. However, the surging idle nightmare is often created by a vacuum leak. Double check every line and the routing. Try temporary plugging the line to the aux accelerator pump (AAP) on the front pass side of the carb. The vacuum lines and diaphragms might be the best place to start troubleshooting.

[dlb]

Amen, the fb group is good for fast responses but unfortunately most of those responses tend to be useless.

I agree with Paul re: doing a compression test, and vacuum leaks being the cause of your hunting idle. I imagine the rings are fine but a compression test will confirm that.

Confirm you have the vacuum hoses routed correctly -- to simplify this, I disconnect the hose I'm working on at its source of vacuum and at its destination (eg, one end at the gas filter on the intake manifold and the other end at the upper port of the vac advance unit on the distributor), and blow through one of the ends. Air should come out the other end, that confirms you have it routed correctly. Then cover that end with a finger and you shouldn't be able to blow air through. If air is coming out somewhere else now, that's a vacuum leak you need to address.

Also check all the diaphragms on the carb/emissions system to make sure they hold vacuum. Suck on the hose going to them and confirm you can't suck air through them. If you can, you need to plug the hose going to that device until you can replace it.

That's what I would start with. Good luck!

[rocksy]

Well, I'm at a loss folks. I am 150% sure that all vacuum lines are routed correctly. I have checked more than 10 times. I did a compression test today and average is around 140 and they are all within 10 psi of one another. I can get it to start and it will fire up and rev up to an extremely high rpm, then fall and die. I can kind of feather the gas and it will just cycle like that. Extremely high rpms down to almost dying.

I am wondering if the carb needs to be adjusted (it is a known good carb taken off of a car that was running fine within the last month or two) but I can't really do that because timing needs to be correct for that, but I can't set timing as it won't idle.

Really close to giving up, as I don't know what's going on.

[rocksy]

Should also mention that all diaphragms appear to be intact. I wasn't sure about the vacuum advance on distributor so both of the lines have been removed and capped til I can figure out why it won't run at all

[dlb]

I hope some others chime in here because I'm running out of ideas.

It doesn't really sound like a timing issue but just in case, have you verified the crank and cam gears are at TDC on the compression stroke, and the distributor rotor is pointing to 10:30?

Next idea is a plugged fuel filter. You can fill a container with gas, disconnect the outlet hose from the fuel filter stick that in the container with gas. See if that helps anything.

Good luck, don't give up! It sounds like you have a nice specimen there, and you are very close to having it in good running order.

[Paul]

Have you checked the 1st fuel cut solenoid on the back of the carb? It should click when you turn the key to the on position. I've seen a spade connection get pushed back on the carb wiring connector. The slow jet or primary jet may have ingested some dirt during the carb swap. During rebuild, this needs cleaned with a fine wire to verify the passage is clear. Check the fuel level sight glass while its running.
Since you have 2 carbs, I would consider rebuilding the original. This problem is frustrating, but solvable.

[Petros]

you can set the timing without the engine running, not perfectly but close enough where it will run fine. you set the crank to TDC on the pointer, and you open the distributor cap, note where the rotor is pointing, and if you loosen the pinch bolt for the distributor timing, you can turn the distributor assembly. look closly at the triggering wheel on the shaft, when it lines up with the pick up, as you turn the distributor, it should set the spark failry close to TDC. Verify the rotor is pointing at the #1 spark plug electrode in the cap. put it together and it should run on that, you can find tune the advance by ear.

if the spark timing is way off it can act this way. a bad vacuum leak will also do this, or running really lean, but that should be easy to check. make sure all your carburtor base nuts are snug, and the intake manifold bolts are all tight, just so you do not have a big leak at the gasket.

good luck.

[NWMO]

rocksy,

Based on your description of symptoms, I wonder about fuel delivery to the carb. You might try gravity flow directly to the carb or letting the fuel pump pull from an auxiliary tank.

Chris

[Nordical25]

Have you done correctly carb and manifold gaskets? And is your TVSV working correctly?

I tried once a bad carb and suddenly a fully functional motor was not working correctly at all. Then I swapped a different carb and I checked also that all gaskets were in correct order. The result: everything worked as it should.

And Petros had a good point with timing. If timing is one gear off, it can cause also issues like that.

[rocksy]

Hello all.

I finally got a friend to come assist me today holding an auxiliary fuel tank while I attempted to start the engine. No dice. I don't think the fuel pump was picking up enough fuel. However, it would not run even with me manually adding fuel to the carb, and it was backfiring pretty violently through the carb.

I am going to get a fuel pump on order, since they are cheap and see if swapping one in will help. The pump I have was taken off of a running vehicle so this seems improbable to me. I verified that timing was at least close by removing and reinserting distributor per FSM instructions. Not sure why it was backfiring through the carb, though. Worrisome to me.

I will try to put a new fuel pump in and see if that helps, as it doesn't look like it's pulling fuel from my aux tank. My motivation is dwindling, but I am hoping I can get it running soon.

[Toyotise]

Backfiring violently back out the carb. Sounds like a timing issue. Where exactly is the question. Timing belt off a toothed, distributor installed a gear tooth over or under. Check your static timing and go from there.

Obviously start with a fuel pump if you’re sure it’s dead.

If TVSV was bad it would still run just maybe not very well. On a side note I highly advocate keeping the stock carburetor system. Test your TVSV and go to whatever lengths necessary to get a good one if bad. Better drivability and efficiency in the long run. Faster warm up. Automatic high altitude compensation. MPG’s.

Love the paint scheme and factory wheels on that thing.

[rocksy]

Thanks, Toyotise. No real question, just providing an update since it's been a while. Advice is welcome though. Gonna let the battery charge back up and recheck timing belt cover, just to cross that off my mental checklist. Thanks again. Love this community

[dlb]

I verified that timing was at least close by removing and reinserting distributor per FSM instructions. Not sure why it was backfiring through the carb, though. Worrisome to me.

I'm not sure what the FSM instructions are but what I do when I have to reset the timing:

- remove the #1 spark plug
- put a ratchet over the crank pulley bolt and turn it clockwise
- shine a light into the #1 spark plug and watch for the piston to start making its way up
- plug the hole with your thumb and feel for pressure building up -- if no pressure, it's on the exhaust stroke and you need to rotate the crank one full rotation
- once you have confirmed the piston is at the top of the compression stroke, put the spark plug back in and make sure the distributor rotor is pointing at about 10:30
- REMOVE THE RATCHET FROM THE CRANK PULLEY BOLT!!

I agree Toyotise that this sounds like a timing issue so if this checks out, I would also remove the upper timing cover and confirm that the timing belt is correctly installed.

Good luck!

[rocksy]

Thanks, dlb. Definitely confirmed engine was at TDC by removing #1 spark plug. Once battery is charged back up I will be removing timing cover and ensuring that the belt hasn't jumped.