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Throttle problem

Tiny
VIPERKING75
  • MEMBER
  • 1980 TOYOTA PICKUP
  • 2.4L
  • 4 CYL
  • 4WD
  • MANUAL
  • 25 MILES
I just finished rebuild a 22R for a friend of mine, everything is new except for the block, rods, and crank.

(bored 20 over, crank was turned, correct bearings, all oil clearances were well in spec)

After getting it all put together and in the truck I got it running, set timing to 1 BTC (that's where it performs the best) it's got 72 psi oil pressure cold, 35 warm, all cylinders have exactly 182 psi of compression, its pulling 21 inches of vacuum, no vacuum leaks of any kind, and the choke functions properly.

When warm the idle rpm is about 900, if I get it any lower the engine surges and misses, I've tried adjusting the idle mixture screw with barely any change. The carburetor sight glass is showing fuel almost all the way up. Upon quick bursts of acceleration it has a bit of lag, then runs like a dream. When the throttle is released it will attempt to die for a few seconds, backfire once, and then bring itself back up. And no adjustment of the idle screw, mixture screw, or timing seems to make any significant improvements.

Any ideas as to what it could be?
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Friday, June 21st, 2019 AT 8:51 PM

30 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Hi ViperKing,

I think your timing is part of the issue. Looking at the spec it should be between 8-12 degrees BTDC. If you are sitting at 1 then that would cause a lag in acceleration.

We always set timing as close to spec as possible first then adjust the carburetor. If you are setting the timing at 1 degree because that is where it runs the best, that is great but your carburetor is not adjusted. So you need to set the timing around 10 degrees to start and then adjust the carburetor so that it runs better. If you need to go +/- 2 degrees after that to get it to run really well then that it fine.

If you timing is not right then this is why you are not getting much change from your carburetor settings.

The progression should be timing, idle speed, air/fuel setting for smoothness, then go back to timing if needed to get that rolling idle.

Let me know what happens after this and we can go from there.
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Sunday, June 23rd, 2019 AT 9:00 AM
Tiny
VIPERKING75
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  • 48 POSTS
My timing is at 12 with the vacuum advanced hooked up, 1 with it unhooked.
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Sunday, June 23rd, 2019 AT 12:08 PM
Tiny
KASEKENNY
  • MECHANIC
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Yeah. You want it at 8-12 base timing. That means you set it with the advance unhooked. Then the vacuum advance will set advance it the amount it needs. The spec is 8-12 base timing and having it that low will cause a lag in acceleration.

The only other thing that will cause a lag on acceleration is the carburetor is not adjusted properly or the carburetor passages are clogged or restricted.

Again, I would set the timing more advanced than 1 degree because your combustion is happening just as the piston is coming to top dead center. This will do two things, cause the engine to be less efficient and down on power due to not maximizing the power from the combustion because the piston is already traveling down before the expansion of the combustion takes place.

You want the ignition to ignite the air fuel mixture about 10 degrees before top dead center so that as it begins to ignite as it finishes compressing and then really explodes as the piston begins to go down.

Also, if the ignition happens to close to TDC then it will actually push the piston down at TDC which will damage the crank bearings.
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Sunday, June 23rd, 2019 AT 12:31 PM
Tiny
VIPERKING75
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  • 48 POSTS
May I ask where you're getting those numbers from? My Haynes manual says to do it based off of a sticker under the hood but there is no sticker and everything I've read has said between 0 and 5.
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Sunday, June 23rd, 2019 AT 1:42 PM
Tiny
KASEKENNY
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I got the information from Alldata. Even if Alldata is wrong 0-5 is very low. I would suggest trying it as I stated above because you aren’t going to hurt anything. Worst case we put it back to where you have it and try something else. However you said yourself that you can adjust the carburetor to make any difference. Normally that is because timing is off.

Let me know what you find and we can go from there.
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Monday, June 24th, 2019 AT 7:31 PM
Tiny
VIPERKING75
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  • 48 POSTS
Well I set the timing to 12, it's got better response but it's still got a miss at idle and surges. Any idle below 900 is horrible. I put the idle fuel mixture back to factory settings.

Also something I forgot to mention, the engine is estimated to be a 1985 model and I did my best to keep all the engine components around that year. I was able to do it for the most part except for the solid metal vacuum lines, those are from an 1980. My friend also wanted to due away with all of the emissions stuff so we did, I did my best to block off everything except the distributor, the booster, and the charcoal canister. It does have an EGR and I've tried running it with and without it connected to vacuum. With how many vacuum connections the carburetor has, could misplaced vacuum lines be an issue? I've looked at countless vacuum diagrams but cant find anything close to the set up he has in his truck. Are there certain things that need to be connected? If so could I run them to straight vacuum or do I need the different jets and valves in between?
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Monday, June 24th, 2019 AT 7:54 PM
Tiny
KASEKENNY
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Oh boy. The misfire and surging based on all that definitely sounds like a vacuum leak. However, let's just start at the basics and hook up a vacuum gauge and see what the needle is doing. It should be very steady and not bouncing at all. If it is moving around, get a video of it and send it over so I can see what it is doing and we can go from there.

If it is steady then we can move on from a vacuum leak and look at the EGR operation and canister. If you still have that hooked up, do you have a purge valve or did you eliminate it?
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Tuesday, June 25th, 2019 AT 5:40 PM
Tiny
VIPERKING75
  • MEMBER
  • 48 POSTS
Vacuum has stayed very steady between 17-21 (depending on idle) goes down and back up smoothly on acceleration, spikes cleanly when letting off, so I know there's no leaks.

There's no purge valve anywhere, EGR has one port, EGR filter has two ports, canister has two ports, distributor has two, and carburetor has twelve if I'm not mistaken.
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Tuesday, June 25th, 2019 AT 5:57 PM
Tiny
KASEKENNY
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Okay. Just to clarify. When the vehicle is idling with the current issue you are having, what does the needle do? Can you send a video of it just idling?
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Tuesday, June 25th, 2019 AT 6:01 PM
Tiny
VIPERKING75
  • MEMBER
  • 48 POSTS
Next time I'm with the vehicle I'll see if I can get a video to send. Also something else that slipped my mind. The engine does run very well when I restrict half of the air flow into the carburetor, however the idle spikes dramatically when I do so, and adjusting the idle doesn't lower it.

And while thinking about it my friend did remove the gas tank to clean it out and replace the hoses. I wasn't around when he did it, and I know he hooked the fuel line up to the wrong pipe, and he used to much extra hose making it very difficult to fallow where the others go to see if they are hooked to the correct lines or not. I know one goes to the canister, two go to the pump, and I'm not sure what the fourth one goes to, he said there was only three connections on the tank, but there are four lines going back to it.
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Tuesday, June 25th, 2019 AT 6:22 PM
Tiny
KASEKENNY
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Okay. So we have a lot of things that need to be tracked down. If blocking off air causes the engine to run better that means you are getting to much air from other places which would indicated a vacuum leak. So the video of the vacuum gauge at idle will help confirm this.

As for the lines to the fuel tank, one may be a vent line however, we will need to get your friend back over to run through that with you just to confirm what each are.
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Tuesday, June 25th, 2019 AT 6:29 PM
Tiny
VIPERKING75
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  • 48 POSTS
I tried asking him where they all went and he had no idea, he just connected them where he thought they went.

But if it has a vacuum leak, why wouldn't it idle down with the screw all the way out and the air flow restricted?
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Tuesday, June 25th, 2019 AT 6:39 PM
Tiny
VIPERKING75
  • MEMBER
  • 48 POSTS
I was wrong, vacuum gauge was lying to me. I noticed the tube I was using had collapsed in on itself under vacuum and wasn't reading properly. Now the needle is vibrating rapidly between about 17 and 22.
Video (Click to make bigger)
Thumb
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Wednesday, June 26th, 2019 AT 2:06 PM
Tiny
KASEKENNY
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Oh yeah. So that needs to be perfectly steady before we can do anything else. That is why you are not able to adjust the mixture screws and make any change. Plus, that is affecting your idle issue as well.

Obvious statement is we need to plug all vacuum leaks and then go back through the setting timing and adjusting carburetor.
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Wednesday, June 26th, 2019 AT 5:12 PM
Tiny
VIPERKING75
  • MEMBER
  • 48 POSTS
I plugged all vacuum connections except for the vacuum advanced, the timing stayed the same and the needle is still fluctuating.
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Wednesday, June 26th, 2019 AT 5:19 PM
Tiny
KASEKENNY
  • MECHANIC
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Okay. If there are no vacuum leaks then this seems like a valve issue. Worn valve guides will cause the rapid fluctuation like this but you said you just rebuild the engine. Did you replace the valve guides?

Before you do anything else with this, monitor the vacuum gauge and then retard and advance the timing back and forth and see where the needle becomes steady. There is a chance that timing could cause the fluctuation so this is the old school way of setting timing, by using a a vacuum gauge.
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Wednesday, June 26th, 2019 AT 6:14 PM
Tiny
VIPERKING75
  • MEMBER
  • 48 POSTS
Head was new from the machine shop, new valves, seats, springs etc. Just checked valve adjustment and a few of them were off, got them all readjusted with the engine hot, about to fire it up and see what happens.
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Wednesday, June 26th, 2019 AT 6:19 PM
Tiny
VIPERKING75
  • MEMBER
  • 48 POSTS
Went to start it and the battery died almost immediately, ran through a rabbit hole of diagnostics. Going to have to get a new regulator tomorrow and try again.
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Wednesday, June 26th, 2019 AT 10:59 PM
Tiny
KASEKENNY
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Okay. Just post an update whenever you have one. I will wait to hear back. Thanks
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Thursday, June 27th, 2019 AT 5:47 PM
Tiny
VIPERKING75
  • MEMBER
  • 48 POSTS
New regulator didn't help, there is an issue in the wiring harness, put in a internal regulatory alternator and got the charging system going good. Got it started up, tried adjusting the timing. All I got was higher or lower vacuum. The needle would start to calm down while moving the distributor, but after letting it settle the fluctuations would go back to the same as before.

I checked valves for any major play in the guides. All of them were very tight with no noticeable movement.

Also I've noticed when I plug and play different vacuum connections on the carburetor to different vacuum tubes the needle either gets a little steadier or much worse.
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Monday, July 8th, 2019 AT 12:42 AM

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