Question about TQ tuning. Off idle hesitation.

8v-of-fury

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So I have an 850, atop a stock 318. LOL, Yes it is over sized. However, the issue is not to do with the secondary situation.. Only off idle hesitation.

So the thing runs about as good as any carb anything i've ever seen except for when it is not at full op temp. Although tonight it was raining and I gave her the beans off a red light in to a left corner to see if she'd slide. It didn't but it did take off and get up in to the secondaries in 1st. Immediately afterwards upon decel and coast it was running really rough and noticeably shaking. So I pulled over and pulled the breather cover to make sure for whatever reason, the choke didnt get buggered and close a little bit (who knows, thats what it felt like anyway..).

Upon pulling the breather lid up, it kinda picked up idle and ran better. odd. (probably needs a new air filter) I adjusted the idle screws out some as a start and got a much better idle out of it, probably went about another turn on each screw. IT raised the idle so i turned down the idle stop, however I got to a point where the idle screw left where the idle would return to. I assume this means the blades are as "idle" as they will be?

I dunno, i took it for a ride with the new setting and air cleaner completely off. It seemed ot run very well, however it was also still full op temp. Will have to test tomorrow.
 

Mikes5thAve

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Nothing is going fully fix wrong carb size and that's probably your biggest problem.
There's an air door adjustment that causes problems like that and it'll probably be next to impossible to set that properly with that carb and engine. Even the proper 800 one can be hard to get adjusted properly depending on how its jetted especially when its up against a weak 2bbl cam.
 

Camtron

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Hesitation off idle is usually a sign of a lean carb, but it can happen with a rich carb too; assuming ignition timing is set correctly and the carb works correctly. Adjusting the air/fuel idle screws will only do so much for coming off idle into the drive circuit. A wide band O2 sensor air/fuel gauge really helps a lot with this, for those who aren’t carb wizards. I’d start with moving the accelerator pump arm to a different slot and see what happens. Depending on the findings, I’d then probably look into bigger/smaller metering rods and jet sizes from there.
But I’d start with moving the accelerator pump arm first. See what a longer/shorter squirt of fuel coming off idle does and go from there.
 

Aspen500

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I concur with Camtron. Chances are the carb had jets that are way too big for a stock 318 and the metering rods are probably too small (diameter wise). There's also the metering rod spring which could be too weak or,,,, too strong. Basically the carb needs "tuned" and without a wide band air/fuel gauge it's all a shot in the dark. First you need to know if it's too rich or too lean and go from there. A properly set up TQ is an excellent carb but they are a heck of a thing to get right.

One thing that does come to mind, are you sure the plastic, excuse me, I mean composite main body not warped? I recall that was a big problem with them back in the day. If it gets warped, you'll have air leakage between the main body and the throttle body. It's been eons since I worked on one (meaning since the early '80's) so a lot of what I used to know about them, I don't anymore, lol.
 

kramer

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I remember when I used to mess with TQ carbs (I have about 7 or 8 laying around in the storage shed) the one condition you talked about that you experienced after you got on it and opened the secondarys and then had a rough idle afterwards is a good chance the secondary air door or secondary throttle blades were hung open for some reason and was causing the carb to want to idle through the secondarys and cause it to run rough or just flat out not happy at all.

I have had ones that worked awesome and then some I couldn't get rid of the off idle stumble no matter what I did and finally figured it out after reading about somebody else with the same issue and the main problem is the new accelerator pump in most of the modern carb rebuild kits are not setup right (or at least thats the way they were about 20 years ago), the rubber lip-seal that seals against the acc pump bore is loose on the acc pump shaft so you will get always get a delay in pump shot until the slack is taken out of the acc pump shaft to seal. So you can either just replace it with a leather acc pump (which doesn't like to sit for long periods of time and then tend to dry out) or somehow tighten up the lip-seal so the acc pump shaft and it move together. Just my two cent's.
 

kkritsilas

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A TQ 850 really isn't "too big" for a 318. The factory standard TQ for the 318 4 barrel is an 800 CFM unit, and I am sure with the right metering rods, an 850 would be fine as well. The only real difference is that the primaries are slightly bigger on the 850 CFM unit, and the secondary side is exactly the same size. On top of that, it is engine vacuum that determines how much the secondaries open, so that shouldn't be a problem if the springs on the air door are right.
 

8v-of-fury

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Right, we can ignore it being an 850 really. I am not stabbing for full throttle ever, because the engine cannot handle it. It doesn't do anything for power so I never romp on it that way. Unless I shift 1-2-3 and allow more RPM to happen before getting in to the pedal. I think we can also just about ignore the secondaries all together, for this issue, because when I do call for them with the skinny pedal.. everything works as it should, and there is no stumble or bog when the secondaries come on (and obviously, you can hear them monsters open over a stock exhaust lol *guuuwwwaaaah*)

This issue is purely idle/primaries. I am unsure (as you say, shot in the dark) if it is lean or rich honestly. At full op-temp it runs like a dream, and will easily grunt to the front of the pack while accelerating with normal traffic. Sometimes when cold and still on the choke a little bit it will also run superbly, but other times it will stumble HARD if you are trying to give it any throttle to leave a stop sign or climb a hill. Flat out feels like you turned the key off. Does that seem like the spark is being drowned out by ultra rich? Or being starved for fuel cause the throttle blades opened and there wasnt enough fuel ?

It is a tricky one, I appreciate everyone's brain tank on this :) We do a lot of building running projects out of mismatched junk laying around at work (marine technician, engines blow up and wear out all the time), but usually.. even wildly mismatched, everything always seems to work out pretty alright.
 

Camtron

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...yea that sounds like it could be either lean or rich. There’s a bunch of things to check and adjust on TQs. I’d suspect things like accelerator pump linkage, metering rods and springs, metering rod primary piston adjustment...there’s like 20 some odd adjustments/checks that have to be done just to make sure it working like normal and get to a fine tuning point.
 

jasperjacko

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I have run the tq for years and have gotten quite good at tuning. As mentioned, the afr gauge like one from innovate motorsports is an invaluable tool. First thing I would do is make sure timing is optimized. Second idle speed, adjust for highest vacuum at lowest idle screw setting while maintaining proper idle speed. Many guys are idling on the transition slots so timng is off and the fueling won't be right when you tip in the throttle. Third, check accelerator pump, it should start squirting immediately upon pressing the throttle, no dead spot. You also mentioned it's worse when not fully warm. Sounds like it could be lean, or it could be rich because the choke pull-off is not working. The jets and metering rods are the last things to mess with.
 

jasperjacko

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Another note, No way should your idle speed pick up when removing the breather cover unless it is caked with junk. your engine uses very little air at idle and no way should any filter be that restrictive. You also mentioned you made a hard left at full throttle, then got of the gas. Could be a flooding, float issue. Like said before, many steps to tuning, but it can be done. What kind of ignition are you running?
 

8v-of-fury

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I cant recall where the timing is as it has been a few years.. but I will check its base and total tomorrow and get back to you. IIRC correctly base timing is at 15* with the mixture screws about 3 turns out, and the idle screw as low as it will go to still contact the throttle arm. Idle speed is probably around 750 in gear? I don't believe I am idling on the transfer slots, but i cant recall how much was exposed from when the carb was off and upside down. Acc pump is a good clean shot AS SOON as you touch the throttle.

It was a hard wide left and good shot of throttle, probably about 3s worth. It coulda been float issue but i doubt it as it did the stumble for the rest of the 5 min drive home. Only when I touched the mix screws did it settle down. Air filter is not caked, but i have no idea on its age or ability to move air through it..
 

jasperjacko

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If the idle screw is as low as it will go and just touching the throttle arm, it should shut off. I'm guessing you have a vacuum leak at that's providing air another way which will make tuning impossible. If you have a vacuum gauge, unplug the vac. advance hose and cap it. Connect the vac. gauge to that port. You should have no vacuum reading at idle. If you have vacuum on that port at idle, you're on the transition slots.
 

80CordobaLS

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A big TQ on a 318 is fine. Unless you've screwed around with the rods & jets, the factory setting is fine for a basically stock engine.

A temporary lean condition will stumble and seem really weak. A temporary rich one doesn't stumble, it just kind of feels not as sharp.

Is your vacuum advance connected to full manifold vacuum or ported? I always use full vacuum. The engine needs advance when it is lean, and off-idle is still a lean condition. But you can always try ported.

I'd say your base timing of 15ºBTDC is a little too much. Try 8 or 10.

Check for vacuum leaks. Tighten all screws and the carb base nuts.

Having the throttle blades closed as much as possible is good, because it means you have all the transition slot to help off-idle.

Remove the idle screws, spray in carb cleaner and blow out with compressed air.
 

8v-of-fury

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If the idle screw is as low as it will go and just touching the throttle arm, it should shut off.

I feel like my throttle isn't allowed to return to absolutely closed.. I recall I have a stronger return spring out to the front than what was originally on here to aid in the throttle returning to "idle"

A big TQ on a 318 is fine. Unless you've screwed around with the rods & jets, the factory setting is fine for a basically stock engine. A temporary lean condition will stumble and seem really weak. A temporary rich one doesn't stumble, it just kind of feels not as sharp.

Nope haven't messed with any hard parts like that, this 850 is a 1975 400 AT truck one. So my stumble when cooler, the engine will straight stop making power. As if you turned the key off.

Is your vacuum advance connected to full manifold vacuum or ported? I always use full vacuum. The engine needs advance when it is lean, and off-idle is still a lean condition. But you can always try ported.

I have tried both in the past, I do believe right now however it is running ported from the carb.

I'd say your base timing of 15ºBTDC is a little too much. Try 8 or 10.

I can't remember why I settled on 15... It must have made the smoothest idle, most vacuum, or best starting. I cant recall.

What ignition are you using?

Sorry, didn't mean to ignore that question the last time. It is a summit/ebay ProForm distributor/ignition box. I also bought some distributor springs a few years ago and tried swapping softer and harder springs around and what not.
 

AJ/FormS

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Carter rated those carbs differently than Holleys rated theirs, to make them seem bigger than they were
The only difference between them was the primary side, which were a tad bigger on the 850s
The 850 had 1.5" primaries, about the same as the factory 2bbls.
I ran those TQ's whatever size on any old 318s and never had a problem. The secondary air-door is fully adjustable to work on almost any engine.

As to the hesitation, check your transfer slot sync, you may just be too far down on the slots,"drying" them up. This usually happens when you try to run too much Idle-timing, and/or too slow an idle speed.
Set your mixture screws to 1.75, then change your idle speed until you get a quality idle. Then, using timing, change your idle speed to 600/650 in gear or to whatever doesn't bang into gear.After that, you may have to re-engineer your Power-timing (max 34/36) and rate of advance, ( I like 28*@2800, all in by 3400; but depends ) engine /combo is different.
 
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8v-of-fury

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13 degrees base idle timing, with an idle speed of 770 in park. 19.5/20 of vac. However AJ after reading your TQ setup in that other thread, I feel like I jsut have the base idle and mixture screws set incorrectly chasing the highest and cleanest idle..

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jasperjacko

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Did you check to make sure there is no vacuum on the ported nipple at idle?
 
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