78 Trans Am getting some love

I had kind of a freak out rant about the Trans Am engine last night but I deleted it this morning. I guess what's still going on with the car is it runs a lot better down the road but I cannot get that thing to idle good. It acts like it is cammed way more than it is. I am still struggling to get 10 in of vacuum and the exhaust fumes will absolutely kill you, it burns your eyes. The idle mixture screws do change the way the motor runs, but I cannot get the fumes down. I have the base timing set at 12°, vacuum it will go to 24. I actually put the vacuum on port vacuum now just to keep the timing back at idle to try to burn up some of the fumes. I can find zero vacuum leaks anywhere. It almost seems like the more it runs the worse it gets. I was thinking about pulling the valve covers off this week and the timing cover and checking the cam timing with a degree wheel to see if that is off.I am pretty much at my end for adjustable things on the outside of the engine.I said in my rant last night that I'm one cuss word away from throwing this POS in the garbage and dropping in an LS lol. In my defense I was quite high and exhaust fumes.

HOLD ON! Don't give up yet. And, lets take one step at a time. It's running rich, we just need to see why, the low vacuum is trying to tell us.
Is the vacuum steady, moving slowly up and down or jumping?
I know you said base timing is at 12°, but did you try the heavy advance springs to see if it's advancing too soon?
Have you checked fuel pressure?

The vacuum is jumpy, not steady. I double checked the springs and they are middle of the road springs and the weights don't move until about 2200. I can adjust the timing good at idle, it will retard or advance like it should.According to the timing light.It will go to about 30 with total which isn't quite enough but I am less concerned about that ight now vs the idle and fumes.I have not checked fuel pressure, One other thing is it will diesel after it is shut off, I assume it is because it is idleing to rich not because of too advanced timing. If I force feed it butane through a vacuum port it will run great.

If it runs good down the road, I’d say the camshaft timing is probably not the problem. If a Holly carb it idling too rich, check the power valve to see if it is blown, and make sure the float levels are set correctly.

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Originally Posted by Driver50x

If it runs good down the road, I’d say the camshaft timing is probably not the problem. If a Holly carb it idling too rich, check the power valve to see if it is blown, and make sure the float levels are set correctly.

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This is a different style Holly, it's called a "Street Demon" ( not to be confused with their old "Demon" carb) and it does not use power valves,. I had this same idle problem wit the Q jet so I'm almost ruling out the carb, hopefully it doesn't come back to the carb, or I'll swear off Holly forever.....again.

Ok. I just googled a street demon, it’s a totally different carburetor than I was picturing. Did you look down the carburetor throat, while it was idling, to see if any fuel was dripping out of the main fuel circuit?

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Originally Posted by Driver50x

Ok. I just googled a street demon, it’s a totally different carburetor than I was picturing. Did you look down the carburetor throat, while it was idling, to see if any fuel was dripping out of the main fuel circuit?

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No I did not, I will check that as well.

I did get to read your rant this morning.. I didn't respond as I needed time to mull some things over.

Obviously it's running way rich, and it's a new carb right? SO did you have to set fuel level during initial setup?
I am not familiar with the new Holley so all I can do is guess. But before installation did you check the new carb for loose fasteners? I've actually had that happen! They must have a fuel enrichment circuit in that carb and it more than likely uses vacuum to draw the gas into the engine,. Have you discussed any of the settings with Holley Tech support?

Seth, I feel your pain, but you’re gonna have to relax a little and not jump around quite so much so we can help you. So lets back up a little and sort this out;

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Originally Posted by 53 Chevy5

The vacuum is jumpy, not steady.

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This could be tight valve lash, compression check is a good idea.

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Originally Posted by 53 Chevy5

I double checked the springs and they are middle of the road springs and the weights don't move until about 2200.

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All in at 2200rpm is a little soon and along with low total timing why I suspect the curve is off, please install heavy springs to confirm. Once we get it operating better we’ll work on the curve.

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Originally Posted by 53 Chevy5

I can adjust the timing good at idle, it will retard or advance like it should.According to the timing light.It will go to about 30 with total which isn't quite enough but I am less concerned about that ight now vs the idle and fumes.

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Everything is relative to the whole.

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Originally Posted by 53 Chevy5

I have not checked fuel pressure,

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Check fuel pressure.

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Originally Posted by 53 Chevy5

One other thing is it will diesel after it is shut off, I assume it is because it is idleing to rich not because of too advanced timing.

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Everything is relative to the whole.

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Originally Posted by 53 Chevy5

If I force feed it butane through a vacuum port it will run great.

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Low vacuum would account for this, check the valve lash and compression.

Attachment 72531

There was no initial setup required according to the installation book. I think I will verify my fuel pump pressure, and any obvious dripping inside the carb, and contacting Holly support is an obvious source that I don't know why I didn't think of earlier.

Glenn, Yes, when I get frustrated I start jumping around too much. I'll start checking some of these things out this week, one at a time.
I've had trouble keeping this car running good since I've owned it, people wonder why I never drive it lol.

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Originally Posted by 53 Chevy5

I've had trouble keeping this car running good since I've owned it, people wonder why I never drive it lol.

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Now we're getting to root. Is this a motor you rebuilt?

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Originally Posted by 36 sedan

Now we're getting to root. Is this a motor you rebuilt?

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Yes it is, I thought I mentioned that earlier when we talked about the cam. I rebuilt it 23 years ago, but there is probably only 8,000 miles on it or so. That's why I started questioning the cam timing, because I know I did not degree the cam when I built the motor. From what I remember, it is bored 30 over with new pistons, and I believe the Pistons were domed a bit to bump up the compression to around 9.25 to 1 versus the factory 8.5 to 1. The heads were redone as well.

OK, I just scanned through seven pages, but I didn't see any motor specs other than above, must have missed them.

I found it, it was way earlier when I started asking about some exhaust advice.No matter, I'm just hoping we can get this thing figured out.


' I need some exhaust advice here. Trans am motor is hopped up a bit, exhaust says potato potato potato but I don't remember the details of what I've done besides a larger cam and higher compression pistons. My old boss helped me out with it and he does know his motor stuff , he wasn't just throwing arrows in the dark."

I was just thinking about my old boss and him building engines. The guy is an arrogant ass but he did know how to put stuff together. He had a '88 Thunderbird with a stroke 351 who ended up being a 377. Ran in the mid 12's at 112 on pump gas. He would drive to the track bolt the slicks on that he had the trunk. After his run he would roll up the windows turn the AC on and then drive through the pits and crack his window open and poke fun of all the guys in the Chevelles and Camaros or what not. They would be sweating their butts off with the windows open and he would just say Burr is cold in here. It would be more funny if he wasn't an ass lol. He didn't want the car to go any faster because then he would be required to install a roll cage.

Lets get back to your present situation.
Do a compression test and a fuel pressure test first, lets see what we're working with.
When you do the compression test, do the first test dry, then do it again wet (a small squirt of oil in the cylinder), doing it this way will tell us if there is any lose past the rings.

After the compression test, adjust the valves with the method I posted above, then test compression again to see if it increased any.

Let us know what you find.

I think we're getting somewhere now. I finally had a chance to go down the list, compression is 150-155 straight across the board, I did not do the oil squirt in the cylinders though. I figured if their that close there shouldn't be any surprises inside. I reset the valves and I was pretty sure they were going to be too tight vs how you wanted me to set them and I was right. I was taught to go 1 turn after 0 lash and that is how they were, so I reset them to 1/4. I checked the fuel pressure and it was at 6 which Holley said is good. The vacuum did seem to pick up to 10 but no real change. I decided to buy an AFR gauge, put it in and It read about 15 at an idle which is stupid rich. I messed with the timing, vacuum advance, and turned in the idle mixture screws and nothing changed, it and it was running like it was before. I shut it off and stared at it a bit and did some abstract thinking and thought gaining vacuum is my #1 goal right now so I started it up and turned the idle mixture screws out 1/2 a turn further than before and BAM, it purrs like a kitten, my exhaust lope is gone, the stink is gone and it doesn't diesel when shutting it off. Vacuum is now a steady 14 and the AFR is nice at around 12. Before I get beat up on not adjusting them right the first time I did it like I always do, turn them in till you hear a change and then back it out 1/2 a turn, it always worked before. So when it was all said and done I needed to give it more fuel to lean it out. Thanks so much for not letting me rip my motor apart right away at the first sign of trouble! Now it should be a breeze to tune the rest of this carb with the AFR guage!

15 is lean, 12 is a little rich but OK with a cam at idle, 13-13.5 idle may be better, but always give the motor what it wants. Shoot for 14-15 at cruise, 12.00 - 12.5 WOT. Hold WOT for at least 15-20 seconds to be sure, it takes a bit for the accelerator circuit to run out and the secondaries to become active (not unusual to be a little rich at the beginning of WOT). Get it dialed in an read the plugs, the plugs will tell you what the motor needs.

An important caveat about AFR gauges, if the motor is missing it will read lean on the gauge.

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Originally Posted by 53 Chevy5

I did it like I always do, turn them in till you hear a change and then back it out 1/2 a turn, it always worked before.

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The ol' lean drop trick, works for stock motor but no so good with a cam. With a cam, go for highest idle vacuum then 1/8 - 1/4 turn out (richer).

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Originally Posted by 53 Chevy5

Now it should be a breeze to tune the rest of this carb with the AFR guage!

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AFR gauges are like a chassis dyno for carbs, and way cheaper than a day (or two) on a dyno!

I got a question on the secondary air flap. I know the primaries all have to be set first, but when does the air flap need to be set and the best way to do it? I know I'm getting a little ahead of myself, but I was wondering that for a long time already.

It comes factory set at I believe 1-1/2 turns which is good for most motors. Lets get everything else set before we worry about the this. Remember, tuning this carb is much like a Carter (Edelbrock), the metering rods and pull up springs are your friends.
https://documents.holley.com/lit731rev4.pdf

I think I may have over carbed the engine, I maybe should have gone with the 650 cfm vs the 750 cfm. I have the jetting down as far as I can go with both needle and seat and the best I can get my AFR at 55-60 mph on a flat road is in the low 12's . While I had the carb apart I swapped the secondary jets to the smallest size at the same time because I could see the writing on the wall. I got that from a solid 10 to about a 11.5 at WOT still plenty rich and it's got a noticeably better pull than before better but I can still tell it's wondering what to do with all the gas at that point. I messed around with the timing from 34 -39 and it doesn't make much difference with the AFR. I'll call Holley and see what my options are at this point which I'm sure will be a smaller carb. On a side not I got my idle vacuum up to 16 and an AFR gauge is the best investment to make tuning a carb!

Have a safe and fun 4th everyone, I think we're going to take Rita out and drive around for the rest of the afternoon and try to find something to do. Most towns around here don't have much going on this year but It's a nice day for a drive anyway.

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Originally Posted by 53 Chevy5

I think I may have over carbed the engine, I maybe should have gone with the 650 cfm vs the 750 cfm.

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750 is a good size for your motor. I have dual quads on my 383 (1000 cfm), it’s all in tuning.

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Originally Posted by 53 Chevy5

I have the jetting down as far as I can go with both needle and seat and the best I can get my AFR at 55-60 mph on a flat road is in the low 12's .

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What primary jets and rods are you using. Keep a log of all changes and what they do (you’ll thank me later)

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Originally Posted by 53 Chevy5

While I had the carb apart I swapped the secondary jets to the smallest size at the same time because I could see the writing on the wall. I got that from a solid 10 to about a 11.5 at WOT still plenty rich and it's got a noticeably better pull than before better but I can still tell it's wondering what to do with all the gas at that point.

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Wait on the secondary jets, most of WOT comes from the primary and the enrichment circuits. Secondaries effect on WOT is about 15-20 seconds out. Most of the rich your seeing is from the accelerator, primary and enrichment circuits, lets tune them first. Move your accelerator linkage to the furthest out hole and see how it performs.

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Originally Posted by 53 Chevy5

I messed around with the timing from 34 -39 and it doesn't make much difference with the AFR.

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Watch the timing for detonation at WOT, 39° is pushing it and may actually lose power.

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Originally Posted by 53 Chevy5

I'll call Holley and see what my options are at this point which I'm sure will be a smaller carb.

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I doubt they’ll recommend a smaller carb, again, tuning is the key.

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Originally Posted by 53 Chevy5

On a side not I got my idle vacuum up to 16 and an AFR gauge is the best investment to make tuning a carb!

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Good job on the vacuum. AFR gauges are great! Just remember a miss fire will read lean, always check and read the plugs.

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Originally Posted by 53 Chevy5

Have a safe and fun 4th everyone, I think we're going to take Rita out and drive around for the rest of the afternoon and try to find something to do.

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I’m changing oil, plugs, wires, cap and rotor on mine today. In the morning I’ll finish with cleaning the air bleeds and changing the coolant, then out I go! Lol!!!

Happy 4th to all!

Here's a carb tuning log to help you keep track;

To help you, I need to know the jets and rods you have installed.

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Originally Posted by 36 sedan

To help you, I need to know the jets and rods you have installed.

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My Sunday afternoon snooze got a little long:)

From the factory it has 56/40 primary needles in it, then I installed 58/44's in. I have some 54/38's that I did not try but they have a smaller diameter which would be going the wrong direction in my mind. So now I have 58/44 primary needles.

Factory primary jets are 89 with 91 and 87 in my kit, I installed the 87

Factory secondary is 86 with 88 and 84 in the kit, I installed 84

I still have the factory 6" hg step up spring in it.

These are the jets available in the 625 cfm kit which will fit in my 750

Primary main jet assorment of .074, .076, .080 and .082
Secondary main jet assortment of .078 and .082
Metring rod assortment of .056/.048, .058/.050, .058/.052, .060/.050, .062/.054 and .064/.056
Step-Up spring assortment of orange, blue, yellow and silver springs

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I’m changing oil, plugs, wires, cap and rotor on mine today. In the morning I’ll finish with cleaning the air bleeds and changing the coolant, then out I go! Lol!!!

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I hope your cruising went better than mine, mine lasted about 12 miles and my fuel pump croaked. The pump lasted only 8,100 miles , I think I'll get a used one from the salvage yard, I'm sick of new junk.

Dang it! Sorry for ya. I've spent my share of time hooked to a tow, I understand.
Even the old mechanical pumps have their problems (probably due to todays fuel additives). After the 3rd one went out on mine (what a bugger to change, had to pull the inner fender out to get to it), I converted to electric and never looked back.

My cruise got diverted by a honey do list, LOL! I'll have to wait til tomorrow...

STREET DEMON FACTORY SPECS;

750 stock jets = primary #89, secondary #86
750 stock rods = 56/40

You installed;

jets = primary #87 (2 steps leaner), secondary #84 (2 steps leaner)
rods = 58/44 (1-1/2 step leaner)
AFR @ idle = 12, AFR @ cruise = 12, AFR @ WOT = 10-11.5

You’re going in the right direction, stay on the primary and rods, should be able to dial it in with them. Change the rods to a 60/50 that will lean the cruise 1 step and lean WOT 3 steps, see what that does. May have to drop primary jets to #82 and rods back to 56/40 rods, to get the cruise. Then if the WOT is still rich 56/48 rods.

To lean = smaller jets and/or larger rods
To richen = larger jets and/or smaller rods

NOTE;

1 - jet size change (.003) with no rod change = 2 steps >/< (richer/leaner)
1 - rod size change (.002) with no jet change = 1 steps >/< (richer/leaner)

1,200 feet elevation is one of the reasons it's running rich. Hang in there, you're almost there.

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Watch the timing for detonation at WOT, 39° is pushing it and may actually lose power.

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I did notice that it lost some pull at that point,no detonation though. I will bring it back down to 35

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Good job on the vacuum. AFR gauges are great! Just remember a miss fire will read lean, always check and read the plugs.

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When reading the plugs, how long must it be driven to get a good reading on the plug? Once it's read and you change a setting, do you put new plugs in every time?

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Originally Posted by 53 Chevy5

When reading the plugs, how long must it be driven to get a good reading on the plug? Once it's read and you change a setting, do you put new plugs in every time?

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You'll be able to see changes pretty quickly. With the AFR gauge we'll stick with same plugs for now, just need to confirm what the gauge is telling us. After it's dialed in, new plugs and a fresh read.

We're getting close now. I have the 82 primary with the 56/40 needle and its running at 13 cruise and 11.5-12 WOT, that is an average of course, it's real hard to read perfect because of the constant rpm change on WOT. I'll try the 56/48 rods tomorrow and see how it acts. Holley recommends 13.5 cruise and 12.5 WOT, what are your thoughts on that? I know on my gauge as soon as it hits 14 the bar goes into the yellow instead of green. Another question is the AFR gauge will climb to 13.5 -14.5 if I'm climbing a slight hill giving it a little extra gas, is this normal?

On a side note this is kinda fun noticing the changes in how it runs. For the first time since I've owned the car it broke the tires loose when I shifted to second, not just a chirp or a squawk. It has 3.23 gears so their a kinda tall for grabbing rubber in all gears.

Almost there, 11.5-12 WOT is GREAT (I prefer this for WOT). What do the plugs say?
13 cruise is a good cruise, but a little on the rich side. Great for responsiveness, but mileage will suffer a little. 14 is a better compromise (let me think about the work around on this). What do the plugs say?
13.5-14 on slight load means the enrichment circuit is not coming in soon enough, install Heavier springs and it'll pull better.

Here's a chart that will help;

Here's a spring chart that will help;

Install the 58/44 rods, it will lean cruise and WOT slightly.

I think I just got myself into trouble. The TA carb It's getting closer to being tuned in, and I would like some real world 1/4 mile times to compare some adjustments. I was wondering how to measure times accurately and then all sudden I thought, there has to be an app for that, yep, I was right lol. I found one that will start as soon as your car starts moving, and it will measure and keep track of anything you want. This could end up costing me some money lol

Here is my nightly update, I drove it again with the 58/44 rods in and it seemed like everything was just a bit rich yet, low 13's and low 11's, a bit richer than what I thought it had the other night. I put in the 60/50 with the 82 primary that are in now vs the 87 that were in there the last time I tried them and my numbers are nearly perfect. 13.5-14 cruise and 12.5 WOT , 12.5 is leaner than you like, but still good? The only issue I have yet is it will still lean out with slight throttle up to 15-16, and that is with my heaviest spring, the silver one. The motor does start to run out of steam at about 5000 rpm's but it seems to pull real good up to 4500 ish. I was thinking about bumping up the secondary jet again. every time I type this the engine is too hot to pull plugs for you :)