Thread: 78 Trans Am getting some love

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Something must be goofed up, 20 is at 750 RPM with the vacuum advance disconnected .I was asking questions earlier about full advance and initial timing because I was having this problem. I better take a closer look at some things. I will double check, but it seemed like I was all in at about 2200

Originally Posted by 53 Chevy5

If I use ported vacuum, wouldn't that completely make the mechanical weights obsolete because the vacuum increases as you rev the engine up therefore advancing the timing?

No, vacuum advance wether manifold or ported sourced will not effect your mechanical, they are two separate things.

And, the only difference between manifold and ported is when the vacuum advance starts. Manifold is at idle through cruise rpm, ported is off at idle and comes on at cruise rpm. Ported is also known as TIMED because it comes on later.

Simply put, vacuum advance is an economizer, it has nothing to do with performance. In theory, at idle and cruise speeds the motor can use more advance to burn leaner mixtures. However, I'm a big believer in giving the motor what the motor wants.

If the advance at idle brings the idle speed up too high, plug it into ported, you'll still have it at cruise for economy. If it idles good on manifold great, leave it there.

Originally Posted by 53 Chevy5

Something must be goofed up, 20 is at 750 RPM with the vacuum advance disconnected .I was asking questions earlier about full advance and initial timing because I was having this problem. I better take a closer look at some things. I will double check, but it seemed like I was all in at about 2200

Sounds like your curve is starting too soon, put heavy springs in it and check it, if the base timing comes down that's the culprit (your idle speed will drop too). You'll have to start moving springs around to get it dialed in. Try a heavy spring with a light spring. It's OK to mix and match the springs to get what you need.

Double post

Originally Posted by 53 Chevy5

Double post

I'm not see your post other than the above???
Is there another problem?

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.

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.

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?

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?

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;

Originally Posted by 53 Chevy5

The vacuum is jumpy, not steady.

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

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.

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.

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.

Everything is relative to the whole.

Originally Posted by 53 Chevy5

I have not checked fuel pressure,

Check fuel pressure.

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.

Everything is relative to the whole.

Originally Posted by 53 Chevy5

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

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

Adjusting hydraulic valves .pdf

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.