Under load or not, but worse under load, the car will hesitate like mad and then go. Sometimes it even stalls. I have a pretty much un-touched out-of-the-box carburator, and I'm running about 20* advanced base timing. The problem seems to get better the more I advance it, but I have absolutely no clue where my timing should be. At all. This is my first experience with a carburated vehicle in general. I'm not even sure if/when/how-much gas to feed it when starting the damn thing.

I was told it is probably my pump-shot. Is that the little squirt that comes out when you give it gas through the barrel? Well, a simple $35 carb calibration kit would solve that much of it, correct? I assume they're available in most parts stores, correct?

Second, as I questioned, what should my timing be set around? I'm running 9-9.5:1 compression. I have heard all the way up to 36 degrees base timing. I have a vacuum-advanced distributor (of course) and it seems to be working well.

Also, just for my concern, how should I start a carburated vehicle? Give it a little throttle while cranking? Tap the gas and let off, and then turn the key? I don't even know. I'm hopeless. Thanks for all of the help, guys.

 

The hesitation could be caused by something as simple as an electric choke needing adjustment, bad plug wires, or any number of simple things. Just check all the basics.

I would run around 16* base and add a light and a medium advance spring to your distributor. That should get you full advance of about 32* or so around 2500 rpms.

As for the initial start up, just press the pedal lightly so you let some pump shot enter the intake and crank it over. You'll eventually figure out what your car needs to fire up successfully.

Most of this stuff probably sounds pretty vague and was already what you were thinking. Just keep playing with it is all I can say. No better way to troubleshoot than to keep tinkering!

 

Ya know, I've never even checked to see if all four barrels open...

 

Yeah, check the secondaries too. Also check that your vacuum lines are connected properly. I had one plugged that shouldnt have been and it caused a lot of trouble, just like what you are saying.

For startup I floor it once, wait half a second, then turn the key. Then as it is cranking I pump the pedal anywhere between 50-100% throttle. Sometimes it doesnt sound like it's gonna catch, but if you disengage the starter and give it gas, it'll go...

 

Be sure the vacuum advance is connected to the right port also, and when you set your base timing it's done with the vac hose removed and plugged. Also be sure the PCV hose is on. And be sure the TV cable is right before you drive, or you'll cook your tranny.

 

yeah I've got the vac advance to the manifold vacuum, because people said I'd get better off-the-line performance. Yes, that's how I set my base timing too. I don't have a PCV either, because it just wouldn't work with my setup right now. Eventually. I jsut have a breather for now.

 

If your vac advance is on the manifold vac then it will end up being pretty high at idle, which isn't a bad thing especially for a performance engine. IIRC it might be over 18* at idle with the hose connected. But depending upon how the vac advance is adjusted, it might be dropping too far back when you punch it, which would definitely cause a hesitation.
You have to adjust the vac advance curve as well as the centrifugal advance curve to really get it working well. You'll have to play around with it a lot to get it right.
It helps a lot if you have a timing tape or better yet a degreed harmonic balancer. Check it to be sure your timing pointer is pointing to -0- when it's at TDC on the #1 cyl, and from there set your timing so it will be where it's supposed to be when fully advanced for vortec heads (32*?) and be sure the vac hose is removed from the canister when you're setting that.
It's hard for anyone else to tell you what's exactly right for your car, but the more you play around with it the better you'll get a feel for it.
Assume that the carb is in the ballpark, if it's out of the box. And if there are any problems with hesitation and your acc pumps are both working, look at the timing as being out of whack. Since that's the part that's up to you to set up, and you're a rookie.
Get a vacuum gauge ! They're as indespensible as a timing light.
Remember that when your foot is to the floor the manifold vacuum will be low enough that all the vacuum advance will be pulled out of the advance curve.

Does that all make sense?

 

You're making a lot of sense, yes. You're saying that when I put the pedal to the floor, the vacuum drops so low that the distributor isn't really doing any special advancements, and it would be approximately at base timing then? Should I try it on ported vacuum and see how it reacts?

 

#1 Did you check to be sure the timing pointer points to 0* when the #1 piston is at TDC?

#2 Do you have a degreed balancer?

#3 Do you have a vac ga?

#4 Is your vac canister adjustable?

#5 Are both of your accelerator pumps squirting?

For starters:
With the engine idling, check the timing with the vac advance hose removed and with the hose connected to manifold vacuum. Then check the timing with the vac hose removed at about 3500rpm. At what rpm does the timing stop advancing with the vac hose removed?

It's a lot easier to discuss what your timing is doing if you have a degreed balancer, cause the factory balancer only has marks that go up to 15deg or so.

 

1. Yes, when I first started the car I had it at zero.

2. My balancer is not degreed, I am using the tab, which is hard seeing as it only goes up so high so I have to estimate beyond that. I'm going to invest in a degree tape.

3. What is a vac ga?

4. The vac piece on the distributor? It is not adjustable to my knowledge. If you were asking if I had some form of aftermarket vacuum canister, no I do not.

5. Yes, both of them shoot diagonally down the primaries. This was one of the first things I noticed


For the advancing testing, you want me to see how many degrees the max-advance is? Aren't most distributors usually about 15 degrees?




Thanks for your cooperation with my newbie-ism

 

Yes, most distributors are about 15deg, but it's good to know for sure.
A vacuum ga is a gauge that measures your manifold vacuum. It connects to a vac port with a hose and mounts in your gauge cluster. They aren't expensive, and they're really helpful for tuning the advance curve.
Try the things I mentioned in my last post, just so you can get a basic clue what your advance systems are doing.

 

I'm not even sure what kind of timing is good and what is bad. I skipped this step and had Brian from TBIChips do it last year for me. I should have learned... I really don't even know more than the fundamentals of timing. I know that too much causes pinging. I don't even know what too little does. I don't know when vacuum is at its highest, either... Sounds pretty sad.

 

Your neighbors must love you if you're out there tuning your car at this hour.

If you set it at about 8* with the vac hose off at idle it will be an OK starting point to begin testing.

Timing tapes tend to fly off, but if you clean your balancer with lacquer thinner or acetone, it will stick for a while.

If you just do those basic things that I suggested, you'll be able to see what your distributor is doing and that will be a great first step cause you'll learn the basics.
You'll be able to observe the timing curve in motion by using your timing light and running it at different rpms with the hose off and on.
Yes, when your foot is on the gas the manifold vac drops to zero. And when it's idling it's at about 15inches or so. That's known as high vacuum.
The vacuum is also high when you're cruising with a light foot on the pedal. The more you step on the gas, the more the vacuum drops. That's why it helps to have a vac ga. Then you can tell what it's doing while you're driving.

 

So typically do you want a higher advance at lower RPM? I thought it was the other way around...

I like learning

 

Not exactly.
But you do want higher advance at higher vacuum.
A vac advance is actually a vacuum retard, it retards the advance curve as you give it more pedal, that keeps it from pinging. But when you're just cruising and the manifold vacuum is high, then the vac advance gives it more advance.
That helps you get better fuel economy.

 

You're extremely helpful tonight.

 

Street distributors have 2 advance curves, centrifugal advance, and vacuum advance. When it's all set up right, the two curves compliment each other. If the thing isn't set up right, the curves conflict.
Race distributors don't have any vac advance because they have their foot into the gas almost all the time and it doesn't matter whether a race car gets good economy when they're cruising on the freeway at 60.
But the extra advance that the vac advance throws in there when the vacuum is at 15-20 inches helps out a lot with fuel economy when the engine is under light load. The idea is to tune it right so that extra vac advance is there when you need it when you're cruising.

 

the secondaries are not opening.

 

I played with it a lot today. I moved the timing all over the place. I could not seem to get it to do anything special.

Streetiron85, the distributor pretty much stops advancing at about 3500 rpm and appears to go a total of 12-15 degrees from base. Should I just advance it as high as I can get it without pinging on 87 octane and leave it at that? I really don't know what to do.

Also, I thought carberators are supposed to be easy to tune and diagnose. I need a calibration kit.

 

Does it still hesitate?
Is your distributor a factory HEI?
Did you get your timing tape yet?
How about a vac ga?

There are some timing adjustments that have a more noticable effect in the SOTP feel, it effects pinging, effects the idle, effects starting, it effects MPG, and effects track performance.
But sometimes in subtle ways that seem un noticable at first.

It doesn't help to tell us that your advance is 12-15deg, that's too vague.
Get a degreed balancer cover, so you'll know for sure. They're less than $20 on ebay. A timing tape will be okay til it flys off, but I have a feeling that your learning experience is going to outlast the adhesive on the back of a timing tape.

Til then set it at 10deg at idle with the vac hose plugged.

I think you'll need a new adjustable vaccum cannister too.
If it's hesitating, your factory vac can is probabally pulling out too much advance for your engine to be happy.

Also, the secondaries are most likely working the way they're supposed to. And the carb you have is a lot easier to jet than a holley. You have to remove a holley and take off the float bowls and change the gaskets when you change the jets.
Worry about he carb later.

 

I had the same problem a year ago, now I'm all good.

Pump shot and power valve plus correct timing fixed it.

First things first, you must have an accurate position of the #1 cylinder @ TDC. Everything else revolves around this.

Next, anywhere from 10-20* base timing. I run 14*, find out what works best for you, my engine starts up instantly with 1 pump. I don't have to hold the key, just turn it over for a fraction of a second and my engine fires and choke takes over. If you engine wants more initial timing to run well and start then give it.

Find out where the engine idles well. If your engine wants 12* at idle to run smoothly thats what you give it.

Put a vacuum gauge on the carb and see what vacuum you have. Once you know what your vacuum is at idle and in gear go HERE and buy the correct power valve.

Then go get a pump shot nozzle around .32 or .35, you'll want to buy a couple and see what works best. Set your pump cam to deliver the most fuel as soon as possible.

You want 36* total timing. Total timing is Initial + mechanical. So if your initial is 12, your mechanical needs to be 24*.

Take your distributor to a performance shop that has a distributor adjusting machine (Whatever they call it). They can set your distributor weights to exactly what you need, and they can set your spring curve to exactly what you need. Your distributor may have come with a chart saying that pink + red spring = this curve. That is junk, the only way to TRUELY know your advance curve it to have it put on the correct machine.

Once you have your initial timing and mechanical timing set, then adjust your vacuum advance for gas milage.


Hope this helps. Your bog is being cause from a half dozen different things. Not doing any of the above steps correctly will affect everything else. Run your vaccum advance off of the ported. If you want to switch to manifold later you can do so.

I run protopline vortec heads and CC XE268H for reference.

 

Just to add to the information (confusion..)

I've also heard to adjust your vacuum advance (after you get the Crane kit...) to avoid detonation. In other words your upper limit of vacuum advance will be to avoid detonation, lower limit is to maximize mileage...

I've never seen a performance shop that does distributor mods... might be a big city thing...? The stats on the bag (ie gold+silver = 800RPM-start 2600RPM-all in) were good enough for me, rev it and watch it to confirm.

MSD timing tape is around $5, comes with an assortment of sizes. I'd say set your timing first, since you can basically set it to the specs mentioned, and your car should run fine. Then tune the carb....
Good luck, should be a really hot ride once it's tuned up....

 

Alright well I went to Autozone today and I bought a set of weights and springs for the distributor. I don't know which curve I want though. You say I want 36* of total timing? How sharp of a curve do I want it? Is a stock (GM production) distributor set up for emissions or mileage? I doubt it's set up for power... And I've also never heard of a distributor tuning thing like you mentioned.

I didn't get a timing tape because they didn't have any. I'll just order from Summit Racing tonight... Actually, I want to get a balancer cover so it lasts longer- but I need to know what size balancer I've got. Am I the 6 3/4 or the 8"? Yeah I know, I could go measure, but honestly I'm bound to screw that up with the way things are going. The engine is from an 88 GTA.

I also did not get an adjustable vacuum canister for the distributor, because I don't even know if mine is adjustable or not. It's factory (GM replacement part distributor, ran me $80 on ebay) so whatever those were.

About the power valve- I have an Edelbrock. They don't have power valves, do they? I am gonna order the 1406 calibration kit tonight too. I imagine I will need it, since Edelbrocks always have room for improvement. It's only $40 anyway. Do Edelbrocks have pump cams? I was reading their little manual and it's easy yet difficult to understand. They make it seem so easy.


When I mash the pedal, I get that hesitation... then it slowly picks up and then takes off like a rocket at about 2000+ rpm. I love that high end power I get. I can't wait to feel it through the whole powerband!

Basically what people are saying is that mechanical advance is more important than the vacuum advance in terms of power. The vacuum is only there to give a better idle. StealthElephant, you've got yours on ported? I have a thread going in CARBS forum about this.



Awesome guys, I'm starting to grasp this.

 

When you get your degreed cover, you'll be able to tell exactly how much advance you actually have. That will make everything so much simpler for comparing notes.
If your dist is a factory HEI it might have 15deg vac advance. That's kind of a lot, and it could be the cause of your hesitation. Cause when you punch it, the vac advance can pulls out all the vac advance that there is. And that wouldn't leave you with much if you have a stock advance curve.

Centrifugal advance is all you have when your foot is really into it, the vacuum advance drops back to zero at that point.
Essentially your distributor becomes a race distributor,
The perfect compliment for a 4bbl progressive linkage carb (like most of the carb guys use)

You can tell if you have an adjustable vac can cause they're octagon shaped at the front. The Crane ones are good bacause they can be adjusted for both the rate of advance and the amount of advance.

Edelbrock carbs don't have a pump cam.

 

Yes, it has this octagon shaped aluminum type thingy on it.



http://cgi.ebay.com/ebaymotors/ws/eB...category=33690

 

Those are adjustable by putting a small allen wrench through the hole where the hose goes.
You'll really be in luck if there's a little gizmo that limits the travel on the arm of the vacuum advance. It should be a little flat piece sort of semicircular and about the dia of a nickel, held down by a screw under the cap.
In fact you could probably make one out of a nickel cut in two, with a hole drilled through it.

 

so how do I adjust it? like, which way do I want to turn it? and what's that gizmo do? lol

 

I'm not familiar with that carb yet (I'm probably going to get rid of my Holley and grab one of those nice Edelbrock 1406s myself, I like the idea of changing jets w/o having to get fuel all over me.)

As I was told on these forums a year ago, total timing is king. Everything revolves around the correct initial and mechanical timing. VA (vacuum advance) is the LAST thing you worry about.

The machine I am talking about has a spot where the distributor install into it. The machine then spins the distributor like it would be when running your engine. There is a circle around the distributor with 8 dots that light up. The dots show you exactly where your timing hits for each cylinder, it tells you exactly how fast and at what RPM your curve is, etc etc. I had my machine shop set my distributor up (curve, weights, total timing, etc etc). 70$ normally to reweight and recurve but they did it for free (plus cost of spring/weight kit) since I bought the MSD distrib from them.

I was having alot of problems getting my weights/springs/mechanical advance where it needed to be. If you try to tune the car around a distributor that isn't custom set up exactly how you need it to be, you'll be shooting yourself in the foot.

https://www.thirdgen.org/techbb2/sho...ng+distributor

Thats an old thread, some good info in there. I had 2 problems you don't have, #1 my old accel distributor was a POS and was completely out of alignment giving erratic ignition, and #2 I had almost 11:1 compression which was giving me problems. But alot of the info still applies for tuning and such.

Your bog problem sounds EXACTLY like the problem I used to have. Mine used to bog really bad from a 5mph roll for like 3 seconds, then just take off. If I had my car at a dead stop and just nailed the gas, my engine would just shut off. good timing from a properly set up distributor, and tuning of the carb fixed all of it. I can mash the gas today from a dead stop and I'll peel out all the way through 2nd. I know how ya feel, just keep plugging away at it.

 

As I mentioned earlier, it's easier to compare notes if we have some accurate numbers to work with.

A vacuum gauge and a degreed balancer are in order here.

Go ahead and measure your balancer.... You aren't giving yourself much credit if you think you cant tell the dif between 6-1/2" and 8"

Didn't your dist come with instructions?

 

It's most likely 6 3/4 but just get a tape measurer, and get the circumference of the damper. I think C = pi * d, to get the diameter, thats what I did. Buy timing tape, but don't actually apply the tape (it always comes off eventually, take a sharpie marker and just mark the 0, 10, 20, 30, 40, 50 spots, then add increments of 5. The sharpie won't rub off and it's easy to see with a light.

As streetiron said, you need to get a vacuum guage as well, like 15$ at pep boys. If you don't know how to adjust your distrib just find the correct size allen key. Plug your vaccum advance into full manifold port and check your timing. Then adjust the vacuum canister in any direction. Recheck your timing again, if your timing when down, then you know turning in that direction turns it down, and vice versa. Those vacuum canisters are very sensitive, like 1/4 turn is 2-3 degrees.

If it's a factory GM distrib like you say it is, then is probably has a terrible advance curve and the wrong amount of mechanical. Definately not set up for performance from GM.

 

I painted my balancer black and used a white paint pen to mark the intervals, the way that Stealth Elephant said. Sooper easy to read.
But someday if I win the lottery, I'll get a $15 balancer cover

 

Okay that thread has been saved to my favorites list. Wow it's full of goodies.

Anyway I'm reading my spring/weight set and it comes with three settings... I'll post a picture to see which one I should use. I'm thinking the gold one...



I HAVE A PAINT PEN, ALSO! I should start markin

 

The graphs of those curves are sort of hard to figure out, cause they show a spring change effecting both the advance rate and the amount of advance, which in reality would be about impossible.
After you get your balancer calibrated, experiment with springs til you get a curve that's like the one F Bird described in the thread that StealthElephant showed.

Some guys say that a dyno tune is best for optimizing total advance, but others say that the track is best.
You can do a track test of your own by stopwatch timing it on an acceleration run in 2nd gear with the converter locked, from about 3000 to 5800rpm or whatever numbers you choose.
That test is greatly simplified if you have a passenger with a stopwatch, and a tach with a shift light.
Use a gear that won't let wheelspin become a variable

When you've found out what your total advance should be, work outward from there. Figure out what your engine likes at idle, and then put together a curve for the lower rpm range that connects the upper and lower extremes.
That curve wil be within the range that F Bird suggested.
You might find out after a few weeks driving that you'll want to adjust it.
Remember that when you're cruising, your rpms are between 2000-2500rpm and that's where you want good economy, but that's also where an engine is prone to pinging. So expect to have to fiddle around with it a lot in that range to find the best compromise.

 

I wish this proceedure wasn't so vague

it's all trial and error!

 

at WOT, the manifold vacuum pretty much always be about zero, correct?

How much timing is good for off-the-line acceleration? From a dead stop, if I slam the pedal the car will stall. I assume it's because I'm going from about 25-30 degrees advanced down to about 14 base.

I'm starting to grasp the timing a little bit better, but I don't know how much is too much yet. I have yet to hear a ping (that I know of) from my car though and I'm pretty advanced... Well, I also had a header leak so now thats fixed I'll hear around for it tomorrow.

 

Vacuum should drop to 0" @ WOT.

You pretty much have to experiment with initial timing to find where the engine wants to be. 14-18* is a good place to start. As someone mentioned before, once you get into the 18*+ area with initial timing your starter may have trouble keeping up.

You can't always hear pinging, esp. light pinging under minor load. With 9.5:1 as long as you run 91 octane I can't image you having problems once everything is where it needs to be.

 

Like mentioned above, vac advance is just added for fuel mileage (and to keep your plugs from loading up with crud).


-> Actually there is an article on the main TGO page about how to setup the crane kit, which is completely similar to what you have, check that out for more info.

oh yea, i'd disconnect your vacuum advance, plug the carb port (or whatever it's connected to), and tune for performance, then plug it back in, and tune for no ping (just tuning vacuum).... but that's just my method, there's a bunch of ways to do it, pick your own I guess....

Your car will actually stall when you tromp on the gas??? ouch... Yea, i'd guess carb, but make sure your timing is set right first.

That's a weird timing chart you posted, it seems backwards (left to right) to me... ? Usually the combination of springs, (you'll use two springs, don't have to match...) will start your timing at whatever RPM, and be all in by whatever.

EG. my crane kit, I have one light and one medium spring - giving me advance starting at 800RPM and all in by 2800RPM....

oh, that "nickel" gizmo someone mentioned, was to limit the AMOUNT of total vacuum advance.... I could delve into explaining that, but I have to get back to work, all this info is on a tech article...

https://www.thirdgen.org/newdesign/tech/hei.shtml

 

Well today I swapped out the springs and weights. I used the gold ones (broadest curve) and the car accelerates much faster- however, my hesitation is still there. I am running too much initial timing I think- it's around 18*. This turns into 36* at 3000 rpm though, so I figured it was good to aim at that. I am hearing some knocking when I'm idling and I pray that it's just from being too far advanced. If you do the math, I'm running a total of approximately 40 degrees of advance at 1500 rpm with my base timing so high.

The car is a friggin rocket from 2000-5500 rpm, but it's even worse than before out of the hole



Also, I filled up my tank with 93 just 5 miles ago. I was originally using 87 octane. In any case, I got 16mpg with my first tank! That's as high as I ever saw with my modded LO3! I'm also using a much higher stall converter without a lockup switch connected yet, more cubic inches, and of course a carberator.

 

I guess it might be possible that your pump shot isn't enough for that intake. Possibly those 600s are calibrated for an intake that has a smaller runner vol and plenum vol. That would explain the hesitation.
But as long as you're into the dist, might as well get that right.
That's a good Tech Article on recurving vac adv.
I should take the time to search there more often.

 

yeah that article is very in depth. I like it, from what I can understand I mean.


Would you think I'm running lean if not the timing?

 

If it ends up the timing isn't the problem, the accelerator pump on the carb would be my next guess.
In fact I'm thinking that's probably the trouble at this point.
If you can put your foot into the pedal slowly and steadily, and there aren't any flat spots or hesitation then it wouldn't be lean. But if you punch it and it stumbles bad, then it's probably the acc pump volume.
I forget how that's adjusted on the edelbrock (carter) I haven't used one of those in a while. When you buy a kit, be sure you get a kit that includes acc pump parts, not just jets.

 

Yeah the car runs really nice with exception to mashing the pedal. I'll get a kit and rock this car out.

Did I do the right thing by setting my springs to the loosest ones? It's got the peakiest curve of advance, and it runs better than the stock springs.

 

So I put the pump-shot up to the highest setting and it did not solve my problem.

it's gotta be in timing then, but I am running plenty of it!!!

 

How much advance is there at the stall speed of the tq converter, with the vac hose disconnected?
Do you have degree marks on the balancer yet?

 

Well, going to a bigger pump shot might not have solved it.... Did you try smaller?
I mean, it sounds like your timing is set up fine, post what you did setup (ie. initial? mechanical? vac?)
I'd guess it's the carb....

 

I'll check this tomorrow and see.

And no, I just found my paint pen about an hour ago cleaning my room. I'll make some semi-accurate lines on the balancer tomorrow as well.

The converter stalls at 2000-2400, and according to the chart on the spring/weight thing, it would be about 15-17 degrees of advance at those rpms. So combine that with approximately 15 degrees of base timing, and that's about 30ish. It feels really good around there, just at 500-1500 if I mash it, then i get nothing.

Could this be any concern with the automatic transmission? I mean, it doesn't immediately downshift becuase of this bogging.

 

Assuming its not some other issue, then it sounds like a text book case of the transient fueling not being quite right. Messing with the timing will just mask the problem, and cause problems elsehwere. Id set the timing to whats typical for your engine, and take a look at the carb.

The easiest way to see how the motors running when this is happening is to just look out the back and observe the exhaust. Go to a LARGE open parking lot with no obstructions in front of you, open the door, look out towards the rear, and accelerate in the area that the car has the problems. If the car spews black smoke after it bogs/hesitates, then your going way rich. If theres nothing, or maybe a little grey smoke, then its way lean. Adjust the pumpshot or whatever you have to do with a carb untill it stops and there isnt any smoke.

Not ultra precise but it worked for me.

 

Could I get an oxygen sensor and do it that way somehow? That would be more accurate at least.

 

Oh, as for the timing, the settings that worked with my vortec 350 where around 20 degrees at idle, maximum of 40 degrees during cruise, and around 34 degrees of timing in around 3200 rpm at WOT.

 

Yes, and no. A narrow band based A/F meter from an autoparts store will be next to useless at all times. A quality wideband O2 will be invaluable for helping getting the car dialed in, but both will be of little use if its way off. The engine misfiring when its totally swamped with fuel can send lots of O2 out the exhaust, which will show up as a false lean condition. As with all of those, you need to take the apparent afr with a grain of salt.

If it is a pump shot problem, then doing it visually untill its sort of ok is the way to go initially. Then after that is the time youd switch over to a wideband if you had it to finish it up.