Tuning Q after a tear-down ordeal...

[colo]

Hi guys, new member here.

I've had my current '72 C20 for about a year now. The engine appears to be out of a 1975 vehicle, likely a Nova.

The truck had a few issues under the hood I wanted to take care of:
-Pinhole radiator leak
-Rochester 2GC carb that was not in sound condition, even after rebuild and electric choke upgrade
-The 2bbl intake had EGR and other unused emissions equipment on it (my truck was non-emissions from the factory it appears)
-Water pump bearings were failing
-Clutch on mechanical fan was failing

Since I was pulling out the 2GC, I figured why not replace the intake and go to a 4bbl carb. So I took it upon myself to replace everything in one swoop, since it all involved draining and flushing the cooling system. Carb, intake, radiator, electric fan, starter (had distributor off by 180 and the engine kicked back against it and broke the nose cone off), fuel pump, fuel line, vacuum lines, thermostat, water pump, and a cheap $25 under-hood tach to assist with tuning.

Now it's two weeks later. I've replaced all the items and have the distributor back in, everything buttoned up. With the help of these forums I also took care of the resistor wire ignition issue that was left over from when the PO switched to an HEI distributor. I ran a new 12v unfused ignition wire to the cap.

Now I am down to tuning the carb and timing. I had never altered both of these components at the same time before. Also, I'm not certain if the heads on the engine are stock or otherwise. I've never had it out of the engine bay to pull the numbers.

I tried timing the engine with the vacuum advance off to roughly 4 degrees advanced as a starting point. The timing mark is jumping around a bit, about a 6-8 degree variation. So I set it as best I could, approximating the middle of the movement with the timing marks.

I took some time to try and reign in the idle mixture and idle speed on the carb but I'm having a lot of difficulty getting the engine to run well enough to get meaningful vacuum readings. Unfortunately the carb is second hand and I haven't identified the rods and springs installed yet. This is on the list for discovery tonight. The carb is from a local carb builder with a good reputation, so I don't have any reason to suspect the carb is damaged or improperly setup yet.


Should I spend more time investigating the timing issue, or hook up the vacuum advance since engine speed is unstable right now? Should I spend some more time trying to get a good idle mix and speed (and if so, any tips on getting it to be stable enough for a good vacuum reading)?

I suppose it is possible I have a vacuum leak, having replaced the intake. How can I determine if that's the issue?

This is ridiculously long... sorry. If anyone can help out I would be very grateful. Some equipment details are in my sig.

[tonypaul]

Which of the vaccum ports do you have pluged?

[K2Orion]

I recently did similiar work on my truck and am also having issues with my tune. Interested in the advice you get.

[Rideto100]

An easy and cheap way to check for vacuum leaks is take a can of starting fluid and spray a small amount at a time in any place you suspect of having a leak. If you spray an area and the engine revs up as if you're giving it a little throttle then you have a leak.

[oldgold70c10]

Get your timing issues figured out first. Find out why the timing is so erratic: sticking advance weights?, erratic idle speed from vacuum leaks, sticky valves, etc. Everything is dependent on everything else working right. get the engine idle speed stable first.

The idle mixture screws are just that-for when the engine is idling with the throttle almost completely closed. Turn the mixture screws in until lightly seated and then back them off 4 turns, then adjust the idle speed. That will give you a preliminary setting so the engine will run so you can set the timing. Now you can turn the screws back in, evenly, 1/4 turn at a time. Turn them in until the engine speed drops by about 50 rpm, then turn them back 1/4 turn. The recheck your idle speed setting and timing and you should be good. You have to do this with the engine hot.

Rod and spring sizes won't have any significant impact on idle, but they will at part throttle (anything between idle and WOT). Ar you having part throttle issues too?

[tncdrew]

Colo,
I've had similar issues since I installed a GM Performance 350/290HP in my '72 C20. After messing with timing for a while, (trying 8 degrees, 10 degrees and so on), I finally tried timing the engine using only a vacuum gauge, (forget the timing marks). Assuming all your vacuum leaks are corrected, simply disconnect the vacuum advance line from your distributor, plug the port at the carb, (no open ports), and connect a vacuum gauge to your manifold vacuum source. Adjust your carb idle screw, (mechanical not mixture), down to the lowest that your engine will idle, then advance your distributor to the highest/most stable vacuum reading on your gauge. If you experience pinging, retard the timing back slightly, (one or two inches on the vacuum gauge).
This method worked great for me!

See the attached link for some great Q-Jet advise. You can also search the authors name on the internet for other tips, (I'd say this guy is a Q-Jet guru)

http://www.scribd.com/doc/24720655/How-to-Tune-a-Q-Jet

Also attached is a good piece I found on Q-jet idle mixture adjustment.

Good luck!

[colo]

Originally Posted by tonypaul

Which of the vaccum ports do you have pluged?

Right now I have the 3/8" manifold port plugged with a pipe plug. The carb came with the rear 1/4" power booster plugged. I am going to pick up a barb adapter for it today; in the meantime I have the power brake and PCV on the front 3/8" PCV port with a t-connector. The right 3/16" carb vac port is plugged and the left 3/16" port is hooked up to the transmission module and vacuum advance.

When I originally made these connections I was guessing. I took a look in the manual last night and found the port assignments. I am going to move the power brake to the rear port after I install a barb, leaving it disconnected until then. Then I am unsure as to whether the dist vac adv and trans module go on the timed or full/manifold vacuum port. The engine does not have any emissions systems present and the fuel tank is unvented, except for the cap. Do HEI units always go on the timed port regardless of emissions?

[oldgold70c10]

Originally Posted by colo

Then I am unsure as to whether the dist vac adv and trans module go on the timed or full/manifold vacuum port. The engine does not have any emissions systems present and the fuel tank is unvented, except for the cap. Do HEI units always go on the timed port regardless of emissions?

Distributor on timed, trans on full/manifold vacuum.

[colo]

Originally Posted by Rideto100

An easy and cheap way to check for vacuum leaks is take a can of starting fluid and spray a small amount at a time in any place you suspect of having a leak. If you spray an area and the engine revs up as if you're giving it a little throttle then you have a leak.

That is a great idea, I'll give it a try. Thanks!

Originally Posted by oldgold70c10

Get your timing issues figured out first. Find out why the timing is so erratic...

The idle mixture screws are just that-for when the engine is idling with the throttle almost completely closed. Turn the mixture screws in until lightly seated and then back them off 4 turns, then adjust the idle speed. That will give you a preliminary setting so the engine will run so you can set the timing. Now you can turn the screws back in, evenly, 1/4 turn at a time. Turn them in until the engine speed drops by about 50 rpm, then turn them back 1/4 turn. The recheck your idle speed setting and timing and you should be good. You have to do this with the engine hot.

Rod and spring sizes won't have any significant impact on idle, but they will at part throttle (anything between idle and WOT). Ar you having part throttle issues too?

I've been looking for a good reference to get idle mix back to "base" settings. I had been starting at three turns out from seated, I'll see if 4 helps. Do most people use their ear to determine the rpm drop? I'm seeing lots of references to detecting 40 and 50 rpm changes in the manual and online but my tach is small and not very detailed.

As to part/full throttle I haven't attempted yet. Once I get the timing ironed out and she starts idling stable I'll take it out around the block.

Originally Posted by tncdrew

Colo,
....Adjust your carb idle screw, (mechanical not mixture), down to the lowest that your engine will idle, then advance your distributor to the highest/most stable vacuum reading on your gauge. If you experience pinging, retard the timing back slightly, (one or two inches on the vacuum gauge).
This method worked great for me!

See the attached link for some great Q-Jet advise. You can also search the authors name on the internet for other tips, (I'd say this guy is a Q-Jet guru)

http://www.scribd.com/doc/24720655/How-to-Tune-a-Q-Jet

Also attached is a good piece I found on Q-jet idle mixture adjustment.

Good luck!

I'll put the vacuum gauge on it and give this a shot, see where it responds best.

Thanks guys, looks like I have some good stuff to keep me busy today. I'll post back with results!

[GASoline71]

One thing about those old Q-jets is... the holes where the throttle blade shaft goes through the main body of the carb will get "egged out" over time. Causing vacuum leaks. The only way to fix this is to have the shafts removed, drill the holes oversized and have bushings installed. There are a few machine shops left in the world that still know how to do this.

But you might have to send it to a "carb shop" to have it done. Either Car Craft, or Hot Rod, or one of the bigger name magazines did a tech article on how to do it yourself.

Gary

[colo]

Originally Posted by GASoline71

One thing about those old Q-jets is... the holes where the throttle blade shaft goes through the main body of the carb will get "egged out" over time. Causing vacuum leaks. ...

I'll be sure to check that when I get the engine started up.

I got all the connections corrected and went to give her a start and the battery is dead/weak. So I put the charger on it and will go back out later.

In my original post I mentioned that I had corrected the ignition wiring for the distributor. I still had the old resistor-wire battery lead left over so I went to cut the spade off and cap it. I noticed there's a red wire and purple-orange wire jammed into it. I thought at first me having cut these apart was causing the low-volt start, but joining them together doesn't change anything. The charger is showing good draw so it does look like the battery drained for some reason.

Just by the colors of those wires anyone have a theory on what they are? It looks like they both run up the harness to the firewall connector.

[colo]

Ok, got the engine started and I think I have the idle mix dialed in. I can't bring it down below 1500 rpm or it will load up and stall. I checked against my timing light and the TDC marker isn't showing up anywhere I can see from up top. The engine doesn't sound quite right, either, which makes me hesitate to run any longer than a half minute at a time.

I tried disconnecting the vacuum advance to see if maybe RPM was high enough it was adjusting but no change, still can't see the marker.

^^While I was writing the above I remembered that my timing light has an advance dial on the back. I went out and double-checked that it was set to "0". It was. Is started the engine after disconnecting the vacuum advance and capping the timed port on the carb. For fun I dialed up the advance on the timing gun to see if the TDC marker would appear. After turning the dial to 60, the maximum, I saw the line approach the ~14 degree advanced mark on the timing plate. Turning it past the end of the dial to 65 or 70 brought it to the 4 degree mark on the plate.

Can this really be true? I wouldn't think an engine would run that far out of time. It would explain a bit, though.

[colo]

Alright guys,

So I got back to it today with a timing light on loan from my father-in-law. This one is known to be accurate.

Sure enough, it agrees with mine. The timing mark is appearing under the water pump near the lower hose outlet. I started retarding the timing and right around an inch from where the marker plate begins it completely bogs out and dies. Probably 15-20 degrees advanced at that point.

Is there some way for me to confirm that the balancer has/hasn't shifted? I hear later engines have the two-part dampener which can degrade and rotate separate of the crank. Since the code on the block tells me it's from a '75, perhaps I am staring down an inaccurate timing mark?

I just want to be sure I'm not dropping the little/no cash I have left on a part I don't need.

[oldgold70c10]

What kind of cam have you got?
If you get yourself a remote starter, disconnect the bat wire from your distributor, you can take out the no. 1 spark plug and crank it over with your finger over the spark plug hole. You should feel it blow air out on the compression stroke, and as it stops blowing, you should watch to see if the line on the damper is anywhere near the pointer.

You can also get a gadget that screws in the spark plug hole that will help you find TDC, but I'll let others chime in on that because I've never used one.

[colo]

Originally Posted by oldgold70c10

What kind of cam have you got?
If you get yourself a remote starter, disconnect the bat wire from your distributor, you can take out the no. 1 spark plug and crank it over with your finger over the spark plug hole. You should feel it blow air out on the compression stroke, and as it stops blowing, you should watch to see if the line on the damper is anywhere near the pointer.

You can also get a gadget that screws in the spark plug hole that will help you find TDC, but I'll let others chime in on that because I've never used one.

Unfortunately I don't know what cam is in the engine. This has been a major problem so far. The engine was timed 4.5 adv when I got the truck, and the timing plate has white paint on the 4 degree advance mark. There's also a white paint mark on the balancer separate of the TDC line, but I assume that was a slip when marking the plate.

When I reinstalled the distributor I used the loose #1 spark plug method and cranked from the cab until I heard a hiss. I went to the engine compartment, TDC mark was at 1 degree retarded on the plate, and I could feel the top of the piston through the spark plug hole with a wire. It was incredibly lucky and seemed to suggest that the mark was accurate. But how on earth could the engine run at ~60 degrees advanced?

I am willing to accept that the PO was a dolt, and everything on this motor could be completely fubar. It ran before the work I performed, but I wouldn't say it ran well. I had attributed this to the ailing 2GC carb and weak ignition.

[oldgold70c10]

That is odd. So you can't get it to idle below 1500 rpm even with the engine fully warmed up? Maybe the cam is not timed right with the crank. Just a tooth off either direction will make it run funny. Also, have you done a compression test? It sounds like you are on the right track with the timing mark on the damper.

[colo]

You know, I have a compression gauge. I will check compression tomorrow evening before I proceed.

[71 super]

Do you know for sure that the timing tab is correct for the engine? Is the motor a later model? chevy used two different timing locations and it is possible that someone has switched out the timing covers on the engine- then had to re-degree the engine hence the two white marks on the balancer. Take a look at the balancer and see if you can see any rubber protruding out from the two halves, this could be the indicator you need to replace the balancer as it may have slipped. To me, it sounds like there is a mix of parts -later engine and early timing cover. By chance does the engine have a long water pump on it?

[tonypaul]

I was thinking it could be the wrong timing tab to, or maybe the the wrong balancer- I think you did get the piston at TDC, so it should be good. Without fully seeing the engine Im only guessing but I would double check the following-

Make sure there are no vaccum leaks- check the line that goes down to the vaccum modulator on the trans.

Double check your carb gasket, you need to have one of those big thick gaskets for a quadrajet. Dont use those real thin style they will leak.

Who did the tear down of the carb? You sure it was do right?

Is the carb spitting? what color is you exhaust- black- grey, wht, none?

Will the engine come up in the rpm's smoothly or is it chocking or stalling?

[colo]

Originally Posted by 71 super

Do you know for sure that the timing tab is correct for the engine? Is the motor a later model? chevy used two different timing locations and it is possible that someone has switched out the timing covers on the engine- then had to re-degree the engine hence the two white marks on the balancer. Take a look at the balancer and see if you can see any rubber protruding out from the two halves, this could be the indicator you need to replace the balancer as it may have slipped. To me, it sounds like there is a mix of parts -later engine and early timing cover. By chance does the engine have a long water pump on it?

The engine had a short water pump on it to start, so I installed a short to replace it. I thought this was a little odd since the engine is newer than the truck but the alternator is on the driver's side, so I didn't give it a second thought. The double-groove pulley that is on there rides very, very close to the water pump housing though.

The engine block stamp numbers from the deck are:
V0712TYW
C772119514

The three groove pulley on the crank keeps me from seeing the front of the balancer. I felt around the back and I can feel the rubber ring sticking out evenly around the half I could get to, but I did feel a ~1/2" notch in it. I would say it's protruding from the back of the balancer's seam by 1 or 2mm. I have attached a photo. In the photo you can see the TDC mark, then a little further south the spot of white paint. Looking at the photo has given me a little more perspective and I bet that if I time the white paint mark to the paint on the tab she'll run. It seems to be close to the offset I am seeing.

Originally Posted by tonypaul

I was thinking it could be the wrong timing tab to, or maybe the the wrong balancer- I think you did get the piston at TDC, so it should be good. Without fully seeing the engine Im only guessing but I would double check the following-

Make sure there are no vaccum leaks- check the line that goes down to the vaccum modulator on the trans.

Double check your carb gasket, you need to have one of those big thick gaskets for a quadrajet. Dont use those real thin style they will leak.

Who did the tear down of the carb? You sure it was do right?

Is the carb spitting? what color is you exhaust- black- grey, wht, none?

Will the engine come up in the rpm's smoothly or is it chocking or stalling?

Since I'm not driving it right now I am going to pull the trans modulator line and cap the port on the carb. That will be one less variable. The carb was rebuilt by a local guy, Rob Mix, that builds E85 carbs and runs the site e85carbs.com . I swapped a rusting small block that I had converted to 4-bolt splayed mains about 10 years ago for the performer I have on the engine now (sig). I have the thin gasket on there now, I'll see about picking up a thick one tonight. This is a standard carb, not E85.

When I pulled the timing in yesterday to match the TDC mark the carb started spitting then caught on fire when it stalled. When trying to get it back to the setting where it ran it belched little fireballs here and there. Once back to about 60 advanced there was no more spitting. The exhaust smells rich and varnish-like but no noticeable smoke. I have been a little concerned by this; the entire time I've been messing with the engine I haven't had smoke in the exhaust.

When I first started the engine after getting the distributor back in she idled at about 1500 and pulled smoothly through 4000. I didn't go any further because it was straight header and I hadn't timed it. When it came back down from 4000 it went down into a stall.

I'm thinking that tonight I'll try matching up the paint mark on the balancer with the mark on the timing tab and see if it runs. I'll also perform a compression test, simply because I haven't yet and I really should have.

[68_chop_top]

My 1985 Suburban timing mark is shot from on top looking behing the water pump.
My 1968 Truck with a 327 is shot from the drivers side.
I agree that maybe you have a mix of parts.
You may have to do some investigating to correct parts and time your engine using the vacuum method until.

[colo]

I performed a compression test and here are the numbers. #6 is 25 PSI short of the highest readings, can you guys help me interpret these?

1 150
3 141
5 140
7 139
2 144
4 149
6 125
8 150

These numbers were taken when the engine was cold. Looks like the heads are older than the block since there is not an alternator mount provision on the passenger side head. There's only one bolt hole on that side and it is connected to the negative battery terminal.

It has become clear that I need to replace the timing cover with one appropriate for the block. When I take off the crank pulley and balancer to replace the timing cover should I replace the balancer as well? Any tips when performing this work? I've never pulled the balancer and timing cover off a small block before.

Also, I happen to have a bunch of performance parts kicking around in the garage. Included are timing chain and gears. Should I replace these while in there?

I'm thinking that if I can get the truck running then I could find time over winter to rebuild the engine. I have new:
Timing chain and gears
Roller cam (might be too lumpy for a truck... included a pic of the spec sheet)
Dual springs
Spring retainers
Valve stem locks
Hydraulic roller lifters
Cam bearings

Even have a set of 0.30-over pistons, rings, connecting rods, and pins... All these parts are from when I was going to rebuild the engine for my '68 about 10 years ago. The engine overheated and cracked a cylinder wall, then the engine came apart. Ran out of time and money, then sold the truck. Haven't had my hands on a Chevy small block since and the parts have been sitting.

[oldgold70c10]

Pass side alt mount only uses 1 hole in the head- all the later head I've seen only have 1 hole in the pass side front, look on the other end of the head-are there 3 holes?

Comp looks OK

You will have to drop the oilpan to remove the timing chain cover. Pulling the balancer is not hard, just use the right type of puller so you don't damage the threaded hole in the crank or the balancer. One that screws into the crank is the best.

[GASoline71]

That's a big cam... I run one a tad bigger... but my engine is set up to match that big camshaft as well.

Gary

[colo]

I just received a suggestion to drop the bolt off the balancer and look at the keyway location on the hub vs the TDC mark. Apparently if the keyway is pretty much in line with the TDC mark I time off the 2 o'clock position. If the keyway is offset by "an inch or more" then I time off the 12 o'clock position.

Anyone think this is a legit method? I'll take a look at this tonight just for the heck of it. Having trouble finding timing covers in stock locally.

I'll also be pulling the valve covers to replace the crap gaskets I got last time. So I'll make sure that TDC is accurate and both valves are closed on #1 just to be sure.

EDIT: I'm going to make a piston stop out of an old spark plug and turn the engine by hand to ensure the TDC mark on the balancer matches up with the tab and actual TDC. If not, I'll mark a new TDC location on the balancer using the existing tab. Thinking that I am going to mark the pulley as well since there's a chance the balancer ring is slipping. Just learned this trick, seems like a reliable way to be certain.