Engine: Need help understanding timing specs

[wdills]

Let me start by saying that I am not good at engine tuning. I also may be expecting more than my 259 can deliver. Everything is new, fresh rebuilt 259 engine, Dave T-bow rebuilt WCFB and Mallory distributor, new wires, plugs, etc. Engine starts easy and idles and runs nice and smooth.

My current problem is coming off idle. It doesn't want to accelerate if I open the throttle quickly. It will stumble and backfire through the carb every time. I thought I may have a problem with timing or advance so I checked it all this morning. I will describe what I found in a lot of detail, because I am not sure if I am interpreting the factory spec's correctly.

I started by disconnecting the vacuum line from the carb and plugging it.
Warmed up the engine and set idle to 600 RPM.
Checked timing and it was right on the ignition mark. I understand that this means 4 deg advance. Timing light was showing 0 deg advance.
I accelerated the engine to 2500 RPM and measure timing again. To bring the IGN mark back to the pointer I had to adjust the timing light to 19 deg. Centtrifugal only advance is supposed to be 22-26 degrees according to the specs.
Here is my first question, Do I add the 19 degrees measured on the timing light to the initial 4 deg for an actual centrifugal advance of 23 deg which is within spec or was I supposed to read 22-26 degrees on the timing light
Next step was to check vacuum advance. I had a vac pump connected to the vacuum advance. Engine back at 600 rpm idle.
Up to about 9" vac I got 0 advance.
At 11" vac I had 4 deg advance on the timing light.
At 12" vac I had 11 deg advance on the timing light.
At 15" vac I had 15 deg advance on the timing light.
I stopped at 15 because that is the amount of vacuum I am getting at the intake manifold at 600 rpm
So the Vac advance numbers seem to be pretty close to spec without adding the initial 4 deg.
Once all that was done I adjusted the idle mixture to the best of my ability. Both screws ended up between 1 and 1.25 turns open.
Engine will still stumble and backfire if accelerated quickly.

Took it for a test drive and the performance is un-inspiring. I can mat the throttle, the OD will kick out and it will begin to accelerate but there is no set you back in your seat acceleration going on. Maybe the 259 is not capable of that type acceleration, I have no frame of reference for comparison. I would hate to get in a race with the wife's 130 Hp Hyundia Accent.

So, are my advance numbers ok or do I need to make some adjustments to the vac advance?
Am I expecting to much as far as engine power and performance for this stock 259?

[karterfred88]

Sorry, I'm used to using a timing light without any built in "adjustments". I'd simply set the gun to zero, and set as per the manual-they didn't have fancy timing lights. The pointer on the cover, and marks on the damper must be right, but can be checked that TDC is actually TDC on the marks. Go from there- the vacuum advance should only be checked for max timing input--that is at anything over 13 in it should show the maximum amount built in. There really isn't any "curve" in the vacuum controller, just de-advances as vacuum falls, not very important for max power-engine will put out max power when it's disconnected entirely, it just won't run very well under light loads. As to performance- have you driven or ridden in another Stude with similar engine/trans combination? Yes, your Hyundai may be faster, and more fuel efficient. For comparison, read some road tests of the 50's and 60's for real numbers- a supercharged Avanti was considered quick at 7.0 seconds 0-60. Most economy cars of today unless set up to get 40 MPG will easily beat that-or come close. But they sure aren't as cool looking.

[rstrasser]

wdills;
Your timing sounds good to me. I do believe you add the 19 degrees you got to the 4 degrees advance to get total advance. The vacuum advance should be connected to the carburetor and not to the intake manifold vacuum source.
As for the stumble; it sounds to me that the accelerator pump is not adjusted correctly or not working at all. Remove the air cleaner and without the engine running look down the carburetor and see if you see a good stream of gas as you open the throttle. The stream should start as you first start to move the throttle.
Ron

[wdills]

Is there a max amount of advance that should be generated by the vacuum advance? I know that at 15" my advance was more than the highest value in the spec I have. I also know that when I went above 15" my advance went even higher. I can adjust it down if there is a max amount I should stay below.

Vacuum advance is connected to the carb. I just had a vacuum gauge connected to the manifold for reference. The accelerator pump works good with a nice shot of gas as I open the throttle.

I am more concerned by the stumble and backfire coming off idle. I am not as worried by the amount of power, just not what I expected. And no, I have never driven another 259 / T86 OD car for comparison. In fact the only other Stude I have driven is Dad's 50 Starlite 170 / T86 OD. Thankfully my Hawk makes more power than his Champion.

[11SecAvanti]

Zero on an adjustable timing light means (in a perfect world) that the damper marker 0 point aligns with the pencil pointer. That is TDC for the piston. If the spark were to occur at that moment the timing would be at 0 degrees. Your IGN line is valid ONLY for a standard timing light. So if your total timing on your adjustable light is reading 19 degrees when you dial the damper TDC 0 mark back to the pencil pointer then the total timing with no vacumn advance is what the dial reads (19 degrees). So you want this 23-26 reading to occur on the dial when you advance the distributor clockwise to line up again that TDC marker 0 on the damper with the pencil pointer. I would recommend at least 26 degrees total minimum. And if you want more power zip then go for 28-30 total mechanical advance. You have low compression and it needs some advance to have some zip. If I raced using factory timing specs I would never win. Set your idle up to around 750 also. Get the air speed moving faster through the carb so that the carb can get some decent plenum signaling from the engine. A 259 is a good engine when tuned and every thing is top notch. Good luck.

[altair]

Graduate back yard mechanic, I would put the timing light in my back pocket for now. Line up the timing mark at top dead center by turning the fan, also confirm it is number one. Remove the distributor cap and rotate the distributor until the points just start to open. That will put you at top dead center, now turn the distributor just a hair counter clockwise and re-tighten it. Recheck the position of the pointer at the timing mark and it should read at four degrees retarded. The moment the engine starts it will advance to just before top dead center and you shouldn't have to do any more than that. Another back yard test is to suck on the vac unit and put your tongue over the hole and it should hold the vacuum indefinitely, if it bleeds off the unit is faulty. When powering up a hill the vac advance becomes unserviceable and the centrifugal system takes over. The advance weights are inefficient at low speeds and the engine relies on the vacuum system for the required advance.

[doofus]

What is your vacuum reading at warm idle? sounding a bit like you need a valve adj. session. set them a little loose .026/.027 for now and drive a little. you should just hear a little valve noise with hood open.if there is no tapping their to tite. Gotta love those solid's! Luck Doofus

[Dan Timberlake]

Congratulations for daring to get so mechanically involved. Stick with it, and the financial and emotional rewards are many.

How old is the gasoline in the tank?
I'd catch a sample in a clean glass container when I was checking the fuel pump delivery, just before checking the fuel pressure.
It should be clean, have a distinctly sharp odor, not be the slightest bit murky or cloudy, and not get any clearer a minute after a splash of ISO dry gas is added.

This page looks to be from a Motors manual. FWIW It claims 18-20 inches of vacuum at idle.

http://restorecarsclassifieds.com/wiki/show_pdf.pdf?n=12794

I'd still check the valve clearance.

On most carbs The idle mixture setting affects the mixture at very small throttle openings to some extent too.
I'd back them out a bit for highest smooth idle and give that at try.

[Lynn]

As with all of my technical responses, I offer this caveat: I am new to the world of Studebakers, but have lots of experience with auto repair and maintenance in general. So.. if there is some Studebaker specific reason my methods won't work on a Studebaker, I would defer to Jack V., Rich, Skip, Fred, or any number of guys who are light years ahead of me when it comes to Studebakers.

I don't think it matters, but just to be sure, what year of 259 are we talking about? I have Sun tune up cards for every year from 56 forward, and believe they are all the same specs., apparently even for 8.3:1 compression, 7.5:1 compression and 7.0:1 compression, which makes little sense to me, but from a bean counter standpoint, would be nice, as different distributors and different vac advance cams would not be required, meaning it is cheaper to make them that way. HMMMM, maybe that is where the CASO dna came from... Studebaker bean counters? I will try to post a pic of the 1958 259 specs with this post, but have had some issues posting pics lately.

Sounds like you have a couple issues. One may be timing, but the other appears to be a lean misfire. As was addressed by rstrasser: "As for the stumble; it sounds to me that the accelerator pump is not adjusted correctly or not working at all." As Dan indicated, you can HELP that lean misfire just a bit by backing the idle screws out slightly. But really, that is more of a patch than a cure. It ought to transition from idle smoothly, and the accel pump makes that happen. So, for the stumble & backfire, make sure you have a good accel pump shot.

As for the general lack of power, here is my two cents on the timing. According to the attached tune up card (and the specs as you read them) initial timing is set at 4 degrees at 600 RPM. But, the mechanical starts coming in as early as 700 RPM (remember, engine speed is 2X distributor speed). Doesn't have to be far off to start messing with your initial setting. I am a firm believer that what matters MOST is the TOTAL of initial and mechanical. I have never seen an old school engine (pre-1970) that didn't run best (i.e. best combination of power and economy) at anything less than total timing of 32 to 34 degrees, and many at even higher such as 36 to 38 degrees. When I reference "TOTAL" timing, I am including ONLY initial and mechanical. Yes, I realize the absurdity of using the word "total" while excluding one of the parameters that contributes to advance.... that's just the terminology as it has come to be used in the performance world, so I will stick with it). Apparently, your mechanical advance is "all in" before 2500 RPM (maybe as early as 2250). I will get to the vac in a minute.

You have the advantage of a dial back timing light. Plug the vac advance, and rev it to 2500 rpm and set the total timing at 34 degrees. That is a good start. Now, if you want to see where your initial is (like I said I don't believe it is all that important in the grand scheme, but you may want to set timing after replacing points and make a note of where your initial is set on this engine for future reference, so you don't have to reset it by revving the engine each time).

Now, plug the vac advance in to a manifold source. It will be a non factor when under a heavy load, but will give plenty of advance when cruising under very light throttle. Adjust your idle back down (it will surely have increased) to 600 to 650, & adjust your idle mixture. I would guess your engine can take another 15 degrees of advance via the vac advance, but if that presents a problem, you can adjust it with washers, right?

Take it for a drive (no radio) and listen very carefully for any pinging sound (if you never heard pinging, it sounds like a bunch of marbles rattling around in a tin can). There will be naysayers who will point out that an engine may be pinging slightly but not be audible. Yes, possible, but mostly not doing damage if it is inaudible. If you want to be sure, but INCREASE the timing a bit more and drive it until you DO hear it ping, then back it off back to the 34 degree total.

Here is a link to a good article written by a friend of mine who worked for GM during the 60's and 70's. It helps explain the overall picture of mechanical and vac advance. It has no relevance on today's computer controlled vehicles, but applies to old engines. http://www.camaros.net/forums/13-per...nce-101-a.html

And finally, here is a pic of the 1958 Sun Tune up card.



BTW, I have tune up cards for almost every American engine from 1956 through 1966. If any of you guys want a copy front and back (you won't get one of my original cards, but I don't mind making a copy for you) just send me a PM. I will be glad to copy front and back (where applicable... some are blank on back) and mail it to you.

[Dan Timberlake]

Hi Lynn.

Is JohnZ still around ? I have a couple of questions I've been meaning to ask him for some time now.

thanks,

Dan T

[E. Davis]

Interesting article Lynn. I have always wondered about the wisdom and value of the ported system as opposed to full manifold vac and didn't realize it was an early "emission" control device. It will also be interesting to see what others think about this.

[Lynn]

I believe John is still around. Active in NCRS.

Will look for his email and send you a PM.

[gordr]

One other thing to check: make sure the copper braid ground wire from the breaker plate to the inside of the distributor body is intact and not frayed, and likewise the "pigtail" from the points to the grommet in the body, and thence to the coil is intact and not frayed. There is constant movement of that breaker plate, and both those wires can fatigue and fail, in which case the movement of the breaker plate due to change of vacuum when the throttle is opened can cause a transient miss.

[PackardV8]

One other thing to check: make sure the copper braid ground wire from the breaker plate to the inside of the distributor body is intact and not frayed, and likewise the "pigtail" from the points to the grommet in the body, and thence to the coil is intact and not frayed. There is constant movement of that breaker plate, and both those wires can fatigue and fail, in which case the movement of the breaker plate due to change of vacuum when the throttle is opened can cause a transient miss.

Good advice, Gord, for anyone who's tuning the old junk, but IRRC, Wayne has a new Thibault Mallory distributor.

jack vines

[rstrasser]

E.Davis and others
All I know about vacuum advance is that on my Avanti that is in the garage at my house has its original AFB and the Vacuum advance unit is connected to the Carburetor and not to manifold vacuum. When I put a vacuum gauge on the port that the vacuum advance is connected with the engine at idle speed (about 600 RPM) there is little to no vacuum at the port. As I increase the engine RPM the vacuum at the vacuum advance port increases. Once I am up to around 1500 RPM with no load on the engine the vacuum gauge reads the same at either the carburetor port or the manifold vacuum. Even though the engine vacuum (on the factory gauge is low) it is still around 12 inches or so at idle. Have not had the ambition to see if there is a leak as the car runs very well. And the thought of trying to get at the back of the factory vacuum gauge is not something that i look forward to.
Call the port that the vacuum advance is connected to what you want but it is not at engine vacuum.
Yes I read the GM fellows article; It just doesn't agree with what I have observed on Studebakers..
I previously checked my other Avanti that has a Elderbrock on it and I have it connected the same way. The other port on the Elderbrock is at manifold vacuum.
I do vaguely remember that some cars; after I was out of working in a tune up shop had full vacuum going to the vacuum advance unit at idle speed
Ron