Engine runs rough with vacuum advance hooked up

[The_Handier_Man1]

From: olivereaman  (Original Message)
Sent: 12/26/2004 12:56 PM

I got the 1971 Winnebago with a Dodge 413 engine after setting for many years. The previous owner, my brother, said it ran perfectly when he parked it, except for one brake booster which he had plugged off on the last run. When I tried to get it running again. the engine fired right up and proceded to backfire through the carburetor and it ran extremely rich. The gaskets were bad in the carburetor. After rebuilding the carburetor and installing it, the engine fired right up but ran very badly. I put new points, condenser and plugs in it and it didn't make any difference. I checked all the lines for a vacuum leak, and didn't find any. In the course of looking for things I pulled off the the vacuun line to do a vacuum test and the engine cleared right up and ran like a champ. I plugged off the vacuum line with the vacuum gauge and had more than 19 inches at idle. As soon as I hooked the line back to the distributor, it ran very badly again.

Does anyone have any ideas? I've actually thought about going to an electronic set-up and doing away with the 70's stuff. Has anyone tried this? And if so how does it perform?

Thanks for any help That I might get on this.

                                                             John   



From: Liv42dayOK
Sent: 12/26/2004 1:23 PM

I have exactly the same problem with mine.  Unhooked--runs fine.  Hooked-up... egad--it's terrible!  So, I'll be very interested to see how this turns-out.

One item I read was to change the diaphram in the distributor where the vacuum line hooks in.  The engine will run smoothly without the line hooked-up but the gas mileage will suffer running like that.

I'll also be changing to electronic ingnition but, that in itself should have nothing to do with it. -Sob



From: olivereaman
Sent: 12/26/2004 8:07 PM

Hi, thanks for the reply. And sorry to hear you have the same problem. I really don't know very much about distributors and vacuum advance other than it sets the timing for the load on the engine at whatever rpm that it's running at.

I'm thinking there is a spring and/or weights or something that balances the vacuum and allows the timing to change as the vacuum changes . But....I could be miles off on this. If I can't get anyone with experience to guide me, I'll just rip into it and see what I find!! However, that's not my preferred method!!
   

                                       John



From: HeavyHaulTrucker
Sent: 12/26/2004 9:05 PM

John, actually the "weights & springs" you refer to are called the mechanical advance.  They provide advance to the timing based on engine RPM when vacuum is low -- such as on acceleration.  When you reach cruising speed and back off on the throttle, the vacuum rises and allows the vacuum advance to kick in and further advance the timing to improve gas mileage

There are two common problems with the 413/ 440 "RB" engines that can cause this:

1.  The dampener, on which your timing mark is scribed, has a tendency to "creep" over the years.  This can cause your base timing to be off by several degrees -- and if you start off out of time, the mechanical and vacuum advance just further aggravates the problem.  Result?  It runs like crap.

2.  Over the years, the springs in the mechanical advance can wear out -- remember, even though they aren't being used, they have been under tension since 1971.  This loss of tension causes the weights to fly out early, advancing the timing more than it should be -- then the vacuum further advances the timing, causing it to run like crap.

You can check for the existance of the first problem by pulling #1 spark plug and bumping the engine over to where the #1 piston is at TDC on the compression stroke.  You might use a socket & breaker bar to turn the engine that last couple of degrees -- you want it right at Top Dead Center.  Now, look at the timing mark on the dampener -- does it line up with zero on the degree scale?  If not, then that is how far your dampener has crept.  The cure to this problem is simple -- take a white paint marker and mark the normal timing mark on the dampener, then take a black paint marker and mark the new TDC position on the dampener.  Once it is dry, re-time the engine based on the BLACK timing mark, ignoring the white one.

There is a "quick & dirty" method to check for the existance of the second problem, but make sure that you don't have problem number one first.  Have a helper run the engine at 2500 rpm -- STEADY -- while you strobe it with a timing light.  It helps to put a timing tape on the dampener beforehand so you can see the total advance.  You should have a total of 35 to 38 degrees of total advance at 2500 rpm -- if you have more than that, and your dampener has not crept on you, it is a safe bet that your distributor is worn out.  The only cure is to replaced the distributor.  This is not the major engine surgery that it can be on other engines, though.  The Dodge RB-engine distributor can only go in two ways -- correctly, or 180 degrees out of time, and it is a 1-bolt swap.  Reman'ed distributors come ready to roll -- pre-gapped and everything, all you provide is rotor & cap.  Just note the general position of your rotor on the old one, and mark the hold-down to give you a reference when you bolt it back down, before you pull it; when you put the new one in the hole, set the rotor to the same rough position.  You will feel the tang on the end of the distibutor shaft go into the slot on the cam gear when it is properly in line, and it will slip "that last little bit" into the hole.  If you have marked the hold down accurately, most of the time you don't even need to re-time the engine -- but it is a good idea to at least check it.

John



From: olivereaman
Sent: 12/26/2004 9:50 PM

Thanks HeavyHaulTrucker,  I don't know if the dampener has moved, but I'll for sure check it. The part that makes me suspect something came unglued in the distributor is that my brother told me it ran perfect when he parked it. I don't know if the gaskets in the carb started leaking because of age or the backfiring that was taking place.

So.... I guess I'm not sure if the carb leaks caused the problem by making the engine backfire through the carb.,  or if the distibutor malfunctioning caused the backfire that caused the gaskets to go.

I really appreciate the tips on changing the distributor. I don't have too much of a problem about working on things once I have a clear understanding of the task at hand. You seem to have a good grip on these things so if you don't mind, A QUESTION: can that TOTAL ADVANCE  be measured with the vacuum advance disconnected, because the engine will never acheive that speed with it connected? If not, is there another way to see where the mechanical advance is? Can I disassemble the distributor, and see if there is anything visibly wrong? I'm not a Dodge man, and besides that, I really don't know alot about distributors. I can rebuild an engine as long as the distributor fits and works right!! Most of my experience is with farm and construction equipment.

Am I correct to assume from your post that if the distributor is indeed broken inside that it is scrap, or can it be repaired? If it can be repaired, does it have to be calibrated or it just a matter of replacing parts? If it can not be repaired, is there a core value on it? Also I'm wondering about getting the same timing curve as it was originally, because my brother said the motor was very strong. He took it over the Rockies and said he passed just about everything going up over them.

We're right in the middle of a cold snap in NY right now, so I've been a little reluctant to work on it until the weather warms up a bit.

I know that's a lot of questions and thank you for any input you can give me.

                                Thanks again, John



From: HeavyHaulTrucker
Sent: 12/26/2004 10:28 PM

John,

First of all, the carb leaks were probably caused by sitting.  Chances are that it has a ThermoQuad?  They are bad about gumming up from sitting, and the venturi seals in the bottom of the primary metering jet venturis are the main cause of flooding.

Yes, I forgot to mention it -- you want to check total advance WITH THE VACUUM LINE TO THE DISTRIBUTOR DISCONNECTED AND PLUGGED.  You are checking total mechanical advance, and you don't want any vacuum making the test inaccurate.

You can take the advance plate out of the distributor, such as you would when changing the pickup coil, and the mechanical advance mechanism is right below that.  But the springs & weights are not available separately, and you have to completely dismantle the distributor (pull the inner shaft, etc) in order to change the weights -- the springs can be changed easily, but replacements are not commonly available.  The distributor only costs $50 at O'Reileys (exchange) and you can change it in 15 minutes right there.  A case of cost versus benefit, I guess.  Oh, also, there was only one distributor timing curve for the RB engines.

Before you do that, though, I would check some of the more obvious things.  Now, what I am going to suggest is based on experience:
Change to a lighter weight oil (especially in cold weather) that will allow the lifters to fill quicker; a heavy oil will keep the hydraulic lifters from filling quickly or completely, changing the valve timing perceptibly.
Flush out the engine real good with "Mechanic In A Can", Gunk's "MotorFlush" or an equivalent product.  After sitting for a couple of years, the lifters may be gummed up -- this will clean out the engine and get rid of any sludge or varnish that has formed while it sat.
Run 1/2 pint of Sea Foam through the carb (per instructions on the can) and put it in the oil and gas tanks as suggested.  You will be amazed at the difference!
Check for a loose spark plug; I have spent a couple of hundred bucks to fix a problem and, I found out later that one of the spark plugs had loosened up a bit.
Check the number 7 & 8 cylinders to make sure the plug boot hasn't come off -- being out in the airflow makes them come off sometimes.  I had #8 come off on me and flap in the breeze -- the was a small decrease in performance, but I found it only by chance when I stuck my head into the passenger side wheel well for something else.
Check the distributor cap itself, that it is on the right way.  When I first bought my Winnie, it ran like a bat out of hell.  Later, in the course of doing something else, I noticed that the distributor cap was on backwards (turned 180 degrees).  Well, the Dodge cap can only go on one way -- it has a notch in the cap that fits down on a wide pin on the distributor housing.  When the PO put the cap on wrong, the hold-downs made it sit at a slant -- it ran fine that way, until the first time I had to take it off.  Come to find out, the "slant" had worn the inside of the cap and the rotor lopsided, so when I "fixed" the problem the engine wouldn't run at all.  I had to replace the cap & rotor just to get it to start.
Check all of your vacuum hoses, especially those on the driver's side of the engine -- they are particularly susceptible to heat damage.  I recently replaced ALL of my vacuum lines, and noticed a big boost in performance.  Even though they might look good, old rubber gets porous and will actually leak right through the hose.
Don't use the fancy Bosch "Platinum" spark plugs.  First, they weren't meant to run in older. low compression engines; second, the protrusion on them is too far -- the electrode is too far out to get the right ignition flame pattern, and it is susceptible to fouling too easily.  And, when they get gas on the electrode (like when you first start up and the mixture is a bit rich) they won't run worth beans.  Believe it or not, good old Champion RV12YC plugs gapped at .035 are the best bet -- they have an anti-fouling design, and the protrusion is just what MoPar calls for.

John



From: olivereaman
Sent: 12/27/2004 9:37 AM

John,

        That's a wealth of info you've given me. Thanks a Lot!! I actually did most of things you have suggested, with the exception of the Sea Foam. The Carburetor is a Holley Carburetor, Model 6189, 600 CFM. I had to go to Holley with the numbers off the carb and they told me the number of the rebuild kit and I had to purchase it through JC Whitney. I can't remember the exact price, but it was around $40.00, shipping included. The whole procedure was very smooth, although you would think that it would be almost a nightmare! When the parts came, they were exactly the correct ones for my carburetor.

I don't have an O'Reiley's around my area but have had very good luck getting things from Advance Auto. So I think I'll give them a call and see about getting another distributor. I fully expect to have many years of fun with the old Winnebago and my family,. (Mostly Grandkids and Wife) so I don't think an extra $50 or so is a great sacrifice. I'm kind of a nut about understanding things down to the smallest detail, so I thank you for your patience and guidance in this one.
    It'll be a few days before I actually get around to doing the job because I don't keep my garage heated unless I really need it with fuel oil around $1.90/gal. Right now the ole thermometer is sitting right on -1F.


                                         John



From: denison
Sent: 12/27/2004 12:22 PM
 
       In the service manual for the 71 413-1 engines, it gives the max Vacuum advance as 11.5 degrees, @ 12 inches of vacuum.  The Centrifugal advance is given as a max of 14.5 degrees, @ 2000 rpm.   So with no vacuum advance, the ignition timing above 2000 rpm would be 14.5 plus the 5 degrees BTDC of the basic ignition timing, or 19.5 degrees.  With the added advance from the vacuum, it would be  19.5 plus 11.5 more, or 31 degrees total advance.   At least that is what it would have been when new - some minor change in the advance curve can be expected from normal aging.    Its enough of a chore just to do the timing at an idle:  I have never tried to run a check of how my ignition advances at higher rpm.    My engine seems to run well at all speeds, so I havent had the need.    <o:p></o:p>

      About your problem with misfiring when the vacuum hose is connected to the vacuum diaphram on the distributor: <o:p></o:p>

     I would take a close look inside the distributor, at the plate assembly the ignition points are mounted to.   It has a lower part, that is held in place by screws coming in from the sides of the distributor- I think.  Its upper part must be able to swivel when the vacuum diaphram arm pulls on it, but still be firmly grounded to the lower plate, and still hold the points in the proper position so the point gap (dwell) is not affected much.    If its ground connection was bad, or if it gets cocked/tilted when the vacuum advance is pulling on it, that could cause the misfiring symptoms you have.    If you pull a vacuum on the vacuum diaphram with the distributor cap off, you should be able to see the movement.    Thats the vacuum advance.     <o:p></o:p>

     You want to make sure your centrifugal advance mechanism is free.   With the distributor cap off, but the rotor in place, you should be able to twist the top of the distributor shaft counter-clockwise 7 degrees, with a thumb and forefinger, and it should spring back readily when you let go.  As the distributor turns half crankshaft speed, you would only see 7 degrees of rotation, not the 14 degrees you would see at the crankshaft with a timing light.  7 degrees isnt much, but it would be visible.  There is a lube point in the end of the distributor shaft, under the rotor.  You put a drop of oil on this about each 10k or 20k miles.  It is very possible it has never been oiled.  If it gets sticky it can result in the ignition being stuck in an advanced or partly advanced position.  If it was stuck, and you then had set the ignition timing to 5 degreess BTDC at an idle, you would have feeble power above 1500 rpm.  That centrifugal-advance-with-rpm is vital to efficiently converting the burning fuel energy into crankshaft torque.  <o:p></o:p>

      Vacuum advance is a different story.  I doubt you would be able to tell by driving the RV whether the vacuum advance was connected or not.   Your miles per gallon would be a bit lower though.    Gasoline vapors burn faster if they are more compressed.  At small throttle openings the smaller quantity of fuel/air mixture wont be  compressed to nearly the pressure it would be if you had the throttle wide open.  Therefore the mixture has to be ignited sooner -- since it wont be burning as fast.   Otherwise the peak of the combustion process would occur after the piston was already too far down on its power stroke.    Thus the reason for the vacuum advance.   Since our motorhomes spend a good bit of their operating time at large throttle openings, the vacuum advance isnt such a big deal.    The air cooled volkswagens beetles and buses didnt have vacuum advance at all.   <o:p></o:p>

    Most of our old mopar V8s used ported vacuum for the vacuum advance.  That is to say there was no vacuum in the line to the distributor at an idle, when the throttle was shut.  You had to have the throttle plates in the primary carb throat partway open to uncover the vacuum ports, then the distributor would see the vacucum and would advance.    Many carburetors have both ported and unported vacuum pickoffs.  Unported vacuum just means you get the same vacuum at an idle as the intake manifold sees.     Later model vehicles with emissions controls might have unported vacuum going to the distributor, via some thermal valves probably, or to other parts of the emissions control system, like the vapor cannister.  But our early 70s vehicles were only made for ported vacuum to the distributor.



From: HeavyHaulTrucker
Sent: 12/27/2004 8:01 PM

Ooops!  I forgot to subtract out the vacuum advance before I told you the total advance to look for!  But it is 8 (initial advance) + 20 (mechanical advance) = 28 degrees of mechanical total advance.

John



From: olivereaman
Sent: 12/28/2004 8:25 PM

Dennison, I really feel that you might be on to at least part of my problem with the idea that the distributor may be stuck in a advanced position. My brother told that the Winnie ran perfect when he parked it. It started right up as soon as it got some gas. I can't remember for sure if I revved the engine, but my guess is that it was on high idle because of the automatic choke. If it was stuck and the vacuum advance moved the timing another 10 or so degrees, that could be be way off where it should be. Another question, when I took a vacuum reading at the distributor end of hose it showed 19+ inches of vacuum at idle. If in fact, it uses a ported system,  shouldn't I  have a very low vacuum reading ? I had just renewed the carburetor using the kit that Holley specified, could it be possible that did something to allow the ports to be opened when the should be closed. I didn't remove or alter the throttle plates in any way. Another thing that might have some bearing on the matter, when the engine started up, it proceeded to backfire through the carburetor and I mean SERIOUS backfire. When I removed the vacuum line she cleared right up and purred like a kitten. Now that I think about it, the motor seems to turn over very hard when starting, I just assumed the starter was going bad, but maybe the timing advance is working against it. Any thoughts? I'm probably just getting carried away with my thinking AGAIN. I really appreciate all the help you provided. I doubt I would have ever came up with lubricating the distribor shaft, that was a great tip!!

                                                            Thanks again,

                                                                John



From: DaveVa78Chieftain
Sent: 12/29/2004 9:44 PM

You can use a hand operated vacume pump available at most any auto parts store, to check vacume advance.  With engine off, remove the distributor cap and then remove the distributor hose from the carb and hook the vacume hand operated pump up to the distributor vacume advance.  Pump the tool until you get 12 inches of vacume.  While pumping the tool up, watch the point plate and it should move.  If it doesn't then either the vacume advance is bad or the point plate is bound up.  Additionally, once pumped up, the vacume should hold staedy (not bled off).  If it does bleed off, then the vacume advance diaphram is defetive or you have a leak in the hose from the carb to the distributor.  Same concept works on a electronic ignition system too.  The vacume advance hooks up to the plate the pickup module is mounted to which is movable.  That is the plate you watch on electronic ignition systems.
The vacume pumps can be used to check any item that uses vacume as a source for operation.  They can also be used to bleed brakes which can be a pain though because air is sucked in from around the bleeder screw threads. 

Dave