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Discussion Starter #1
Alright so I'm at a total total loss here. I've posted before about this car. '68 Mustang with a '73 302. A week ago I had to have the distributor all the way to the left touching my thermostat housing. After taking the rebuilt carb off, I noticed the economizer valve on the bottom of the carb was warped. I had an extra one and I put it in and I was able to put the distributor right back in the middle where it's suppose to be. It has a new timing chain, firing order is right, timing is dead on. 3rd new fuel pump in less than two months. New cap, rotor and distributor/vacuum advance. New coil. New plugs. New wires. Pertronix ignitor (it had the same problem before with the points too.) Carb was rebuilt. In idle, 15 on the vac gauge. No vacuum leaks. Oil has less than 200 miles on it and is clean as a whistle. Gas is clean as a whistle. Carb bowl is clean and full. New fuel lines, away from heat so no vapor lock. Plugs were a little fouled today, but not all of them. Dry fouled, not wet.

The car starts EVERYTIME with just a half pump of the accelerator. And it idles and runs perfectly. No misses, no sputtering, no ticks. Shut it off after letting it run for 10 minutes, fires right back up no problem. I took the valve covers off of both sides, and everything seems to be ok. I even took the push rods out and none are bent.


So here's the problem. If I put it in gear, it runs a-ok. Smooth as can be. But as soon as I get it up to about 35-40, it starts to bog down, and starts making a "pop" in the carb. Not really a backfire, more like a burp. So I took it out of town tonight on a back road, and all the way getting it up to 55, it was making this popping sound through the carb. Well I turned right, and it started to lose power, and it died. But it started right back up with no problem. So then it wouldn't even go up to 30 and then it came out of it and got back up to 55, still burping. So I took a right to circle back into town, and it started to stall but I tapped the gas and kept it from dying. And then I just got into it and it got up to about 100 and it ran like a pi**** ape. It ran perfect. So I came to a dead stop, took another right and it started actually backfiring. I could see it under my hood!!!! So it would only do about 30 again. Came into town and I had to baby the pedal all the way home to keep it going as soon as I got in my driveway, it died on it's own. And the smell of fuel was really really rich when it shut off. It had even sprayed gas on the bottom of my hood. (running with no air filter so in case of a serious back fire) It also seems like hit and miss, the RPMS have to build up a bit before it will shift. Other times it shifts fine, but still has the popping going on.


I'm totally lost guys.:crying:

Today I heard a bit of a squeal. Not sure if it' was from the belt or what. What would be the signs of a bad cam? Does it sound like it's the carb? It just idles/starts too good and easy and that's what has me lost. And it runs so smooth going up to 30, and then splat. Only have a couple months left and after putting a whole new front end under it over the spring part of summer, it does this to me and I've only got to drive it about 3 times only to try to figure out what this deal is. As usual, any help would be great. Thanks guys and drive safe. :grin:
 

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You sound very frustrated and I would be too. I will throw in my opinion to start the ball rolling for more experienced guys. I am leaning toward timing. Are you sure the new timing chain was lined up perfectly? You would still see the correct timing with a light but the cam would be advanced or retarded. My other thought is with the mechanical advance in the distributor. Check that the weights and shaft are free to move and the springs are both there and not rusty. You said that you had the same problem with the points but you might reinstall them in case you have cured the original problem and the pertronix is giving you a new problem.
 

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I agree with above ...also.....because of the alcohol enriched fuels, they can create pinholes in the fuel pump diaphrams......typically symptons are initial missing at high RPm slowly/progressively getting worse at lower RPM's...idle speed is typically good....up to about 35-40 mph.
 

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Discussion Starter #4
You sound very frustrated and I would be too. I will throw in my opinion to start the ball rolling for more experienced guys. I am leaning toward timing. Are you sure the new timing chain was lined up perfectly? You would still see the correct timing with a light but the cam would be advanced or retarded. My other thought is with the mechanical advance in the distributor. Check that the weights and shaft are free to move and the springs are both there and not rusty. You said that you had the same problem with the points but you might reinstall them in case you have cured the original problem and the pertronix is giving you a new problem.

Yes very frustrated. Yes the timing chain was set right. The vacuum advance is working in the distributor. It wasn't on my old one, I sucked on the vacuum hose and the arm wouldn't move. So that's why I got a new one, and I put a vacuum line on the new one and it worked like it was suppose to. One thing that has got me, is how I had to advance the distributor all the way to the thermostat housing, (literally touching up against it) but after putting that economizer valve in the carb, I can set the distributor right in the middle where it's suppose to be and it idles perfect. Both in park and initial take off. That's the last thing in the world I would have ever thought about looking at.
 

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Discussion Starter #5
What would the signs if a bad or wiped cam be? Like I said, for as good as it starts and idles, it has to be something small.

One thing I forgot to mention though is when it's in park, every other rev will make it puff a little white smoke out of the carb. I can rev it a few times and it will sound good, then it'll puff. Then I can rev it a few more times, and then it will puff.
 

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First, slow down. Old school methods always work. An engine needs three things to work: fuel-air, spark and compression. Of these, the least dependable (and least expensive) is spark, the most dependable (and most expensive) is compression. So work with spark first, compression (including a cam) last.

Check that your distributor rotor is pointed at the #1 plug when the #1 cylinder is at TDC of the compression stroke. I've explained how to do this in other threads and there must be thousands of youtubes on it so I won't repeat it here.

Modern fuels burn slower than when Ford made your engine so forget the factory recommendations and set your initial timing to about 14 to 16 degrees before TDC. Do this with the vacuum advance disconnected and the tube plugged. Once you get the car idling and warm check the mechanical advance. It should start to increase at about 1500 RPM and advance smoothly a total of about 18 degrees by 3500 RPM. Your vacuum advance should be connected to a port above the throttle plates. Test that with a vacuum tester- it should increase the advance about 6 degrees.

Do all that first and let us know how well it runs.
 

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What would the signs if a bad or wiped cam be? Like I said, for as good as it starts and idles, it has to be something small.
As Yadkin mentioned, you are imagining the least likely cause to be your problem. You don't have a cam problem. Your engine starts and runs as it should until 40 MPH. That says either fuel or timing to me. Bad cams are bad at any speed.

If you want to check your cam then do a compression check of your engine. If you have a problem you won't have much, if any compression on your 'bad' cylinders. I expect they will all measure as they should.
 

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I'd look at float level in the carb. If it is too low, it will start and run fine until the engine starts requiring more fuel than the bowl holds. No matter how much fuel pump capacity you have it won't compensate for too low a float setting. I agree with the comments regarding the basics and the chance of it being a cam issue.
WDZ
 

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just because the coil and dist. is new does not mean they are good. Many people have problems with the petronix stuff. try a ready to run distributor from summit or the like. The on again off again problems sounds electronic to me. Also dont assume the firing order or plug connections are correct, go over it with a second party to verify it.
A bad cam is where the lobe is wiped off and there will be a constant dead miss.....all the time. Verify you installed the plug wires in the correct order in relation to #1 and rotation of the dist. rotor button...my $.02 and make no mistake a new bad coil will do almost exactly what your car is doing. Also is the engine to chassi ground in place and in good condition?
 

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Seems silly, but it sounds like you have a rag or something that got stuffed into your gas tank and is intermittently sucking up onto the pickup tube. A quick way to tell is to drive around with a fuel pressure guage hooked up. You'll see the fuel pressure drop right before it starts to run poorly. Hey, you never know.....
 

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Many good places to check mentioned. I will put in my two cents. I believe the small hidden hint could be in the white puff of smoke in park. White smoke (in the form of steam) can always be water. However, your transmission fluid will also burn white (not steam) and you may be sucking off transmission fluid at periodic intervals. Check you modulator and fluid levels to start. You might also have someone run behind you an look for white smoke at certain speeds as an unsophisticated way of checking for more evidence.
 

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Discussion Starter #12
Alright so I got some...."good" news. I took my vacuum hose off of my distributor to reroute it. I put it in top of my overfill hole on top of my carb, and I heard the rpms change and the motor started idling perfectly. So just for the heck of it, I drove it, and the problem I had is gone. No popping, no hesitation etc. And if I pull the hose back out of the carb, you can hear the rpms change and if you drive it, it starts doing the popping again. I have an open face breather with knockout holes in the bottom, so I knocked one out and I ran a vacuum hose up through there and it runs like it did after the motor was rebuilt.

Anyone have an idea as to what is going on? I've worked on a lot of carbed motors and never had this problem and nobody else has any ideas either. But that's what I came up with guys. Thanks for all the help!
 

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There are (basically) two types of vacuum connections on the engine. One is below the throttle plates on the carb (manifold vacuum) and the other is above the plates (ported vacuum). Manifold vacuum is highest at idle and lowest at Wide Open Throttle (WOT) Ported vacuum is the opposite.

At the factory your distributor vacuum advance was connected to ported vacuum, and initial timing set to 8 degrees BTDC. Mechanical advance would start just off idle to 24 degrees or so at 2500 RPM. Vacuum advance adds in about 4 degrees. Total is not 8 + 24 + 4 because the total advance is limited to 24, so the vacuum just changes the shape of the curve, depending on your throttle position.

50 years later and pump gas has changed significantly. It burns slower. Ideally initial timing should be in the 16 or so range, and the mechanical advance should begin at 1500 RPM and add 18 or so at 3500 RPM.

It is difficult to re-curve an original Ford distributor for these "new" conditions. Instead some guys attempt to mimic the new timing by using manifold vacuum for their distributor. Play around with the math a bit and you can see how that "kinda" works.
 

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What I ended up doing was to replace the distributor with a Pertronix. It comes with 3 pairs of springs, three sets of limiters, and these are changed easily on the unit without removing lots of parts. The points are replaced with a trouble free electronic system. It's about 1/2" taller than stock so clearance issues with the stock air cleaner have to be addressed.
 

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so it sounds like at the end of all this the problem is over advancing , I had similar issues a while back with pertronix fitted to a 289 in my 66 ,the air gap is critical........and I had to open it slightly over the supplied "plastic" gapper to get it to run nice ...it did in the end ....but also remember with pertronix need a full 12v feed and a matched coil is also critical for the system to run 100% and last.......when u run them thru the original wiring they only get 9 -11v and they work but in my experience dont last.......just saying , cheers glad its running ,cool !!:wink:
 

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Your description of what you have done it not very clear so I am not sure what you did. However, its is plenty easy to have too much vacuum advance if you just bought an advance unit and stuck it on your distributor. They have to be adjusted for your engine with proper shims under the internal spring and also be fitted with the appropriate stop to limit the amount of vacuum advance. The bare parts you buy aren't even close to what your engine needs.

There were dozens of different setups over the years so you need a shop manual for the year you are trying to recreate. For a '66 the static advance was 6 degrees, mechanical added anywhere from 18 to 30 degrees at 4000 RPM and vacuum advance was anywhere from 12 to 22 degrees with 15" of vacuum. Your total advance will never be the total of those maximum numbers since that isn't how it works. At high power/RPM you will run out of vacuum so that advance goes away. Vacuum advance is only used for better MPG. Many 'performance' engine don't use vacuum advance at all such as the Ford HiPos. Setup your distributor per the shop manual specs and it should run fine.
 
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