67 GTX 440 - Poor Driveability Issues, Need Help

[RT K_line]

Sounds like too much cam duration and too little stall speed.

 

[747mopar]

Unfortunately re-curving the distributor is trial and error which is why it's important to get a rough idea of where it should be from the beginning, another option is sending it to FBO (they'll set it up matching it to your needs) but it can be done yourself but plan to pull it multiple times. One thing you could do is try different initial settings, go out and test the throttle response and acceleration but not upper rpm's and see where it likes it then do the same only testing upper rpm's. Once you find what makes it happy in both rpm ranges you should have an idea of where how much advance it needs. Like I mentioned before using a vacuum advance allows a lower initial setting for easy starts while the manifold supplied vacuum advances it once started helping with the doggy throttle response. Like mentioned it's best to figure out the cam timing and specs first otherwise your chasing your tail when it could be the cam.

As far as plugs go I like NGK's not that it matters but they lasted the longest back when I raced motorcross under extreme conditions so I never looked elsewhere.

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Sounds like too much cam duration and too little stall speed.

I agree with this but you need to get it dialed in without any missing before you start thinking about swapping converters, it might wake up once the other issues are resolved.

#1 confirm the easy things like ignition issues, plugs, wires, etc.... fuel pressure, etc

#2 confirm cam specs & timing

#3 confirm compression

#3 resolve timing

#4 tune the carb

 

[coloradodave]

I still would go by what I stated (Post #12) about doing all the diagnostics before throwing parts at it. Any of the basic things like distributor cap/rotor condition and plug wire/plug viability could be causing the "half missing" condition. As far as re-curving the distributor, the easiest, fastest way is to have it done by a competent speed shop or send it to Don at FBO (http://www.4secondsflat.com/). You can do it yourself with a timing tape and a timing light, but as 747mopar said, you'll spend a lot of time pulling and re-installing the distributor, and need to have brazing/welding skills available. Your call. First get the motor running smooth through the RPM range. As far as plugs, I use NGK or Autolite (whichever are cheaper), but I've never had a problem with AC, Champion or Bosch. My choice for plug wires is MSD but I'm not concerned with OEM routing.

 

[AR67GTX]

Lots of possibilities to chew on here. I drove the car yesterday, it is NOT happy starting in cold weather, seems like heavy missing until it warms up and I need to keep the revs over 1000 or it loads up bad, maybe the choke is still set too rich. Once it warms up it seems to be running on all eight and feels ok with light acceleration. There is a roughness on heavy acceleration, not missing but like half missing. I ran it up to 60-65 mph, same feeling there and felt some missing punching it from that point, also some pinging.

My first steps will be a compression test and timing check. The comments about plugs and plug wires are good, the "half missing" feeling might be explained there with high resistance or cross leakage. I have Champion RJ12YC plugs in there now but will replace them after the compression test, is there a better choice? The plug wires are 1967 date coded Mopar which I assume to be from the stock 2001 restoration. I will check resistance but if I replace them what is a good choice that will fit in the stock wire looms?

As far as the timing checking and setup in the distributor that is something I have never gotten into, does it need to be done on a distributor machine or can I do it myself? Unfortunately this will probably take awhile, whoever did the A/C addition located the heater hoses so they look good but they totally block the distributor and I can't even get the cap off. I plan to fix this with longer hoses combined with a coolant flush and replacement and that job will definitely need a warm day!

Sometimes you can identify leaking plug wires by simply running the car one evening in the dark and watching the engine for flashes and shorts from the wires. Also a phenomenon I've experienced is that an engine with a bad wire will still accelerate strongly w/o missing, but at cruise in a higher gear, will miss under moderate load.

Don't know about Mopar restoration plug wires but Corvette restoration plug wires are junk. I've installed black Taylor wires from a kit on my car. That way I could cut them to length and even re-use some of the boots from the Mopar wires. I think they are 8 mm but they fit the looms OK. I've heard Pertronix makes a 7 mm black wire that works very well and looks stock-ish.

Another phenomenon I've experienced when running a stock distributor with vacuum advance on an engine with more compression and cam - is an over-advanced situation at mid to highway cruise. In my Corvette it feels like a constant light miss. It's caused by the engine firing so far in advance of TDC that it is actually trying to kick backwards lightly until it rotates through TDC and into the power stroke. Hit the throttle (vacuum advance drops out) and it responds smoothly. It's an easy situation to check for - just plug the vacuum advance and test drive it to see if it goes away. If you are experiencing it then you would need to find an adjustable vacuum can for the distributor that allows the amount of advance to be limited.

You do not need a distributor machine to tune a distributor but you will need a dial-back timing light so you can map your centrifugal advance curve out in the car and check your progress. I did this about a year ago on my 67. I have a wire welder but rather primitive welding skills. I managed to goober enough weld material into the slot to close it up and then I had quite a job finishing it up on a bench grinder and with files. It's important that the slot the cam pins ride in is not filed over-width when dressing up the slots. The pins need to be pretty snug in the slot but still work smoothly. If the slot is widened to where the pins are not pretty snug - the timing will dance around at idle.

I would do a compression check - do it on a warm engine and not a cold one - sometimes with built engines and forged pistons they don't seal up well when cold. If the compression test is OK you probably don't need to mess with a leak down test yet.

From your description of how the car behaves when cold I suspect it could have a big cam in it - probably too big. I have an old Corvette with a 256/266 @ .050 lift and until it's thoroughly warmed up it doesn't want to run well at all.

 

[SlinktRR]

This is probably not a carb issue, although the loading up and sooted plugs is probably too rich carb jetting. If you plan on keeping the edelbrocks its worth getting the tuning kits. Can also try starting up with choke disabled and plate wide open to see if its easier to start.

I would take a close look at the ignition. Pull wires one at a time from the dist cap while smoothly idling and see how the motor reacts...if there is no effect when pulled check that cylinder. Also check distributor, like reluctor gap..should be .008".

What is your idle speed at max vacuum?

 

[TxDon]

Sounds like too much cam duration and too little stall speed.

I think you are right about the cam. No stall speed problem though, its a 4-speed.

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Thanks, these are great comments and very helpful. I disconnected the vacuum advance because the ran worse with it. After some research I verified it was connected to the manifold vacuum source and reconnected it after bumping the initial advance and adjusting idle speed/mixture. The car ran terrible with even the low speed driveability bad, missing and surging, so I pulled it off again. I assumed it was the low vacuum making the stock can hunt all over. I do need to start with the basics that I can handle then we'll see what else happens, I'll keep you posted.

 

[AR67GTX]

You may be right about the vacuum can - although 12 inches vacuum is not real low it could cause a problem with advance hunting as you described. That brings to mind another item - with vacuum advance plugged is your timing at idle stable? Some people put the lightest springs they can into the distributor to speed up the advance curve and end up with the weights swinging in and out at idle, creating an unsteady idle condition. You can temporarily put rubber bands around the advance weights to see if that helps the idle quality any.

 

[lewtot184]

i was just re-reading some of this and something came to mind. a few days ago i was buying some tune-up stuff for my riding mower. it has a briggs engine and they recommend a champion rc12yc. so i bought one and got to thinking that i use autolite 3924's(same heat range) in my 65 dodge with an 8bbl 440. i always check ohm resistance on plugs anymore and was floored at the difference between the champion and autolite. the autolite had 7,000 ohms resistance, the champion had 70,000ohms! yes, 10 times the resistance! i checked several times and the results were the same. anyhow, maybe between the cam killing the carb and too much resistance in the ignition there's an issue. also voltage check at the coil is in order.

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another thought; if the engine runs crappier with the vacuum advance connected it could be your getting reluctor to magnet contact. if the two are hitting the engine will run rough. pop the cap and see if there's any contact. a metallic dust will let you know if there's contact and check the ohms resistance on the ballast resistor.

 

[miller]

Good stuff! Good info!

All in all, from the description of things, even if the cam timing is off, or wrong, wouldn't expect it to cure it. Could very easily be a combination of things, and you might have to hunt each one down. Simply because one thing affects another. Heck, it could be 'all the above'! But, hope not. Getting the basics taken care of first, will tell the tale.

 

[SlinktRR]

I think you are right about the cam. No stall speed problem though, its a 4-speed.

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Thanks, these are great comments and very helpful. I disconnected the vacuum advance because the ran worse with it. After some research I verified it was connected to the manifold vacuum source and reconnected it after bumping the initial advance and adjusting idle speed/mixture. The car ran terrible with even the low speed driveability bad, missing and surging, so I pulled it off again. I assumed it was the low vacuum making the stock can hunt all over. I do need to start with the basics that I can handle then we'll see what else happens, I'll keep you posted.

Try running it on timed vacuum port on carb. You don't want manifold vacuum at idle. Remember that vacuum advance is strictly for highway speed drivability and mileage. You can run without it just fine. It's nice to have. If you have an adjustable vacuum canister you can reduce the advance with a wrench. For reference I run vacuum advance with a cam that gives 7" at idle.

 

[TxDon]

Try running it on timed vacuum port on carb. You don't want manifold vacuum at idle. Remember that vacuum advance is strictly for highway speed drivability and mileage. You can run without it just fine. It's nice to have. If you have an adjustable vacuum canister you can reduce the advance with a wrench. For reference I run vacuum advance with a cam that gives 7" at idle.

I found this post on a Chevy forum (Relax now...) read the answer to the first question titled "Timing and Vacuum Advance 101". This is actually part of a longer article written by an engineer. I am definitely not an engineer but it seems to make sense. For now I'm leaving it unplugged until I check a bunch of other things.

http://www.chevytalk.org/fusionbb/showtopic.php?tid/239321/

 

[Garys1969RR]

Be sure to check the strength of the spark coming out of the coil! Hold the coil wire close to ground while someone cranks the engine over. You should have strong blue white sparks an inch or longer jumping from the coil wire to ground. If they are orange and weak, (1/4 to 1/2 inch) you have an ignition prob. My sons 383 had the same probs you are describing. Hard to start, no power. Found out the elec ign box was bad. Replaced it with one from Advance, and it runs great! A properly tuned big block with good compression should fire almost immediately when you crank it.

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Try a stock Mopar elec ign system, since you already have the elec ign distributor.

 

[AR67GTX]

Try running it on timed vacuum port on carb. You don't want manifold vacuum at idle. Remember that vacuum advance is strictly for highway speed drivability and mileage. You can run without it just fine. It's nice to have. If you have an adjustable vacuum canister you can reduce the advance with a wrench. For reference I run vacuum advance with a cam that gives 7" at idle.

I have to respectively disagree about not using full manifold vacuum advance at idle. This is an excellent way to smooth the idle of a rough cam and also keep your engine temperature in control. I have a 66 427 Vette with 12:1 compression, old GM aluminum heads and a 256/266 @ .050 cam, L88 intake, mag pulse distributor, etc. Built in the mid-80s before I bought it and it was barely streetable at first. After a Holley restoration of the carb, drilling the primary throttle plates so I could close them down on the idle transfer slot, limiting mechanical advance to 24 deg crank and installing a vacuum advance can that comes in below the 8 inches of vacuum the motor pulls - it now starts on the choke and has become almost civilized. Moreover after replacing the vacuum can with a low vacuum model the engine runs much cooler in all conditions. Only problem I had was an over-advance condition miss at highway cruise which I cured by fabricating a limiter to limit vacuum advance timing to 8 degrees additional.

Now, if you modify the distributor to limit mechanical advance to about 16 crank degrees so that you can run an initial timing of 20 degrees (and have a starter that ill turn it over reliably) then I agree you probably should not use vacuum advance with manifold vacuum.

 

[TxDon]

I finally got to spend some time on this car this week after putting out other fires for over a month. Prior to this I found that the choke adjustment had slipped and it was hardly opening resulting in a very overrich condition. Fixing that and adjusting it farther lean than before helped. I checked out the plug wires and verified correct firing order and no crossed wires, no obvious damage although they are hidden pretty well. I still need to do the nighttime spray bottle test. Basic spark is strong and compression is good in all cylinders. I changed the plugs to Autolite 85's and fiddled with the carb idle adjustment a bit. I also played with the remains of the heat riser valve, the shaft is there but the counterweight and thermo spring are gone. It was frozen but a little WD-40 freed it up, it only rotates a little less than 1/4". I know its open position is all the way to the left but I can't tell for sure if its open.

It now starts better and doesn't load up as bad cold, runs better initially cruising around but as it warms up it roughens up, I think the heat riser under the carb is percolating the fuel. The intake manifold heats up instantly there when I start it so I'm sure the passages aren't blocked off. Combined with the heat riser valve possibly fully or partially closed I'm wondering if this may be a big part of my problem. I will need to pull off the passenger side manifold and be sure about the valve, eliminate it if the flapper is still there, but I'm a little nervous about breaking a manifold bolt...

 

[69Runner]

Since the question of fuel boiling point comes up time and again I added a 1" phenolic spacer under my Eddy carb. After a 45 minute run on the highway it was warmed up. The intake manifold just under the spacer was 240F, the spacer itself was 200 and the carb was 165F.

Here is an interesting video of a crazy guy who boiled some gas in a pot of water, and found the BP of gasoline to be ~160F. Interesting!


https://www.youtube.com/watch?v=d7AkcjnCTVU

So the carb will remain at 165 until all the fuel boils away, then heat up if the intake/spacer is still hotter. The spacer seemed to help with hot re-starts but time will tell when it really gets hot this summer.

 

[TxDon]

That's interesting. doing searches here I have seen many threads about heat related fuel problems and beginning to think it is a major part of my issues. I'm thinking about deleting the heat riser, blocking the intake heat passages and adding a carb spacer but your video indicates the gas would still boil. Has anyone done these same mods and still had a problem?

 

[TxDon]

I had an interesting new development this week. I have been thinking about taking the car to a local shop that works on all types of muscle cars to see if they could help narrow down the problem. I had not personally used them so I went there to meet the owner and check it out. We talked at length and he mentioned a number of possibilities so I added my name to his list. One of the things he talked about was the ballast resistor creating too much resistance when combined with an internally resisted coil. I checked and the coil on my car is a Pertronix Flamethrower with a 1.50 ohm internal resistor. I searched this forum plus read the Pertronix instruction sheets and it looked like the coil resistance is all I need, so I made a jumper wire and bypassed the OEM ballast. I took it for a ride today and noticed improvement! It starts better and runs a little smoother at slow speeds but there was a big difference at higher speed, where it used to hesitate and fall on its face now it takes off and feels more like it should. Apparently the over-resistance was killing the spark as the rpm increased. I've still got issues and will have this shop take a look but I am now much more encouraged than I was before.

 

[miller]

Good to hear your finding answers! All that small stuff adds up.

 

[747mopar]

This new fuel boils at a much lower temp so anytime I build a motor the heat crossovers in the intake get blocked off, lines near heat sources get insulated and a phenolic spacer goes uner the carb. Doing these things eliminated my heat related issues.

 

[AR67GTX]

I don't use Pertronix stuff but I as I understand you do bypass the ballast resistor when using it to replace points.