Time to Fix It Right

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danielb927

danielb927

Well-Known Member
Joined
Jun 16, 2009
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Location
Southeast MN
I've been a member here since I got my 73 Duster back in 2009 as a high school senior. Kind of hard to believe I've had her for 11 years already! We've had some awesome times including a 10-day road trip down Route 66 when I moved to CA for grad school and having her as my daily driver for my first 3 years out there. I haven't been on FABO much for 6 or 7 years as I never had the time or place (or $) to really work on things while I was in school, other than a radiator swap.

These days I have a (small) garage and I am blessed to have a few more disposable funds. Also will be hitting the big 3-0 milestone later this month. I still cruise the Duster every now and then, but I always feel a bit on edge when I do -- the list of "tricks" I have to use to keep it running gets a little longer every year.

I think it's time to start doing some real repairs the right way, not the way I did them when I was 20 and looking for easy answers. And, while there are many things that need a bit of work (tires, body, interior), the one that impacts me the most & where I need the most help is getting the engine running like a 70's V8 should.

At some point I'd like to do a full-on rebuild (engine swap, crate build, something like that). I don't feel I have the space or money for that right now -- that said, there's a cost to patching things up, and in this case maybe the full rebuild is really the only thing that makes sense. That's part of what I'd like to figure out!

Goals (for now)
  • Cruising. I would like to be able to go for a drive without stalling out at intersections or overheating in traffic (to the extent that this is possible in a ~50 year old car).
  • Understanding. I'd like to know what the underlying issues really are, what adjustments I can make, and what the response to those adjustments should be.
  • Safety. Night/rain driving are a bit hairy with no cabin air controls and an engine that runs noticeably worse with the headlights or wipers on. That was fine when I was younger, but now it really limits how often I go for a drive.
Current Problems
  • Neutral idle has to be set to ~1500 RPM to avoid the engine dying in gear.
  • Stumble (miss?) on light throttle cruising (say, 30-45 MPH)
  • Engine takes a second to go after a big throttle increase
  • Engine runs worse with headlights on -- more likely to die at intersections.
  • Seems to run OK for the first few minutes after cold start, then get worse as it heats up to operating temp.
  • Hard to set timing. Seems to wander a lot on idle.
Possible Causes
  • Mis-matched setup (carb/engine/cam etc. just not right for a street cruiser)
  • Carburetor tuning (I've tried doing this but not with enough patience)
  • Engine in need of rebuild (a specific problem e.g. jumped chain or just old)
  • Electrical system (battery/regulator/resistor/coil new, everything else old)
Technical Specs (top of my head -- will add to this)
  • 1975 360 V8 ("built" and swapped in before I bought the car)
  • Stock heads
  • Comp cams Magnum 280H
  • Holley 670 CFM Street Avenger (vacuum secondaries, electric choke).
  • Electronic ignition (stock, I think? It's a distributor but doesn't have points).
  • Stock intake manifold (I think I plugged the EGR port at one point, though).
  • Stock exhaust manifolds, 2.5" pipes with an X crossover. Driver's side has a 2" section as the shop I used couldn't bend 2.5" but needed a custom piece there.
  • 904 transmission, stock torque converter (as far as I know)
  • 7.25 rear end w/ either 2.76 or 2.94 gears, not sure which. Runs ~2800 at 70 MPH, if memory serves.
 
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The biggest issue is you don't know how the engine was rebuilt, being you don't know the true static compression. To do it right you at least need to pull the heads and see what is going on.

If this we're mine to tackle and i didn't want to remove the heads, I'd put a smaller cam that works with the stock converter and possibly a Performer or Action Plus intake betting it has re-builder or stock replacement pistons sitting in the hole and open chamber stock heads. I hate Avengers so I'd sell it for a Eddie 625 AVS, Street Demon, or 3310 Holley. This all if you want a cruiser that is easy to drive with some fun factor. Sort out the exhaust, Jegs and Summit make a kit. Headers if you want, Dougs and TTI are the best for the street.
 
In my opinion, let's get the motor running well and reliable (maybe just a good tune-up?). Then if other issues still exist, deal with those then.
 
Added a bit more info above. The heads are definitely stock. dano, those are all good suggestions and things I'd like to do eventually, and you're right that it's difficult without more knowledge of the internals of the engine.

I'm not opposed to pulling heads at some point (have helped a friend with a head swap before). But given how little I knew the last time I tried to tune up the engine, I think Murray's suggestion of a tune-up is probably a good place to start.

I'll do some forum searching but maybe someone reading already knows this -- is there a good, comprehensive guide to tuning up a carbureted V8 starting from the basics?
 
A book would be great but I'm not aware of a tune-up type guide. The suggestion to get the engine right first is a good one.

The forum is a "challenging" since you'll have 47 different people telling you 47 different things to do, lol.

I would begin with some diagnostics. First, I would get a loaner compression test kit from a parts store such as Advance Auto Parts. Go though the process of checking each cylinder and report back. It's a fairly simple test that will show the health of the engine.

Just take it one step at a time and you'll get your engine running smooth before you know it!
 
Tuning any combo correctly will always help. Buy a dial back timing gun and a vacuum gauge (I have a Harbor Freight one, works fine for me). I like the guns with a tach built in. If your more flush buy and install a wide band O2 and gauge, AEM makes some nice ones that are not too spendy. All of these move forward with any engine you build so they are worth having.

Honesty I for one don't like taking an engine part that runs unless there are internal issues.

Just know that with that 280 cam you'll likely get lower numbers if you do a compression test. It will be how even they are to one another that counts to some degree.
 
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Starting with a compression test will assure us that the basic engine is sound and worth putting some money into it. You may need to buy some tools if you don't have a friend to borrow from.
 
Get a headlight relay kit from Crackedback on this forum to ease the burden on the electrical system. Lights will be brighter from less voltage drop and you'll get better voltage at the ignition module for better drive ability. Probably should bypass the feed connection through the firewall and jump the ammeter as well.
Carb needs to be tuned or rebuilt. Easy button is a new AVS2 or Street Demon if you have $350 to throw at it
Sounds like it needs a timing chain if the timing is bouncing around. Maybe a distributor rebuild.
 
Thanks for all the advice so far! I have been on a lot of message boards for various things over the years (mostly computer-related) and FABO really is as good as it gets. If the downside is 47 different ideas, that's way better than 0.

  • Sounds like the consensus first thing to do is a compression test to assess the overall engine health. I will get that run and report back with the numbers.
  • I wouldn't be surprised if the carb is in need of a cleaning, that's a good suggestion. Given how little I've driven the car the last 2-3 years (with ethanol gas, yep) there has been plenty of sitting
  • I did do the ammeter bypass and installed a headlight relay a few years back after seeing those suggestions around the site.
  • Timing chain, distributor, all good ideas. For now I will start with the compression and then decide what to look at next.
 
Sitting is the worst thing you can do to a vehicle. I sold my truck because it sat too much and needed too much and the Dart is Project #1. Old gas will cause it to run poorly. Water can get in it if it sits. Typically you can smell water burning through the exhaust.
 
Kind of turns into a feedback cycle, doesn't it? Car runs poorly -> I don't enjoy driving it as much -> I don't drive it as much -> it sits a lot -> it runs even more poorly. I'm excited to break that spiral!
 
danielb927 said:
Kind of turns into a feedback cycle, doesn't it? Car runs poorly -> I don't enjoy driving it as much -> I don't drive it as much -> it sits a lot -> it runs even more poorly. I'm excited to break that spiral!
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Me too and why I scaled it to 1 project vehicle. I've has this 24 years, since I was 20. So its been a long time coming. Too many other cars came and went that in hind site I should not have dabbled with, but they grew my experience because of them too.
 
Start with a compression test and oil pressure test to see if the engine in in sound condition. I'm assuming it doesn't make and out of the ordinary noises? Once you establish that the engine is in good shape internally, work on the carb and ignition systems. Your symptom that it runs worse with the headlights (or other current draw) on is troubling. I'd take the bulkhead connector apart at the firewall and check for corrosion to start. Next would be a charging system test and voltage reading at various points to find any bad voltage drops.
 
Ignition timing at idle?

Sounds like it may be low, big vacuum leak or carb funneling fuel in unmetered.

Good timing specs takes care of LOTS of carb issues. No reason a magnum 280H cam can't idle at 750-800. Something else is causing the issue. It's bouncing all over because the mechanical advance is likely active at 1500 rpm.

It's going to like 16-20* initial timing is my guess
 
cudamark said:
Start with a compression test and oil pressure test to see if the engine in in sound condition. I'm assuming it doesn't make and out of the ordinary noises? Once you establish that the engine is in good shape internally, work on the carb and ignition systems. Your symptom that it runs worse with the headlights (or other current draw) on is troubling. I'd take the bulkhead connector apart at the firewall and check for corrosion to start. Next would be a charging system test and voltage reading at various points to find any bad voltage drops.
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I've had a look at that bulkhead connector and don't remember any major corrosion but it has been a while. There are lots of little electrical things that seem problematic -- for example, the voltmeter I installed in the dash shows a ~1V drop/rise as the turn signal goes on/off. Not sure if that's normal for a lumpy V8 at idle with a stock alternator or if it's reason to suspect bad wiring/connections. Anyhow -- don't want to attribute the engine issues to that until I've started at square 1.
 
Carb issue. Probably 1 side of the idle circuit is plugged with ethanol jello. Remove, flush and rebuild with a new accelerator pump. Holley metering plate gaskets pucker if left to dry unless they are the blue ones. I think those are o k for the long haul. I'd start there. Where are you located?
 
All good suggestions above.

I would add that if the gas had been in the tank for periods of a year or more you may want to drain it out and blow air through the lines (disconnect both ends of sections starting from rear of car).

If there is any gunk in the system you will want to get it out so your rebuilt carb gets fresh clean gas. Also change the fuel filter.
 
Assuming the engine has good compression, my first looks are at carb, dist., and gas tank!!!! Has the tank been off and cleaned ever?
A new Edelbrock would be a good investment.
I have had many issues with old distributors. Maybe a re curved one for your setup?
Like said above, these mechanical wonders need to be driven regularly!!!! Man problems will develop when not taken out to stretch their legs. And open them up too!!!!!
 
Ok guys, sorry for the slow turn-around here, been a busy week.

Yesterday I ran a compression test. Drove the car around for 10 minutes to get the engine up to temp, then pulled the plugs. The tester I have is a manual push-in type from a friend — it was difficult to get it seated properly on the Driver's side due to the high-rise manifold, but I was eventually able to get it seated and hold it in place without hearing any audible hiss on the compression stroke. Unfortunately for cylinders #1 and #5 I wasn't able to watch it on each stroke as the dial face had to be down to get it seated.

Anyhow, here are the results. Numbers were reached on the first stroke and didn't increase with subsequent strokes (these are averages of a few tests). After testing I realized I forgot to have the throttle blocked open, which I know will cause lower numbers overall — if that's enough of a reason to re-run the test I will definitely do so. Still, these are really low and the inconsistencies on the driver's side are worrying, right?

Driver's Side:
1 - 88
3 - 99
5 - 78
7 - 105

Passenger's Side:
2 - 98
4 - 99
6 - 98
8 - 89
 
I also snapped a pic of the plugs. The two sides look noticeably different — the driver's side are darker colored, while the passenger's side has a bit of toasty brown build-up.

IMG_7795.JPG
 
Compression numbers are way low but that is probably the gauge and method. Fairly consistent though. Maybe go by an engine shop and have them measure one or two cylinders with their gauge for a baseline. I don't think you can do anything with that data.
 
Doesn't the local autozone or parts house have a tool rental deal. Lots of times it's FREE. Leave a deposit, get it done, return tool for deposit refund.

Was the throttle wide open during the test? Not having the throttle open will cause low numbers.
 
Yeah, if that gauge is accurate, that's awful compression......even without the throttle open, which I've never seen much difference personally. I'd do another test with a different (as in known to be accurate) gauge. Those plugs look like they've been in there awhile!
 
cudamark said:
Yeah, if that gauge is accurate, that's awful compression......even without the throttle open, which I've never seen much difference personally. I'd do another test with a different (as in known to be accurate) gauge. Those plugs look like they've been in there awhile!
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Get/rent guage that screws into plug threads. The pressure should build with 2 or 3 compressions.
 
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