Did a compression test last night and recorded vacuum readings too.

The reason I started this is because my car has always idled rough, sticking in an rpm range from 830 to 890. It hard to dial it in lower than that but it fluctuates pretty wildly. Also eats gas like no tomorrow.

Vacuum reading was a wild flicking of the needle between 15 and 17 inches. I took this reading with my mityvac off the hose that goes to the preheater valve, plugged right to the carb. think it could be Scenario 6, 7, 8 or 15. I've screwed with the idle plenty though and could not eliminate this so I don't think it's 15.

For the compression test it was 145 psi accross the board. Slight variation but no more than +/- 5 between any cylinders. Took about 4 strokes to get it to max, most cylinders would go 60-90-120-145/150. Each cylinder was almost identical.

I was really hoping to find something wrong here (hah). Does anything seem out of the ordinary other than the vacuum?

I'm still thinking it's the valves, I wonder if i should take the head off too get a better look.

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1978 4 door Dodge Aspen, Super Six

Have you completed a proper valve lash to eliminate that they aren't too tight?

-D.Idiot

I followed SlantSixDan's prodecure on doing it hot. I had some trouble with it to be honest. I can try it again to be sure, I was thinking of doing it with the engine off but warmed up like he described. The connector on my #2 plug wire came off the wire so I'll have to go to NAPA to get it replaced. I guess NAPA Echlin wires are not the best.

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1978 4 door Dodge Aspen, Super Six

Relash the valves to .012 intake and .022 exhaust with the motor HOT and idling as slow as you can get it to go. The best description of the right "feel" to a properly lashed valve is tat inserting and removing the feeler gauge should feel like dragging the gauge across an oiled refrigerator magnet.

Adjusting isn't hard, just use the right feeler gauge and a good wrench. Go slow, don't forget the valve pattern changes after #3.

If you want to elimanate fuel mixture (lean run) as a possible cause then add fuel to the engine while it's idling. I use a propane enrichment tool (you can take a small plumber's torch & remove the metering orfice from inside) & feed gas into the carb airhorn. If it smooths out/ speeds up then there's a big vac leak or carb problem. If it runs worse then you're likely to have mechanical fault.

Definitely reset lash - a bit too loose is better than too tight. Also give a close look for any broken valve springs- the effect can vary wildy depending on I or E valve & how it's broken. See if all valves appear to travel (open/close) the same amount.

Another test to do is called the "running" compression test. A cranking or "static" comp test measures gross engine sealing & valve timing. A running test looks at dynamic valve function & cylinder airflow. To do this run the eng until hot. Remove one plug (carefully ground the plug wire with a jumper) Screw comp gauge (not too tight!) in & start the eng. Once you "stabilize" eng speed at idle- release pressure in the gauge & watch it build back up. Record results & repeat for other 5 cylinders.

On a normal eng that pulls 20" vac near sea level I expect running press to be about 1/3 of cranking press- all cyl should build press about the same rate (we're looking for an odd duck here). Your eng has 15-17" then I'd expect a bit under 1/2 of cranking press- remember that we want to see consistancy from cyl to cyl.

Yet another test I would do before teardown is a "leakdown" test- this feeds a calibrated amount of air into the plug hole while the piston is at TDC & valves are closed. Any leaks are read as a pressure drop on the gauge. If % leakage is excessive then you can listen for the source- int, exh, crankcase, etc. I've had some pretty bad valves that would still produce comp. The tool costs some $$ & you need a decent air compressor so this isn't for everyone.

If you have a tight or galled valve guide or a very intermittant valve seal then you might not find it without pulling the head & checking/ removing valves.

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63 Valiant Wagon
225 - 4 bbl

If you get the style that is not self igniting(aka no turbo torches) and has just the 'knob' on the side it will be plenty for the slant at 1/2 to wide open with the nozzle stuck in the upper carb horn...these are getting harder to get in Oregon as no one wants one they have to pack around a lighter or matches for anymore. If borrowing one from a buddy make sure you use propane from a camping lantern, as the plumbers use MAPP gas which will not work for this.

Another fun test to check for "sticking valves" if you suspect such instead of the other items, is to use your timing light with the valve cover off and watch the rocker arms and valve springs with the strobe calibrated to the timing...if something is not returning properly it can show up here...

-D.Idiot

I've read of this propane thing on the stickers under my hood but it always confused me as to how. Doesn't seem so complicated though.

So is it best to just run a hose from a torch to the top of the carb or is it better to feed into a vacuum port? There is one at the base of the thottle body that isn't being used but you guys said air horn?

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1978 4 door Dodge Aspen, Super Six

I just stick the hose into the airhorn & turn the gas on slowly. I also use the hose to direct a "stream" of propane aroung intake gaskets, carb base, anywhere I'm checking for intake leaks (works fine for this as long as fan/wind isn't too strong in engine bay)

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63 Valiant Wagon
225 - 4 bbl

Alright, sounds good. I think I'll take this this time with my car grounded to get my carb rebushed and while i'm at it my rocker arms and shaft hot tanked. I was thinking I'd go to Archie Somer's in Vancouver, WA.

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1978 4 door Dodge Aspen, Super Six

You should really try to eliminate all other things before doing a drastic thing like that.
I think this may be a clue to your problems, have you ever rebuilt the carb? Check for leaky floats. A too rich mixture may also give the same readings on a vacuumgauge as incorrect setting for the idle mixture screws. (scenario 15) You will also smell a too rich mixture, and see a black oval on the ground behind the exhaust outlet when idling.
You can get the best from http://magnecor.com/.

Olaf

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Aspenized

I definitely have a black oval behind the tail pipe when idling. I'm thinking this may all be stemming from a leaky throttle shaft on my carb. It's the only place I could detect a leak. I will tackle that issue first. I'll be calling around shops today to see who can do it.

What are reccommended ways to set the mixture? I had tried watching the vacuum pressure as I adjusted it on D.Idiot's advice but because of the flucating pressure reading I found it difficult.
I have looked into them. In retrospect I don't know why I didn't spend the the extra to do it right in the first place.

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1978 4 door Dodge Aspen, Super Six

Some of the former members of the board back when used to take their carbs to Savas Tuning on McLoughlin... http://www.savastuning.com/

They used to have a good reputation and did a complete job.

FYI.

-D.Idiot

I swapped out the BBD I had on there with a 318 BBD I picked up at a swap meet that I just finished rebuilding. The idle smoothed out quite nicely. So it was the throttle shaft this whole time. The 'new' carb was a bit damaged so I compared the two and read the literature on the differences between 318 and 225 BBDs (can't find the link but it's on here). It turns out I've been running a 318 BBD this entire time but with the rods and jets out of a BBD for a '79 Truck Super Six. So I swapped the throttle bodies and put the carb I had on before back on.

After replacing the 5W-30 oil my car loved to burn back to 10W-40 and some new plugs I got it running and have been taking it to work this week. I found out yesterday I've been getting 9.7 miles to the gallon. Still coating the ground in black soot behind the tail pipe. This weekend I will be pulling the carb and going through all the adjustments again then going back and relashing the valves just to be sure.

I'm very concerned on getting my mpgs up, Im shooting for 20mpg. I know my car is heavy, but is this achievable?

I'm trying to find a real Super Six BBD although it seems difficult. One is listed on Ebay but the throttle body has notches on the underside, tell tale of a 318's carb.

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1978 4 door Dodge Aspen, Super Six

If I remember correctly former user StephanieBrite77's 77 Volare 2 door super six and power brakes and steering was able to achieve 21-24 mpg highway once everything was tuned up and dialed in (she even cut a perfect light at Woodburn in that thing too...LOL).

Not bad for a $700 junkyard find...


-D.Idiot

One of the main differences between the 318 and 225 BBDs is the orientation of the choke thermostat eyelet on the side of the choke butterfly valve. The 318 BBD has this eyelet oriented to be pulled straight up and down, while the 225 BBD has the eyelet oriented to move in a diagonal fore and aft motion. Using a 318 BBD on a slant six without address the difference in the choke linkage will lead to a choke that does not operate properly, and usually stays partially closed. A partially closed choke will lead to poor MPGs and leaving black soot on the driveway. User Fab64 came up with a very simple and elegant solution to using a 318 carb on a slant six. Do a search for fab64 and choke linkage to find threads with the pictures and description.

20 MPG is achievable, but you really have to get the motor and carb tuned well to do it (and drive to maximize MPG).