Slant Six has No power. will not accelerate

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CMaddux92

CMaddux92

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Owned my 68 Valiant for almost a month now. Since I've had it it has had a serious issue with power under normal acceleration. It starts fine and idles fine but does shake. But when I put it in gear I have to barely push the gas pedal down or it will stall on me. Anything more than say a quarter push down on the peddle will cause it to stall. Recently I've changed the spark plugs and fuel filter. Today I just tested the fuel pump and there is good suction from the pump inlet and fuel does come out of the outlet. I'm stuck on what to do next. I'm thinking maybe something with the distributor or the vacuum advance diaphragm. Any help and advice would very much be appreciated! Thank you in advance
 
Both. I bet your accelerator pump is shot, your centrifugal advance is frozen and your vacuum pot is leaking. Is it a 1bbl? Look into Carb while motor us off and see if a healthy squirt happens when you move the throttle arm. If it does, look at distributor. Pop top and pull hose off Carb. Suck on hose to see if the plate rotates, if it does, hold suction with tongue and see if it holds vacuum, 2 down! You'll need to rotate rotor by hand. Does it turn a few degrees then snap back? That's your mech advance. All else fails, check timing first. I think it'll run decent straight up at 0 but consult year manual for spec. Damper can move over gimme so its best to degree it gut that's more in depth. Ported or manifold vacuum. Try ported first then manifold.
 
sorry forgot to add some more details. I took the carb off yesterday. and surprisingly it was pretty clean inside. and the accelerator pump looked very clean and almost new
 
No all advance is in distributor, just do as I said and report back.
 
68 225 is 0, tdc. Also valve adjustment is critical .010 intake and .020 exhaust HOT (and running if you can do it), otherwise idle until hot and adjust right at shutdown.
 
pishta said:
68 225 is 0, tdc. Also valve adjustment is critical .010 intake and .020 exhaust HOT (and running if you can do it), otherwise idle until hot and adjust right at shutdown.
Click to expand...

Exactly what I was going to say...I had the same problem with my motor this summer, turns out I had 2 dead cylinders because I hadn;t adjusted the valves.
 
CMaddux92 said:
Owned my 68 Valiant for almost a month now.
Click to expand...

Sometimes a "shotgun" approach is actually a pretty good idea. If I had just bought this, I would do a "stem to stern" engine diagnostics

Get yourself a factory service manual. You can download one, free, right here:

http://www.forabodiesonly.com/mopar/showthread.php?p=1970088617

1...Check the engine condition.

Pull the valve cover and inspect for sludge. Adjust the valves. Run both a compression and a leakdown test. In this day and age, where may O'Reallys parts stores have tools to loan, and where Horrid Freight is so cheap, and where you can find info on the internet on building your own leakdown tester, there is no excuse to NOT have and obtain some diagnostic gear

If the compression doesn't seem too bad, and the plugs are not showing signs of oil fouling...........

give it a good ignition tune--up. Unless it has been recently replaced, replace the points / condenser if it still has them, rotor, cap, wires, plugs. Set the timing, and if anything, lean towards some "before" TDC.

Got to garage sales, craigslist, and get a tach/ dwell meter and timing light.

2....Fuel system. Replace both hoses, one at the tank, one at the pump inlet in the fuel line. Refer to the service manual and check fuel pump capacity. Replace the fuel filter and any other questionable components, and keep in the back of your mind that the tank filter an be gummed up. consider cleaning or having cleaned, or replacing the carburetor. Many times you can tell by the accelerator pump working or not, and the way the idle screw adjusts

3....Charging system. Check running voltage, check condition of brushes, check belt(s) for condition and tightness / slippage. READ this article on the problems with wiring in these old cars. Even if you do not perform this modification it gives you insight into what you might expect.

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

More here

http://www.madelectrical.com/electrical-tech.shtml
 
ok this morning I popped the top of the distributor cap off and then I pulled the hose off the carb that goes to the vacuum advance on the distributor and sucked on it. the inside of the distributor didn't move at all, tried sucking on it a few times with still no movement. tried moving the gear inside it by hand and didn't seem to want to move either
 
Was there any air flow when you sucked on the vacuum advance line? If so, you have a vacuum leak in the advance dashpot.

Have you checked all of the vacuum lines around the engine for leaks? The shaking idle is a clue that it could be such a leak. Also, you could have an intake system leak. Once you get through everything else, and when the eninge is cool and before the exhaust manifolds get hot, you can CAREFULLY try spritzing the intake manifold flanges and carb base gasket with tiny bit if gasoline; if the idle increases and smooths for a moment, you have found a vacuum leak.
 
pishta said:
Both. I bet your accelerator pump is shot, your centrifugal advance is frozen and your vacuum pot is leaking. Is it a 1bbl? Look into Carb while motor us off and see if a healthy squirt happens when you move the throttle arm. If it does, look at distributor. Pop top and pull hose off Carb. Suck on hose to see if the plate rotates, if it does, hold suction with tongue and see if it holds vacuum, 2 down! You'll need to rotate rotor by hand. Does it turn a few degrees then snap back? That's your mech advance. All else fails, check timing first. I think it'll run decent straight up at 0 but consult year manual for spec. Damper can move over gimme so its best to degree it gut that's more in depth. Ported or manifold vacuum. Try ported first then manifold.
Click to expand...


turned the rotor by hand and it does just turn slightly then snap back. what does this mean?
 
Were the distributor gears on these plastic? I remember having on in my 65 that had tons of wear on the distributor gear.
 
yea I believe the gears were nylon or plastic or something. I haven't removed the distributor yet but I cant today because today is football day! lol
 
That your mechanical advance seems normal. It advances ignition timing as RPM's increase.

If the vaccum advance dashpot is not leaking, then did you look down inside the distributor with the rotor button removed and see that the plate (on which the sensor or points are mounted) did or did not move when you sucked on the vacuum hose? This plate should move when you suck on the hose, not the rotor button.

There should be a little bar from the vacuum advance dashpot that connects to that same plate; as I recall, the bar is under the plate on this distributor so may be hard to spot. See if you can spot the little bar and if it moves with the sucking or not; it should move towards the dashpot with vacuum.

The plate can be stuck/frozon, or the bar disconnected from the plate or broken inside the dashpot.
 
My 69 Dart 225 idled like that - rough and wanted to die in D or R, though I had ample power off idle. I just hated worrying about it dying at a stop light (drove w/ 2 feet). When it still acted the same even after a totally new long block, I tried my ~4th Holley 1920 carb and it ran amazingly smooth. The problem is that the metering block is sealed in those, so can't be truly rebuilt. One guy here reported luck in blowing it out from a hole in the base of the carb (off engine). When it acts up, close the choke plate a bit and see if it smooths out. If so, it is running lean at idle.

Re distributor, rather than fool with yours, I suggest start looking for an electronic one (71+) and using an HEI module with it, as many her have. BTW, mine still idled rough with a Holley XR700 electronic ignition on it, so don't expect better ignition to cure all. Your low power problem could be from poor spark timing. Give it as much advance as it likes, until you start getting pinging going up hills. Use a timing light (cheap at garage sales) to insure the timing increases ~30 deg as you rev the engine, or spring for a new light w/ digital delay (~$30 Amazon) to measure exactly. The suggestions that "50 mph max is typical" is total bunk. These engines were used in trucks and full-size vans. One guy added a turbo and runs 10 sec qtr miles. When the slant first came out, one guy even ran a drag rail with one.
 
I've never been able to move the distributor plate just by sucking on the advance hose. I don't think you would be able to either unless your name is Monica Lewinski. It's better just to rent or buy a suction source (mighty mite comes to mind).
 
I had the same problem with my 63 valiant 225 slant six, 1920 holley 1 brrl. When I first bought the car the bowl gasket was leaking. When I went to replace it I noticed that they gobbed on silicone sealer to the gasket. Some strans of silicone were starting to come loose. I cleaned all that i saw, but of coourse the little tiny piece that i must have missed found its way in the metering block and clogged it. This time I took everything apart and gave it a good cleaning (i hope). Put it all back together and the car runs great!!
 
Sounds just like mine....did a compression check and eventually found a couple bent push rods!
 
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