Stumbling Slant --what is left??

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wrock

wrock

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The story so far: 68 Dart with a slant. I noted that the distributor shaft was getting a bit wobbly when I last tried to change the points, so I tried rebushing the distributor I had, failed at that, and replaced the distributor with a used one I had. I might have had a bit of hesitation before this, but now I had real stumble--at idle, under load, all the time. OK, so I replaced the distributor (cap, wires, plugs, points, etc) with a new one. No change. Changed the coil. No change. Looked at the timing chain. It was loose, but not bad. But I replace the chain and cam gear anyway. No change. Checked the compression--all six between 90 and 118 PSI. Checked the valve lash, tweaked them a bit (none more than 1/8 - 1/4 turn) No change. Took a 2 liter bottle of gas and fed the carb with nice clean gravity-fed fuel. No change. Installed a rebuilt carb. No change. Wife suggested exhaust, so I just now unbolted the exhaust from the manifold. No change. Early on had installed new PCV, fuel filter to no avail. Interesting: the new plugs with barely 30 minutes of idling on them are showing carbon black. The old plugs that came out were fairly black, too.

Any ideas? Please let me know.

Thanks.
Bill
 
wrock said:
The story so far: 68 Dart with a slant. I noted that the distributor shaft was getting a bit wobbly when I last tried to change the points, so I tried rebushing the distributor I had, failed at that, and replaced the distributor with a used one I had. I might have had a bit of hesitation before this, but now I had real stumble--at idle, under load, all the time. OK, so I replaced the distributor (cap, wires, plugs, points, etc) with a new one. No change. Changed the coil. No change. Looked at the timing chain. It was loose, but not bad. But I replace the chain and cam gear anyway. No change. Checked the compression--all six between 90 and 118 PSI. Checked the valve lash, tweaked them a bit (none more than 1/8 - 1/4 turn) No change. Took a 2 liter bottle of gas and fed the carb with nice clean gravity-fed fuel. No change. Installed a rebuilt carb. No change. Wife suggested exhaust, so I just now unbolted the exhaust from the manifold. No change. Early on had installed new PCV, fuel filter to no avail. Interesting: the new plugs with barely 30 minutes of idling on them are showing carbon black. The old plugs that came out were fairly black, too.

Any ideas? Please let me know.

Thanks.
Bill
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Black plugs indicate either very rich fuel condition or very poor spark. If you're running a rebuilt Holley 1920 that could be the problem. Many rebuilds have problems out of the box.
 
Ricks70Duster340 said:
Black plugs indicate either very rich fuel condition or very poor spark. If you're running a rebuilt Holley 1920 that could be the problem. Many rebuilds have problems out of the box.
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Well, there is only a few minutes on the rebuilt 1920. And it shows the exact same stumble with new carb as old.
 
wrock said:
Well, there is only a few minutes on the rebuilt 1920. And it shows the exact same stumble with new carb as old.
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Like MOPAROFFICIAL said, likely time for a rebuild. You have a lot of new parts to go along with the rebuild!

How many miles are on that engine?
 
Ricks70Duster340 said:
Like MOPAROFFICIAL said, likely time for a rebuild. You have a lot of new parts to go along with the rebuild!

How many miles are on that engine?
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Bought it in 2010...the guy I bought it from claimed it had 80K on it. My odometer has been broken since 2007, but I drive it every day 30 miles RT to work, so figure maybe 8K a year, so that's somewhere north of 170K on this engine. I had 285k on the 170 (this one's the 225) before I replaced it.
 
Timing, vac advance weak. Carb needs a cleaning/rebuild.float could be bad.
 
wrock said:
Bought it in 2010...the guy I bought it from claimed it had 80K on it. My odometer has been broken since 2007, but I drive it every day 30 miles RT to work, so figure maybe 8K a year, so that's somewhere north of 170K on this engine. I had 285k on the 170 (this one's the 225) before I replaced it.
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Mileage is important, but so is the history of that engine. A well cared for engine can go a long time without a rebuild. If the heads never had hardened seats that could be one reason for low comp.
 
Can you do a cylinder leakdown test on your low cylinders? Ie. put some air pressure in the spark plug and see if its escaping out the carb or exhaust? Im thinking spark too as your getting alot of unburned fuel and carbon on the 30 minute plugs. Correct gap, Electronic? .010, .020 valve lash.....
 
I am thinking there is something wonky with either the used distributor or how it was installed.
Distributor: mechanical advance stuck or center rotor worn and affecting dwell or other failure like a bad distributor cap or rotor or points set or condenser.
Installation: mis timed or spark plug wires faulty or in the wrong order, these days new does not guarantee good.

Have you tried re installing the old distributor?
90 compression won’t rocket you down the road, but it should run.
 
RustyRatRod said:
Where did you set the timing?
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Where "it ran best". It would be impossible to start (kicking against the starter), I'd move it a tooth, then it would be OK to start and I'd time it by ear. The odd thing is that the timing appears way advanced (CCW of the plate) when I look at it with a timing light. But it will not run with the timing set back on the plate.
 
my68barracuda said:
I am thinking there is something wonky with either the used distributor or how it was installed.
Distributor: mechanical advance stuck or center rotor worn and affecting dwell or other failure like a bad distributor cap or rotor or points set or condenser.
Installation: mis timed or spark plug wires faulty or in the wrong order, these days new does not guarantee good.

Have you tried re installing the old distributor?
90 compression won’t rocket you down the road, but it should run.
Click to expand...

Have not tried to reinstall the old distributor. I assumed since the problem was completely unchanged, that it was not the issue. The replacement distributor was new from Rock Auto.
 
Sounds like the balancer has slipped. You need to find TDC with a piston stop and check the balancer.
 
Try and make sure your balancer shows true TDC with a piston stop or something. It could have jumped a tooth.
 
90 lbs wont run for **** guys.

After reading all the post seeing something in there about it should have lasted longer Etc. Fact is it's not uncommon for the 225 to be done at or around 170- 200k. Many are toasted by a number of things, infrequent oil changes...tune... many kill the no.4 or 5 cyl due to the carburetor or intake having issue...like a lean mixture issue. I gave my brother 4 225 engines with 2 of them low miles rebuilds... he swapped his same carb/intake onto each....and all of them 'though the plugs looked ok' killed the no.4 exhaust valve...i mean burnt and 1/4 of the valves satellite missing...cooked..gone.
He ran around all over the place with 'electronic ignition' and no hard seats...on an lean tune that would run decent at 2800 or so ft elevation....3 on the tree buzzing in 2nd in LA traffic, san diego, shaver lake, china lake...they are a great motor but one that was designed 60+ years ago. I spec if you had it all right and used a manifold that was dialed and a nice 390 holley or 350 holley that metered better... it would last longer than my own that never burnt seats or had issue but were ridged and starting to vary on cyl pressure at the same 170-190k mileage. Slant 6 engines ,no matter what anyone says.. are engines you will have the head off at least once if not twice in its lifespan.. 2-3 carb go throughs in its lifespan....and if you rev it hard... 4-5 distributor gears....dont forget the 10 valve cover gaskets you end up putting on it.
Its toast....90lbs is for ****.... all the exhaust valves are probably sank...especially the problem cylinder. Slant 6's are so cheap to rebuild...it's like 1500 bucks and you time..If that.
 
pishta said:
Try and make sure your balancer shows true TDC with a piston stop or something. It could have jumped a tooth.
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Not sure how a balancer slips a tooth. I was very careful to get the cam aligned with the crank when replacing the timing chain. Looks like a Doorman balancer is about $130. Also looks like the one off of my 170 will not work:-(.
 
wrock said:
Not sure how a balancer slips a tooth. I was very careful to get the cam aligned with the crank when replacing the timing chain. Looks like a Doorman balancer is about $130. Also looks like the one off of my 170 will not work:-(.
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Paint pen mark across the balancer is good for checking slip...over time..but that will not fix the 90lbs compression issue...so I'd not even focus on that atm.

Do yourself a favor take the valve cover off...take the rockers off.. go get a ruler and place it edge down across the valve stems and tell me how big a gap there is between all the intake valves and which exhaust valves are the highest ones holding up the ruler.
That's telling you your valves are sunk ,the higher the stems... compared to others/intakes... the more sunk that valve is... And the further it sinks... the more it can not cool and the less it flows..and does not seal.... volume grows larger as a byproduct and the compression gets weak ..and that weak compression also leaks past the exh valve.
You might be able to get away with just a cylinder head job on this, might.
The results will determine this.
 
All you gotta do is use a piston stop and remark whatever you got to TDC and adjust from there. if the 170 has the marks on the other side, just remark the tab. This is just to make sure the cam timing is legit If its not on the original balancer, it may have slipped (its ring is only held on by bonded rubber) or not slipped but shows the cam jumped a tooth if the marks no longer line up.
 
Cam timing wont cause only one cylinder to be 90lbs.

Done. The info has been stated.
You can't tune broken ****. Lol
 
Pop the head. itll only cost you a head gasket and about an hour. without a cylinder leak down test, your hoping for a bunch of burned exhaust valves instead of shot rings. If you can get the coil onto a scope (old tune up place) you can tell if a cylinder has bad compression by the spark cylinder drop test, the spark pulse shape, and the distributor signal itself.
 
MOPAROFFICIAL said:
Cam timing wont cause only one cylinder to be 90lbs.

Done. The info has been stated.
You can't tune broken ****. Lol
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Post #1 says all six were between 90 and 118, don’t think he ever said only one cylinder was low, they all are.
But it should still run. Just not have much power.
 
The FSM says minimum on the cranking test is 100. There's no arguing it's worn, but it should be able to run smooth......albeit weak. lol
 
[1] What heat range are the plugs? Too cold will quickly foul. With such low cranking #s [ did you have the throttle WOT, as reqd for the test? ], I would fit one grade hotter plugs; & they should be projected nose. Champion used to make a plug, the U series, specifically for high mileage engine but I believe they are discontinued. Try NGK 4 heat range.
[2] Fuel pump? Pressure too high causes rich mixture. Unlikely to cause the problem but since you tried so many things, worth checking.
[3] Points ign is not helping. Low on spark energy. Elec ign is cheap & worth it if you are keeping the car. May not cure the problem, but would likely improve it.
[4] Valve guides/seals worn. Replace seals at least, easy to do in situ.
 
Worn guides would smoke, seals would smoke on startup. I was gonna say they were all between 90 and 118 but @my68barracuda beat me to it. Slants are very forgiving as they were a lo-po/lo maintenance motor to begin with. Did you remove the seals on those new plugs? The drool tubes are the washer on that (non) tapered plug head.
 
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