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Stumbles under load only
https://www.slantsix.org/forum/viewtopic.php?t=65606		 Page 1 of 1
Author:  62Dudley [ Wed Dec 02, 2020 2:02 pm ]
Post subject:  Stumbles under load only
Hi all,
There appears to have been a number of posts with issues similar to mine. Have tried various fixes from them and I am stumped.

62 Dart with a late 60's/early 70's (5 freeze plug) 225 with the 3 speed manual.

Has been dead reliable since we did a soft restoration on it 2006-2008ish.

About a year ago it started stumbling intermittently in gear at ~30 in 2nd and ~50 in 3rd. Rarely stumbles in 1st. I'm able to rev freely in neutral, but maybe 1/3-1/2 throttle in 2nd or 3rd gear and it falls on it's face. Almost feels like its flooding itself. Worsens after driving it a few days at a time. Letting it sit for a week or so and it runs much smoother, however still stumbles under load.

Local mechanic told me it was due to the choke, that the spring was old and brittle. Picked up another off a low mile manifold, issue persisted.
Thinking fueling (flooding) issue, I picked up a remanufactured carb. No luck. Both are the single barrel carter.
Rebuilt old carb, no luck. Went back to to remanufactured carb which was in better shape.
Replaced fuel pump. No change.
Then thinking maybe the fuel sending unit's filter is clogged (sitting let the rust/dirt settle, then extended use sucked it back up against the filter). Replaced sending unit, tank for good measure, and lines complete back to front with new in-line filter. No change. In line filter did have a good amount of rust/dirt, so this needed to be done regardless.

Thinking "okay maybe it's electrical." I replaced coil and plugs and wires and re-set timing. No luck. Battery is new.
Finally, last weekend I converted to electronic ignition with a new distributer, ECU, and ballast resister. Timing set, smooth and purring at idle and city streets (35mph). Was sure that was the end of it.
Got it out on the road to test out highway speeds. Didn't change a thing.

If anyone has any ideas, I would greatly appreciate it.

thanks,
Dave
Author:  volaredon [ Wed Dec 02, 2020 3:46 pm ]
Post subject:  Re: Stumbles under load only
I once had a 69 d100 with a slant in it, 2 young brothers bought it to get them home from the Carolinas. Idk how they ever got it back to illinois. They sold it because they couldn't figure out why it would barely run.
They put an aftermarket floor shifter in, a bunch of tune up parts and finally they bought a new clutch for it, they (wrongly) came to the conclusion that it must be the clutch, as it wouldn't be bad in 1st or 2nd/ but as soon as it got shifted to 3rd it fell on its face something terrible.
I checked compression it had absolutely none on 3 holes.
I then adjusted the valves and it came back to life.
When I later sold it the new clutch went with it still in the box.
Author:  plymouthcranbrook [ Wed Dec 02, 2020 10:24 pm ]
Post subject:  Re: Stumbles under load only
Look for a vacuum leak. Part throttle stumbling can be a symptom of that.
Author:  62Dudley [ Thu Dec 03, 2020 7:58 am ]
Post subject:  Re: Stumbles under load only
Thanks both,
Will keep you posted!

Dave
Author:  62Dudley [ Sat Dec 12, 2020 4:29 pm ]
Post subject:  Re: Stumbles under load only
Just following up with an update.

Checked compression - all good, with ranges from 125ish on 3 and 4, up to 150 max on 1 and 6.
Checking for vacuum leaks with carb cleaner, and found one at the manifold/head joint on the 3/4 arm!

Ordered a new gasket, and planning to put that on early next week.

Thank you both again, hopefully this does it.

Dave
Author:  plymouthcranbrook [ Sun Dec 13, 2020 8:33 pm ]
Post subject:  Re: Stumbles under load only
Hope that cures it.
Author:  62Dudley [ Fri Mar 26, 2021 9:02 am ]
Post subject:  Re: Stumbles under load only
Hi all,
Just some follow ups.

New manifold gasket did not cure it. Dropped one of the conical washers in the downpipe (stupid on my part for not putting a rag in it). Had to cut the old muffler off to get it out!

Back to the stumbling!
Could this be a fuel pump issue? I've been told that any slant pump will work for all years. Now I'm thinking though, that the pump I put on seemed to have a smaller actuating arm than the stock one in my box of parts.
Does it sound like a transmission issue? Its odd that its only in gear, and limits me from hitting higher speeds in 2 and 3.

thanks again for input!

Dave
Author:  Greg Ondayko [ Fri Mar 26, 2021 9:58 am ]
Post subject:  Re: Stumbles under load only
Do the Valve Adjustment Procedure

And you also might want to check to be sure that the vacuum advance Can is working properly as well as check the basic (initial) timing.

Getting those 2 things right can help tremendously and eliminate chasing other issues that are not there.

Greg
Author:  Jase [ Fri Mar 26, 2021 10:31 am ]
Post subject:  Re: Stumbles under load only
Have you got a vacuum gauge?

They usually can read pressure as well as vacuum. You can test the fuel pump with the gauge. Do not have the vacuum gauge in the cabin while driving/testing. Find some way to have the gauge outside but visible while you are driving the car under load.

I kinda doubt it is a fuel delivery issue, but testing it will tell. You can also hook the vacuum gauge up and observe the vacuum that the engine produces.. more information, makes for easier diagnosing.

My uneducated guess is to look in the direction of the ignition system.

Check voltage on the primary side.
Test the coil. Did you change the coil when you put on the electronic ignition?
A points coil will work, but one designed for electronic ignition is a better idea in the long run.

Observe the spark produced at the spark plug..
Author:  62Dudley [ Thu Sep 01, 2022 5:28 pm ]
Post subject:  Re: Stumbles under load only
Hi all,

Just wanted to finally close the loop on the old Dud’s issues!

My dad visited me last weekend and reignited the push to get it back on the road.

Turned out to be carb issues back to back to back. Talk about bad luck.

1. Initial carb’s choke would stick closed (and I’m assuming bad float adjustment as well).
2. “Remanufactured” carb, #2, had a stuck float thanks to an oversized needle shoving it stuck - this has to have been the main source of it for literally years now. This was also clearly thrown together as the threads were all but stripped when taking it apart. Also missing the ball bearing from beneath the plunger!!!
3. Had initial carb rebuilt, and for whatever reason, the float was not adjusted at all when they did it. Nearly completely shut off the gas flow to the engine once the bowl had time to fill.

Just took it on its maiden voyage with a new, properly rebuilt carb, and he is back to his old self!

Thanks to everyone that gave me tips along the way. Even though frustrating, I’m happy I got to play around with the slant and learn how it works. First time I adjusted valves on anything other than my motorcycle, and setting the timing even after turning the engine over with the distributor post out turned out to be a piece of cake.

Also pieced together the 2 other carbs so now I have a spare :)

Thanks again,
Dave
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