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Misfiring in third gear
https://slantsix.org/forum/viewtopic.php?t=61361		 Page 1 of 2
Author:  Zack [ Thu Jul 13, 2017 1:46 pm ]
Post subject:  Misfiring in third gear
The slant in my 69 D100 is misfiring, most noticeably when I first shift into 3rd. Once the RPMs go up it runs OK. It was flooding last week so I rebuilt the carb (Carter single) and adjusted the float level, so I figured one of the plugs might be fouled. The 4th plug from the 'front' of the motor was indeed fouled, and I replaced all the plugs (gapped at .035) but this did not fix the problem :?

The mechanic I occasionally work for told me he thinks it's the points ignition that's to blame. Should I upgrade to electronic distribution or lash the valves and try to find a vacuum leak first? The rebuild kit I used came with most of the gaskets so I can't imagine it's one of those. For what it's worth, I also get some hesitation when first applying throttle, but that seems to alleviate once the engine is warmed up.
Author:  Rick Covalt [ Thu Jul 13, 2017 3:37 pm ]
Post subject: 
Quote:
Should I upgrade to electronic distribution or lash the valves and try to find a vacuum leak first?
Lash valves and find/fix any vacuum leaks first. These need to be fixed either way. Electronic (HEI) is a great upgrade and is not at all hard to do. But you can put a set of points in it for a couple bucks and gather the HEI stuff as you get the time.

Rick
Author:  Zack [ Thu Jul 13, 2017 4:50 pm ]
Post subject: 
I'm going to follow this guide to set valve lash, any other guides you would recommend? Also a bit iffy on how to locate vacuum leaks... Sorry for the newbie questions, I'm burning up the search bar as it is. Just really itching to drive my truck every day!
Author:  DadTruck [ Thu Jul 13, 2017 6:08 pm ]
Post subject: 
does your truck have a 3 speed tranny, if so the mis fire is occurring when the engine has the least mechanical advantage and the highest load relative to RPM.

probably a weak spark issue,
I second the recommendation to go with a HEI conversion, but even that wont address: a worn or dirty distributor cap and or rotor or shot sparkplug wires..

for the cap and rotor,, take em out and give them a good cleaning and visual inspection, look for cracks, burnt conductors, if you don't know when the points and condenser were changed, install new ones.

for the sparkplug wires,, be sure they are not oil or grease soaked, look for cracks in the insulation, corroded connectors at the sparkplug or distributor ends,,be sure the sparkplug wires are firmly attached to the sparkplugs and distributor cap.

for vacuum leaks:
verify that the carb is bolted tight to the intake
use a good flashlight and look closely at the exhaust manifold to head joints, if you see evidence of exhaust leaks, you probably also have an intake to head leak. Also look closely to verify that each manifold mounting stud is present and has a nut on it, if a stud or nut is missing, you will have a vacuum or exhaust leak.

if everything looks good, on an engine with a cold to cool exhaust manifold, spray engine starting fluid at the intake to cylinder head joint, if the RPM increases, you have a vacuum leak at that location. Be careful, starting fluid is flammable.
Back to your initial comment that the motor misses under load, that is typical of an ignition problem, a vacuum leak would result in a rough idle and issues at all rpm/gear levels
Author:  Zack [ Mon Jul 17, 2017 10:07 pm ]
Post subject: 
Quote:
does your truck have a 3 speed tranny, if so the mis fire is occurring when the engine has the least mechanical advantage and the highest load relative to RPM.
It is the 3 speed.
Quote:
Back to your initial comment that the motor misses under load, that is typical of an ignition problem, a vacuum leak would result in a rough idle and issues at all rpm/gear levels
That does sound logical. I replaced plug wires with no luck. Cap looked nice and clean last I checked but I bought replacement cap and rotor anyway. Fingers crossed.
Author:  Joshie225 [ Mon Jul 17, 2017 10:11 pm ]
Post subject: 
Highest engine load is also the highest ignition voltage requirement as others indicated.

Change the condenser and the points if they aren't clean and flat. Check the dwell too.

How did the valve adjustment go?
Author:  Zack [ Mon Jul 17, 2017 11:10 pm ]
Post subject: 
Quote:
How did the valve adjustment go?
It didn't! I've been pretty busy, went to a wedding this weekend and other personal stuff going on... I think I'll have plenty of time this week though. I'll add the condenser to list of things to change, tried to get points at Autozone but they didn't carry it.
Author:  Zack [ Tue Jul 18, 2017 3:24 pm ]
Post subject: 
I think I'm going to bite the bullet and install Pertronix electronic ignition. I can't find new points for sale locally and I'm already going to have to remove and return the Champion plugs I bought and replace them with NGK ZFR5Ns, so might as well. I have read a couple threads on Pertronix installation but still a little unsure about whether there's a specific model to buy. The motor is a 69 225 original to my truck.
Author:  emsvitil [ Tue Jul 18, 2017 3:47 pm ]
Post subject: 
The cheapest pertronix is the pertronix 1

Also recommend getting the pertronix 3.0 ohm coil and remove/bypass the ballast resistor.


I've had the petronix 1 (with 3.0 coil) installed for over 10 years without any problems
Author:  Zack [ Tue Jul 18, 2017 4:11 pm ]
Post subject: 
https://www.amazon.com/dp/B00199BO4C/

https://www.amazon.com/dp/B000N2WAVC/

Are these the droids I'm looking for?
Author:  emsvitil [ Tue Jul 18, 2017 4:36 pm ]
Post subject: 
Those are the droids I have... :wink:

I kept the old points and condenser in my trunk.


There's also the HEI conversion to consider.



RockAuto should have the points and condenser. (don't forget the 5% discount (see the slanted network forum))
Author:  Zack [ Sat Jul 22, 2017 7:08 pm ]
Post subject: 
I bought those droids. Points delete was supposed to come today but it did not. I got the coil though. Went to install it and was surprised to see that even though I still had the stock coil marked "use with external resistor," there was no ballast resistor to be found. Weird. I wonder why someone might have removed it?
Author:  wjajr [ Tue Jul 25, 2017 5:43 am ]
Post subject: 
Quote:
there was no ballast resistor to be found.
Running a coil requiring a resister at 12 v will heat it up and over time degrade its guts. Chances are good your coil is fried just enough to make a weak spark resulting in misfire under load; that is lugging in third gear, or ascending a steep grade.
Author:  Zack [ Wed Jul 26, 2017 9:45 pm ]
Post subject: 
Success! Electronic ignition fixed everything. Super easy starts, much more pedal responsiveness, no more hesitation and no more misfiring. Now just to replace the clutch and set up my stereo and I'll be driving it everywhere. Only shame is I might have to cut up the perfect door metal to get the 6x9 speakers in.
Quote:
Running a coil requiring a resister at 12 v will heat it up and over time degrade its guts. Chances are good your coil is fried just enough to make a weak spark resulting in misfire under load; that is lugging in third gear, or ascending a steep grade.
I thought that might be the case but no dice. Just changing the coil might have made some difference but definitely didn't solve the issue like replacing the points w/ pertronix did.
Author:  Louise76 [ Sun Jul 30, 2017 5:33 pm ]
Post subject: 
Alternative to cutting: mount the speakers up under the dashboard, facing toward the center of the cabin. Be creative with a thin piece of aluminum sheet and with tin snips to bend up and cut a custom framework to fit the speaker and to reach any other screw hole (or drill as needed) to suspend the bracket with 2 to 3 self-tapping screws. If you plan it out, when you need to get behind the speaker, you just have 2 or 3 screws to remove and the whole thing drops out of your way. Tuck everything up fairly high and paint it all flat black so it won't be so noticeable to critics. In our cars I mount one far right corner high against the kick panel, and the other above the trans. hump, left of the heater box assembly, as I like to leave the far right side to be open for egress to the cluster / controls area.
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