Idles and revs great in neutral, runs like crap around the block

[LowNSlow]

‘77 Wing. Dyna ignition
Same behavior before and after single carb conversion, so I don’t think I’m really having a carb problem. I had thought I had a carb plugged up and wanted to try the single carb anyway.
Starts cutting out/stumbling a couple hundred yards from the house. Gets worse as I go. Got around the block and back to the house. The longer I sat there the smoother it ran, in neutral (no load).

Anyone experienced something like this?

**4/11/20 edit**
Post #111 has a summarized list of all diagnostics to this point.

**4/25/20 edit**
In summary: had to clean out my tank, single carb conversion was problematic. Went back to original 4 carb setup. Getting back to normal.

**7/28/20 edit** Previous edit was not getting very close to normal. And don’t think I was having a real problem with the single carb after all, but I had already removed that setup and went back to stock. Still didn’t seem to be hitting on all 4 consistently. Advanced my timing a bit and it sprang to life at part throttle although above 1/4 throttle it would bog badly. I found both main jet needles on the right side had fallen out of the slides. Fixed and this thing screams now. It’s never ran so well before

[gltriker]

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[TNTbefree]

Coil issue?

[robin1731]

Check fuel flow through the petcock. Then check flow from the fuel pump. Also check to make sure the gas cap is venting properly. Take a ride with the cap loose and see if it runs any better.

.

[ericheath]

Rule out carb/ fueling issues Mike Nixon uses a rag to begin partially blocking the carb entrance and see how it responds. If better, it’s probably fuel related. If you have a choke, you can do that easier.

If it isn’t, start checking ignition components. It will help if you can figure which cylinders are dropping, but if it idles great that makes it tougher to check temperature, but you can look at the plugs for hints. An easy potential problem is the copper plug wires getting corroded at the plug cap. Unscrew them, cut 1/4 -1/2” off to get new clean copper and replace. They also have resistors in the actual plug cap. They can corroded away to nothing and then your spark has to make that jump and hope to have enough energy to make the second jump at the plug. Even if it does, it’s late. Watch for the small spring that comes out with it. Some remove the resistor and replace it with a proper length of copper.

Check connections and don’t rule out just a low battery charge. Dyna doesn’t like low voltage or bad grounds.

[LowNSlow]

Rule out carb/ fueling issues Mike Nixon uses a rag to begin partially blocking the carb entrance and see how it responds. If better, it’s probably fuel related. If you have a choke, you can do that easier.

If it isn’t, start checking ignition components. It will help if you can figure which cylinders are dropping, but if it idles great that makes it tougher to check temperature, but you can look at the plugs for hints. An easy potential problem is the copper plug wires getting corroded at the plug cap. Unscrew them, cut 1/4 -1/2” off to get new clean copper and replace. They also have resistors in the actual plug cap. They can corroded away to nothing and then your spark has to make that jump and hope to have enough energy to make the second jump at the plug. Even if it does, it’s late. Watch for the small spring that comes out with it. Some remove the resistor and replace it with a proper length of copper.

Check connections and don’t rule out just a low battery charge. Dyna doesn’t like low voltage or bad grounds.

It wouldn’t idle if choke butterfly was closed at all.
I kept giving it more air via the air screw and ran the mix screw in a little as well. Disabled the choke completely to help out matters.

I opened up my plug caps from the plug side. Nothing under the screw at all. I’ll add a short piece of copper. I am trimming the spark plug wires a 1/4” for good measure, although they look good.

I’ll keep going through the diagnostics.

One word if recent history: it was running fine until one day it ran down to reserve and I couldn’t keep it going. Later in the day it started again on reserve and I drove to the gas station and filled up. Got caught in a rain storm and it started running like crap from then on. Like dropping cylinders.
I was able to crank it again and get it the last 1/2 mile home. Hasn’t been right since. I did clean out the fuel filter. Something still wrong

[tlbranth]

Your last comment suggests junk from the tank got into the fuel line and plugged the petcock or the filter.

[LowNSlow]

I suppose I should pull the tank and give it a good cleaning.

[LowNSlow]

I did just find my coil secondary resistance in spec, but all four plug caps out of spec.
#1 & 3 at about 10-11k each
#2 reading 28k
#4 reading 9k

[pidjones]

You can pull the screw ends out of the caps (held in with friction washers) which allows the resistors access and you can clean all connections and check to see if the resistors are Ok, or just buy new caps. Also, make sure you are not using resistor plugs.

[LowNSlow]

I did just find my coil secondary resistance in spec, but all four plug caps out of spec.
#1 & 3 at about 10-11k each
#2 reading 28k
#4 reading 9k

Now #2 reads 36k. Just getting worse the more I fiddle with it

[LowNSlow]

You can pull the screw ends out of the caps (held in with friction washers) which allows the resistors access and you can clean all connections and check to see if the resistors are Ok, or just buy new caps. Also, make sure you are not using resistor plugs.

Nothing under my caps. No resistor or spring.
I am running dyna elec ignition. Maybe I don’t need the resistors? Bought it this way. Have run it a fair amount the way it is. Just starting running bad recently.

[Explorer]

[/quote]Now #2 reads 36k. Just getting worse the more I fiddle with it[/quote]

New plugs, wires and caps. I would certainly try that before I pulled the tank.

It'll thank you for it.

[LowNSlow]

Now #2 reads 36k. Just getting worse the more I fiddle with it[/quote]

New plugs, wires and caps. I would certainly try that before I pulled the tank.

It'll thank you for it. [/quote]
It has new plugs. I believe the wires are integral to the coils and that checks out fine.
I’ll start with caps.

[ericheath]

Since you were caught in the rain when you also ran low on fuel, one of the two is likely a red herring. You’re right on the wires on the coils. How are you checking resistance of coils with no resistors in them? I would get some copper slugs, or 5k resistors and springs, in the caps before going by your readings much. Otherwise you need to remove the screw in the cap. It’s a little deep for most probes to reach in there.

Maybe get a decent look at the coils to see if they are cracked. A crack and rain and they’ll do what you’re describing. They are buried pretty well, but with the tool tray out and side covers off you should be able to get a decent look with a light. The rain issue is making me lean that way.

Simple and cheap replacement for coils with a Dyna is gl1200 or 1500 coils. The 1500’s are plentiful and cheap on FleaBay.