Ignition causing "carb issue"?

[JerseyJoe]

Put a Thumper Carb on my 493/4 speed Charger in the Spring and it ran like an absolute beast. Idled nice at 13.8 AFR,
WOT was 12.3-12.5, cruised at 13.0. Fuel pressure is 6 psi as recommended by Thumper.
Driving back to the hotel at Carlisle last month, I noticed the AFR was dropping into the low 12's/high 11's cruising at 1800-2000 rpm and fouling the plugs.
I contacted Dominic, tried the leaner (BLP) idle bleeds and hi speed bleeds he sent with the carb and at cruise saw almost no change. Just tried bumping initial timing up from 16 to 22 and fresh plugs to see if that cleaned it up. Idle afr came up a little but it still cruises around 12.0 AFR. I put the carb right back to the original setup Dominic sent.
I tested the MSD Blaster 2 coil and it's at the high side of spec at .7 ohms. I have an analog 6AL box. Plug wires are 6 months old.
Am I going in the right direction suspecting the ignition causing problems only at cruise?
I'm convinced it's not the carb since it ran so well for months before Carlisle.

 

[qkcuda]

While discussing a friend's carburetor issues at the shop where it was going to be dyno'd, the engine builder said most carb issues are actually ignition issues. I mentioned my slight bog when the secondaries kick in and he suggested a faster advance curve. I currently have the stock points distributor in the car, but I kept my recurved electronic distributor set up from my last car, and I think I will install it over the winter and see what difference it makes.

 

[R413]

Blaster 2 is a cheapo coil, try an crusty old original mopar one, just for a test.

Do you have electric pump? Turn it off and see how it runs.

do you have a fuel pressure regulator? Maybe went bad and
it is too high? Check pressure anyway

do you have a return line? Is it plugged?

anything can go bad at anytime.

 

[steve340]

Have a look at the needle valves and float settings.
You may have a weeping needle valve.

 

[Nxcoupe]

Ok, ignition will not cause AF to show rich. It will cause it to show lean. The reason for this is because an O2 sensor reads, well, Oxygen, not fuel. A value denoting a rich condition actually is showing you there is very little oxygen left in the exhaust passing by the sensor. So, ignition is not your issue, too much fuel is. I would suspect a blown power valve or as mentioned, too high of a float setting or a heavy float.

 

[JerseyJoe]

Thanks guys, Dominic suggested putting more idle bleed air in. Just waiting on parts and got to overthinking. I had already lowered the float level slightly, but out of the box it was set up so we’ll it’s not making sense that it’s changed so much at cruise without any other changes.
I’ll find out what’s up after I get some bleeds from BLP.

 

[Nxcoupe]

Thanks guys, Dominic suggested putting more idle bleed air in. Just waiting on parts and got to overthinking. I had already lowered the float level slightly, but out of the box it was set up so we’ll it’s not making sense that it’s changed so much at cruise without any other changes.
I’ll find out what’s up after I get some bleeds from BLP.

Has the engine backfired through the carb ever?

 

[JerseyJoe]

Has the engine backfired through the carb ever?

Never. Carb is only 6 months old and I was taking it easy driving it up until the issue started. When I had the carb apart yesterday I put a little suction on the PV and it opened.

 

[Nxcoupe]

Never. Carb is only 6 months old and I was taking it easy driving it up until the issue started. When I had the carb apart yesterday I put a little suction on the PV and it opened.

Well, something is allowing more fuel than the engine needs to get into the intake. Something has loosened up or changed to allow a bunch more fuel to get into the cylinders. Good luck, hope you figure it out.

 

[steve340]

If the air bleeds and jetting was once OK - something else has changed.
A weak ignition can cause a rich condition if it does not have enough power to burn the mixture correctly.

 

[Nxcoupe]

If the air bleeds and jetting was once OK - something else has changed.
A weak ignition can cause a rich condition if it does not have enough power to burn the mixture correctly.

Then his wideband would show 15 to 1 or higher. What you are saying is true, but not aligning with the facts he's presented. It is running rich, meaning more fuel than air is present in the exhaust, which is what his Oxygen sensor is seeing. Something has changed that is letting more fuel into the mixture. I have to explain this stuff to customers all the time, widebands are great tools, but you have to understand they only look at oxygen content, not hydrocarbons. For that, you'd need a 5 gas analyzer. I tune a lot of EFI cars on my dyno and I have a good grasp on what a wideband is trying to tell you, but it is a steep learning curve for those who don't work with one often.

OP, did you recently fix any exhaust leaks? Could the O2 bung have had a leak that rusted or carboned itself shut?

 

[Geoff 2]

Spark plug heat range? Should be a 5 in NGK. People foolishly fit colder plugs when not needed; they then start to foul.....

 

[steve340]

You are interpreting the reading the wrong way around. His AFR is reading 12 which is rich. This means 12 parts of air to 1 part of fuel.
15 is actually leaner than 12 on an AFR meter.

 

[JerseyJoe]

Well, something is allowing more fuel than the engine needs to get into the intake. Something has loosened up or changed to allow a bunch more fuel to get into the cylinders. Good luck, hope you figure it out.

Thanks for your help. I won’t be able to get back to it until after the weekend. I checked the bung when this started and it’s good.
Strange that something I managed to catch when it was happening is tough to figure out.
At 11-1CR I’m running NGK 6 heat range, that’s what my build called for.

 

[Nxcoupe]

You are interpreting the reading the wrong way around. His AFR is reading 12 which is rich. This means 12 parts of air to 1 part of fuel.
15 is actually leaner than 12 on an AFR meter.

I know what I'm talking about. If his ignition was the culprit, then it wouldn't be burning all the fuel and air up. Again, O2 sensors sense OXYGEN not fuel, so if the ignition was not igniting the a/f mixture as you suggest, then there would be an abundance of unused, unburnt air along with this unburnt fuel. The O2 sensor would see the oxygen and read lean as in 15 to 1, because again, it reads oxygen in the exhaust, not fuel. I can't explain it any clearer. I could demonstrate or you could get a wideband and experiment for yourself. Take a plug wire off, and it'll read 16 to 1, and smell rich. That's why on EFI systems, a misfire causes the PCM to dump fuel because it is trying to richen up a lean mixture, that really isn't lean as it's seeing the unburnt oxygen in the exhaust from the misfire.

 

[68 HEMI GTS]

If the tune was good and now it’s not something changed I wouldn’t be swapping bleeds as that’s not the issue. Have you verified the 02 sensor is good?

 

[Nxcoupe]

If the tune was good and now it’s not something changed I wouldn’t be swapping bleeds as that’s not the issue. Have you verified the 02 sensor is good?

That's a good point and I considered that, but these Bosch sensors fail to around 14 to 1 or so, usually, so I didn't mention that. I agree, something drastic changed, or he had a vacuum leak that fixed itself, lol!

 

[bobsgtx]

I have found the easy way to test ignition is to use a test plug. I have a couple of KD brand and use the HEI one. Basically a spark plug with a 3/16 to a 1/4" gap with an alligator clip to ground it. If your ignition can put a blue spark with that it's not an ignition problem. I've found many including myself chasing fuel problems when they are ignition problems.

 

[1967coronet]

What do the plugs look like ?

 

[JerseyJoe]

Tonight I was going to try a new power valve just to rule that out. My blocks have an O-ring for the PV and the one in the primary wasn't sitting in it's groove right so I made sure that went back together correctly and fired it up. Idle was better but still gets fat (low 12's) between 1500-2000 rpm. Had to pull the car back in because a storm came through so tomorrow I'll check the plug in the secondaries.
I have no reason to believe the o2 sensor is bad yet, the plugs were fouled, black and sooty.