Flathead Running rich
- Thread starter bmwillia
- Start date
Ken Henry
Senior Member
In my experience, plugs like that have always been due to too much fuel. I didn't think a misfire on the proper air fuel ratio would cause plugs like that but could be wrong there?? I would check the float, needle valve, and power valve while waiting for your ignition parts
drolston
Well-known member
Lurching is not typical of a vacuum leak. Vacuum leak will generally manifest as poor idle with little effect from idle adjustment screws, and running rough at higher rpm, but not the lurching. Lurching is usually ignition, possibly carburetor.
john in illinois
Well-known member
What air filter are you using. The small hot rod ones do not flow enough and can choke the carb.
John
John
bmwillia
Senior Member
New plugs and condenser installed.
removed the air filter and when I did that, I would hear steady pops/back fires out of the tail pipe during idle. That issue went away with the air filter installed.
here is a video https://youtu.be/tExmaCIlNdg - you can hear the occasional popping.
Here is a video from the Engine side, revving it up and if you listen, you can hear the backfiring out of the tailpipes in the back ground after I let off the accelerator. This is what happens on the road when shifting between gears. I took it for a short drive right after this video, and it performed much better than it has been but I did get the occasional back fire out of the pipes between gear while shifting. Not nearly as much as it used to.
https://www.youtube.com/watch?v=YFUjZCBjjYs
I'll pull the plugs this afternoon and have a look at them to see what they look like after that short run.
Brad
removed the air filter and when I did that, I would hear steady pops/back fires out of the tail pipe during idle. That issue went away with the air filter installed.
here is a video https://youtu.be/tExmaCIlNdg - you can hear the occasional popping.
Here is a video from the Engine side, revving it up and if you listen, you can hear the backfiring out of the tailpipes in the back ground after I let off the accelerator. This is what happens on the road when shifting between gears. I took it for a short drive right after this video, and it performed much better than it has been but I did get the occasional back fire out of the pipes between gear while shifting. Not nearly as much as it used to.
https://www.youtube.com/watch?v=YFUjZCBjjYs
I'll pull the plugs this afternoon and have a look at them to see what they look like after that short run.
Brad
Last edited:
drolston
Well-known member
First, the small hot rod air cleaner (if the filter element is clean) does not choke the engine until the rpm is way up. It is not going to cause the engine to run rich for normal driving.
Second, did the lurching (intermittent momentary total engine not firing) go away with the new condenser and plugs? If so, great - that makes trouble shooting the remaining problem much simpler.
If the only remaining problem the exhaust popping, something is causing some unburned fuel/air to enter the exhaust stream. Main jets too large can cause that to happen, and it will be most pronounced when decelerating in second gear. Since you get popping at idle when the idle circuits determine the mixture, not the main jets, I would rule out the main jets for now.
Having hopefully fixed the ignition problem, maybe you need to adjust the idle jets. Close one until you hear the rpm drop a little, then open it back about a quarter turn. Then do the other. Reset the throttle idle adjust screw to get a nice idle (about 600 rpm or a little less), then do the idle jet adjustments again.
If you are still getting exhaust popping at idle, run some MMO through the carb while jazzing the throttle. If that does not fix it, run a compression test on all cylinders and report back.
Second, did the lurching (intermittent momentary total engine not firing) go away with the new condenser and plugs? If so, great - that makes trouble shooting the remaining problem much simpler.
If the only remaining problem the exhaust popping, something is causing some unburned fuel/air to enter the exhaust stream. Main jets too large can cause that to happen, and it will be most pronounced when decelerating in second gear. Since you get popping at idle when the idle circuits determine the mixture, not the main jets, I would rule out the main jets for now.
Having hopefully fixed the ignition problem, maybe you need to adjust the idle jets. Close one until you hear the rpm drop a little, then open it back about a quarter turn. Then do the other. Reset the throttle idle adjust screw to get a nice idle (about 600 rpm or a little less), then do the idle jet adjustments again.
If you are still getting exhaust popping at idle, run some MMO through the carb while jazzing the throttle. If that does not fix it, run a compression test on all cylinders and report back.
drolston
Well-known member
My previous post went up before I saw the black #4. Were all the rest okay?
First check that you are getting a strong blue spark at that plug to jump about 1/2". If not run down the ignition problem. Bad spark plug wire; distributor cap crack or carbon trail.
If spark is good at #4 do the MMO and compression test things.
First check that you are getting a strong blue spark at that plug to jump about 1/2". If not run down the ignition problem. Bad spark plug wire; distributor cap crack or carbon trail.
If spark is good at #4 do the MMO and compression test things.
bmwillia
Senior Member
The lurching did go away with the new plugs and condenser.
I still feel a bit of a miss when I put my foot in it at times, almost imperceptible, but there. Cruising at about 45-50 in 3rd feels great.
I haven't had time to pull the rest of the plugs. Hopefully will get to that tonight. I imagine they are all the same since they were all black before. Some worse than others, but all of them were real black.
I still feel a bit of a miss when I put my foot in it at times, almost imperceptible, but there. Cruising at about 45-50 in 3rd feels great.
I haven't had time to pull the rest of the plugs. Hopefully will get to that tonight. I imagine they are all the same since they were all black before. Some worse than others, but all of them were real black.
BobR35
Senior Member
Hey Brad, I just popped on and saw your post. I have been through this same nightmare since I purchased my '35 in Dec. After doing everything several times over, my problem was all carburetor. I even rebuilt the carb but the carb was worn out and it still was running rich and also leaking fuel after turning off. I decided to purchase an aftermarket carb for $150 on ebay to try lastly before spending the big bucks for a new one and since, the car never ran so goooood! Went form 10 mpg to 15mpg. Just my input. Good luck !
bmwillia
Senior Member
Update.
Had a little time today so I pulled the plugs and while they were not all black, all had a little bit of liquid on them.
Went ahead and got the engine warm in the driveway and tried to adjust the idle screws. With the air filter on I screwed the first screw all the way in and nothing changed. Then screwed the second in and nothing changed. Backed them out 1/4 turn. Removed the air filter and tried again. The idle did drop a little and it seemed like it was struggling just a little but not much. The popping never completely went away, but it was mess often and less pronounced. Took a drive down the road and I am still getting gargling/popping on deceleration between 1st and 2nd and between 2nd and 3rd.
Also checked the spark on 4 and it was a good strong spark jumping 1/2 inch. (BTW: Make sure the handle insulation on your pliers is good before handling live plug wires.)
Here are picks of the other 7 plugs to go with #4 above.
Sent from my iPhone using Tapatalk
Had a little time today so I pulled the plugs and while they were not all black, all had a little bit of liquid on them.
Went ahead and got the engine warm in the driveway and tried to adjust the idle screws. With the air filter on I screwed the first screw all the way in and nothing changed. Then screwed the second in and nothing changed. Backed them out 1/4 turn. Removed the air filter and tried again. The idle did drop a little and it seemed like it was struggling just a little but not much. The popping never completely went away, but it was mess often and less pronounced. Took a drive down the road and I am still getting gargling/popping on deceleration between 1st and 2nd and between 2nd and 3rd.
Also checked the spark on 4 and it was a good strong spark jumping 1/2 inch. (BTW: Make sure the handle insulation on your pliers is good before handling live plug wires.)
Here are picks of the other 7 plugs to go with #4 above.
Sent from my iPhone using Tapatalk
