dontreadonme

long story short..
installed new carb, intake, distributor, wires, plugs in the last month.

It has been running PERFECTLY until today.

feels like I have a plug wire unplugged now.

Vibration at idle, you can feel vibration under acceleration.. Feels exactly like it did before the new parts when I noticed I had a plug wire burnt through by the headers.... Sounds like its missing too..

Came home, checked the wires, no issues... Tightened up the plugs. Some a little loose... Retightened all down and reinstalled plug wires...

Plug wire to #8 was really really hot.. Wierd?? I dont know...

Still feels and sounds like I have a cylinder not firing. Have a pretty strong smell of raw fuel out the pipes too...

Stumped.. Anybody with suggestions as to what to check next?

Msbfdx

Loose plugs? How did plugs look when removed...any wet...all the same? Perhaps a bad plug.

army

One way to troubleshoot this is to run it with the #8 plug wire off and see how it behaves. If it isn't firing the engine should run the same as when the wire is on. If it runs worse, put the #8 wire back on and try taking the #7 wire off ..and so on. Another way is to use a spark tester on each wire. They're about $10 at NAPA and other automotive stores like that. The tester goes between the plug and the plug wire and allows you to visually confirm there's spark.

Any chance you have a bad cam lobe? I've had a couple SBC bumpsticks do that over the years. Runs like it's a misfire, gets a lot worse as the revs go up. A test for that is to pull the valve covers and look for a rocker that isn't moving up and down the way it should.

jb78L-82

First thing I thought of is a burned plug wire...check to make sure that a wire is not burned through and arcing. I had a bad lope on a cam about 25 years ago that also did what army alludes to...

toobroketoretire

It is very easy to troubleshoot a missing cylinder ESPECIALLY with headers. Just put a small match-head size dab of grease on each of the pipes next to the head then start it. The dab that doesn't melt off after several minutes is the missing cylinder.

army

Sounds like a good trick toobroke. I'll have to try that next time.

dontreadonme

really great ideas guys and thank you! I will give these a try later today after work.

It feels exactly like a burnt wire but a close visual inspection showed them looking ok..

REALLY hope its something easy.. Time and updates will tell.

leadfoot4

If nothing looks obvious, take an Ohm meter and check the wires. If they were bought as a completed set, maybe there was a bad wire or bad crimp, and being in use for a while has brought the issue to light.

dontreadonme

Dont know if it will help diagnose, but before work today started it up and was going to temp headers with a laser thermometer. Side pIpes were spitting out a little raw fuel and I heard a few 'pops'. Nothing extremely loud, but they did it. Shut it down for fear of hurting her.

mysixtynine

Dont know if you have points or hei or what kind of carb? You could be rich due to missing or too much fuel. Is the popping from the exhaust or carb?

Basic test can be done with a timing light ... just attach the pickup lead to each plug wire while running and make sure the light is rhythmically flashing when attached to each wire.

I like to use straight pins inserted into the boot of the plug wire at the cap and then use a meter lead to jumper the carb stud to the individual pins in each plug wire to see if the problem gets worse or stays the same. If it stays the same you have the plug in question. (DO NOT just unplug spark plug wires... you can cause cross firing in your cap and ruin it you always want to ground out the arc to ground.)

If everything is firing correctly then it sounds like a hung / stuck float or if its a holley a bad power valve / hng float / hng or dirty needle and seat. My holley rubber products suffered a major deterioration issue this year and my power valve and accelerator pump diaphragms were all damaged. Not sure what carb you have but I had to replace my powervalve as the car was running really fat and poping out of the exhaust.

dontreadonme

thanks for the advice '69.
I have a two week old ultra street avenger on it.
Have NOT had the time to tune it properly, but it ran quite well out of the box.
The popping came from the side pipes not the carb.

I like the timing light trick. Makes sense!

Im still dead set thinking its a plug wire.. But testing is needed and itll get it later tonight.

Thanks to you all, I have a good plan of attack.
Hoping its simple still.. Dont want a new cam or carb problems.....
Thanks again guys. Ill let everyone know what it was later today

dontreadonme

and now that I am thinking about it, the popping probably just from the raw fuel spewing out the pipes from the lack of being fired... About to tear into it. here goes nothing!

mysixtynine

With it running you can look down the carb and see if fuel is dripping out of the boosters. The carb sounds like its newer than the other stuff so maybe start there.

If it is you may have your fuel levels set too high in your bowls.

I dont know the avengers but I just looked them up....looks like they may have sight glasses in the bowls to check the levels on some of them.

I was not expecting to find issues in my carb as it has very little use on it... but the ethanol in all of our gas now a days seems to be having an affect on these cars that sit more as the gas will evaporate quicker with the alcohol content. My car is seldom driven as it is being put back together. My powervalve was a perforated mess. I cant see yours being bad when it so new but u never know.

good luck finding the issue.

jb78L-82

I hear all these stories about ethanol in the gas causing carb problems, but my 1985 Holley 4175 650 CFM Q jet replacement carb has had zero issues in almost 30 years-rebuilt it in 2010 and everything looked great...just an FYI...

hugie82

The harbor freight lazer thermometer works well to find a weak or dead cylinder.

dontreadonme

Great thing about my profession as a chef.. Picked up a new one with all the bells for 'work'

Figured itll come in handy!

army

Hey.. I need one for work too. I'm in IT. Hardware temps are very important. I do quite a bit of after hours stuff so my employer provides me with a laptop and a workstation for my home office. I would hate for one of them to overheat. Laptops are especially prone to that. I better get a temp reader for them too.

Can you think of anything else we need for work?

mysixtynine

My understanding is if you use the car often enough then it should not be an issue. The problem is for cars that sit long enough for the fuel to evaporate faster due to the alcohol content . I didn't make it up. This came from edelbrock tech (my fuel pump). I don't have a pic of my fuel pump diaphragm, wish I could show u those. But below is my powervalve with a completely eaten away diaphragm and my accelerator pump which was cracked to no end. Two different companies holley and edelbrock. You tell me.

Anyway NOT saying this is his issue especially since his carb is so new just saying it can happen. His condition sounds like a hung float or blown or broken powervalve.

jb78L-82

Understood....My 78 L-82 4 speed with the Holley 4175 spreadbore 650 CFM sits in the garage 99.9% of the time...maybe 500-750 miles per year/every 2-3 weeks in the summer months, less in Fall/Spring, zero in the winter...That's been my personal experience with my 30 year old Holley 4175...

spjrr

Just went through the same problem with my 69. stock original quadrajet and point ignition, so car is a little different, however it was running great first few trips of this cruising season, then last week started missing and backfiring just a few blocks from home. To make a long story short. The condensor was bad and the points were burnt. So lightly burnt that you had to take them out and get them under bright light and then they just looked dull. Replaced them and the condensor and all is well. That set of points and condensor had maybe 200 miles on them and they failed. The were bwd brand from orielly auto and this is the second set I have had fail. Am going back to Echlin points from NAPA That is what I used years ago and always had great luck with them. I now carry a spare set of points with me and enough tools to swap them on the spot when they fail. I also carry a jumper wire with a ballast resistor to supply battery to the coil in case the resistor ignition power wire fails (which is common on early c3's with point ignition).

Mark Smith