stumbling cat

OK, I went to the MSD website and checked the distrib, and the 6a box. Both passed the tests. When the car is in the garage it revs great. It only misses under a load. What does that mean?

I'm getting frustrated. I changed the plugs, no difference. Makes me want to belive the carb is the problem. But when the car is parked it revs up perfect.... When I put the least bit of load on it it stumbles and misfires. This has to mean somthing, but what?

I once had this same problem minus the backfiring. After going through my ignition system over and over again...I discovered it was simply a clogged fuel line.

Kevin

Tune the carb. Sounds lean.

Had the same problem under load - change the coil!

...DEEB could be right! The Coil is 'Suspect', AND intermittant(I.E. Gets Hotter(You should have a 'Ballast Resister OR a resister WIRE) or from movement/vibration). Test It! by trying a second Coil that You KNOW, works! Also, BE Absolutely SURE of the GROUNDING for the Engine Block, this is essential for the fireing of the spark plugs. And Test for GOOD ground AT the Distributer HOUSING, OR Where ever You have Grounded The Electronic Control Module. "You can't have a good Positive; if You Don't have a Good Negitive!" Last, I get the feeling of a intermittant chafing/shorting of the 'HOT' (12 Volts +) Wire. How is the Tachometer Behaveing!? If it is 'Bouncing Around', this indicates One or a combination of any of the Above. Best of Luck with it! And let us know What and When the problem was.

...One last thing BE SURE of the Polarity of the Coil Primary Wires; Positive to + and Negitive to - ...

Thanks you all! I changed the fuel filter and it skipped to the gas station. I put 18 gal in and it quit skipping. I had put half a bottle of Dale Ernhardt jr outlaw octane booster in the last time I filled up, maybe it was contaminated with something. I had drained a carb bowl to look for water but did not see any. It sure feels good to have my power back!! You are correct about grounding, I learned that lesson a long time ago. I still can't say for sure what was wrong, I'm just glad it is gome!!

Well I went by a friends garage today he had a Yellow 71 Push button #1116 sitting in the garage waiting to be worked on,Very clean and sweet looking ride !

Finally, You know it is always somthing simple! The carbon ball in the center of the distributor cap has fallen out and dissapeared. I noticed that it looked like a diamond ring with the jewel missing, never thought much about it untill it started scrapinf the rotor button.I ordered a new one, should be here tomarror. I ordered it out of frustration, figuring if this did not stop my problem. I would go to somthing besides ignition. I just know this will fix it!!!

Well I am glad you figured it out,so when ya gets it running I want a ride lol.........Just kidding..

Oh NO!! I spoke too soon! I installed my new cap and rotor and it still cuts up. Did compresson check on 345 cyl and they pump up to 175 psi. The plugs looked great. Ok I had a small pinch in the fuel line and have replaced it with a loop to be able to overcome the sharp angle.Still sputters only when driving. In the shop it screams? My carb man is coming Thursday, although I just know it is ignition related. But Then again; I just knew it would be fixed with a new cap and rotor. Very confused in SC

if it runs ok in neutral, but stumbles under load, then a fuel supply problem gets my vote.

was the car running OK & developed this problem with no changes having been made to the motor? or did the problem crop up after a change was made?

George

Thanks George, I pulled the coil wire and turned the motor over and dumped fuel into a jar, It was not very impressive. I have a manual pump. I just changed it, and the new one pumps no better. I mean when I turn the motor over 5 times it might fill a cigarette pack with fuel. The new pump is no better than the old. There are no bubbles in the fuel as if it were sucking air. I am still confused. The problem started when I added the octane booster. Since that time I have sucked fuel from the bottom of the tank and used a full tank... You know if you look back at this thread you will see where I thought it was fixed when I filled it up. Maybe I should get a pressure gauge and see if I have about 8 lbs? If a full tank helps the pressure? Maybe that is a sign.

Are you saying you installed a bottom feed from the fuel tank when the problem started?

If so, why not go back to the top feed & see if it clears up? Hose clamp a bolt into the end of the bottom feed line to temporarily plug it.

George

I have not changed the fuel pickup.I put a clear hose with a nipple on the end a nd put it in the tank fill port and created a vacuum as I wacthed the contents from the bottom of the tank fill the 8 foot tube I saw no contaminets. I have checked thr bronze filters in the carb and they are clear. Still concerned about fuel pressure, will have gauge soon to measure. Thanks for input, I'm gonna sleep on it.. really!

thanks for clarifying.

There is a little nylon filter sock on the end of the fuel tank pick up tube, inside the fuel tank. Chances are this sock is partially clogged. With the filler cap removed to prevent pressurizing the fuel tank, BLOW air down the fuel tank pick up tube, thus blowing the little nylon filter sock to smithereens. You have sock bits settled on the bottom of your tank, but your pick up tube should be unclogged.

George

Good idea! I removed the suction line from the top of the tank, then put my clear plastic line on the outlet and sucked on it. I easily drew fuel up into my clear tube, and it looks ok. Then I loosened the fill cap and blew 100 psi into the tank, then put my old fuel filter that was not resrtricted there to catch anything before it gets to the pump, I also put a fuel guage @ the carb and when we run the motor in the shop it maintains 4.5-5.0 psi. It is raining outside so I am stuck in the shop for now, Still, I do not see a major breakthrough. What about somthing mechanical, valvetrain? there are no noises......I will continue compression tests on remaining cyl. Tomarrow is carb rebuild day, but I don't think thats it either.

Sounds like a problem I had several years ago; I'd check your accel circuit on your Carb. If it is a Holley check the cam lobe on the driver side of the Carb. and make sure that it has .015" clearence to the plunger lever. you describe the issue as a "stumble" which leads me to think that as you throttle up the carb is not supplying enough gas as the carb transends between the idle circuit and the accel circuit.

It is much worse than a stumble. It feels like multiple misfires, sputtering.The car is basically not drivable. Not through carb, not backfire. What do you think about the 5psi fuel press? Now I have my hands on an electric fuel pump. But it would seem to me that there is enough fuel in the bowls to get the car up to speed, this SOB won't get out the drivway without spittt,sputt,skkip.

Sorry for joining late on this one......... how about this. (and because you say it runs great in the driveway).

Is it possible your primary float is too low, meaning sure, at idle...etc (no load) the fuel pump is getting you what you need but if the pump (@ 4-5psi) has to "react" and fill up its just not fast enough as if your float were higher)....... starvation? I'm running the Holley Red on mine now which maintains 7psi w/o regulator (I also have a russel in-line gauge on he carb to see it).

...just a thought...........

I checked the fuel level today by removing bowl level screws and rocked car. The new plugs I just put in are gapped at .060 I also tighented the disributor down.....mmmmaby it has to be tight to be grounded?

LPB,

first, I didn't mean for you to pressurize the fuel tank (air down the filler). I suggested you blow air backwards through the fuel pump suction line, blow the sock off the end of the line, inside the tank.

second, if your car's ignition was "mis-firing", it would back fire & make pops in the exhaust system due to the unburned fuel that would be dumping into the exhaust from the unfired cylinders. Make sense?

so, you poured octane booster in the tank, the engine began running poorly, you ran a tank through the engine, re-fueled, the car started running better after re-fueling, now the engine is running as a bad as before? worse? is the fuel level in the tank down or still full?

Are you sure you didn't change anything else just prior to the problem's appearance?

I would still advise you to blow the sock off the end of the fuel pump suction line.

George

To level set here...... Is it true that your car starts. Idles fine, and you can also "rev" it a bit in the driveway?

Question #2. Lets say you get up-to-speed (50?), will it hold w/o any stumble. (And I ask that as a general question for any maintained speed)........ will she run fine?

you know .060 gap for a spark plug seems large. I looked at older posts and the largest I have seen was .051. You know the best history of your car but too large of a gap could cause off idle problems. Perhaps go back to a stock gap and work from a known baseline.