Holley 850 stumbles and stalls

[72 Charger SE]

Are you sure your fuel lines from tank to pump are clean and don't have **** in them?

That's exactly what I was just thinking...

A few years ago I had a problem like this in my Charger. The factory pickup in the tank had clogged up with rust scale from inside the tank. I would randomly have the engine shut down to an idle, and sometimes die. But most of the time it just wouldn't run above idle. Fuel pressure gauge at the carb was showing 0 once, but the engine was still running. That's when I decided to pull the pickup/sending unit from the tank. My car had sat with a mostly empty tank for almost 4 years prior to that, and we have a lot of moisture in the air, so it was prime conditions for rust. New sending unit and it ran great with consistent fuel pressure.

I would start with your fuel filter(s) first and then check the sock on the end of the pickup in the tank.

 

[john.thompson068]

That's exactly what I was just thinking...

A few years ago I had a problem like this in my Charger. The factory pickup in the tank had clogged up with rust scale from inside the tank. I would randomly have the engine shut down to an idle, and sometimes die. But most of the time it just wouldn't run above idle. Fuel pressure gauge at the carb was showing 0 once, but the engine was still running. That's when I decided to pull the pickup/sending unit from the tank. My car had sat with a mostly empty tank for almost 4 years prior to that, and we have a lot of moisture in the air, so it was prime conditions for rust. New sending unit and it ran great with consistent fuel pressure.

I would start with your fuel filter(s) first and then check the sock on the end of the pickup in the tank.

Okay. I have a fuel cell in the trunk and a fuel filter right after the line comes out of the tank. I can take apart the fuel filter and make sure a piece of foam or something has not clogged it up. The line is 1/2 aluminum line that was installed when I put in the motor. None of this stuff on my car is very old.

 

[john.thompson068]

Here is my fuel filter screen and a piece of foam I found stuck inside the filter against the screen. It is a Summit bullet type filter. Anyhow, it was a little dirty and did have a little piece of foam, but flow did not seem to be affected. I unclamped the braided fuel line and it was flowing just fine through the filter. So now I will go put it back together and see what happens.

 

[70rr-brian]

That foam is not insignificant in size. Perhaps that solves your issues!

 

[john.thompson068]

You guys were right. Problem solved. As soon as I fired her up she had 9 psi fuel pressure. So I backed out the adjuster and bought the pressure down to 6 psi. And the guage responded immediately to my adjustments. In fact, I had to back the adjusting screw out much father than where it was last time I had 6 psi. Looks like all the full throttle running last time out really sucked that junk into the screen and clogged it up. I had no idea so much dirt came out of a gas pump along with the gasoline. I will take the car out later to test it out, but I already now this was the problem. Thanks guys.

 

[john.thompson068]

I still am in need of a holley carburetor tuning kit and need to call Holley to discuss the stumble issues. Now that I can drive the car again I will also call the speed shop where I bought the number 37 squirter to see if I can try out some different stuff from their kit and then just buy what I need. I could test the car out on their side street, but will see how cool they are with that idea. Probably not to cool but we'll see.

 

[john.thompson068]

Actually, the stumble seemed to have went away maybe with out a clogged fuel filter. But I won't know for a while since I barely drove the car 10 minutes and hit the throttle two times before it was back to what it was doing before. I came back and my fuel pressure guage showed 3 psi no matter what I did with the regulator. Looks like I may be posting some more pictures of a clogged fuel filter here in a little while.

 

[john.thompson068]

Look at this! What is going on? This foam was brand new in like 2007. What should I do? Drain the tank, clean it out, and NOT install a new piece of foam I guess.

 

[john.thompson068]

Wow this is really pissing me off. Now I start the car up with the newly cleaned filter I am not getting any response at the fuel pressure regulator. I think the filter is clogged up and needs to be replaced. I think there is a bunch of that black goop I have been picking out of the screen with a needle head that is stuck inside the filter between the two layers. The fuel pressure won't go above six now even when screwed all the way in. It will go down as low as three when screwed all the way out.

 

[john.thompson068]

Okay I am sure all of my problems lay in the fuel pressure. When the fuel filter is clean and the car has adequate fuel pressure the car does not have any stumble off idle. I have not been able to drive the car far enough to test out the full throttle stumble because the filter becomes clogged right away. This second time out I did not make it 1/4 mile before I knew there was a problem. The car developed a stumble right off idle that only worsened as I made my way around the block to the test street. When I got back the car was only getting 3 psi no matter what I did to the fuel pressure regulator. The filter element is clogged and will have to be replaced. I will have to cruise the car around the block whenever I feel like it until the tank is almost empty. It probably has 12 gallons in it now so I better cruise up and down the freeway at 80 mph for a while first. Then I will pull the tank out of the car and throw away the foam. I will have to clean out the tank and then reinstall with a new filter. I am not putting a piece of foam cell in my tank ever again. Once I am back to normal fuel pressure I will put back in the original number 33 squirter and I bet it runs fine with that. So the carburetor must have the correct fuel pressure for it to run correctly even under normal driving conditions, not just WOT. It probably never did this when I originally put this combo together. But then I drove the car maybe 30 times in five years while in the Navy, and it sat in Public Storage for two years while I was at college. And then the problem became worse slowly over time, and next thing I know, I don't remember if it always did this or not. So I will check back for all of your comments, and will post here again once I can get this next problem resolved.

 

[70rr-brian]

Well, I am pretty confident once you do what you are saying...it will likely clear up all your problems. Good luck!

 

[john.thompson068]

Sure enough, with proper fuel pressure the stumble off idle went away. I even put the original number 31 squirter back on the front and still no stumble. I put the number 35 on the rear but there is still that split second hesitation from 45 or so mph to instant full throttle in third. When downshifting to second and going full throttle there is no hesitation, so I need to call Holley to figure out what I might need to do to fix that. I'll post that solution once I find it.