Acceleration problems

[$MoneyGreen]

Hello all. Im new to this forum, as well as a rookie owner of a 70 Chrysler 300 with only 20,000 original miles. I traded it for a similar age Ford 100. Everything is working great on this rig, except some acceleration problems. I starts well, but if I step on the gas HARD, she dyes. If I give it slow and steady gas then it runs fine. The carb is a Carter 4640, and is in good shape. Please help with any ideas. Thank you

 

[MacLebaron]

Nice ride!

 

[MONC440]

Super nice car. I would start with checking the accelerator pump by pulling the air cleaner off, look down the carb and opening the throttle. You should see a big squirt of gas. If not the pump seal could be shot. If that looks good check the timing. I would check the timing anyway because it is a new car to you.

 

[MJFUR]

And if the carb needs rebuilt here is one of the Forum Sponsors
Carburetor Restoration in Youngstown, OH | Woodruff Carburetor Specialties

 

[Grannys67]

+1 on checking the timing... my 383 carter used to bog on hard acceleration like that, even with a rebuilt carb. turns out the timing was a hair off. a little twist smoothed it out perfectly

 

[$MoneyGreen]

Thanks for the reply. Ill check timing tomorrow, and update.

 

[$MoneyGreen]

I adjusted the timing, but that didn't help my stalling problems. When I was checking the accelerator pump, I noticed that the secondary throttle valve opened way later then it seems it should. I feel like this could be the issue. I haven't figured out how to adjust that yet.

 

[57fury440]

What about the float settings?

 

[$MoneyGreen]

I think the float is good. It fills up.

 

[MONC440]

I adjusted the timing, but that didn't help my stalling problems. When I was checking the accelerator pump, I noticed that the secondary throttle valve opened way later then it seems it should. I feel like this could be the issue. I haven't figured out how to adjust that yet.

Usually a stalling issue at initial full throttle is too much air and not enough fuel. I don’t think the secondary opening late shouldn’t affect that.

When you checked the accelerator pump fuel shot, was it allot of fuel or just a small shot.

 

[$MoneyGreen]

@MONC440 It looked like a good amount of fuel.

 

[Sixpactogo]

I adjusted the timing, but that didn't help my stalling problems. When I was checking the accelerator pump, I noticed that the secondary throttle valve opened way later then it seems it should. I feel like this could be the issue. I haven't figured out how to adjust that yet.

I too would bet on the accelerator pump being the culprit. More than likely someone put ethanol laced gas in it. The ethanol will eat the pump material causing your issue. Been down that road myself. I think some of the newer kits have upgraded the pump material to better handle the alcohol but I don't take the chance. I run premium in everything that has a carburetor.

 

[david hill]

There are part throttle transfer slots that get plugged up w/ varnish deposits A through carb rebuild by an experienced rebuilder (@Carburetor Restoration in Youngstown, OH | Woodruff Carburetor Specialties), will solve the problem. Be sure to include a revised acceleration pump to handle todays methanol blended fuels.

 

[Mntac]

I had the exact same symptoms after replacing a bunch of parts in a tune up on the caddy. Scratched my head for months trying to figure it out. Turned out to be the little black rubber plug in the end of the new fuel filter for the Qjet carb was restricting flow. Looks like a little spring check valve setup inside. Pulled it out and the WOT issue was fixed.

 

[$MoneyGreen]

I cleaned out the carb, put in a new fuel filter, adjusted timing. The acceleration issue didn't change. It still dyes at full throttle. If I give it heavy and steady gas it will stall for just 1 sec and catch up and accelerate kind of fast. But it still feels like something is not right. Next step I want to put in a new accelerator pump and see if that helps.

 

[MONC440]

I cleaned out the carb, put in a new fuel filter, adjusted timing. The acceleration issue didn't change. It still dyes at full throttle. If I give it heavy and steady gas it will stall for just 1 sec and catch up and accelerate kind of fast. But it still feels like something is not right. Next step I want to put in a new accelerator pump and see if that helps.

How did you clean out the carb? Did you disassemble it or what? If I were you I would do a complete rebuild of the carb so you can clean out all the circuits. They are not a complicated rebuild. As others have mentioned make sure you use a pump that is compatible with todays fuel. I have a few different carbs on the shelf that I would just swap out to see if that was the problem before rebuild but if you don't have that option I think rebuilding the carb is your best option.

One question, while driving the car if you push the throttle very slowly to full throttle will it hold high RPM without a problem or does it struggle? I suggest trying this in manual 1st or second because in high by the time you get high RPMs you will be doing well over 100mph, fun but cops don't seem to like it.

 

[$MoneyGreen]

@MONC440 I opened the carb and did a quick and dirty clean out. A partial clean out. I tried doing 1-2-D gear shift, but that didn't make a difference. While driving at 20 mph and if I let go of the gas, then stomp on the gas it will die. At 30 MPH, let go of the gas, then if I stomp on the gas it will stall for a sec and then give me full throttle. Also, I just wanted to double check if my timing is set right. What should my timing be at? If I where to switch to an edelbrock carb, what would you recommend?

 

[MJFUR]

In Post 15 you adjusted the timing, in Post 17 you ask what should the timing be. Huh?

The Green & White sticker on the driver side inner fender gives you the Idle and Timing recommendations. (Most likely 7 1/2 BTC, 600 RPM) These are typically lower and less aggressive of settings that will actually work.

Are the mechanical weights working, expanding-retracting as they should? At what RPM?
Is the vacuum advance working as it should?

My 69 Chrys 300 which has a bigger cam is set to 18 initial, all in 34@2500. (Do you know what this means? If not, you will be chasing your tail making adjustments to the Timing and Carb at the same time when you don't know if either one is set up correctly.)

You don't need an Edelbrock, you most likely need to send your 4640 to Woodruff Carb as mentioned above multiple times. My 4640S worked flawlessly from Woodruff.

If you don't know how to tune up a car that's ok. You can learn.
If you don't know how to tune up a car and are making adjustments to multiple things at the same time not knowing what they do you are making things worse.

 

[Just Carbs]

I sounds like a bad carb accelerator pump.

 

[$MoneyGreen]

@MJFUR I appreciate any advise given by all the members here, as I am learning about cars. What I don't need is being talked down to, and receiving negative remarks. I would really appreciate some helpful and constructive insight. Thank you.