[Guest]

I cannot get my Autolite 4300 on my 69 Mach (351 W, 4V) to run right. It will run for about 15-20 seconds, then it just dies. I can crank on it a few time, pump the throtle, and it will again run for a few seconds. I have rebuilt it twice, blew ALL of the ports and such out with compressed air, checked the float level, blahblahblah, but I can't get it right. I have two choices at this point, they are as follows:

1) Go the Advance Auto Parts and get a rebuilt Autolite 4300 with a one year replacement waranty, $215.00 plus my core.

2) Get a replacement carburetor. I want to be able to hook all of the factory vacuum lines though, and I want the heat riser to hook up for the choke if possible. Basically, if I get a replacement carb, I want to cover it up with the factory breather assembly so it won't be seen. I also would like to keep it under $250 or so.

The main reason I am considering a replacement is because it may be easier to maintain.

What do ya'll think? And if you would vote for a replacement, which one. The car has a 4spd Toploader, and is bored .040 over, if all of that matters. It also has air, but does not have power brakes. I may also change to a pertronix ignition system.

Thanks
ssscode

 

[sharkmouth]

HAve you checked the remainder of the fuel system?

 

[Guest]

I have taken the fuel filter out of the carb, cranked on the engine, and fuel squirted like crazy (Yep, I had the coil wire off). I did replace the fuel filter as well, just for good measure.

 

[cousin_jd]

Do you have a vented fuel cap???? Did the engine run OK before you replaced the carb?? Keep us posted as to what you find. Jim

 

[ylexot]

If your core is the orig carb - DO NOT TURN IT IN! Get another core if you are thinking the mass-parts rebuild route. The one you get in return will only vaguely resemble your original. Every "rebuilt" one I've disassembled (because they all sucked) had mismatched jets. Don't do it man! Holleys are $200 at the same place if you need it now.
Did you dip the carb in that bucket-o-crap-disolver for a while? Carb dip is nasty and effective. 4300's have lots of little anti-siphen ports and hoo-rah holes that all have to be clean for it to work right. Not easy.

 

[Boss_Hoss]

I don't kow what cfm a 4300 is equivalent to. I bought a '71 Mach last year with a 750 cfm carb on it. It wouldn't run very well when I got it. We ran the numbers and it looked like it was too big a carb for the engine. I still wasn't convinced though. A farmer down the road came over and looked at the car. He said he had a combine that had too big a carb on it. He put a hose clamp on the fuel line on my car and restricted the fuel flow. Whalla! it fired up and ran reasonably well. I bought a 650 cfm and now it runs great. I wish I could find the sheet where we equated stock engine cubic inches to maximum air flow. Ask an expert they could tell you what your maximum cfm should be about. You can be close and it will still work. If its just a bad carb, then bite the bullet and buy a new one. They're worth the money.

 

[camachinist]

Will it run at all, if you open up the throttle after the engine starts? Or is no fuel at all getting to the main jets or idle circuit? You've established that the accelerator pump circuit works...

Any odd exhaust emissions to note during the period the engine runs? Is the choke system operational?

Is it possible that the needle/seat is restricted and the bowl isn't filling the way it should? (remote but possible)

4300's can be cranky....what's the application? Stock, performance or ??

Let's see if we can figure it out before throwing more money at it *G*

Why did you rebuild the carb in the first place? Or, what were the symptoms prior to pulling it the first time? Has operation changed at all since then, in light of the work you've done?

Get back to us...

 

[khodgens]

It sounds to me like the needle and seat may be sticking. When you start it and it runs, when it dies you need to pull the top of the carb and see if the bowl is dry.
Keep us posted.
Ken