Rochester Carb Help

[checkers]

My 1969 with original P engine is running lean. Backfires through carb unless choked about half way. The only way I can get the car to operate is when the choke is pulled about half. I don't know much about what parts are called so I have pictures. I rebuilt the carb and noticed that it only has one hole where I believe fuel travels. My other carb which cannot be rebuilt because of damage has two. Would this have an effect similar to my problem or what? Do all of yours have 1 or 2 holes? If it doesn't matter then I'll need to start checking other things.

[RiverPatrol]

Wow, great photography! I can hardly even see those things in real life.

The number of holes doesn't seem to make a difference. I just checked 3 carbs and 2 had 2 holes and 1 had one. Have you checked everything else? Fuel filter? Are you running the original mechanical fuel pump? How about the points, rotor, distributor cap? Are the plug wires routed correctly?

[bosque]

I got two holes....ehhhhem

[checkers]

HAHA. Didn't even think about how that could be taken. I wonder why some had one and some two? Car hasn't ran in a few years. I unblocked the fuel lines and put a new fuel filter on it. Has about 1hr on it and now looks rusty. Probably needs a tank cleaning but wanted to have cheap fun first. Has an electronic fuel pump hooked up. The mechanical one is still on the block but not being used. Probably bad. The electronic one has a really low psi rating, can't remember but it's like 2-4psi. Could be a problem. Haven't changed anything in the distributor but it doesn't look too bad. I know the vacuum advance is bad. Doesn't move when I suck "can't think of a different word bosque" on it. Does the vacuum advance have that great of an affect? I adjusted the valves. Played with timing before but I need to adjust it again now that I have rebuilt the carb and fixed a massive exhaust leak. Just learning as I go.

[miksum56]

Ive seen fuel pump rebuild kits come up on Ebay before. I just exchanged my carburator for a rebuilt last year for $190 after 2 rebuilds. Works great now. We think a PO lost a piece during a prior rebuild. My 64 vacuum nipple at carb base drew thru a special notch on one side of base gasket. Notch must line up with nipple or you cut off vacuum. Riverpatrol knows what Im talking about and may add to my description(I hope)

[RiverPatrol]

The fuel filter being rusty already could be an indication of some blockage, possibly even in the line. As I recall when using an electric fuel pump the pressure should be around 6 - 7 psi. You might also have an air leak in the fuel line somewhere; that will certainly cause issues. You said everything in the distributor looks okay, but have you checked the point gap and the condition of the contacts on the points? The vacuum advance wouldn't cause an issue like this; the vacuum advance works at higher RPMs while under load on acceleration.

Miksum56 - you used the word "nipple" in front of bosque...

[Esteban]

The fuel filter being rusty already could be an indication of some blockage, possibly even in the line. As I recall when using an electric fuel pump the pressure should be around 6 - 7 psi. You might also have an air leak in the fuel line somewhere; that will certainly cause issues. You said everything in the distributor looks okay, but have you checked the point gap and the condition of the contacts on the points? The vacuum advance wouldn't cause an issue like this; the vacuum advance works at higher RPMs while under load on acceleration.

According to the Service Manual, the fuel pump pressure should be between 4.2 to 4.83 psi (after converting the value from inches of mg) [0.3 - 0.34 kg/cm2]. In your case, this shouldn't play a major issue, since you're using little fuel at idle. You might have a very low fuel level inside the carb. When you close the carb a little bit using the choke, the vacuum created will help draw more fuel from the bowl and correcting -momentarily- the condition.

I agree with RiverPatrol that the vacuum advance shouldn't play any factor on your condition. Check the timing though.

[checkers]

Thanks for the help. Forgot to mention two things. 1. The engine will idle fine with choke completely pushed in. If I try and give it gas then it pops and hesitates. Once I pull the choke half way then it will take fuel OK. 2. When I turn the ignition switch on I can hear the fuel pump kick on. I have to wait like 45 seconds for it to pump enough fuel to start the engine on the first start of the day. After the first start of the day I only need to wait a couple seconds. Probably needs a clean tank, new fuel lines, and fuel pump. What do you make of that?

[MadTripper]

Sounds like my plow patrol when the fuel pump shit the bed. I've always had an electric on that setup. I did manage to get a new pump from Napa. They recommend placing it as close to the tank as possible because it pushes better than it pulls. I think I spent about $50 for the pump. You might be able to troubleshoot that by setting up a gas can and just gravity feed or start a syphon directly into the hose for your carb. In other words, set a gas can on the hood so it feeds the carb bypassing the filters and pump. If that works, then I'd lean towards a shotty pump.

Tripper

[Esteban]

Thanks for the help. Forgot to mention two things. 1. The engine will idle fine with choke completely pushed in. If I try and give it gas then it pops and hesitates. Once I pull the choke half way then it will take fuel OK. What do you make of that?

I will check the acceleration plunger at the carb. With the engine off, and while actuating the throttle manually, you should see a stream of fuel being injected by the accelerator plunger. It might be clogged, or a small ball that acts as a check valve inside is missing and the plunger doesn't fulfill its mission.

When the choke is half way, the added vacuum inside the carb helps draw the additional fuel.

If you raise the rpms gently, does the carb maintains the speed? If so, the problem could well be the accelerator system (plunger, ball, passages)