Carter BB Accelerator pump question

[Jims68]

A few pics to show my Carter BBD setup. These were taken before I cleaned it and rebuilt it a few years ago. Are the rods in the correct holes? I was wondering if that would affect the accel. pump action. The Vac. advance hose is connected to the bottom of the carb as you can see in the first photo.

I had checked the float level last time I had it apart, but not this time. I 'could' check it again and the floats did not have any gas in them.

[PwrWgnDrvr]

You'll get a bigger squirt if the rod is in the end hole of the throttle shaft arm.

[IHWillys]

I'm assuming your 1970 Carter is like the BBDs I have. Both my '67 225 and '85 318 have one on top.

"Also, if I'm cruising and "punch" it, it'll give a small cough"
This says "lean backfire" to me.
Which is most often an accelerator pump issue.

Neither of my currently functional BBDs have leather accel pump diaphragms. They use a sort of flexible plastic/rubber.

The BBD on the 1985 is a new one from China off ebay. It had a black rubber diaphragm that lost a small chunk off it earlier this summer. At that time, I had the same symptoms in this truck that you have in yours. It wasn't a complete failure of the accel pump but the reduced volume was enough to cause the issue. I swapped in a new(ish) diaphragm from my parts stash and all has been fine since.

Also note that there is adjustment to the placement of the arm on the shaft, just as with the adjustment for the mechanical lifters on the metering rods. This has small affects on the overall volume of the fuel charge and also on the volume of fuel for a given amount of rotation. This function follows a curve that maxes when the arm is at 90 degrees to the plunger. So for a given amount of rotation, more fuel gets squirted out when the arm/plunger angle is near 90 than when further away from 90. All this to say, there is some tweaking that can be done there.

[PwrWgnDrvr]

The squirt has more volume the higher the plunger, even if "past 90". That is because the arm does not "PUSH" the plunger down. The arm simply releases the plunger and the spring inside pushes it down.

[Jims68]

Thanks for ALL the advice given here. I really appreciate this. Today, I thought I would check my vacuum advance. I thought it was working because I could "feel" it when I stepped on the gas. But, I suppose that was the weights pulling it around. Anyway, I pulled the hose and sucked on the end of it... HUH? NOTHING... it didn't work. Luckily, I had a spare distributor and used that one. So, I figure, THAT is surely my problem. Nope... it ran about the same.! LONG story short, I put the accel. rod on the outside hole on the throttle arm. The TOP part of the rod I left alone figuring it would give me the max in that position. So, Off we go for the test ride and it was a LOT better! My homemade timing tape on my harmonic balancer came off and I noticed that because I heard this "ticking/slapping" sound which was the tape flapping around in the breeze. It was just masking tape with lines every 5*. Now that I know the Vac Advance is working, and the accel. pump in a better position, I think another hour or two going over the timing check and tweaks as mentioned by Martin for the timing and it'll be as close as I can get it. Oh brother... I feel kind of dumb not giving it the Vac Advance "suction" test before today , and THAT is how I found that part wasn't working!

So, today on one of my last test rides I did a burnout (lightly) and then I even squealed the tires in 2nd gear! First time I ever did that!

I believe you have a timing issue. Your truck likely had a factory timing spec somewhere around 5* BTDC. The mechanical advance of the distributor is likely somewhere around 20*. The vacuum advance around 15*

Martin, I am not forgetting all that you wrote and spent time helping me. I too think I need to go over my timing again now that the vac adv. is 'fixed'. I am going to make these checks probably this weekend. Tomorrow I have to get caught up on my "around the house" stuff... cutting grass and other little things. As you can read above, I have it "close" I believe but I want to be 100% sure I can do no more.

don't do it when running
but look down the carb and should have a steady stream of gas as you open the throttle
i know holly carbs spray more of a mist
the other thing is hot soak ...but never seen a 2bbl carter have that problem

Yeah I was expecting it too look like the Holley on my Roadrunner which is a NICE spray.

I'm assuming your 1970 Carter is like the BBDs I have. Both my '67 225 and '85 318 have one on top.

"Also, if I'm cruising and "punch" it, it'll give a small cough"
This says "lean backfire" to me.
Which is most often an accelerator pump issue.

Neither of my currently functional BBDs have leather accel pump diaphragms. They use a sort of flexible plastic/rubber.

The BBD on the 1985 is a new one from China off ebay. It had a black rubber diaphragm that lost a small chunk off it earlier this summer. At that time, I had the same symptoms in this truck that you have in yours. It wasn't a complete failure of the accel pump but the reduced volume was enough to cause the issue. I swapped in a new(ish) diaphragm from my parts stash and all has been fine since.

Yep... I'm thinking that a purchase of a new accel pump may be in my future at some point. It can't hurt. But, with the engine OFF I do see a NICE stream and as mentioned above, I was expecting the same type of squirt like the Holley on my Roadrunner. But... seems they don't squirt like that.

[Jims68]

Looking at my engine I removed from a 1970 D-200 Camper Special. (My truck is a 1968) It has on the block after the 2536030 318-11 What does the 318-11 mean? Looking at the timing specs in the service manual, it says 318-1 gets 5*B and the 318-3 gets 12.5*B So, what does 318-11 mean? I've seen on posts about the 318-3, but not any 318-11 (I took a photo of it in a mirror and then "reversed" it to SEE it in a photo to post) The "2" doesn't show up on the picture because it's under the manifold... but you get the idea.

Not going to do much today... raining out.

[PwrWgnDrvr]

It means its a 318-1.

[Jims68]

It means its a 318-1.

Thanks Terry!

[martincom]

The "318-11" cast into the block is not relevant to the 318-1 or 318-3 set forth in the service manual. If you check the specifications pages of the service manual, it will become obvious. The 318-1 was utilized in the smaller trucks, such as the D100. The 318-3 was utilized in larger trucks, such as the D500. One of the differences you'll see in the actual build is the timing chain. The 318-1 utilized a fiber tooth top sprocket and a laminated link chain. The 318-3 utilized a double roller chain and corresponding sprockets.

The significant reason for the timing differences is likely emissions, as I believe the Cleaner Air System (CAS) began in 1968. The timing was intentionally retarded from the previous norm for emission vehicles. With retarded timing, a much leaner idle mixture could be utilized, improving the illusion of reduced emissions. As CAS emission requirements did not apply to larger trucks, their timing was not intentionally retarded.

[Jims68]

The "318-11" cast into the block is not relevant to the 318-1 or 318-3 set forth in the service manual. If you check the specifications pages of the service manual, it will become obvious. The 318-1 was utilized in the smaller trucks, such as the D100. The 318-3 was utilized in larger trucks, such as the D500.

HAHA... I found that section now and now understand it was the larger trucks that used that engine. You must've spent a lot of time reading the service manual. Me? well... if I use it, it's to look up something specific. The 318-1 vs 318-3 is NOT something I would've even thought about being in the manual Something else I've learned! I just hope I can remember it!

Thanks for pointing me to there!

[Jims68]

I got it fixed.... I found that the VENT VALVE on the carb was closed and the accelerator pump wasn't set correctly. It FIXED my problems!! I suppose it wasn't really a timing issue after all. Well, that isn't exactly true either. I had it moved all over the place and most likely just got it way out of WACK! But when I saw the vent valve/pump height thing was wrong, I fixed that part first, and then I set it all back to "spec".

My timing is now set at 5* Before and the Dwell is at 32 and the points at .015. Runs great without the coughing/bucking/hesitation etc.!

I want to thank each and everyone that helped me out.

[Wildergarten]

I got it fixed.... I found that the VENT VALVE on the carb was closed and the accelerator pump wasn't set correctly. It FIXED my problems!!

When a complex system like a carburetor undergoes long periods of refinement in the name of reducing toral manufacturing cost while improving performance, elements of the designs tend to get simpler, but the complexities remain, often hidden by the subtlies of precision in those simplifying elements, each with their own subtleties.

[nutz]

great find
how did it get out of wack
how much more volume do you think it made

[Jims68]

great find
how did it get out of wack
how much more volume do you think it made

I bought a 1970 D-200 just for the engine. It ran sooooo good, I didn't even do a tune up. I put in new freeze plugs and a timing cover gasket. That's all I did to that engine. So... what I'm saying is... that setting on the accel. pump and vent valve was like that when I got it. At that time plus all these years later, I never knew anything about that vent valve setting. If you look at the rod, it looks "bent" so maybe the last guy thought it was bent and he straightened it out?? I can't say for sure. I came across this info when I was thinking about how the other day when I changed the "throw" rod to the outer hole to give it more "push" and it improved the way it ran so I started looking at the paper (and also in the service manual) that came with my rebuild kit that I had from when I rebuilt the carb. At that time I had basically just cleaned it, blew it out and just replaced all the bits and gaskets. Martin asked if I set the fuel bowl level and I DO remember doing that, but as it's my fault... I never really read all the paper. THIS did tell me that I should adjust the vent valve and it gives all the settings to do that. OR, maybe I did read that part and thought... what difference can that tiny opening make? BUT, the other night after I saw this setting on the paper I lifted the accel pump up by hand over 1/4" and about when the vent valve opened up. The light bulb went off and that's when I realized that this needed to be set to get that extra "throw" for the accel pump the engine needed to keep it from stumbling. I put the throw rod back into the center hole at the bottom to match the clip on the accel. pump. The clip is what raises the vent valve. Probably gave it more than half the throw I was originally getting and that way it acted like it was a bad accel pump. And why didn't I notice this stumbling before when I drove it? I don't know... the best I can think of is that I really didn't drive it that much OR that far so I may have assumed it was doing this because it was still "cold". But...alls well that ends well I guess! Another really GOOD video I found on Youtube is one of those Rob Roy film-strip / records that the dealers used to get. Here is the link to that. HIGHLY recommended for any Carter bbd owner: https://www.youtube.com/watch?v=w9WxF2RZp8c&t=558s

[martincom]

I'm glad you found your trouble. The external bowl vent was a give away. A carburetor performs the best when utilizing the internal vent. This is typically a tube with an angle cut projecting into the airhorn. As the air filter becomes restricted from foreign matter it collects, the atmospheric pressure of the air entering the carburetor is less. Not only does this pressure impact the volume of air entering the intake manifold, but the volume of fuel as well. Fuel is not "sucked" into the carburetor, it is driven in by atmospheric pressure applied to the fuel, in the float bowl, which seeks to fill the vacuum. So for a carburetor to deliver the designed ratio of fuel to air, the atmospheric pressure applied to the fuel in the float bowl must be the same as the atmospheric pressure of the air entering the airhorn. Thus, why the float bowl has an internal vent.

The issue with internal vents is when a hot engine is shut off. There is no longer this large volume being drawn into the carburetor, which also kept it relatively cool. The heat from the engine quickly causes the carburetor to warm, rapidly vaporizing fuel in the float bowl. As it is expanding volume of air/vapor in the float bowl, it vents out of the float bowl. Once it contacts the cooler air, it condenses back to liquid fuel. When carburetors are just vented internally, this vapor condenses when it contacts the cool air within the airhorn. The liquid fuel drops into the airhorn. When attempting to re-start the hot engine, it is flooded from this condensed fuel and flooded engine procedures are required to start it.

To prevent this, an external vent is added to the float bowl. However, to prevent unequal atmospheric pressures between that applied to the float bowl fuel and that of the air horn, this external vent is only open when the throttle is at idle position. So when the hot engine is shut off and the fuel begins to vaporize, it takes the path of least resistance out the external vent. The hot engine re-starts normally.

In Jim's Carter BBD, the external bowl vent valve is the washer placed over the accelerator pump shaft. When the throttle is at idle, the pump is drawn out of the float bowl, lifting the washer and opening the external vent, which is the somewhat enlarged opening around the accelerator pump shaft. When the throttle is depressed, the accelerator pump shaft is lowered into the float bowl. The accelerator pump has a circlip around it the external bowl vent washer rests upon. So as the accelerator pump shaft is lowered into the float bowl, the external vent valve washer rests on top of the float bowl bowl, closing the vent.

Emission carburetors have an enclosed external bowl vent, to prevent the vaporized gasoline (hydrocarbons) from escaping to the atmosphere, as they do with Jim's carburetor. This enclosed vent has a hose barb connection, so the gasoline vapors are collected for storage in what is typically a charcoal canister. When the engine is running, they are drawn out of the canister, by engine vacuum, and burned. My '71 California truck once had such a carburetor with an enclosed vent. It didn't have a charcoal canister. Rather, the external float bowl vent was plumbed to the crankcase breather. Depending on the amount of vapor and how hot the engine was, the vapor would condense in the air cleaner or within the breather. If within the breather, the condensed gasoline would be drawn into the crankcase by the PCV system. This wasn't a good method to deal with the vapor, as the condensed gasoline would mix with the engine oil and thus why charcoal canisters were later utilized.

[martincom]

My timing is now set at 5* Before...

You'd probably realize much better performance with your timing advanced significantly. Fuel blends have changed dramatically since your truck was built and require more "time" to achieve optimum combustion pressure. I'm just finishing up, today, the timing optimization and carburetor re-jetting of my D100. When I've completed it, I'll author a thread on timing optimization and carburetor re-jetting.

Like your truck, the factory timing spec for mine was 5* BTDC. It would had a very rough idle at that setting. The optimum initial timing was 28*, which I reduced to 25*, to provide some headroom from detonation attributable to uncontrolled variables, such as fuel quality and air temperature. More on this later.

[Jims68]

My timing is now set at 5* Before...

You'd probably realize much better performance with your timing advanced significantly. Fuel blends have changed dramatically since your truck was built and require more "time" to achieve optimum combustion pressure. I'm just finishing up, today, the timing optimization and carburetor re-jetting of my D100. When I've completed it, I'll author a thread on timing optimization and carburetor re-jetting.

Like your truck, the factory timing spec for mine was 5* BTDC. It would had a very rough idle at that setting. The optimum initial timing was 28*, which I reduced to 25*, to provide some headroom from detonation attributable to uncontrolled variables, such as fuel quality and air temperature. More on this later.

Thanks for that update. I didn't realize that todays fuel would cause that type of issues. I never really looked into it before as I had no cause to. I look forward to reading your post about your timing optimization and carb re-jetting. I'll keep my eye out for it!

[nutz]

great info guys
couple of things i have found
one is todays fuel will kill any rubber in your fuel system so make sure when your replacing any o-rings or parts
it is with new nitrite seals and hoses
when choosing an air filter watch the clearance over top of the carb because the air flow can effect the internal vent

[712edf]

This thread just furthers my desire to ditch my Carter & switch to the simpler brand.

Bucky

[Jims68]

This thread just furthers my desire to ditch my Carter & switch to the simpler brand.

Bucky

Awww... don't do that. It's an easy carb to work on and it really RUNS good too on my 318. You just need to understand it. Same with (opening a can of worms here) a distributor with points work GREAT. Auto manufacturers used the points system for years. I don't think young folks would even know how to adjust them. The other day when I replaced my points, I showed my nephew the new set and asked him what they were. He thought it was some type of switch. OK... so he wasn't 100% wrong, but he really had no idea of how they work or their usage. ME? I will always stay with the points, condenser setups. Ah... come on now... don't hate me for saying that!