Vacuum line location?

[superc_1]

Where does the vacuum line go that comes off of the B.C.D.D. valve? Its located on the drivers side of the carb, some people call it the coasting valve? If anybody has a picture or diagram that would be great! Like they say a picture is worth a thousand words! Later:cool:

 

P.S. The truck is a 77 KC 620.

[superc_1]

Nobody have an idea? Would it hook to the manifold? Would you just cap it off?

[420n620]

what is a B.C.D.D vavle and where is it located, I got a 78 KC unmolessted and I could post a picture if I knew what to look @. :blink:

[650savag]

SuperC, The Hitachis on my 78 and the one on my 80 model, L20B, neither one of them have a vacuum hose outlet on the B.C.C.D. valve but the rebuilt one that I bought from National Carbauretor has a vacuum hose outlet and also a place to screw some type of fitting into (tubing or fuel line or something). I still have it in the box and haven't used it yet but if I install it on one of my trucks, I will need to change out the BCCD valve or either find out what to do about these two outlets. I suppose you could just plug them off. Thats what I would try first. I will post some pics later but I'm working 12 hr. nites and have to get some rest. Later, Dan

[datzenmike]

what is a B.C.D.D vavle and where is it located, I got a 78 KC unmolessted and I could post a picture if I knew what to look @. :blink:

 

Boost Controlled Deceleration Device It's job is to introduce an extra amount of fuel and air on sudden deceleration to promote more complete combustion on an otherwise very lean condition.

 

The vacuum line should go to the Boost Control Unit located on the driver's fender behind headlights. '75-'77 49 states and Canadian modes did not use this tube. (California carbs did use it) From '77-'80 all 50 states and the Canadian cab chassis model used this tube. All other Canadian models did not.

 

SuperC, The Hitachis on my 78 and the one on my 80 model, L20B, neither one of them have a vacuum hose outlet on the B.C.C.D. valve but the rebuilt one that I bought from National Carbauretor has a vacuum hose outlet and also a place to screw some type of fitting into (tubing or fuel line or something). Dan

 

For the tube see above. For the fitting, this is where the vacuum solenoid valve screws into the BCDD. It was used on pre '78 carbs and in operation, the solenoid would open to vent the vacuum signal (to stop boost) with a signal from a speed sensor in the transmission. The '78-'79s didn't use them. I don't know what would be involved in de-activating it... maybe put your BCDD on the new carb??

[superc_1]

Datzenmike and Savage 650 thanks for the help! Mike, I ordered a reman'd carb from national carbs and I believe its the right one, but I just didn't know where I should hook up the vacuum hose at or even if I should. All of the emission eq. is gone on the truck from PO. Now for the question!! I put the carb on last night with new gas filter and she purs like a kitten, BUT when I took it on a test drive it started stumblin bad when I'd give it gas even die all together. Any suggestion? Would the points, plugs, or air filter cause this? The only other thing I can think of is I had three gaskets and the gasket I used partly blocks the screw on the bottom that has the hole in it? does that make since? Savage I think your 78 model is a totally different setup than mine '77. Also; the carb I got off of you runs better than the new N/C I just got. Maybe I haven't adjusted it right or something. I'm going to mess with it tonight and see what happens. Man I was so looking forward to getting it running good. If it wasn't for bad luck I'd have no luck at all!!

[datzenmike]

Well if it idles good theres no vacuum leak and it has fuel to the idle circuit.

 

Can you drive it from idle and then it quits or does it do it as soon as you step on the gas?

 

If it drives away fine and then stumbles, the float may be set to low and the fuel bowl does not fill up properly, or there's an obstruction at the needle valve and not enough fuel gets in to keep things running under load. Take it for a drive and when it quits, shut off motor and stop and look at the sight glass (bull's eye) in the front of the carburetor. Is the fuel level in the center?

[superc_1]

I'll do that tonight. It drives off at first then it starts to stumble. does it have an exterior float adjuster or do you have break it apart? When its idling the gas is in the center of the glass like it should be.

[650savag]

SuperC, Sorry to hear you are having troubles with the new Hitachi. Have you checked to make sure you are getting a good fuel supply and pres. from the fuel pump. If the sight glass in the front of the carb isn't staying half full when it's running, then like DatzenMike said, you have a problem with the float, neddle valve, or fuel delivery (fuel pump or plugged fuel line). I have in-line 12v. fuel pumps on both of mine and I know how they act when they are going bad but I don't know how the mechanical pump acts. Also, if you have pluggage in the fuel line from the tank, that could cause you problems. Unhook your fuel line and blow back into the tank with some air pressure. Don't tear into the rebuilt carb! If the carb is the problem, then put the one I sent you back on and run with it, and send the rebuilt one back in the box they sent it and they will repair it or send you a new one and pay the shipping. Call their 800 number and let them know what happened and they will tell you what to do about returning it. Hope you get it running good! Dan

[superc_1]

Savage, hows it goin? Well last night I called and old friend and he's been around a long time and if anybody can fix something he's the man. Well at first we thought it was the choke but no luck. We got it back home started look at thing. Pulled the dist. cap off, pulled the rotor to check points. In the mean time his sharp eye found a small hair line crack across the top of the rotor. You wouldn't think it would affect the spark but his years of messin with old tractors and wore out cars new better. So, a long story short, I went and got a rotor put it on the truck and shes purrin like a kitten. I don't think I would have ever found that problem! I would not have even looked that close, it was a brand new rotor I put on when I first got truck. The only thing I can think of is I pushed down on the coil wire going into the top of the dist. cap and the pressure broke the rotor right in the center and the spark was jumping down on the dist. shaft. Weird!! Later

[650savag]

Savage, hows it goin? Well last night I called and old friend and he's been around a long time and if anybody can fix something he's the man. Well at first we thought it was the choke but no luck. We got it back home started look at thing. Pulled the dist. cap off, pulled the rotor to check points. In the mean time his sharp eye found a small hair line crack across the top of the rotor. You wouldn't think it would affect the spark but his years of messin with old tractors and wore out cars new better. So, a long story short, I went and got a rotor put it on the truck and shes purrin like a kitten. I don't think I would have ever found that problem! I would not have even looked that close, it was a brand new rotor I put on when I first got truck. The only thing I can think of is I pushed down on the coil wire going into the top of the dist. cap and the pressure broke the rotor right in the center and the spark was jumping down on the dist. shaft. Weird!! Later

 

superc, glad to hear you got your 620 purring. what did you do about the bcdd valve (the vacuum outlet)? Did you plug it off? Does your carb have the outlet for the vacuum solenoid valve to screw into it? My new one has a vacuum hose fitting and a female thread outlet to screw the solenoid valve into (both of these is part of the bcdd valve). I'll send you a pm. Dan