Manual Throttle Cable: when and how to use it?

[thelawdoc]

Hello to the forum. I am trying to educate myself about the manual throttle cable in my '65-'66 C10 250 Inline Six. I have had this truck for about 8 months, since January. She is stock, my only vehicle, with a single barrel carb. When starting her up in the winter here in New York, I always pulled the choke out. She always started up easily. I have never used the manual throttle cable. Today, a gorgeous, sunny day in August, she would not start for me. The symptoms were those of an empty gas tank, clogged fuel filter or line, etc. That is, she would need cranking more than usual, then turn over and seem to want to run, but instead -and with a lot shaking, sputter out after maybe 5 seconds of rough running. I attempted to start her about 10 times, choke knob pulled out full, and almost every time brought the same response. Sometimes she would not even kick over or run for the 5 seconds. After I spent some time going down the 'check list,' I was out of ideas. While sitting behind the wheel and trying to imagine what was ailing her, I noticed the throttle control knob that sits at the bottom of the dash, in front of my left knee. I had never used this control. Out of boredom, I pulled out the knob and pushed it back, making a mental note to find out exactly what this control is good for. I then decided to try starting her one more time. I pulled out the choke and cranked her. She roared to life. I let her warm up for a few moments, and then pushed the choke knob back in and drove off. It seems to me that something good happened when I played with the throttle control. When I got back home I looked in the manual to see what it might say about this magical knob, but the manual simply noted that the throttle control was an option. I searched the forums but have not found any discussion about when and how to use this control. It seems to me that it is used to raise the engine revs without need to step on the accelerator. But it also seems to me that it let me start my truck today when it otherwise would not start. Anyone have some familiarity with a manual throttle control in this truck? -Alden

[ACK]

I don't have the throttle knob, but I do have a '64 with a 250 and manual choke. Each morning (winter, spring, summer, or fall), I pull the choke about 3/4 of the way out and turn the ignition without giving it any gas and she wakes right up. The speed in which I start backing off the choke depends on the sound of the engine, only on the coldest days does she occasionally sputter out. Have you done any work on the carb since owning the truck? I'm wondering if it needs adjusting or a rebuild.

[63burban]

Sounds to me like it was flooded and simply letting it sit for a few minutes let some of the extra fuel evaporate or run down the cylinders.
I grew up with hand chokes on everything, generally in the summer less choke is needed. On my 65 I generally pull the choke as I turn the engine over and the engine will find it's sweet spot, but every engine is different.

[jtrichard]

hand throttle is for things like a pto for winch ECT. can be used as primitive form of cruise control (when your right foot gets tired) on very long drives (not really advised) i have done that..anytime you need higher RPM like jumping another vehicle when you dont want to sit there with your foot on the pedal..... as for it helping your starting ... just a co-quittance

[thelawdoc]

Ack, thanks for responding. I have not done anything to the carb. Until today, it never gave me cause for attention. The truck has always started right up in the same way yours does for you. I do not have any deep knowledge of carbs or adjusting carbs, but except for today's start, she has not misbehaved on me. And today I did not do anything to the carb except take off the air cleaner and have a look inside. When I looked I did not see any gas inside, but when I checked the fuel line and filters, there were no issues that caught my eye. At one point I began to take off the fuel line where it enters the carb, but when gas began to drip out, I retightened it up since I understood she is getting gas. Just prior to pulling the manual throttle control, I was thinking about checking the fuel pump to verify operation, but I was not sure how to do that and I considered it unnecessary since I had fuel at the carb. Then she started up, as I mentioned, and I can only imagine that something beneficial happened when I pulled out the throttle control. -Alden

[thelawdoc]

63burban, Yes, I do that, too, pulling the choke out as I crank and finding a sweet spot. So you suppose that the manual throttle control did nothing for me? If the carb was flooded, would I have not seen fuel when I took off the air cleaner and looked down inside? After each attempt at starting, I did let her sit for a moment or two to let the starter cool. But over the course of an hour, she would not start. -Alden

[thelawdoc]

Jtrichard, well supposing you are correct -and it seems you would be, why did she suddenly start up for me? It really seemed to me that pulling out the throttle control did something, but if you say it cannot be, then I have to figure out what was the trouble. Never had any issue starting her before today, for that one time. Do you think it was simply not necessary for me to have pulled out the choke when I went to start her initially and then each time this morning? -Alden

[Bears63]

When the engine started sputtering and stuff you should have backed the choke off. You had it flooding because of the full choke. Messing with the throttle cable probably helped get more air into the intake to offset the flooding. It opens the throttle just like putting your foot on the pedal. Like jtrichard said, that is meant to have a way to rev up the engine for PTO's and such.

[thelawdoc]

Bears63, I did not know that opening the manual throttle control permits more air into the engine. Actually, I did not know anything about this control. But I was beginning to understand that it puts more fuel into the engine -not air. I am a little confused... -Alden

[Bears63]

Any time you push down on the gas pedal the throttle plates on the carb open up further and further. So, with the throttle plates opening up it is going to allow more air to come into the intake. When running the engine and you open the throttle it dumps more gas in and the air flow increases as well in order to burn the extra fuel. It's basic operations. I think you are overthinking the throttle cable. Think of it this way, it is exactly like using the gas pedal, only it's easier to keep the engine at a certain rpm with the throttle cable.

[thelawdoc]

Bears63, So then what is the difference between the throttle control and the choke? I see now that I was probably flooding the engine. I suppose that, had I closed the choke and floored the accelerator, she would have started right up, right?

[thelawdoc]

Ah. Maybe I have it: the choke gives the engine a richer mix while the throttle gives the engine more of the same mix?

[Bears63]

The choke closes the butterfly on the top of the carb and restricts air flow so that the engine gets a richer load of fuel while the throttle cable simply acts just like the gas pedal itself. If you had stopped choking and floored the gas pedal it probably would have started right up.

Edit: You posted the same time I did...lol.... Yes, that is the idea right there.

[thelawdoc]

Bears63, thank you. Thank you guys. I think I got it.

[thelawdoc]

Yes, thanks to you guys. My mind got tossed out of kilter today with this throttle control thing. But, as usual, there is always something to be learned here on the forum. I could not keep this truck without the help that guys like you graciously give. God bless you all. -Alden

[jtrichard]

pulling the cable is nothing more than pushing the pedal with your foot .... if you watch the pedal when you pull the cable, most likely it will pull the pedal down

[thelawdoc]

Jtrichard, yes, it all makes sense to me now. It might come in handy some day.

[thelawdoc]

Today she started right up, no choking at all. I did give just a little throttle for a moment or two until she warmed up and sounded happy. But as I let her idle there were instances when the idle got rough. That is, she idles smoothly for a moment or two, then sounds as if she wants to sputter out. I give a tad of throttle for a few seconds, and she returns to smooth idle. After another moment, she again idles rough until I give another moment of slight throttle. If I do not give some slight throttle, she continues to idle rough -though she does not sputter out. I am suspecting that my flooding yesterday may have fouled my spark plugs. I should take them out and have a look at them. I also know there is an idle adjust screw on the carb, but it seems to me that one ought properly have nice plugs on the engine before deciding that one needs to adjust an idle that has been just fine until one flooded the engine. Anything else that I should check? Thanks for all of the attention guys. -Alden

[aerotruk63]

When it is warm and somewhat running with the air breather off, cup your hands slowly over the top of the carburetor. If you have a vacuum leak the idle will change rev's and go higher, if you have no vacuum leak it will die out. A vacuum gauge is the computer of the early engines tells you all sorts of things.

[thelawdoc]

Aerotruk63, thank you. And I know that you are right about it being time for me to get a vacuum gauge and to start using it! I recently got this truck. It is the first one I ever had. I would not have thought that flooding the engine yesterday could affect vacuum. I figured I fouled my plugs. I spent most of my time today looking for my spark plug socket and then my old lady hit me with a list of errands and chores to be finished "before going out to play with that thing." Thanks! -Alden

[Bears63]

One other thing with these old trucks that I have experienced many times is that sometimes the engine can be well tuned and happy and it will still idle rough until it reaches a certain temperature. It does happen sometimes and every engine is different. That's part of the charm in my opinion.

[thelawdoc]

Bears63, Thank you for responding. I got this truck about 8 months ago, in January. Except for the one instance that I mentioned above from the day before yesterday, she has always started right up. Even this past winter, on very cold mornings. She does need several minutes to warm up while I gradually reduce choke, and then she will idle smooth as a baby's butt. I understand that every engine has its favorite temperature to reach before getting comfortable. But yesterday, she did not seem to be getting comfortable even with plenty of time to warm up. As I described, she started right up yesterday, no choke at all but with a bit of throttle, and idled smoothly after a few minutes. As it happened, I did not then drive off because a phone call came in. During my call I noticed that every minute or so the idle would become rough. Rough enough that I had to give a bit of throttle to smooth it out. She would smooth out, I would come off throttle and she would be smooth for another moment or two. Then roughen again. After this continued for about 5 or 10 minutes, I wanted to see whether she would sputter out if I did not give some throttle. She did not, though the roughness became somewhat of a shake. I gave some throttle, and she went smooth again. The only event that I can imagine brought on this situation is the flooding of the engine that I caused the day before. I am not a mechanic, but I figured I might have a look at the plugs to see whether I fouled them up. I am about to do that today. I did not drive her yesterday because I wanted to first resolve this issue. What do you think? Also, since I do not have any service records for her, I figure I should change the plugs anyway. I hesitate to fiddle with the idle adjustment on the carb because, as I said, when she idles she is smooth and it does not seem to me that my having flooded the engine the day before would cause any maladjustment of the carb. It seems more likely to me, that all evidence points to fouled plugs. Of course, I am about the greenest mechanic you have ever met, with no budget right now for a real mechanic to have a look at her. I don't want to simply throw money and parts at her, but if it isn't the plugs...well Lord help me. -Alden
{Edit: P.S. I forgot to mention that, on Saturday, after my flooding incident, I did drive her a bit. She drove fine, but did stall one time -right in an intersection!}

[Vernski]

On the inline 6 motors there is a rock-wool filter behind the brass fitting as the line enters the carb this can get plugged with gunk from the stock tanks behind the seat. If it will continue running with the choke pulled the filter is the culprit pull it & clean it then happy motoring...Vernski

[thelawdoc]

Gentlemen, Please excuse the fact that I did not update this thread sooner. In the passed few months I learned that this knob is not, in fact, the optional throttle control or relevant to any pto. It is, actually, the manual control for manifold heat. I eventually investigated and found that the cable goes to a swivel gate in the exhaust manifold that is directly under the intake manifold. It seems that in cold weather, one may open this gate to facilitate warm-up. Once the truck is warm, one closes the gate. I guess this is what Chevy offered prior to the heat 'stove' that goes up into the air horn. In any event, in the past few months I learned how to tune up my truck, and now she starts as easy as a new Toyota. I never realized just how good a tuned up engine can be, no matter how old she is!

[OldGMJon]

Interesting...I have never heard of this application for the throttle cable