Carb iddle issue, Chev 350

[Josie]

Hi folks;

I had been hunting around looking for a winter vehicle now that my CRV is gone and I made a wonderful choice. a 1970 Chevrolet C10. Complete with original 350 V8. It is a fixer upper but the basics are all there.

That said, I had a vacuum leak in the carb that I hunted down using carb cleaner. Turns out the base gasket that bolts to the intake (dome) was leaking. When I would spray carb cleaner at the base I would hear the idle pick and and start running better, then when it dried it would go back to chugging. (note this is no aftermarket carb, its an OEM 4 barrel Rochester)

Therefore what I did was buy a new base gasket and swap it. 4 bolts and away it came off. Left the fuel line on. Now when i was taking the dist advance line off the carb, the metal tip that goes into the carb came right out of the base with it :blink:

I pushed it back in though, I hope that didn’t cause what was about to happen next.

Note that I did tinker getting the throttle springs back on the carb. Had them wrong twice and the accelerator pump was open. (oops) So I got it reconnected properly and and the pump arm came back up to the top position. The rod “sinks” when the accelerator is pressed

Next I reconnected the vacuum advance line, tightened the bolts on the carb down and then went for a test start.

VRRRRRRROOOOOOOOMMMMMMMM!!!!!!

Ya, the old girl woke up with an roar!. Basically, the engine is in full throttle as soon as she turns on!!! :ohmy:

So that said, The carb does have mechanical secondaries and by the looks of the linkage they are not even hooked up. I can also look down to the rear butterflys (the big barrels in the back) and about 3 inches down I can confirm they are closed.

Choke is also closed when starting.

That all said, can you help me figure out what could be causing this?

1) Could something have failed on the Dizzy vacuum advance when that whole metal port came out?

2) Could I have hooked the throttle up wrong? (check out the pics below)

3) she makes a whistle sound when I start so I am thinking vac leak again…but one that would make a full throttle noise?

Here check out some pics of my project. And if you can help, please do, My landlord needs me to more her but she won’t run like that

thanks all

GSR

NOTE# The second picture here was taken before I took the carb off.

Edit #2 Just a thought, is the accelerator pump stuck inside by chance? Can that be fixed by tapping on the side of it? (like lawn mower carb when the float sticks 😉

Please help if you can. Any old school-ers out there see this before?

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Topic

[Joe]

I’m going to guess you’ve just got a decent-sized vac leak and it’s basically operating like the throttle plate is wide open.

Silicone up the dizzy advance vac port and make sure it’s not leaking. Also check and make sure your vac lines are all hooked up to the right ports and that they aren’t broken or anything. Double check your throttle cable and make sure it’s set up right.

If you can block off the top of the carb and smoke the system it would probably make troubleshooting a lot easier. I’m thinking it’s most likely an issue with a vacuum leak(s) but it could also be a problem with your throttle cable.

[Tom]

Unless you know something about the Rochester Q-jet carb that I don’t know, that is NOT a mechanical secondary, they are vacuum actuated.

Nothing in the distributor should cause the idle to go high.

One thing, and one thing only causes this, too much air getting into the engine. Either it is because the throttle blades (either in the primaries, or the secondaries) aren’t closing enough (double check secondaries, and primaries, adjust idle stop screw if necessary for primaries) or there is a loose, cracked, disconnected, or missing hose, or vacuum cap somewhere, or there is still a leak at one of your gasket / mating surfaces.

Also check all of the choke linkages. There is a fast idle cam on the choke. If that is sticking, it will hold the primaries open. Make sure that the choke is opening as the engine warms up, and that the fast idle linkage is moving freely, and allowing the primary throttle blades to close properly.

[Joeseph Mama]

what’s a carburetor…??

[Tom]

[quote=”Ratchet Face” post=105643]what’s a carburetor…??[/quote]

lol, you young whipper snappers better leave this one to us old farts banana:

[Josie]

HAHAHA!!

Thanks so much guys!!! I learned a lot of things about cars from older cars first. But it has been a long while since troubleshooting a carb. I honestly needed to sleep on this one before going back out there.

And for the record, That’s why a call to my dad went out last night about this as well and not a garage. 😉 Who would help me at a garage? LOL Dad figures the vacuum leak idea as well.

As for the secondaries they could be vacuum, I guess I saw the linkage on the right (passenger) side of the carb and figured mechanical. Honestly, the carb is do for rebuild anyway. I have the gasket kit and all but I just need to move the truck for Saturday before rebuild. I got a text from my landlord who also said he would give me a hand today. What is it about an old car being broken huh?

And since that vacuum port for the dizzy advance pulled out, I’ll echo you all in saying that I bet this is the issue, and its not sealed at the carb (even though i pushed it back in.) I have some really good sealer I’ll try for the outside(around the port) and see if that works.

QUESTION: That said, (and since I have never taken a carb apart before), Would pulling that metal port out cause something INSIDE the carb to drop, fall out, etc and now the vacuum inside the carb would cause this high rev? Just asking, because I am sure that port should not move out of there.

Alright, off to my office day job for the day. I’ll tinker tonight when I get home and let you all know what I found.

I’ll try re-seating that gasket base again too, that was a point of failure then as well.

I am going to give it another shot tonight and let you know.

thanks so much!! banana:

[Lorrin Barth]

It is not the vacuum port for the distributor. It would take more air than that to make it roar. BTW, when that port pulls out, which is normal if the hose is old, all you need to do is stick it back in firm enough so that it is not loose.

What you said about the accelerator pump not wanting to move makes me think you have the springs on the throttle plate connected wrong and the throttle is open or something like that. Worry about how the secondaries work when the primaries are all fixed.

[Josie]

HERE IS THE FIX:

Hi again all; thank you so much for everyone’s reply and those of you who said it had to be vacuum you were right. This is a classic case of trying to rush a job and not paying attention to some important steps. in this case, GASKET PLACEMENT.

I think I said earlier that I did not take the fuel line off the carb to swap the base gasket, and hence never looked to see how the new one would line up. I was paying attention to bolt holes, NOT barrel holes :whistle:

IN short, I had the gasket 180 degrees wrong, the rear large barrel holes at the front, small front ones at the rear. :blush:

So once I put the gasket in right, truck started up just fine. banana:

I can still hear some vacuum leaks so I will be hunting those down today and getting it running better for now. A carb rebuild is in the future but not just yet.

So there we have it. Engine -1, GSR chick – 0. I must admit, these older vehicles are much easier to work on. I just have to work on me first. 😛

thanks again guys. I know where to turn for the next issue with my new project. This site (and a mirror 😉 )

[Lorrin Barth]

Great story! It brings back a lot of memories.

[EricTheCarGuy]

You might want to check for vacuum leaks at the base of the carb again. Q-jets are famous for the throttle shafts leaking. Also, if you ever do a full rebuild, put some JB weld on the bottom of the jet wells on the underside of the carburetor body. The reason is they tend to leak and drip fuel into the engine.

It just so happens that for the next few weeks I have videos on carburetors coming out.

Thanks for the updates and for using our little forum.

[Tom]

I’ve had a couple of Q-Jets apart in my time . .. I would pay to have it rebuilt. I’ve messed with a lot of them, never really got any of them set up 100% properly. Had some that ran pretty good, but they are a complex little beast to work on.

That having been said, there is nothing quite like the roar of one of those bad boys when those monster secondaries pop open, and that engine comes to life!

[Pat61]

As you found out, it’s easy to get the gasket misaligned …and G.M. made a scad of gaskets for Q-Jets. They were a great carb in their day and offered reasonable performance and economy. They were so well thought out it didn’t take much to modify them for better performance, and even G.M. modified them as smog regulations grew more restrictive. That can’t be said about Autolite/Fomoco or 1/2 the Carter and Holley carburetors of that era.

Your picture (_015jpg) shows the choke pull-off dash pot. This little plastic gem can cause much grief (flooding/rich symptoms)and merits a check too. A vacuum leak here can cause the choke to operate erratically and other issues. The same picture shows the choke pull-off linkage, about the only thing on a Q-Jet that can be bent without causing grief, and secondary lock out (that backwards looking L shaped gizmo)

Lastly, put the air cleaner back on before you test for a vacuum leak. Half the noise I think you’re hearing is the normal carbruetor hiss that old timers miss so much…

[Lorrin Barth]

[quote=”Tomh” post=105914]I’ve had a couple of Q-Jets apart in my time . .. I would pay to have it rebuilt. I’ve messed with a lot of them, never really got any of them set up 100% properly. Had some that ran pretty good, but they are a complex little beast to work on.

That having been said, there is nothing quite like the roar of one of those bad boys when those monster secondaries pop open, and that engine comes to life![/quote]

It is not a very hard carburetor to take apart. About the only thing that doesn’t involve screwdriver use is knocking the pin out of the accelerator pump lever. BTW, drive the pin toward the center but not all the way out, just enough to release the lever. When assembling lever the pin back in place with a screwdriver.

But yeah, getting the secondaries to hit when you wanted them too that was the trick and a trick I never quite mastered. I became envious of carburetors with mechanical secondaries. But drive around on the primaries and get 20 mpg out of a 400 cubic inch engine.

[Tom]

Taking stuff apart usually isn’t too difficult. Putting one of them back together, and getting everything adjusted, and working properly, that is all together another story.

[Lorrin Barth]

I just didn’t want to scare the OP off of tackling it. I’m sure after all these years of accumulated grime just getting it clean would be a major upgrade.

In 1978, after bringing home a brand new Trans Am plus about 50 miles of driving the float mechanism fell apart. So, I had to delve into it to set it right. Without diagram or instructions I had no problem.

[Author]

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