Guys I have a 69 350/350 car that has been a pretty flawless running car since buying it back in 2003. It's a very clean numbers matching car that I drive pretty easy. Well this weekend we did a little cruise and when with the boys of course we had to play a little. The only thing this car has always done is if I try to get on it at too low of a RPM it will just fall on it's face like the secondaries are opening too soon? It will recover if I back off and step into it lighter OR if I stab it when the RPM's are above say 2000 or so she goes fine. Makes it hard to kick my brothers *** in his GTO from a light....

Any help on what to adjust or a link to it would be great. I don't want to mess with it until I know what to mess with!

Thanks!

 

Assuming that you have a Quadr-Jet carb (which you didn't mention), I suspect the accelerator pump [or pump seal] is shot in the carb. To check that out, pop the hood [engine cold..engine OFF], remove air cleaner, open choke plate with your left thumb, and while looking down into the primary venturi exercise the carb throttle linkage FULLY with your other hand. You should see two squirts of fuel...one going into each venturi. If you don't see them, or they are very weak, this is likely your problem.

This is usually not something that requires getting a replacement carb....just a replacement for the accelerator pump. You can order on at NAPA for less than $20. Or since the carb will be somewhat disassembled, you can do a rebuild on it, while you're at it.

If you don't feel comfortable doing that work, send an e-mail to Lars Grimsrud at V8FastCars@msn.com requesting his services to rebuild the carb. He is very reasonable (much less than buying a replacement carb) and will do a fine job. The carb will probably perform better than when it came from the factory. He can also rebuild and set up your distributor, if you send them both. Ask for his prices and turn-around time; he's usually pretty quick.

If you decide to do this job yourself {Good for you!!}, buy Cliff Ruggles booklet on "How to Rebuild and Modify the Quadra-Jet Carburetor". You need it to see how the carb is disassembled/rebuilt.

Good luck!

 

Sorry, yeah it is the Rochester that came on the car. Someone was telling me at a cruise night that there is a way to adjust when the secondaries come it? The car runs very strong and has a fairly fresh resto on it. But I will run out there and do the test you mention. What makes you suspect the pump or seal? Would this cause too much fuel being dumped in it? Because that's what is seems like it is doing (flooding) when I mash it down low. The car starts, Idles and runs flawless if I stab it if the R's are above 2K or so. Choke works like should the whole 9 yards...

So if I do pump the throttle and have strong squirts into the primaries then what's next?

Oh and thanks for the lead on Lars. I may go that route if need be, but I am not sure it needs it just yet...

 

Your secondary air valve (flap over the secondaries) is opening too soon. Look for an allen head screw, loosen that to permit adjustment of the spring tension - increase it in small increments. Try it after each resetting. That will cure the problem.

 

I just found this post by Lars who apparently is the "dude" on these...lol

Heading out now to go adjust it. I figured they were opening too soon. Just did not want to make it worse by messing with anything until I asked around...

Lars posted:

Secondary airvalve adjustment is made using the spring windup adjustment screw and its lock screw located at the secondary airvalve lever. Procedure is as follows:

The secondary spring windup is adjusted with a small, slotted-head screw on the passenger side of the carb, right at the top of the carb on the secondary side. The screw head points right out to the side. 90 degrees from this, on the bottom, there is an allen-head lock screw that keeps the slotted screw from turning. If you have trouble seeing it, place a mirror under the area until you spot it. With a small slotted screwdriver holding the adjustment screw, loosen the allen screw about ¼ turn. This will allow you to turn the slotted adjustment screw. Counting the turns, allow the slotted screw to slowly unwind until all spring tension is gone. You can use your mirror to see the spring disengage contact from the pin lever underneath the air horn. If the spring tension was lost after only ½ turn, the windup was too loose. Bring the spring into contact with the lever. Note when it just barely touches. From this point, wind the spring up between ¾ turn and 7/8 turn. This is a good starting point, and will prevent any bogs or hesitations due to premature secondary opening. From here, you can loosen the windup about 1/8 to 1/4 turn at a time and test-drive the car - when the car falls on its face or feels "flat" going into the secondaries, you've hit the max point. Tighten the spring back up 1/8 to 1/4 turn, and you have the quickest secondary opening rate that your car/engine will handle.

 

The stock setting for the secondary air valve spring is about 7/16 of a turn from just closed.

 

I assume by just closed you mean from where Lars describes bringing the spring back in contact with the lever after backing it off fully??

 

as you tighten the spring the valve will get to the point where it no longer hangs open, from that point go an additional 7/16 which will bring you back to stock setting.

 

Thanks,

Heading out there now to adjust it...

 

Well I played around with it today and I got it much better but it still is not quite right. Before it would fall on it's face. At least now it will somewhat recover and go, but if I hit it down low it struggles. Anything over 2500 R's she runs great. I am being told to check the accelerator pump...

 

that sounds correct

 

Post #2

Secondary airvalve would cause a 'sluggish' response; a major bog is usually due to the accel pump.

 

At this point, I would give some thought to just removing the carb and rebuilding it.

http://www.vetteprojects.com/kstyer/quadrajet.htm

Scott

 

Wow, that's a great page Scott. Thanks. I am still not sure I would tackle this as carbs intimate me. I know I could probably do it but how well it will run when I am done is the question Then comes the tuning. This is a bone stock car in great shape and the carb looks like new, but I know there has been ethanol in the gas for years now AND the previous owner did NOT drive it all that much over the time he owned it. I also let it sit all last summer and most of this one because I had half the interior out to do some minor cosmetics and of course I got sidetracked. The car is back together now and in 2 weeks I threw 1100 miles on it so I am driving it. We have had fantastic weather!

 

I'd be willing to help someone via video teleconference if they'd like to try rebuilding a QuadraJet.

 

WOW...you guys are way too kind...Thanks for all the help here.

So I drove the car to work today. before I fired it up I looked for the squirts you guys mentioned in the primaries. The drivers is nice and strong and the passenger is not. After the car was warm it seemed it was better but still not squirting and atomizing the fuel like the driver side was. So does this mean the pump is bad as mentioned? If I drive the car normal it's not eben noticeable and runs fine. It's only if I jump on it when the R's are below 2500. What I don't get here and maybe someone can explain, why would the fuel going into the primaries effect how the car runs when it's opening the secondaries? And why is the car running basically flawlessly when it's only using the primaries? It's not making any sense to me.

BTW, it's almost like the squirter on the passenger side may be blocked or gummed up the way it is coming out of it. Is that possible and is there a way to just try to clean that squirter? If you guys think it's just the Accelerator pump should I just replace that and see how she runs or do you really think it needs a total rebuild? I swear the thing looks like new....

 

Looks can be deceiving...who knows what it looks like on the inside. If you're scared to take a crack at a re-build, ship it of to Lars over the winter, he'll spiff it up like brand-spankin' new...probably better than new, actually...

Scott

 

It *might* be the pump, but more likely there's some crud blocking the passenger side fuel passage.

As to the why: When you change throttle angle very quickly, the car gets a big surge of air that the main boosters can not respond to as quickly as the throttle is opening. The accelerator pump circuit compensates for this. So what's happening is that you're getting a lean surge on the cylinders fed from that circuit.

So, why's the primary have such a big effect? Well, the secondaries aren't engaged at all at throttle angles <~2/3 of the total travel. They also have a slight delay as they respond to engine demand via the air valve system. The bulk of the air-fuel mixture in that instant you hit the throttle is provided by the primaries, with the secondaries coming in just after.

HTH.

 

My current carb is doing the same thing yours is. I messed around with the secondary adjustments and could get it lightly better but not where i want it to be. I'm actually having Lars rebuild a holley for me and it's being shipped back to me this week. Lars is a great guy to work with and has a ton of great information. Once i have the Holley installed i'm actually going to send out the Rochester to him to rebuild.

 

Ok....that all makes sense. Thanks for the explanation. So any idea what Lars charges for a rebuild? I have heard his name mentioned a few times around here so apparently he is the dude to go to for the rochesters huh?