Secondaries not opening???
Thread Starter
6th Gear
Joined: Jun 2009
Posts: 6
Likes: 0
Secondaries not opening???
I own a '70 with a 350 / 350 HP, Rochester 4 BRL and I don't think the secondaries are opening. Once warmed up, the linkages etc... are free, but the secondaries don't appear to open......the engine is pretty flat. When I remove the air cleaner and open the throttle, the secondaries do not open. Not sure if that is a valid way to check or not, but I would appreciate any advice.
Thanks
TM
Thanks
TM
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
The top plates on the Qjet are not the throttle plates. Push them open with the engine off and look down and you will see the throttle plates. The top plates are opened with vacuum. You will not get them to open winging the throttle in park.
Drifting
Joined: Sep 1999
Posts: 1,970
Likes: 91
I own a '70 with a 350 / 350 HP, Rochester 4 BRL and I don't think the secondaries are opening. Once warmed up, the linkages etc... are free, but the secondaries don't appear to open......the engine is pretty flat. When I remove the air cleaner and open the throttle, the secondaries do not open. Not sure if that is a valid way to check or not, but I would appreciate any advice.
Thanks
TM
Thanks
TM
On the vacuum end of things...If all functions properly, the rod "B" will be held in the forward slot in the air valve via vacuum from the dashpot, locking out the airvalve. Opening the throttle will cause the engine to lose vacuum, allowing the rod to more rearward in the slot,(as seen in the pic) unlocking the airvalve.
On the mechanical end of things... The secondary throttle shaft/pin,"A" will be engaged by the lock out lever(drawn in yellow) at start up when the choke,"C" is closed. Preventing the secondary valves to open, even as the throttle is fully opened.
There are other possibilities but good place to start checking. BTW a fully warmed and functioning carb WILL operate the secondaries if you "blip" the throttle
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
The secondaries will open because they are mechanical. The air valve will maybe just crack open but will not open very far if at all unless you leave it wide open and the rpms are climbing high. Not ideal way to check the carb operation.
Thread Starter
6th Gear
Joined: Jun 2009
Posts: 6
Likes: 0
Thanks for the advice.
Thanks for the input. I did some more digging and found that the main problem was the accelerator cable. It was either stretched or assembled incorrectly. With the accelerator to the floor, I was not getting WOT....3,000 RPM max. I added a spacer to the cable at the pedal bracket and that made a world of difference. I think I still need to check timing etc...., but at least I can get off the line.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
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Melting Slicks
Joined: Oct 2005
Posts: 2,056
Likes: 8
From: Redruth Cornwall
Glad you got it sorted.....sometimes its the simple things we overlook!
The secondary air flap will not open on a correctly set up carb if the throttle is blipped in N or Park. The secondary throttle plates will open but not the air flap. You will not see the air flap open, this is normal.
The secondary air flap will not open on a correctly set up carb if the throttle is blipped in N or Park. The secondary throttle plates will open but not the air flap. You will not see the air flap open, this is normal.
Burning Brakes
Joined: Jul 2008
Posts: 876
Likes: 0
From: Canastota Ny
also the spring may be way to tight for the secondary air flap to open under any vacuum. also there is and ajustment for the cable that doesn't require a shim so to speak. unlatch the cable where its held on the intake by the clip. put the throttle in full WOT position and then reinstal the clip./ you should now have it adjusted correctly. if this doesnt work then yes for some reason your cable is stretched
