THSCC Forums

You might be able to hear if that second valve is opening with the filter out of the way?

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In need of car.

Mike - I assume that when you took things apart that the secondary parts all moved freely by hand (i.e. that you could open the secondary manually). I don't know how the Toyota or the Ford secondary works (I sold the ford 30 years ago).

However, here is how the secondary on the Weber/Holley on my FF works which may provide helpfull hints:

Overall throttle linkage has a second "stage" that allows the secondary throttle to open after the primary is opened a certain amount. As far as I can tell the secondary is actually opened by the intake vacuum "pulling" the secondary plate open. There is actually a return spring that the secondary has to fight against to open. If this spring breaks, the secondary stays partly open and the engine "races" (FF guys carry spare springs). The "suction piston" in your carb would need a vacuum source which may be internal to the carb casting and could easily be obstructed. However, it is possible that the piston is actually a damper for the throttle plate. If so, it may have a "relief circuit" which could be plugged.

In addition to making sure the secondary linkage, etc. move freely (don't forget to check to be sure the plate isn't sticking in the bore), make sure that the secondary fuel passage/jet circuit isn't obstructed.

I don't know whether the secondary should freely open all the way under minimal load. Its about time to warm up my FF again, so maybe in the next few days I'll get a chance to see what mine does.

I'll also see if I have some other carb books that might explain the "theory of operation". My Weber books don't explain what actually opens the secondary.

Finally, have you verified that you are getting full mechanical advance in the distributor?

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Dick Rasmussen

FS 50 2018 Mustang GT

mike,
other ideas:

-timing belt "jumped time" See if the belt is really loose, and check timing marks. Usually, when it skips, it will "retard" the cam, which kills low end torque and actually cleans-up with rpm. Sometimes, though, it will jump and advance the cam, when this happens you may get an idle shake and good low end rpm, but at a certain rpm the pwoer will completely flatten out. It almost feels like the rev limiter, but has no other real symptoms.

-fuel filter is a good canditate (it will starve fuel at a time of highest fuel demand which is high rpm at high load

-clogged cat almost always has a sound of rushing air like a big, "swooooooshhh" at high rpm (it will do it regardless of load at high rpm)

-inactive secondaries will usually cause a severe lean condition at high load but not necessarily high rpm. The resulting lean condition causes pinging real bad when the secondaries where supposed to have kicked in.

If it has high mileage and hasn't had a belt in a while, I'd look at the timing belt and perhaps do a compression test too.

good luck,

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Jim Williams
'94 GSR Integra, TIR 12

A 1989 Toyota Corolla with a carburetor? Does it have a crank on the front to start it? Good grief, my Mom's old '85 Tempo at least had throttle body injection... the Tempo that she traded in on a Toyota Corolla .... shut up, all of you.

I think you should go beat up the guy that sold you the car.

Mike,

The secondary on my FF DOES open under minimal load! Very rapidly!!!

I checked my Holley book. The progressive versions of Holley 4V's use a vacuum diaphram assembly to pull the secondary open with the vacuum source comng from the primary originally and then supplemented by the secondary.

I checked my Rochester book. The QuadraJet uses a mechanical secondary throttle plate with an "air valve" (looks like a choke plate) that opens as the airflow increases. The air valve has a damper. Now that I've refreshed my memory I recall that the Ford carb used the same approach.

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Dick Rasmussen

FS 50 2018 Mustang GT