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After the reinstall, I cannot get the rear back barrels to open up at acceleration (yes, fully warmed up). I have not seen this issue before, so any trouble shooting ideas would be appreciated. Before the rebuild, I had issues with not starting without some effort. Now it starts perfectly, but now the rear barrels seem almost stuck.
Its hard to get the back flaps to pull open with the car just sitting there and reving the engine, it really needs a load to do it. Make sure your choke is completely open.
Theres a small alen set screw and a crew to adjust. The screw is kinda behind the choke linkage on the passenger side.
The screw tightens a spring so when you adjust it, you have to keep pressure on the screw driver part of it. Dont over tighten the screw or the set screw ( allen head)
Can you open the upper air valves and lower throttle plates to pen manually when the engine is not running? There could be something interfering, such as the edge of a gasket, tight throttle shaft, misaligned air valve/throttle plate, etc.
First, the air valves above the secondary bores are NOT throttle plates, they are the secondary air valves that only open when the carb has enough mass airflow to overcome the spring force.
Second, you will typically NOT generate enough mass air flow to open them if you are simply revving the engine in park with the air cleaner off. More questions are written on the forum about this than nearly any other topic. People just do not understand how the Qjet works.
Third, DO NOT arbitrarily adjust the air valve warp spring in an attempt to get them to open faster. There is a specific adjustment process that is detailed in the CSM. IF the spring is too loose, the air valves will open too soon and the engine will fall on it's face when you step on the gas.
Fourth, there is a vacuum controlled diaphragm that also delays air valve opening under high vacuum conditions (part throttle).
Finally, there IS a choke-controlled lockout tab that locks the air valves closed until the choke is fully open. If this is not adjusted properly or if the choke is not opening fully, it will hold the air valves closed. (And yes, I realize this is not a 1970 carb, but the lockout tab in the red circle is the same)
Personally I always remove the lockout tab. It was put there so some fool would not go WOT before the engine was warmed up and especially when the choke was still on. It can interfere with the secondaries opening even when the choke is fully open. Easy to remove with a small drift. Tap tap and the pin is out. Just be very careful the pin doesn't disappear into the carb. I keep a magnet handy while taking it off. The lockout tab is useless in my opinion.
I can tell you that my last two carbs on different cars would always pop open the rear air valves/flaps (yes, assuming the choke was open) once the car was warmed up (whether driving down the road under acceleration or sitting in the drive way). Come to think of it, I can recall this with 442's I have owned back to 1980. I did hold the lock out tab to allow the rear air valves to open and they would go down upon me trying to push them down, but they are under fairly extreme tension. Right now, all I know is that whether in the driveway or under acceleration the carb is only operating on the two front bores (2 barrels) and there is little acceleration on a very fast car.
It can interfere with the secondaries opening even when the choke is fully open.
No, it really can't. If the choke linkage is adjusted properly and the choke is fully open, the tab is retracted out of the way. This is an unnecessary concern and unnecessary mod.
I just went out and started the car, let it warm up
The choke, as it should, fully opened and therefore the lock out tab moved up to allow the rear air valves to clear and open freely. I then took the car out and those rear air valves are not opening up. When I manually push them down, they will go down, but I mean under a ton of tension. I would be surprised that they would be able to drop down under typical load/acceleration (maybe I am wrong, far from the expert). Is there a chance the carb rebuilder somehow over tightened the adjustment that regulates the amount of tension over the rear air valves?
The choke, as it should, fully opened and therefore the lock out tab moved up to allow the rear air valves to clear and open freely. I then took the car out and those rear air valves are not opening up. When I manually push them down, they will go down, but I mean under a ton of tension. I would be surprised that they would be able to drop down under typical load/acceleration (maybe I am wrong, far from the expert). Is there a chance the carb rebuilder somehow over tightened the adjustment that regulates the amount of tension over the rear air valves?
The choke, as it should, fully opened and therefore the lock out tab moved up to allow the rear air valves to clear and open freely. I then took the car out and those rear air valves are not opening up. When I manually push them down, they will go down, but I mean under a ton of tension. I would be surprised that they would be able to drop down under typical load/acceleration (maybe I am wrong, far from the expert). Is there a chance the carb rebuilder somehow over tightened the adjustment that regulates the amount of tension over the rear air valves?
It is certainly possible that the spring was not adjusted properly. It's also possible that the shaft for the air valves is hanging up.
I typically use another builder, but this one was purchased as rebuilt by someone who was really good. When it comes to repairing carbs or household plumbing needs, I have learned the hard way to leave it to the pros. I will let you guys know how it runs once I get it back. Thx for the feedback.
I picked up a rebuilt qjet frm Rock auto. I went thru it w the CSM setting everything up according to spec, nothing was off real bad but many adjustments were off some. The carb now works just like you remember them new back in the day!
I picked up a rebuilt qjet frm Rock auto. I went thru it w the CSM setting everything up according to spec, nothing was off real bad but many adjustments were off some. The carb now works just like you remember them new back in the day!
It only took maybe a half hour to set it up.
Can some one tell me , what is a (CSM setting) please.
I feel kinda dumb here as I have the same problem with my 66 Q-jet on my Toro with a brand new motor and new Carb overhaul done by "Carb Rebuilders"
in Ontario Canada.
My car falls on it's face when you put load to it!!!!!
CSM = Chassis Service Manual
This is the book that the manufacturer made and furnished to the dealerships when these cars were new. It has detailed information on assembly, maintenance, and repair of all parts of the vehicle.
Update: I did decide to send out my carb vs attempting to repair it myself
Upon examination, my carb had too many issues to list. Whoever rebuilt it before ( I failed to mention that I purchased the carb from a guy stating the carb had been recently rebuilt by a reliable carb rebuilder), used all 72 Cutlass 350 internals (he mentioned that the jets installed in the carb would provide 30-40% of the needed fuel for a 70-442). The carb had a warped/incorrect accelerator pump, wrong coil spring inside the cover. He said there was a major issue with the float that was causing a high level of fuel overfill into the bowl which is often a cause for car fires (said it would have burned at some point). Bottom line, like I said, unless you know your carbs or know who rebuilt it, leave it to someone that has experience (which is not me). Once I rec it back, I will update how the car runs vs before.
Last edited by capstoneclub; September 7th, 2017 at 07:03 PM.
August 25th, 2017, 06:03 PM
