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Discussion Starter · #1 ·
Working on my street car. I have decided to ditch the 750vac carb due to a odd stumble that I cant iron out. So I am going back to my tried and true 850 annular dbl pumpr. Problem I am having with this carb is I cant get it to idle down. I welded up the drilled primary throttle blades. The secondaries are not drilled and it doesnt have the secondary idle adjustment. Right now the best I can get it is 1100 rpms. Which might be fine in a auto with a bigger cam but the 4 speed likes about 800. Any ideas why it wont idle down. No cables were hooked up so nothing is binding. blades appear to be closed when looking down inside.. I also sprayed carb cleaner around it and no vacuum leaks.. Any Ideas?
 

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Discussion Starter · #3 ·
I didnt check the baseplate but all the other gaskets are nice and in good shape. The blue ones.. The carb was totally tore down a year ago or so and new gaskets through out.. I doubt it would have dried out.. I ran it about 4 months ago..
 

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close the secondary screw up some more. It would be under the baseplate and needs a small flat blade screwdriver to adjust it. Basically would be down where the carb gasket would go between the intake and carb. So carb needs to be flipped over to see.
 

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Any choke mechanism?
 

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Put a timing light in it. See what it's doing. The weights might be hanging up. Or not coming in as it should. Was chasing a similiar problem for a buddy and after fiddling with 2 different carbs it was the distributor.
 

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It doesnt have the secondary Idle screw
Then you need to find one.

The throttle blades need to be adjusted so the transfer slots are exposed ~ .020" to start. Both primary and secondary should be opened the same amount.

Set the idle speed.
Remove carb and check if primary is opened more or less than the secondary.
Open or close the secondary throttle blade with the goal being to get them both open the same amount at idle.
Install and repeat.
 

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Discussion Starter · #10 ·
It doesnt have a provision for the secondary idle screw. they are both closed equally. unless it different than my other 850. My other has the small screw on the bottom side of the baseplate that you can adjust while running. Is there something completely under the carb that would require removal?
 

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It doesnt have a provision for the secondary idle screw. they are both closed equally. unless it different than my other 850. My other has the small screw on the bottom side of the baseplate that you can adjust while running. Is there something completely under the carb that would require removal?
Yes, the carb has to be removed. The procedure had been posted above
 

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you have to remove the carb off the engine and flip it upside down to adjust the secondary side.
You can take an old "pocket" std. screwdriver, cut off most of the handle, and adjust it while still on the engine.

Along the same lines, if you are swapping vac. secondary springs and don't have the newer style top cover (or an aftermarket)...rather than removing the vac. sec. housing to swap springs, you can simply drill down through the top of the air filter flange (carefully) to expose the hidden cover screw. To be safe you can remove the carb to clean all the shavings...but you'll make the next spring swap a lot easier.
 

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Wierd not on my other 850..

Here are some pictures of the problem carb..







Here is my other 850 that has the secondary idle adjustment on the side..
Right off, your squirters are too small. Step up to a 0.034 orifice on both sides.

As the other poster said, take the carb off and check the butterfly adjustment screw in the baseplate by the accel pump bellcrank.
 

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What the....? Thats a strange looking secondary linkage...
 
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