Sounds like your timing may have been off, and was compounded by a lean spot.


I used some very small gauge wire. I don't remember where I got it from since I had had it on the shelf for quite some time. Small gauge from around 26 - 30. Grab a few different sizes if you see a selection. Obviously, the larger you make it, the richer it'll make your idle, so don't be surprised if you only need 3/4 out on the mixture screws to set it right.

But, what it does is give the carburetor a smaller requirement of air to get the fuel flowing properly. Makes sense since a 600cfm is generally calibrated for engines that are pulling a lot more air at lower RPMs.

If you ever get serious about tuning, you can always drill the air bleeds out and tap threads in place and get an assortment of screw-in air bleeds. But that's some serious stuff. But for a single issue, this is a great workaround since it basically does the same thing.

This is the best way I've found to install it. Make a piece of long wire that's this shape that goes into both.



Then, take the loop that sticks up at the top and fold it back and pinch it tight against the other side of the air horn. It holds itself in place so it doesn't bounce or fall out and go down into your intake.

This drastically reduced the tip in bog that both my 600s were dealing with.



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Great information and helpful illustrations [photo], AbandonedBronco. Your willingness to help is muchly appreciated by members of this forum!

 

Thanks man. Always glad to help!

 

Still haven't gotten to ordering the calibration parts for my Holley, so the truck has been sitting around a lot. My dad has dangled the offer of a Edelbrock 1407 (750cfm) carb in front of me to try out.

My brain says that this is entirely too much carburetor for such a comparatively "small" engine. But on the other hand, I'm thinking that it can't hurt to try it and at least see if things are any better with it.

Opinions guys?

Whenever my taxes come back I'm still getting the parts for the Holley, but I'd like to be able to drive my truck in the mean time.

 

Why aren't you able to drive your truck as it is now? Is the Holley completely shot without a rebuild kit? Or just not calibrated? If it's just not calibrated, it should at least still be driveable. Just boggy in spots, or what not.

As for the Edelbrock, I imagine it'll be too big, but like you said, it couldn't hurt to try it!

 

I can drive the truck as-is right now, but I'd rather have everything dialed in and calibrated before I decide to trust going very far in it. It only bogs when I have to accelerate pretty hard, like jumping out into traffic. If I stab it too hard it'll choke and sputter and I'll have to back out of the throttle to get it to go.

I think I'm going to drive my truck up to my dads shop this weekend, weather permitting and try out that Edelbrock. He tells me that it came off a 350 Chevy, so the tuning couldn't be too far off on it.

If it works, then I'll save the Holley for my 74 F100, since it won't see as much road time and it'd look a bit more correct with that Holley on top of that 390.

 

The "too big" part is the secondaries added to the primaries and with the secondary air flap adjusted properly, they would open less than 100% leaving one with basically a 2v+ carb and IF the flow were evenly divided between the primaries and secondaries that would only be 375 cfm through the primaries at WOT.

Some run a Qjet...JMO, the perfect 4v carb for our engines when properly tuned.

 

All things mentioned are good items. Here are a few more.
Since engine hasn't run correct since rebuild, check cam timing.
Are the secondaries coming in way too soon. Both mechanical and vac secondaries can be trouble if wrong.
Is ignition strong? Long blue spark or weak, short and pinkish? A rich mixture as you have when you hit accelerator requires a stronger spark to ignite effectively.
Coil leads reversed equals a poorer spark. I'm an electronics tech by degree and training but still don't clearly understand how polarity affects the effectiveness of the spark.
Last but least probably least likely is a huge exhaust cross section. Really leans
out the engine and makes idle thru mid range worse than a small single exhaust.

Keep us informed.

 

The Holley that is on the engine now was apparently tuned for another probably larger engine, so it isn't quite right for the 300. I haven't a clue what power-valve is in it, the squirter is a 31, has the white accel pump cam in it, set on the 1st hole.

Vacuum secondaries have the black spring in them, so I doubt they are even opening when I nail the throttle. The exhaust smells "normal" for an engine with a proper fuel mix, and the plugs are all a normal tan color.

Coil leads are correct, as I think it is impossible to put the factory "horseshoe" clip on backwards on the coil. Exhaust is factory sized w/ EFI manifolds so it is just Y'd back to the factory pipe.

Since I just discovered the secondary spring is practically the stiffest one you can get, I wonder if changing it would help with that bog I've been having?

 

Since the secondaries are probably not opening and when they do it won't be until the engine is running at a fairly high rpm. One can't force feed the engine more than it can handle at low rpms without bog problems. Leave the secondaries alone until you get the carb dialed in running on the primaries. Once it is running properly on the primaries then you can start tuning the secondaries by progressively going to lighter springs. If the power valve wasn't messed with that carb probably has a 6.5. Sometimes going to an 8.5 will help cover the lean hole that is causing a bog.

But, before going through all that, try the Edelbrock...the price should be right?

 

Price is Free so the price is indeed RIGHT!

 

Are you using a DP manifold? If you are, carb orientation is important.
How do you have the carb mounted? throttle linkage to the front or rear? To the rear is correct. Differences in cross section and length will make an engine bog with linkage to front. I learned the hard way. No reasonable amount of jetting, spring changes, tuning or timing adjustment combo can clear it up.

 

I'm using the Clifford "C" manifold with the open plenum so I don't think I'll have to worry about carb orientation issues. Right now it is mounted like it would be on a v8.

I thought about the carb orientation as well, but for me it would be a PITA to change as it would require re-fabricating my transmission shift cable bracket, throttle bracket, and require picking up a longer throttle cable. And the TV cable on these AOD's are a very finicky beast, the less I have to mess with it, the better.

 

No worries, if it's an Offy C, any orientation works.

 

What AB said...it's a benefit of running the Offy C.