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This bogging has to be fuel, right?

DynaBro

DynaBro

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1970 SuperBee 383 (20k miles on rebuild), brand new Edelbrock AVS2 650 (vacuum advance), brand new Vapor Separator w/ return line (from the good company I cannot recall the name), all new rubber, vented gas cap.

Bogging down under load. Mostly when shifting into 4th and stepping on it. I can finesse the pedal to drive fine otherwise. But it got REALLY bad going up a steep incline in third and second, which has never happened before. The only major thing I have done to the car recently is installed fresh plugs and set the timing as it was heavily advanced.

One weird aspect of this car is that it is a 383 with a return line. But it's worse. The return line delivers into one of the vent lines. And the return nipple on the sending unit where it is supposed to run is crimped shut and useless. I do not know why this was done. This is why I use the vented gas cap, as pressure was building up and causing fuel seeping from the vent lines between the metal and the hose under the car. Yes, I want to put in a new sending unit and correct this but it's a messy job I have been avoiding as I do not have access to a lift.

So this bogging has to be fuel related, right? But what to do? Try deleting the return line and trying again? Run some seafoam through the tank just because?
 
So it didn’t do this with the prior carb - ”Never happened before" What carb did you replace with the AVS2

Anyways have you ever checked fuel pressure at idle and under load at RPM , hence the venting mess What type of fuel pump are you using

Bogging with the AVS2 could bee a few things - Float level - Air door spring adjustment to loose
Accelerator pump adjustment

It didn’t bog with the prior carb ?
 
Try changing your fuel filter first,
Fuel filter’s are not made the way they used to be. You may get lucky.
Lots of trash in fuel these days.
 
Charles Cook said:
Try changing your fuel filter first,
Fuel filter’s are not made the way they used to be. You may get lucky.
Lots of trash in fuel these days.
Click to expand...
Thing is, he's running a vapor separator so there is no filter unless it has a filter in the carb inlet which most aftermarket carbs do not have....
See item 53...

1755921622118.png
 
Bee1971 said:
So it didn’t do this with the prior carb - ”Never happened before" What carb did you replace with the AVS2

Anyways have you ever checked fuel pressure at idle and under load at RPM , hence the venting mess What type of fuel pump are you using

Bogging with the AVS2 could bee a few things - Float level - Air door spring adjustment to loose
Accelerator pump adjustment

It didn’t bog with the prior carb ?
Click to expand...
The stock Holley. Honestly don’t recall how it performed then as I did a lot of fuel system maintenance to stop numerous leaks and poor previous work.

It did have a split line to dual feed above the fuel filter (then) and now just a single hose from the vapor can.

Thing is I really feel like this is a clean flowing setup that should perform well despite the return going to the wrong port as the vented cap should accommodate that issue. Everything is ran nice and is new. I’m really stumped.
 
Last edited:
It does sound like fuel......but it could be ign. Ign was heavily advanced? So you retarded it & maybe went too far such that it is retarded NOW??????

Retarded ign produces less hp than the optimal ign timing would produce. Engine cannot carry the load.....& you feel a bog.
Make sure you have the correct heat range plugs; many [ wrongly ] fit cold plugs; should be no colder than a '5' heat range in NGK.

Carb: check float level [ 7/16" ]. Wind up spring on the air valve a further 1/2 turn. Sec jets may need to be bigger. Do not go up one size. Go about 3 sizes to get you pointed in the right direction.

I am betting on ign timing.....cause my horse won today.
 
Advance the timing again.

Did it ping before with timing advanced? Advance till it slightly pings and check with a light see where it is set at that point. Then retard it some somthe ping is gone and see of the power is back
 
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And dont forget old harmonic dampners can slip and mess up your timing mark! Maybe it wasn't all that advanced.
 
I always draw a line across the outer ring to the hub center with a Sharpe. If the outer ring slips, it's would be pretty easy to check.
 
So a few things happened today. Installed new V belt and filled the tank. Car still bogged under load. I identified a small kink in one of the fuel hoses. Fixing that improved the bogging. Power is still weak though. The second is there’s a pickup in the distributor. When I time the motor with the vacuum advance removed and plugged the timing never holds after reattaching everything. It retards like a thumb's length. And when I drive it and time it again it's always retarded by like 15 degrees again. No matter how many times I set it.

We hooked up that meter that reads off the coil. I can’t remember the name. The good one. Didn’t get any readings off the coil at 2000 OHM. Now that’s odd. SO I bought a new Edelbrock coil. Seems to have improved a lot. Still not getting the power I used to when the timing was significantly retarded though.
 
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If.................the timing changes when you reconnect the vac adv [ which it should NOT do ], there two possibilities:
- the VA unit is connected to manifold vacuum instead of ported VA [ MVA is a good idea { not, it's great actually...}, but it needs to be done properly. It is more than just connecting a hose....
- pri t/blades are open so far at idle that vacuum is accessing the PVA port. Remove carb & report how much T slot is showing above idle.


Did you read the Edel instructions about klong duration cams???

img287.jpg


img333.jpg
 
Geoff 2 said:
If.................the timing changes when you reconnect the vac adv [ which it should NOT do ], there two possibilities:
- the VA unit is connected to manifold vacuum instead of ported VA [ MVA is a good idea { not, it's great actually...}, but it needs to be done properly. It is more than just connecting a hose....
- pri t/blades are open so far at idle that vacuum is accessing the PVA port. Remove carb & report how much T slot is showing above idle.


Did you read the Edel instructions about klong duration cams???

View attachment 1906835

View attachment 1906836
Click to expand...
I came to this same conclusion late last night! The directions read this way:

3/16” MANIFOLD VACUUM(Except Marine Models)(Distributor vacuum advance port for non-emissions controlled engines)

or

3/16” TIMED VACUUM(Except Marine Models)(Distributor vacuum advance portfor emissions controlled engines)

I went with the non-emissions option because why wouldn't I? Turns out that was "misleading" according to the source I found that corrected my mistake. Planning to try this out today.
 
This can be a can of worms for the novice....
If the engine is modified & has less idle vacuum, then a stock VA unit may not work...or give erratic timing at idle....& can be hard to pin down. Low idle vac can also cause the PCV to operate erratically & cause your problems.
Do you know the cam specs &/or idle vacuum?
 
Sure don't! I am assuming the cam is nothing special. Motor is a donor from an XS Charger so just a basic 383. Notes in the binder from pervious owner said
"Complete engine rebuild hardened valve seats, rings, bearings, etc. 46k miles."
That was 20k miles ago.
Car ran smoother with the vacuum advance corrected. Not a whole lot of HP anymore. Seemed more aggressive with significantly retarded timing.
 
Is the PCV hooked up? It should be connected to the 3/8" port in the carb base, front. I
If it is connected, try this: engine idling, rest your fingers on the PCV. You should feel nothing. If you can feel movement or pulsating, PCV is not working. Report back.
 
You said this in your initial post:
"Bogging down under load. Mostly when shifting into 4th and stepping on it. "

The air door in the secondary's needs to be adjusted.
There are videos on YouTube showing how to do this.

My buddy has the same carb on his 340 and had the same issue - we adjusted the air door a little tighter so it would open the air door later and voila....no more bog.

Try it - you can always put it back if it doesn't work by marking it before you adjust it.
 
71Beeper said:
You said this in your initial post:
"Bogging down under load. Mostly when shifting into 4th and stepping on it. "

The air door in the secondary's needs to be adjusted.
There are videos on YouTube showing how to do this.

My buddy has the same carb on his 340 and had the same issue - we adjusted the air door a little tighter so it would open the air door later and voila....no more bog.

Try it - you can always put it back if it doesn't work by marking it before you adjust it.
Click to expand...
Just to double check, he is loosening it in this video, NOT tightening, correct? Sometimes you just can't tell but this appear

 
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