Thermoquad tip in bog

[eric2632]

Looking for some expertise tuning the thermoquad. There is a part throttle tip in bog that I just can’t seem to get rid of. Idle is great and full throttle is good, its just when I do a moderate acceleration from a stop there is a little hesitation and then it catches and goes. I have adjusted the air door I know this can cause bog on the secondary side but my issue now is on the primary side. I have not tried to adjust timing, it seems to be right where it needs to be at 6 deg BTDC as far as I can tell. The accelerator pump seems to be working and spraying fine. Any suggestions? This is on my 77 Cordoba 360.

 

[pnora]

Raise the metering rods slightly.

 

[eric2632]

Raise the metering rods slightly.

From what I have found the initial set point for the metering rod tree is clockwise on the screw until it just starts to move the tree up, then 1.5 more turns clockwise. Another source I found said after contact turn the screw 1.5 turns COUNTER clockwise. I have tried both and neither solve my bog, but the 1.5 turns clockwise seems to be too rich and actually causes backfires out of the carb. I notice when I apply light throttle the rod tree pops fully up immediately as the bog is occuring, then then engine will catch and the rod tree will go back down. Not sure if this is normal or something isn‘t right with the carb. I’ll try to post a video.

 

[eric2632]

From what I have found the initial set point for the metering rod tree is clockwise on the screw until it just starts to move the tree up, then 1.5 more turns clockwise. Another source I found said after contact turn the screw 1.5 turns COUNTER clockwise. I have tried both and neither solve my bog, but the 1.5 turns clockwise seems to be too rich and actually causes backfires out of the carb. I notice when I apply light throttle the rod tree pops fully up immediately as the bog is occuring, then then engine will catch and the rod tree will go back down. Not sure if this is normal or something isn‘t right with the carb. I’ll try to post a video.

The forum won’t accept a video from my iPhone.

 

[pnora]

Try unplugging the EGR and see what it does.

 

[69L48Z27]

The tree is what you’re after I think too. The tree pops up as vacuum is removed. That pop is probably lean. I had a TQuad that I just kept scre that rod in until it worked out. It was in the hole way further than I would have guessed. Bigger accelerator squirt could help to. Either way it sounds like you need more fuel at tip in. At least from this side of the keyboard.

 

[GTX JOHN]

Different take from me:

More Air Dore Tension 3 to 5 turns.

Play with linkage on Accel. Pump for more or less early squirt and test for effect.

Recurve ignition for a quick curve.

 

[Geoff 2]

Try advancing the timing to 12-15* BTDC. The engine will make more HP with the extra timing, & it makes a BIG difference with low compression engines. Making the extra HP, the engine can take the load when you apply throttle. Try this first. Is the engine stock? Cam?

 

[eric2632]

Thanks again for the replies everyone. Yes its all stock, 360 with the thermoquad. It had some kind of Holley on it when I bought it and didn’t run well, I’ve since found and installed the correct numbers Thermoquad. I could probably save myself some grief and just put an Edelbrock or someone on it but I like originality and trying to make the original equipment right. Anyway, I did study the system more yesterday and discovered the system has an electric delay solenoid that dumps vacuum to the EGR valve until 35 seconds after engine start. So it makes no sense trying to tune anything until after this 35 seconds has passed and EGR is functioning. So I let that happen then raised the rod tree again and it seemed to work pretty well with no backfiring through the carb.

I also did advance the timing to what I believe is about 12 degrees, but its very difficult to read the scale against the timing mark with my timing light. But anyway the engine responded very well to this so I’m going to leave it alone for a while and see how that works in daily driving. Thanks again!

 

[eric2632]

Also just curious what are thoughts on the OSAC valve for the vacuum advance? I’m currently using the original one for the car and it seems to work as intended, to delay the vacuum advance when accelerating. Are these beneficial or just an emissions era nuisance that is better off being bypassed?

 

[pnora]

Myself I always eliminated all that BS. Early emission controls had a ton of undesirable drive ability woe's.

 

[Geoff 2]

Agree with pnora; block or get rid of the emissions crap. Things like ign timing were done for emissions, not best performance or drivability. A low compression engine such as this requires more timing, not less, because the mixture takes longer to burn.
My Motors Manual, which covers 72-78 models, has a 78 360 with 20* init timing.
For reasons known only by Chry, they used ridiculously low init timing on low comp engines. In contrast, 76-78 Pontiac/Olds engines, many had 16-20* init timing.