409 Questions

Don Jacks

Well Seasoned Member
Supporting Member 3
Have you tried a run as before,but sans air filter housings at all? This would tell you if the air cleaner housing itself is causing this richness.As to the feeling of the timing retarded at a cruise,the solution to that is vacuum advance,and it should be hooked to manifold vacuum.John has a good point in that half of that engine is nice and the other is pig rich.Possible air leak on the "lean" side?
 

409acoupe

Active Member
409a unless I counted wrong it looks like 2,5,and 8 are all on the same plane of the dual plane intake.
I was looking at the manifold tracing the path of plenum and it seems to somewhat mix to where some of the rich plugs mix with the good ones but I may be mistaken
 

409acoupe

Active Member
Have you tried a run as before,but sans air filter housings at all? This would tell you if the air cleaner housing itself is causing this richness.As to the feeling of the timing retarded at a cruise,the solution to that is vacuum advance,and it should be hooked to manifold vacuum.John has a good point in that half of that engine is nice and the other is pig rich.Possible air leak on the "lean" side?
That’s the next step I’m gonna try before getting too excited about anything else. Distributor is a new pertronix with vacuum advance I have hooked to full manifold. When I was dealing with the shit speedway based on the secondary carbs I went through the entire intake carbs etc hunting for any vacuum leaks. With the new bases she’s sealed tight, no leaks anywhere that I have been able to find. Sprayed carb cleaner all over testing for leaks while running and nothing.
 

409acoupe

Active Member
How is the idle? Will it sit and idle?
Idles fine. Once I got the new GOOD secondary bases installed we did a full tune on the motor. Idle mixture screws, timing, idle screw etc. Like I said the motor runs fine for the most part other than this slight miss which I would think is a result of these plugs looking shitty but why they are still has me wondering. Throttle response is great, acceleration is strong it just has this stupid little miss. Ah the joys ha ha
 

rstreet

Well Known Member
Supporting Member 17
Remember the old spark plugs cleaning blaster ????? Our shop had one and it cleaned them with a blast of fine media,stick it in the rubber faced grommet hit the button and a blast of air and media and very clean.

I remember the blue AC ones very well. When the EPA mandated lead free gas in the late 70’s they disappeared over night.
Robert
 

Don Jacks

Well Seasoned Member
Supporting Member 3
They often didn't work on gas fouled plugs.In 1975,when cat.converters and unleaded fuel became mandated,their usefulness was pretty much done.Unill that time,the life of spark plugs when subjected to leaded gas was maybe 15,000 miles.
 

Fathead Racing

Well Known Member
Supporting Member 7
Never say never but in my opinion the jetting is still lean. Problems lay elsewhere. It's mighty strange that seeing the condition of the plugs that the engine would even idle if it were that fat :dunno. Have you tried running down the road with no air scoops at all? I sure wish you lived closer, I'd like to get my hands on the engine.
 

Fathead Racing

Well Known Member
Supporting Member 7
View attachment 70767
With the intake runners traced out, it looks like you have a problem with the left side of the carburetor.
Thank you James, that gives a place to start looking. Without a two barrel in front of me I'm a little lost but I'd love to take a crack at that carb. I used to love working on and modifying the Rochester 2G's.
 
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