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440 very rich at idle, lower vacuum

Rick69

Rick69

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Working on a 440 that I did not not put together. Problem is at idle it is very rich and about 15" of vacuum. Stock heads, intake, exhaust. I believe the cam has been changed but I don't have any specs. Engine compression is 160psi across all cylinders. I've already advanced the timimg. No vacuum leaks. Had the Holley 770 rebuilt at a local carburetor shop. When idling in traffic the fumes burn the eyes. Also, a safety problem because it tends to lose the power assist to the brakes. Accelerates good and cruises fine. How do I tell if this is still a carburetor problem or do I look at another cam?
 
I don't know anything about a Holly, but I had the same problem on my Edelbrock. I just changed the metering rods and jets. I leaned it out 2 stages in the power mode and one in the cruise mode if I remember correctly. It made a world of difference. Even increased my fuel mileage by about 2 MPG.
 
Do you have a PCV, or is the port on the carb for it capped off?

What happens when you adjust the idle mixture screws? Any effect? Are they all the way closed? If mixture screws have no effect, one cause could be a blown power valve.

Is the choke adjusted correctly, is it open when the engines warm?

Some things to start with anyway.
 
For starters 15 in/hg should be plenty of vacuum. Having the carb rebuilt is good, but it has to be tuned and configured properly for the engine's needs and personality.. the brake issue is likely something with the braking system itself, maybe leaky/failing booster?
 
Also, how are you ascertaining it's too rich? Plug color or A/F meter? A too-lean mix can also burn the eyes and be stinky. For a quick easy check, while the engine is idling at operating temp, gently bump the accelerator pump arm; if this small amount of extra fuel causes the RPM to momentarily drop, it wants less fuel at idle, if the RPM increases for a second it can use more idle fuel (again, this is just to see if you're in the ballpark). This is all assuming the carb was set for baseline properly--transfer slots not too exposed, float levels etc..
 
Agreed, 15"HG should be more than enough for the brakes & to satisfy a power valve/power enrichment circuit... Tuning & a brake booster issue... BTW if you booster looks like this one it's made by CPP & should probably be thrown in the trash...
Screen Shot 2019-08-10 at 18.21.06.png
 
If you have a vacuum gauge, you might try reading vacuum off the carb port. Adjust your carb mixture screws for the highest vacuum reading you can get.
That's how I tamed my Eddy twins. Couldn't get much reaction, trying to set 'em by RPMs.
 
Beanhead,
I think you've pointed me in the right direction. When I first brought the carb to the shop for rebuild I told them I thought I heard a hissing sound from the air horn. They gave me the carb back assuring me it was good to go, set up to basic conditions. After your comment I took it back off and began looking. I noticed the secondary throttle plate was open slightly. Someone had turned the screw in. I backed it off til the plate just touches and reinstalled. Improvement!
If I turn the mixture screw in on the driver's side the engine stalls. If I turn the mixture screw in on the passenger side the engine slows down and gets rough but runs. Problem??

As for the power booster, picture shows the one in the car. Does this one fall into the "trash" category?

20190811_083830.jpg
 
All it takes is one backfire, or even just a minor phhfftt back up the carburetor when cranking and presto,..... high probability the power valve diaphram could be blown, and very symptomatic of rich idle(burn you eyeballs) and limited idle screw adjustment effect.

Did you ever get a little "phhffft" back up the Carb when starting ? or a real backfire ?

Google Holley Power Valve symptoms, easy/cheap fix.... world of difference.
 
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