66 devile convertible carburetor confusion.

[Frank g]

Hello ladies and gents !

Long time ... hope everyone is well .. well this is driving me nuts on what to do ... 7 years ago when I got my 66 devile caddy , that sat 3 to 5 years in a garage... I did a bunch of work with my b.f.mechanic buddy a top mechanic type.. well I took out the original rochester carb and put in a holley 4160 600 cfm in since it was on shelf. Car runs great for all 7 years but horrible gas mileage like 8 to 10 mpg more or less.. in 2017 I paid 350$ for it from OPGI online. Well the other day .the caddy kept stalling unless I kept gas on .had to drive back to storeage at time with brakes and gas pedas being  used lol... stressful lol.. well my new mechanic buddy .great guy found a few leaks in carburetor at base plate at bottom and above amd acouple other spots .. he said if ur lucky may just need to tighten it up and need gaskets  carb in 7 years I've put 6000 miles north east summer driving .using sunoco 93 and extra ethanol fighting additive. I may switch to non ethanol but it's an hour away to get.. will bring 10 cans.annywayyy today I read all kinds of stuff that the holley isn't the greatest .better to use original one rebuilt but I wanted it fixed quick to drive so took the holley off shelf...orrrr to get an edelbrock.. I hate to waste the holley it ran great but seems always rich and I'm wondering if it's not a good match ..we are gonna take it off and swap gaskets .he doesn't think I need full rebuilt ..but still we gotta fix cause it's the therapy caddy lol makes everyone feel good.. so do I'll probably fix holley gaskets to stop air leak and get driving ..but I may rebuild original one keeping in mind I'm not matching vin #s but still nice car so I start wondering would orig carb designed for car best ? Or is holley andnits bad guzzling since it's paid for and in nice shape or should I buy the edelbrok1405 which is so highly rated ? ITS CONSUMING ME LOL PLEASE HELP !!! AND THANKYOU IN ADVANCE AND GOD BLESS YOU ALL....

[James Landi]

I've used Holleys for years, and I discovered an issue that MAY likely be plaguing yours.  Fuel separation, a situation that occurs when liquid gasoline evaporates over long periods of time, and a gritty brown powder that gets stuck in the internal idle passages of the Holley.  The only way "to unstick" this crud is with compressed air through the two idle screw holes at the base of the carburetor.  Products, such as "GUM OUT," WON"T move this crud. You need compressed air jetting in against those screw holes.  As you remove those screws, you'll need to return them to their approximate position.  It's usually a full turn and a half. So essentially, you have no idle passages working now-- the reason why you have to press on the gas to keep the car running.  And by the way, simply "rebuilding" the carburetor WON'T fix this imbedded crud in the idle passages... I've wasted hours and been  frustrated with  ineffective dissembly and assembly, and would have pitched the Holley, but tried the compressed air as a LAST ATTEMPT... I saw the crud shoot out of the carburetor throat! The problem with gas mileage is likely a bad vacuum advance on the distributor. Many of us don't understand the importance of this device and either fail to check it (easily done-- it should hold a vacuum when you suck on the inlet tube).  A non-functional vacuum advance will badly degrade gas mileage and cause your engine to lack smoothness and crispness on acceleration. Hope this helps, James

[Frank g]

Hi thankyou for your response .my mechanic and I feel foolish. My problem was so simple we are embarrassed we didn't catch it ....the cap came off a port so it was sucking in air lol .nooks we are lol .. but it may have saved the old girl due to the fact that I developed a water pump leak... original water pump ... so the carb thing prevented me from driving it possibly saving the motor thank God lol.but I will save ur valuable information.thankyou. next post will be on water pump if theyres any tricks I need to know about lol .thanks again
Frank G .