To check for a vacuum leak get a can of starting fluid or carb cleaner and start spraying. I was having hell with the idle on my 5th Avenue last days off and found a leaking carb base gasket.
Carburetor cleaner will make RPM spike if it finds a vacuum leak – so good for finding vacuum leaks. I have seen what Lowbudget has, a few times.
For whatever reason, the fasteners that attach carburetor to intake will loosen. I suspect as gasket gets saturated with fuel, they seal off the vacuum leak – but when cold (ie: dry) it will leak air, thereby increasing engine idle speed.
Leasuretime, did you purchased a NEW carburetor from RockAuto?
I checked and the only ones I saw were reman’s (re-manufactured), which is not new.
On eBay, there are some new BBD’s out there, for less $ than reman’s are. They are Chinese knock-offs. I have been using one for 5 years now without any problems and I think others are here as well.
I wrote up a piece about reman carburetors some time back – went to look for it and couldn’t find it – but something that people need to know about.
To recap, carburetor remanufacting companies will “process” about 30-50 carburetors at a time. It would be, for example, a batch of 30 BBD’s, a batch of 50 QuadraJets, then a batch of 40 Holley’s, etc. What happens is they grab, say 30 BBD’s off of the shelf and strip then down – tossing all of the contents of that batch (all 30 units), into piles (Jets in one pile, linkages into another pile, etc.).
All parts get cleaned. Metal items get re-plated, defective parts get tossed, and so forth. When re-assembling the units, they grab one of each part and go back to re-assembling them. This is where problems arise. Linkages change over the years, jets change on engine sizes, and so forth. You would not want /6 jets in a 360 engine (or vice versa). What comes out – is a very clean unit – but nothing like the original unit. It would be very unlikely that finished unit had the same exact parts on it, as it went in – which is one of the reasons I do not like reman carburetors. If the rebuild companies would keep all parts together – I would have a different opinion on the matter – but the way that business is structured – this is best for them.
I cannot tell you how many reman carburetors – I had to “rebuild” to get it back to specifications for it to be roadworthy again.
Now with that said, if a person rebuilds a carburetor (self, friend or even taking it to a rebuilder), then all original parts are re-used, except for defective ones, and you are back to where it should be. If part is marked “reman” then that is not the case.
Carburetors and distributers are the two items I run across being problems. Most everything else (alternators, starters, transmissions, etc.) I don’t have much problems with. Carburetors (and distributers) were not meant to be remanufactured – because of the calibration factor and there is just SO MANY variations of parts used on them.
I suspect you might be a victim of mis-matched parts – this case linkages and/or fast idle cams, etc. – possibly – and those are hard to fix (and diagnosis) – without having an original close by to compare to.
That said, get some carburetor cleaner and with engine running, spray some at the carburetor base, and around intake, etc. – and make note of any engine RPM spikes – before doing anything else.
BudW