Nailhead Buick idles like shit with Q Jet until I cup my hands part way over the choke horn. That gets it very smooth. So, I spray some carb spray around the base of the carb and it loves that too, yet I can't find one single vacuum leak in that area. Not yet anyway. I've checked the base to intake gskt, base to main body gskt, + all vacuum lines in and around that area.............Anyone have a similar prob? Thanks
The throttle shaft bores are wore out.If you have a carb shop that can rebushing it for you go that way or switch it to an Edlebrock,just remember nailheads like big CFM carbs.
Using a vac gauge what is your vacuum when it runs poorly? What is your vac supposed to be at the specific rpm designated, what is your vac when you cup the carb? Sounds like you are sucking air at the carb base if you can get the thing to smooth out by spraying carb cleaner at the base of the carb. That'll do it.
Idle passages could also be partially restricted due to dirt, and the vapors from the spray are being drawn through the air horn, rather than a vacuum leak at the base. ---John
10" til I cup the carb, then it's around 15" but real smooth. The base gskt has a perfect impression of all the details of the bottom of the carb on 1 side and perfect impression of the intake on the other. I replaced with a thicker, softer gskt anyway and no change. The base to main body looks fine as well. Throttle shafts are tight.
I was wondering a similar scenario too. But, I'm using one of those red straws that pin points the spray pretty good.
I agree....I have seen this many times and its not always apparent.The boars become egg shaped over time and allow vacuum to leak around the shaft.
OK, it MIGHT be the throttle bores are worn to the point of needing bushing; however: ONLY the 1966 Buick nailhead came originally with a Q-Jet. Questions: Do you have a 1966 with original intake? Are you using a 1966 Buick Q-Jet? Is the carburetor to intake gasket the proper gasket for the 1966? If you answered no to any of the three questions above, it is possible that you actually have an internal leak causing a lean condition. Placing your hand over the airhorn artificially richens the mixture (by the way, this can be dangerous; guess what burns with a backfire!!!). Similarly, squirting a flammable liquid around the throttle bores can also artificially richen the mixture. Before installing bushings (which still might be needed), I would suggest checking out the compatibility of the manifold, carb, and gasket. Not disagreeing with anyone on the necessity of bushings, just suggesting other less drastic measures might solve the issue. And one other item, how far out are the idle mixture control screws? Jon.
OK, I may have found it. I took the top of the carb off and the top of the main body looks like it bounced around a core pile for a very long time with it's top off, badly damaging the gskt surface in the area where fuel transfers up from the well, across, and then down towards the mixture screw area. Thanks for the replies.
In lean conditions like you have spraying the carb base may mimic vacuum leaks when no vac leaks are present THERE. Vac leaks may still be present somewhere else. I stopped using carb cleaner because the possibility of lighting the engine off is very real. We now use a smoke machine. Not everyone has access to one of those. Much cheaper is a very common ( in CA) adaptor for a hobby propane bottle that injects a short blast of propane through a hose directed at suspected leaks. If you have PCV, temporarily disable it and add propane or carb cleaner ( don't recommend!) to oil fill hole and see if engine reacts. It may be that you just have a lean carb. Needs to be fixed, adjusted, replaced, rebuilt whatever. Many Rochester-style carbs can also leak through bad choke pull offs and if the hot air choke stat is still being used there is an airbleed that pulls hot air into the choke stat that can leak.
So I think the main body was bounced around extensively, possibly in a core pile without it's top and suffered damage in an area that causes my probs. The 1st pic shows the tip of the screwdriver between 2 ports. 1 goes towards the idle circuit near the idle mix screw, and the other to the main jet. Vacuum pulls from the idle circuit area where it transitions through a void in the gskt, and that area's pretty damaged with no real witness marks of the bottom part of the gskt sealing. The rest show more damage to that gskt surface. So, pretty sure no real fuel to speak of reaching the idle circuit. Thoughts?
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