DV8 Posted August 25, 2015 Share Posted August 25, 2015 So ever since I restored and fixed my AC system I seem to be having a slight problem with vapor lock on our typically hot summer days here in Las Vegas, NV. Not major but here is what will happen: Today the outside temp was 105º F. I drove for about 20 minutes on the highway, got to where I was going, parked, had about an hour of the car being off and in the shade, and then it started right up again but I stalled out a about two or three times while maneuvering out of the parking lot. Once I'm back on the highway, have the throttle down even a little bit and wind is blowing across the engine there's no problem. It's just when when I'm pulling out of a parking space or making a three point turn after the engine is hot. So, any thoughts on how to remedy this? Here are a couple more questions: What do you set your fast idle to? The shop manual specifies 550 RPM's (w/AC) which I did to the bast I could and it actually feels a little low. In fact the fast idle adjustment screw was all the way out and the lowest I could get the RPM's to was a range of jumping between about 575 - 700-ish. More consistent fuel to the carb seems to solve the vapor lock problem so I'm wondering if setting the RPM's at idle a little higher than the shop manual specs is something that is done due to the car's age and as I understand it our carbs were designed to work with less volatile gas than is available today hence the vapor lock problem. My main fuel line is routed in a very tight space in front of the water pump and while it's not constricted it does seem tight and very close to the hot engine. Is this the correct routing? I'm wondering if routing the main fuel line so that it is a little free-er and away from any metal would help. I've also heard that a carburetor spacer to keep it a little further from the manifold helps to prevent some heat transfer to the fuel system. I'm not sure how much space I have between my air filter cover and the lid though so I'm wondering if anyone has had good results with something like that. Link to comment Share on other sites More sharing options...
alini Posted August 25, 2015 Share Posted August 25, 2015 (edited) The fast idle wont have anything to do with it once you have been driving more than 15 minutes, your choke butterfly should be straight up and down by then and the fast idle screw should be completely off the plate at that point. You can put a spacer in between the carb and manifold, most arent much more than 1/2 inch anyway, Is it possible that you have a vacuum leak at the manifold. Many times those don't come to light til the car is hot. I have a lazer thermometer you can use to help diagnose temps to help find a cause. Edited August 25, 2015 by alini (see edit history) Link to comment Share on other sites More sharing options...
alini Posted August 25, 2015 Share Posted August 25, 2015 Also whats the state of your fuel filter? could it be clogged and restricting flow to the carb Link to comment Share on other sites More sharing options...
DV8 Posted August 25, 2015 Author Share Posted August 25, 2015 (edited) Fuel filter was replaced a few weeks ago. As best as I can tell there are no vacuum leaks. I've replaced most of the vacuum hoses and it's holding a steady 17 in. anywhere I check it at the manifold. Also, I didn't mean the fast idle even though that's what I typed I meant the idle speed screw. Edited August 25, 2015 by DV8 (see edit history) 1 Link to comment Share on other sites More sharing options...
alini Posted August 25, 2015 Share Posted August 25, 2015 If its the true idle speed screw and you have it backed all the way out, you have a vacuum leak. The motor wouldn't get air any other way since the butterflies are completely closed. Its possible the gasket under the carb or between the manifold and heads have dried out or corroded. If you take a can of carb cleaner and just spritz around the gasket areas, if it speeds up thats where the leak is. Link to comment Share on other sites More sharing options...
60FlatTop Posted August 25, 2015 Share Posted August 25, 2015 If its the true idle speed screw and you have it backed all the way out, you have a vacuum leak. The motor wouldn't get air any other way since the butterflies are completely closed. Its possible the gasket under the carb or between the manifold and heads have dried out or corroded. If you take a can of carb cleaner and just spritz around the gasket areas, if it speeds up thats where the leak is.X2Bernie Link to comment Share on other sites More sharing options...
Jim Cannon Posted August 25, 2015 Share Posted August 25, 2015 Are you using the original stock fuel filter that these cars had when equipped with A/C? Does it have one nipple in and two out, one in the center for fuel out and one on the end but to the side for vapor out? If not, try one. The vapor return line runs back to the tank. Make sure it is hooked up to the tank, not left open. Link to comment Share on other sites More sharing options...
DV8 Posted August 26, 2015 Author Share Posted August 26, 2015 Yeah, I have the proper fuel filter on there and the return line is in place. I'll try to do the vacuum leak test with carb cleaner soon. Link to comment Share on other sites More sharing options...
DV8 Posted September 8, 2015 Author Share Posted September 8, 2015 Finally did the carb cleaner vacuum leak test. Sprayed all around the carb, the manifold, gaskets, etc. and no noticable change in engine speed. Link to comment Share on other sites More sharing options...
alini Posted September 8, 2015 Share Posted September 8, 2015 How old is your PCV valve? How about your brake booster, is your brake performance consistant? Check the connection there too it could be loose. Link to comment Share on other sites More sharing options...
DV8 Posted September 9, 2015 Author Share Posted September 9, 2015 (edited) PCV was replaced a month ago or so. Haven't looked too closely at the brakes yet as they seem to function just fine and consistently. Edited September 10, 2015 by DV8 (see edit history) Link to comment Share on other sites More sharing options...
alini Posted September 9, 2015 Share Posted September 9, 2015 With your idle screw backed all the way out, you engine shouldnt be getting enough air to run at a decent idle. You mentioned that it stalled at low speed (parking lot) there is a spring dampner in front of the throttle, does yours have spring tension? Is it touching the throttle plate? Its there so the plate doesnt slam shut choking the motor as it decelerates from letting off the pedal. Without seeing the car myself its hard to make suggestions at this point because you have checked almost everything Link to comment Share on other sites More sharing options...
DV8 Posted September 10, 2015 Author Share Posted September 10, 2015 Chris, I've seen the piece I think you are describing referred to as the 'dash pot.' I did replace mine a few months ago and it does touch the throttle plate but I've never been totally convinced that I have it adjusted correctly. You bring up a good point. I wonder if I need to move it a little closer to the throttle plate. I also took a close look at the gasket between the carb and manifold and I'm a little dubious that the gasket is the exact piece that it should be and I understand that there should be a metal plate between the gasket and the carb which helps in keeping the bowl warm in cold weather but I'm not sure there is one there. The absence of the metal plate probably wouldn't affect the problem I'm having with the hot weather but I have a feeling that I don't have the proper gasket in there. To be honest I haven't tried backing the idle speed screw out ALL the way but I have backed it out to the point that it seemed that it wasn't having any effect on the idle speed. From what you're saying it seems like I should be able to stall the engine by backing it out all the way. I suppose all the more reason I need to come up and see you. Link to comment Share on other sites More sharing options...
RivNut Posted September 10, 2015 Share Posted September 10, 2015 The idle screws only make adjustments when the throttle blades are fully closed. Once you open the throttle blades, the idle cuicuits are nil and void. Backing them all the way out will cause a rough idle but once you open the blades, that's all nil and void as well. You need a metal gasket between the fiber gasket and the base of the carb to keep the exhaust gasses that pass under the carb from corroding the base of your carb. The dash pot is designed to allow the throttle blades to close slowly rather than slam shut. If you're having problems only when the engine is hot, perhaps the carb is getting too hot. ????? Or, corrosiion has eaten into the carb and you've got bigger problems. Do you have a Carter AFB or the Rochester 4GC? Link to comment Share on other sites More sharing options...
DV8 Posted September 12, 2015 Author Share Posted September 12, 2015 (edited) It's a Carter AFB. I can't find any evidence of any corrosion on the carb. Here are a couple photos of what is at the base of the carb: I only see one layer sandwiched between the carb and the manifold and it doesn't seem to match the shape of the carb. Can some one confirm if this looks correct or incorrect for me. The dash pot doesn't seem to have enough spring resistance to really slow down the throttle from slamming shut. It presses against the spring but it doesn't seem to shut any slower than if it wasn't there at all. I ordered it from C.A.R.S. Edited September 12, 2015 by DV8 (see edit history) Link to comment Share on other sites More sharing options...
alini Posted September 12, 2015 Share Posted September 12, 2015 The corrosion he is talking about is under the carb. There is a port in the intake that has exhaust gas running through it when the butterfly on the passenger side manifold is closed. Regardless if you have disabled it or not the exhaust gasses still corrode the metal...and the gasket underneath may be eroded away. You wont know til you remove the card and turn it over. Link to comment Share on other sites More sharing options...
alini Posted September 12, 2015 Share Posted September 12, 2015 Here is a shot of the top of the intake. That U shaped runner is actually exhaust. When the car is cold the passenger side exhaust manifold has a butterfly valve on it that closes causing backpressure to push hot exhaust gas up to this point helping heat up the carb. Your carb has a matching channel in it and the metal there is known to get corroded away causing a vacuum leak and allowing exhaust gas to mix with the clean intake air. Link to comment Share on other sites More sharing options...
RivNut Posted September 12, 2015 Share Posted September 12, 2015 You want the bottom of the carb to be warmed by the exhaust gasses but you don't want the gasses coming in contact with the aluminum; that's where the corrosion starts. In order to heat the base of the carb and not have the gasses come in contact with the aluminum base, a stainless steel gasket is sandwiched between the carb and the fiber gasket. The fiber gasket has a channel in it just like the channel in the intake. The allows the gasses to pass and come in contact with the stainless steel. The heat is then transferred to the base of the carb with the absence of the exhaust gasses. You'll never see evidence of corrosion until 1) you take the carb off and inspect it or 2) your car just won't run right because there's a hole through the body of it that corrosion has caused. Gaskets are cheap. Carbs are easy to take off. Don't second guess what you may (or may not) have. While you have the carb off would be a good time to paint the engine the correct color: Silver for a '63, Buick Green for a '64 or '65, red for a 66. That's the end of the nailhead years. Ed Link to comment Share on other sites More sharing options...
DV8 Posted September 12, 2015 Author Share Posted September 12, 2015 I wonder if my problem with the vapor lock is that I'm missing the fiber gasket and the manifold, in direct contact of the steel plate, is heating the base of my carb too much or too efficiently.Are you normally able to see the fiber gasket if it's in place? Can anyone tell from my photos if it looks like mine is missing or not? Link to comment Share on other sites More sharing options...
alini Posted September 12, 2015 Share Posted September 12, 2015 You dont have the gasket that Ed is referring to yours is too thin. Do you know if your passenger side exhaust butterfly has been disabled? Link to comment Share on other sites More sharing options...
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