This isn't a Chevy question, but I frequent this site all the time because I think it to be one of the best of its kind.

Carb is a '63 Autolite 2100 2 barrel on a Ford 292 Y-Block. This carb model has no float bowl vent on the cover (some of the later ones do), but has the brass tubes sticking up above the air horn. The thing starts great cold, idles well, and drivability is perfect. Re-starts easily when warm. Get it good and hot though, let it sit for 15-30 minutes, I can smell fuel, and I have to crank 15+ seconds to get it to fire. I have been all though the carb with new needle & seat, float level is fine, power valve is tight. I see no fuel dribblibg out of the discharge tubes when I look down the carb throat when its hot. I have even taken the air horn off the carb when its hot and fuel level looks good.

If I leave the lid off off the air cleaner, the hot start problem goes away, making me think that fuel vapors comming up the vent tubes are accumulating in the air cleaner, causing the hard starts.

Do the tubes need to be in the air cleaner(near intake air) or can they be extended somehow above the air cleaner lid. I realize I would probably have to drill holes in the lid-and I realize this would be pretty weird-but provided that this could be done neatly, would it cause trouble?

I don't understand it- Many older carbs vent to the air cleaner and don't have this trouble. Could higher fuel volatility in winter gas cause this? By the way, the carb has a 1" metal spacer for the PCV hookup-very common to these carbs-

Can someone shed some light on this for me? I don't understand the whole carburetor vent theory beyond that the float bowl needs to be vented to the atmosphere so vacuum can draw the fuel-
Steve

[This message has been edited by Steve B (edited 12-05-2002).]

Maybe you could use some thicker gaskets to better insulate the carb from the heat. That mention of a PCV on a 1963 seems awfully early; was it a California retro fit maybe?

Could be that the fuel is percolating in the bowl, and causing your problem. Do you have any heat sources nearby.. heater hoses, rad. hose, etc. If I remember right the Autolite 2100 is a Holley clone with a Motorcraft number on it.

Try a simple trick, wad up some aluminum foil and wrap it around the feed line, and make a "heat shield" on the manifold under the bowl with some. See if it helps.

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'64 El Camino
383 - TH-350 - 12bolt - 4wh pwr discs
Bedded down for the Winter.

If your your motor is not running to hot and the carb is insulated from heat then sometimes when the cab is just at a normal heat soak temp after a hot shutdown the fuel under pressure can be pushed by the needle and seat. Assuming your running the stock fuel pump with correct psi for your application,the needle & seat plus float currently in the carb are not defective and set correctly then i would try installing a regulator in the line with a pressure gauge and set it for approx 4psi for your setup and see what happens.

Also,there have been cases where the old carbs have developed fine cracks and or have become pourous over 30-40yrs and can not leak at all or much when cold but will leak hot. This happens because the metal has expanded due to heating esp after the extra heat introduced to the carb during the 1st few mins when the motor is shut down which heatsoaks the carb more from the 220-240 deg the motor may reach durring this time in the summer. There are special epoxies out there i think are fuel proof that could be used to coat the inside of the carb bowl if need be if another correct carb is not available if this turned out to be your problem.

You mentioed the problem goe's away if the filter lid is removed which will let some heat/vapos out so make sure your motor is not running too hot (should be 180-200 deg range) before you go nuts trying to correct the problem. I think the fuel vapors could possible cause the motor to spin a little more to start but should not cause it to start real hard hot which yours is apparently doing so raw fuel must be dumping into the motor durring heat soak post hot shutdown.

If available try another stock carb,if it works fine then the motor is not running too hot and your fuel pressure is ok and it would show that particular carb is the complete problem and not motor temp or fuel psi being too high etc.

let us know what you find out.

Scott

[This message has been edited by SWHEATON (edited 12-07-2002).]

Sounds like good old vapor lock to me..... Get a wooden clothes pin and clip it to your metal fuel line. Why or how this works is beyone me, but I have proved it myself many times on really old carbs.
Good Luck

The engine is in a '56-F-100 and actually runs cool (180 degree thermostat). My mechanical guage never reads more than 190 degrees running down the road. The fuel pump is stock, although it seems to put out a lot of fuel-the other day I idled the engine with the fuel line discharging into one of those huge 2-quart pickle jars. It filled it within 40 seconds. I haven't checked the pressure, although I have checked the fuel level in the float bowl with the air horn removed, and the needle and seat seem to hold the pressure.

If I look down the throat of the carb after a 15 minute hot soak, the venturies and the throttle plates look dry. So if raw fuel is entering the manifold, it would be comming in from below the throttle plates. The only place I can think that fuel could be comming from then would be through the idle ports. The idle mixture by the way seems to adjust normally-both idle mixture screws want to be at 1 1/4 turns out, and I can get the engine to run lean or rich with the screws closed or open too far.

So this brings me back to bowl vents. If pressure was building up in the bowl, could it be pushing fuel through the idle circuit?And how much vent is really neccessary with the engine off-it would seem to me very little, although the later model Autolites seem to have bigger holes for the vents. Unfortunately the air horns have different screw patterns.

I'll certainly try the tricks to combat fuel percolation mentioned above. I may also try drilling two holes in a wrecking yard air cleaner lid to accomodate two vacuum lines extending off the vent tubes and through the holes in the lid just for grins.

Those old fords were notorious for vapor lock and fuel filter problems. The filter is easy to fix, pull the internal and replace with an metal inline. Non metal spaced will help with the vapor lock as well as insulating the fuel line. Also, be on the look out for hard starting or sporadic running when hot because of the coil overheating. When I wrenched in AZ we saw a lot of Fords in the summer with those problems.

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OrrieG
64 Malibu HT Survivor (http://www.chevelles.com/showroom/OrrieG1.jpg)