1960 - Hard start when hot

[Stuart F.]

Re: 1960 - Hard start when hot

Nice to see this thread continue as it is a subject that will be with us for some time. I have curred my percolation problems (knock on wood) down here in Florida using a number of tricks described herein or in previous threads I have participated in. I still use my standard manifold gaskets with cross over and my operating heat riser valve. Of all the other measures I have taken, none is more significant than locating a station that sells me 90 octane non-ethanol gas. Having an original L-76 engine the inside of which has not seen the light of day since it was built, and still running the advertised 11.25 to 1 compression, I have to tip in more Max Lead 2000 to keep the pings away. But other than that, I have now got a situation I (and the wife) can live with regarding gas smell in my attached garage, and the performance is like the days of old in POT and WOT with either one of my 2 favorite AFB carbs (one at a time). On this point, I admit I'm still trying to sort out the jetting on my 3461S as it seems I can't get it rich enough to run smooth on this gas combination.

Just a couple of points on the use of the spacer under the carb; remember that if you have a steel fuel line directly to the carb you may not be able to use it without bending it to achieve the extra carb height, specially if the line runs to it from a close location such as a fuel filter mounted on the manifold like my 63. On mine, I had to go to a fuel hose to make the connection. Like Tim has said, if you have a manifold with heat passages under the carb, you must either block them or make sure to use a SS plate under the carb. On mine, with the aluminum manifold, I had to use a "sandwich" of 2 gaskets with the phenolic plate to block (seal) off the heat passage in the plate itself as my maniflod does not have matching heat holes in it. One other item to consider, if you want to isolate the carb further from any conducted heat, go to an electric choke as I have done. You eliminate the steel heat tube and all the potential problems associated with it (including tube burn through in the exhaust manifold). All toll I have my carb elevated close to 1/2" and I have plenty of hood clearance.

Stu Fox

[Duke W.]

Re: 1960 - Hard start when hot

Blocking both sides of the heat riser can cause severe driveability problems for the first 10-20 minutes of around town operation even in warm to hot weather due to insuffiicient fuel vaporization.

A first step to cure percolation is wiring the heat riser valve open. And any "hot slot" in the manifold should be plugged.

If this is insufficient, recommend you block ONE side of the heat riser, not both. This creates a dead end passage that allows some heat to reach the base of the carburetor, but since there is no exhaust gas flow, the amount of heat is significantly reduced.

If the choke coil is mounted on the inlet manifold above the heat riser passage, block the opposite side. This will allow enough heat to reach the choke coil for near normal operation, and, if necessary, it can be adjusted to less closing torque when cold.

If your engine is hard to start hot due to percolation flooding, get in the habit of opening the throttle full when you crank. This should help clear an overly rich mixture from the engine. Also, if the float level allows too high a fuel level in the bowl, the bowls can seep fuel into the carburetor at closed throttle. You can test for this by removing the air cleaner and observing the main venturi discharge nozzles at idle. You should not see any liquid fuel dribbling out. Sometimes a small blob of fuel will form at the nozzle every few seconds, which then drops into venturi. This is an indication that float bowl fuel level is higher than the main discharge nozzle, which is not correct.

Also observe for main discharge nozzle flow immediately after shutdown. There should be none. If there is, the needle/seat may be leaking.

Everyone blames ethanol as the big bogeyman. There may be some truth to this as ethanol boils at about 170F, but I believe that mechanical problems may also be a factor since some with the same engine configuration report vapor lock, but others may not in similar temperature driving conditions.

Verify that the carburetor(s) (and ignition system) is not the source of the problem before you start messing with the heat riser.

Duke

[Stuart F.]

Re: 1960 - Hard start when hot

I have found that the better hot starting procedure for my 63, on which I've cured most of the heat soak problems, is based on the assumption that there is some "puddling" of fuel built up in the intake manifold due to any number of "near normal" operating conditions with a carburetor. On Hot Start", turn engine over about 3 to 4 seconds without opening the throttle, then open it slightly until the engine fires, and give it your usual blip to impress the commandos. Allowing the engine to turn over this initial period without throttle gives it a chance to discharge the too rich fuel mixture out of the exhaust, preventing flooding, and allowing a proper air/fuel mixture into the cylinders. I wasn't a believer when first advised of this as it went against everything my Daddy taught me, but it works every time for me - regardless which carb I have on the car.

Stu Fox