Hot start, Ethanol and the AFB...

This is nothing new to us, but in the process of putting my 65 back together I came across a very interesting scenario. When I first purchased the car, here are the things that needed correcting..

- Heat riser valve seized about 80% closed

- AFB needed rebuild. Metal plate under the carb was burned clear through from the exhaust coming up. I was lucky that it did not start eating the bottom of the carb yet.

- All the hot air tubes were clogged and thus the choke was not working at all.

With all this, the car actually ran ok and started perfectly hot or cold. Turn the key and it would fire instantly even after sitting for a while after running.

I corrected all of the above and used a new base plate under the AFB. I did not fill in the passages and left it as designed. All the hot air tubes are back in order and the choke works as it should. Only other change was going from champion plugs to ACR45s. Currently the car runs very well and fires instantly when cold, and also fires instantly if it sits a few hours after shut down. If however you shut it down at a gas station and let it sit for 15 mins, it will crank for 2-3 seconds and then fire. Obviously the fuel is getting hot. The obvious question is why now, and not before? Can the hot air tubes really introduce so much heat to the carb after the car was turned off? Im not quite sure. Spark plugs? Fuel pump & filter are new. This is an AC car so it has the fuel return on the filter. Timing and everything ignition related is unchanged.

Try here:

http://www.thecarburetorshop.com/Troubleshooting.htm#Hardstarthot

Jon.

Yes I understand why it happens. Question is why now, and not before? Same fuel, same heat.

It MAY not be the same fuel.

(1) Modern fuel goes bad in "x" weeks (you can fill in the blank), so even if it was the fuel in your tank it won't be the same after a few weeks.

(2) Even if the same station, they may have a new supplier

(3) Don't know about the plugs, not my field.

Jon.

If however you shut it down at a gas station and let it sit for 15 mins, it will crank for 2-3 seconds and then fire. Obviously the fuel is getting hot. The obvious question is why now, and not before? Can the hot air tubes really introduce so much heat to the carb after the car was turned off? Im not quite sure. Spark plugs? Fuel pump & filter are new. This is an AC car so it has the fuel return on the filter. Timing and everything ignition related is unchanged.

YES, the newly cleaned out hot air passages built into the intake manifold, where the carb mounts, really can introduce so much heat to the carb that the fuel will boil when the engine is turned off. The ethanol in the fuel boils very easily.

Is the heat riser valve opening fully?

If you have ANY imbalance between the two sides of the exhaust system, exhaust gases will go through the intake manifold and really heat it up.

Spark plugs are OK. Fuel pump and filter are not the problem.

The boiling fuel actually floods the engine. Read the owners manual about hot starting.

When my engine does not start in this sort of scenario, I crack the throttle and crank the starter. That will clear the excess fuel. Stop cranking and do not move the gas pedal at all. Then crank again and it will start. Keep it on a fast idle, once it starts, for about 30 seconds.

Thanks Jim!! I locked the heat riser valve in the the 100% open position. Im in FL so dont really have the need for it. This way Im certain nothing is getting pushed back up into the intake.

My situation is really minor. The motor will fire every time after cranking for 2-3 seconds and run fine so the boiling is not so severe that it floods the intake to the point where it is very hard to start. The reason I posted this was to see if those heat tubes really carried enough heat to create this condition. You answered that one for me, so once again...thank you!

As a test I am going to disconnect the fresh air tube at the top of the carb to see if there is any change.

This is nothing new to us, but in the process of putting my 65 back together I came across a very interesting scenario. When I first purchased the car, here are the things that needed correcting..

- Heat riser valve seized about 80% closed

- AFB needed rebuild. Metal plate under the carb was burned clear through from the exhaust coming up. I was lucky that it did not start eating the bottom of the carb yet.

- All the hot air tubes were clogged and thus the choke was not working at all.

With all this, the car actually ran ok and started perfectly hot or cold. Turn the key and it would fire instantly even after sitting for a while after running.

I corrected all of the above and used a new base plate under the AFB. I did not fill in the passages and left it as designed. All the hot air tubes are back in order and the choke works as it should. Only other change was going from champion plugs to ACR45s. Currently the car runs very well and fires instantly when cold, and also fires instantly if it sits a few hours after shut down. If however you shut it down at a gas station and let it sit for 15 mins, it will crank for 2-3 seconds and then fire. Obviously the fuel is getting hot. The obvious question is why now, and not before? Can the hot air tubes really introduce so much heat to the carb after the car was turned off? Im not quite sure. Spark plugs? Fuel pump & filter are new. This is an AC car so it has the fuel return on the filter. Timing and everything ignition related is unchanged.

One thing I don't see mentioned and I know that Jim and others have done this is to install an electric fuel pump close to the tank and use it in line with the stock mechanical fuel pump. Let it pump some gas from the tank into the bowl before cranking. This will replace any atomized fuel with fresh liquid and fill the bowl on the carb.

Ed

One thing I don't see mentioned and I know that Jim and others have done this is to install an electric fuel pump close to the tank and use it in line with the stock mechanical fuel pump. Let it pump some gas from the tank into the bowl before cranking. This will replace any atomized fuel with fresh liquid and fill the bowl on the carb.

Ed

I had that setup on my boat and it does work well. At the time I had an edelbrock carb (same as AFB) on there and no matter what I did, the thing would not want to restart after sitting. Spacers a nd heat shields were of no use. An auxilary electric pump worked well. Because we are talking boat this concept introduces a bit of a fire hazard even when wired through the oil pressure sender, I put a holley on there and no more issues.

Interesting story about the edlebrock carb which was purchased brand new... It would always drive me nutso because one day it would idle at 600 and the next day 900 with all else being equal. No vac leaks anywhere and I knew this for a fact because that holley I mentioned earlier would idle rock steady. Anyway...after pulling my hair for a while I come to find that the seconday throttle shaft had so much play in it that I could push it with my finger and hear it suck air. And of course see the idle jump. Brand new carb mind you!! Called edelbrock and explain the situation. They claim the vac leak is metered and as designed. I kept pushing them as this claimed metered leak is BS. They told me to send the carb to them for a rebuild. I asked to speak to the rebuilder and explained the situation. Needless to say the carb came back rebuilt with exactly the same issue!!

A lot of older cars have idle problems where a steel throttle shaft runs through an aluminum housing. After a while the steel will wear and elongated hole in the housing which allows air to leak in. The aftermarket folks have come up with a bushing kit to solve this problem. Best let a professional drill out the base and replace the bushing. All you need to do is get the hole off center. Then the carb is toast.

This was a brand new carb Ed.

OUCH! Sometimes old rebuilt is better than new. If you have the old carb, it's probably worth rebuilding. Jon Hardgrove, Carbking (Post #2 this thread,) probably has everything you need to make the original carb like new again. The correct carb for a '65 401 is AFB 4453 (4453S).

The Carter AFB carbs (aluminum four-barrel) have a large bearing surface for the throttle shafts as compared to many other carburetors.

Think about it. The body of the carburetor is aluminum. Aluminum has a much greater expansion rate from heat than cast iron or steel. If the tolerances from the throttle shaft to the throttle body are too tight, then the throttle shaft will NOT rotate when the engine is at normal operating temperature.

Moving the throttle shaft with one's finger would be possible, and would probably change the idle.

I do not know about the e-clone (totally different in many respects from Carter AFB's), but the total design COLD tolerance from throttle shaft to body was 0.016~0.022 inch on the genuine Carter AFB's (so the shaft to body on each side would be 0.008~0.011 inch. Putting this number in perspective, the equivilent numbers on a Rochester 2-G (cast iron throttle body) was/is 0.004~0.006.

When we first starting bushing throttle bodies, I did a set of tripower Rochester 2-G carbs for my own GTO and set the clearance at 0.004. To my embarrassment, THE THROTTLE STUCK WHEN THE ENGINE GOT TO NORMAL TEMPERATURE!

Thereafter, we bushed carbs with 0.004~0.006 spec to 0.0055 without any issues.

As stated earlier, I do not have the specs on the e-clone. Not any desire to learn them.

Jon.

Don't have this issue with the original AFB on my 65, and the throttle shaft does not move enough to change the idle. When I say I moved it with my finger, I mean there was a significant amount of play in the secondary shaft. This I believe is a major flaw with the Ebrock.