| Pair of 40's | -- 04-05-2015 @ 9:24 AM |
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My 6 volt flat head starts great cold and after a short run. Following a long run in warm Fl temps it cranks very slow and usually will not restart. After a cool down period an hour or so it restarts fine. I changed the starter but this did not cure the problem. Battery is fully charged. Engine was rebuilt 2010 with low mileage on it. Grounds have been checked and good cables used. Wondering now if fuel is getting hot to carb? Thanks for any tips. Russ
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| Old Henry | -- 04-05-2015 @ 12:04 PM |
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Sounds like classic vapor lock symptoms to me. There's an easy test to see if that's it. Take a gallon of water with you next time. Then, if the engine does not start as quickly hot as it does cold, pour a quart or two of water on the fuel pump and try it again. If it starts up you know it's vapor lock. Best solution (other than carrying a lot of water with you) is a backup electric fuel pump installed back by the gas tank.
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| trjford8 | -- 04-05-2015 @ 12:40 PM |
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Cranking slowly is not a vapor lock issue. It's usually a sign of poor grounds or using the smaller battery cables and not the larger 6 volt ones. Pull the starter and make sure there is good clean metal between the starter and the pan to make a good ground. Make sure you have a good ground from the body to the frame and run an extra ground from the starter to the frame. I would be surprised if this doesn't solve the problem. On a '40 the ground from the stud on the firewall to the frame is critical.
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| Pair of 40's | -- 04-05-2015 @ 4:44 PM |
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Have proper cables for ground up top and from starter to frame. Vapor lock appears to be the problem. On the street rods we add a spacer under to the Carb to cure this problem. I have now just found a source for non ethenal fuel, as ethenal's boiling point is lower than straight fuel.I'll see if this helps.
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| Super41 | -- 04-05-2015 @ 5:14 PM |
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My '41 (original flathead, 6v system, etc.) had the same problem a few years ago. It would fire right up every time, but then after a run it would refuse to start after being shut off. When the engine temp had enough time to return to cool/cold, it would start without any problems. If you've tried what these other members suggested, and are still having the problem, you may want to consider the coil. After I had mine rebuilt by Skip Haney, I never had that problem again.
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| cliftford | -- 04-05-2015 @ 8:35 PM |
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You stated that this is a rebuilt engine. Possibly the ring end gaps are a little too small or the piston to cylinder clearance is too small.
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| TomO | -- 04-06-2015 @ 7:00 AM |
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Vapor lock is when the fuel in the fuel pump boils and no fuel is delivered to the carburetor. Check this by looking down the throat of the carburetor while operating the accelerator linkage. Two streams of fuel will be seen if the carburetor has fuel and is operating correctly. Hard starting when hot can be caused by weak spark and/or fuel delivery problems. The most common cause is weak spark when the coil is hot. Next on the list is flooding caused by fuel leaking out of the carburetor bowl. Another cause could be timing caused by a worn rotor or worn distributor. Your fuel pump could also have a vacuum leak on the supply caused by poor connections or a bad sediment bowl gasket. Slow cranking can be caused by several things. he first step that I would take is to do a voltage drop test in the starting circuit. Connect your volt meter from the NEG battery post (COM lead) to the starter terminal(+ or POS lead) and crank the engine with the ignition off. The volt meter should read 0.3 volts or less. Any higher reading will indicate excessive resistance in the circuit. Move the + lead back toward the battery one connection at a time until the problem is isolated. To check the ground circuit, connect your volt meter between the POS terminal of the battery and the case of the starter. The reading should be 0.1 or less. If those readings are OK, connect the volt meter from the starter terminal and the starter case and read the voltage while cranking the engine for 15 seconds. The reading should between 4.5 and 5.5 volts. If it is less check the battery capacity. Tom
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| fordv8j | -- 04-06-2015 @ 5:57 PM |
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My 38 didn't want to start when I shut it off when it had ben run for a while..I changed carb. fuel pump,and dist, didn't help..called Dick Flynn,he asked what coil I was running,I run a 48 dist with 50 style coil,he said the original coil use low voltage,the round ones 6 volts,he said to put wires on the same side of the resister..did that will start now,no matter how hot it is
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| Pair of 40's | -- 04-08-2015 @ 5:50 AM |
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Thanks for the advice.
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| Bertha | -- 04-09-2015 @ 4:39 AM |
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TomO mentioned Bertha's problem.... After checking all the above mentioned concerns I bumped the timing forward 5* and re-set the dwell . Okay since. Bob "it's only original once" --- This message was edited by Bertha on 4-9-15 @ 4:43 AM
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| 51f1 | -- 04-12-2015 @ 1:37 PM |
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An outside chance is a bad coil. Usually if that were the problem, it would shut-off after heating without manually shutting it down and start again after cooling. Richard
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| supereal | -- 04-19-2015 @ 2:49 PM |
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I finally found my "quick start" page. This easy to make and costs little. It give the coil a shot to compensate for the system voltage drop caused by the draw of the starter.
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