Reply To: Petronix

[Gregory Long]

Thanks Tony, yes LOKI is far from ‘snobby’, he happily accepts any and all attention from us humans. AND he just loves to ride in old cars. Especially open cars.

Tim: If you don’t have one installed yet, make a battery cable from heavy copper wire, like welding cable. Solder ‘loop’ ends on the cable, and put one end under a cleaned bolt that holds the starter to the engine, the other end on the correct terminal of the battery, I’ll assume the Seagrave fire engine is positive ground, so put the end of the new cable on the bolt of the positive battery cable clamp.

This new, low resistance ground cable will greatly improve current flow to the starter. On most cars I’ve worked on, the direct path for current through the cable instead of via the frame, a riveted on crossmember, then an oily or rusty engine mount then to a oily, dirty starter to engine connection, etc results in a noticeably faster engine cranking speed, and a measurably higher cranking voltage.

This would be the first place to go, before you spend money on a starter rebuild that quite possibly is not needed. I’ll stick my neck out and say is not needed, since the engine starts cold.

A jumper wire for testing and diagnosing this problem from the switched side or not grounded side of the battery directly to the ignition side of the coil on the engine should result in a hot start voltage at the coil being the same as during a cold start.

That’s the electrical and ignition side of the typical hot start problem.

Now, for the fuel side of the hot starting problem: Unless you have access to and are using Ethanol Free gasoline, you might be experiencing dry carburetors when you are attempting a hot start of the engine. Ethanol-tainted gasoline boils at around 150-160*, pure gasoline boils nearer to 200*. The under hood temperatures, and more importantly, the temperature of the carburetor body, bolted to very hot intake manifolds that are bolted to the exhaust manifolds may be MUCH higher than just the coolant temperature of your engine, which is probably running at around 160*.

When you park the pumper after its been running at temperature, the fuel in the carburetor bowl will experience temperatures near 300*, from the exhaust manifolds and parts of the engine that are not well cooled by the cooling system. So the fuel in the carburetor will boil away, leaving a dry carb, and often dry fuel supply lines as well, the fuel in the lines gets hot, boils and since the floats in the carb have dropped due to the boiled-away fuel, the remaining fuel in the lines also vents out to the atmosphere.

The above description is why many, if not most of the fuel pump supplied [not vacuum tank systems] have an electrical fuel pump to make sure the carb has fuel in it when the car is started hot. The method I use is to run the electrical pump to prime the system, I run the electric pump until it slows down due to building up fuel pressure, this occurs only after the float bowl is full, the float closes the needle and seat in the carb, then the fuel in the fuel lines is under pressure from the electrical fuel pump. Then I start the car. Without using the electrical fuel pump, the engine must crank a LOT to fill the empty fuel lines and carburetor bowl before the engine will fire.

I don’t know from your description when the hot starting problems occur for you, but it might very well be a fuel issue, not a problem with your spark ignition system.

Hope this helps.

Greg Long