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Poor starting when hot

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bob hughes

Luke Skywalker
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My BJ7 is displaying a problem on starting, when hot anyway.

Starts up from cold - no trouble at all. Once the engine is hot, you have to keep the finger on the button until it catches.

I have changed the coil and working on the mixture as it is a tad rich.

Any other ideas please?

Bob
 
Heat soak; sounds like the heat is expanding the fuel in the float bowls when you shut off the car. It overflows into the cylinders and floods them.

My Webers do the same thing. Once hot, I have to hold the throttle to the floor to introduce as much air as possible (unfortunately, with an accelerator pump, also means another squirt of fuel). Next time, try holding your throttle wide open until it fires.

If you're still stock, perhaps the tiny tubes that drain from the ends of the manifold are plugged; clearing them may give you some relief...?

Edit: Just for kicks, next time you drive the car and get home, open the hood so as to let some heat escape that way. Then try starting it after a "normal" interval and see if it made a difference.

True too, the heat could be affecting the coil. Try the Bosch blue one, it's the one I've had fitted the longest.
 
I had a similar problem and also changed the coil first. Turned out my points were worn and getting rid of them by going to electronic ignition made an immediate improvement. Check your points.
 
Just to bring you up to date.

The plugs were black with carbon deposits

Have leaned the mixture, hot starting is now much better, just a bit of over-run when switching off, so will slightly richen the mixture a tad.

Points don't look to bad, not sure about timing, have not checked it since 2002 when the car was purchased. Will check up on that shortly.



Bob
 
Mine runs a little rich also. The suggestion above is how I start it once it is warm. Push the pedal down at least half way to get more air in there.

Jerry
 
If you refer to "over run" meaning "dieseling" or running on.... richening the mixture id diametrically opposed to what you should do. Run on is caused by too much fuel being introduced into the cylinders with a hot engine during shut-off, the hot internal components actually ignite the fuel inside the cylinder from latent heat.
 
Richening the mixture will help prevent dieseling by keeping the combustion chamber temps down. As long as there is something hot enough in the chamber (carbon, sharp metal edge), it will continue to ignite the new fuel/air mixture pulled in from the carbs. If we had fuel shut-off valves, this would not be a problem... IMMHO...

Mark
 
You are correct in that reducing combustion chamber temperature will reduce dieseling tendency... so what other ways can one reduce temp without adding more fuel, which exacerbates the problem? Well, reducing initial timing is one... even by a couple of degrees makes a differemce... also, running a cooler thermostat helps, and, running premium fuel helps. When I first became a professional mechanic in the mid seventies, dieseling was a common problem. These were a few ways we cured run-on problems... Today, with fuel injection and electronic engine control systems, run on is a thing of the past.... but fuel-related carbon issues are a huge problem. I add a few ounces of Sea-Foam to gas tanks when they are full(Especially LBC's), and my customers report better performance and fuel mileage. I get it at Car Quest. It stopped my own personal 1969 TR6 from running on. Try it.
 
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