I have a 85 model 12a that will start up and run for hours great with no back firing, no smoke, just wonderful. This car runs strong even when the engine heats up. However, when I turn the engine off and attempt to restart the engine turns over (sounds sluggish) and will not fire. I pulled the plugs with the engine still hot and found that neither trailing plugs had any fire. I swapped the ignitors and still no fire. After the engine cools off it start up again with no problem. Any recommendations would be appreciated.

 

change the trailing coil if this occurs only when the coil is hot.

 

Yes, I replaced both coils.

 

Sounds like it simply isint cranking fast enough when hot. Hot compression is lower than cold so you need good cranking speed to get it started hot. Check and clean your main cable connections off the battery, starter and chassis grounds. The stock positive main cable is a big culprit in this kind of problem. Mazdas use of aluminum cable was fine when the car was new, but with age the resistance has gone up from years of corrosion, leading to slow cranking.

You also might want to do a compression test.

 

What I recommend that you do is get the engine up to full operating temp like normal. Do not shut the engine off, get a timing light and check for leading and trailing fire. If you have both, then shut it off, if it won't restart. I would lean towards the following areas. 1). If the engine cranks very slowly. Then proceed with rx7carls suggestions about cables/grounds. If they are tight and free of corrosion at the mounting points. Including grounds then you may have a bad starter not allowing the engine to crank fast enough. You can also check the plugs to see if they are wet. 2). If the engine is cranking normally then I would lean towards compression. 3). I would also verify that you have fuel getting to the carb when this happens. If there is a saturation problem with heat and the trailing side of the ignition is having a problem with either the coil or the ignitor then the fuel pump may not be getting it's signal to turn on. This could also be the fuel pump relay.

 

It could be an restrictive exhaust caused by a clogged cat. That happened on one of my engines. It had trouble starting when hot. Then I swapped the engine into a different vehicle and it would fire up quickly every time. The only differences were the starter motor, battery cables and exhaust system.

 

Excellent recommendations!!!! I removed the internal components from the cat, but the end result did not change and I even considered modifying the muffler as a last result. At this point I will replace both cables from the battery and replace the starter. The engine does sound as if it is turning over sluggish when it is hot in comparison to a cold start. No problem with the plugs flooding and the carburetor is functioning correctly. For the amount of time that I have invested, cost to purchase these parts is small. Thanks for your help.

 

Well, RX7Carl got it right. I replaced both battery cables and BOOM it starts up perfect hot. It has setup over a year because of bad battery cables. What a waste. Thanks!!!!!!!!!!