I have a 1999 harley sportster 1200, it runs fine fo about 15 mins , then it starts backfiring and dies. It has to sit for about 15 mins, then starts right back up. It also has a funny rumble in the motor just before it starts backfiring.
I’d be willing to bet the problem you are having is NOT heat.
The symptoms you are describing sound more like a failing charging system.
What I believe is happening is that, after the bike sits a while the battery recovers, the bike starts, you ride ( Running off the battery) until the charge gets weak( and so the spark gets weak) then finally too little juice to produce a spark and the bike dies.
The bike sits, the battery recovers , and the cycle is repeated.
If you are able, check the alternator and the voltage regulator, or have someone check it for you.
I’d bet that is where you will find you trouble.
It’s your ignition module (Black box) It gets hot and fails. Once it cools enough it runs good until it heats up again. Time for a good after market ignition.
To check this, when the bike quits on you take a spark plug out before it cools down, careful, that’s going to be one hot plug, insert it back into the plug wire and ground the plug to the side of the engine then turn the motor over and look for a fat blue spark. You might want to do this in a shaded or kind of darken garage. If there is no spark then you know it’s the ignition. If there is a fat blue spark then it just might be the valve guide like “The Man” said. Good Luck
I’d do an ohm’s resistance test on the coil before replacing.
set your ohm meter on Rx1 and read 2.0 – 3.5 ohms on the primary side
secondary resistance will be 10,000 – 12,500 ohms between the two high
voltage terminals (assuming dual fire coil)
Make sure you are getting primary voltage. Lay a connected spark plug
against a cylinder as you crank and observe if spark is blue and “fat”
If this theory checks out then your problem is obviously in your rev limiter (Module). Both will act up when hot.
Also scope out www.sportster.org for more sportster information.
Try this get a heat gun and aim it at the point’s cover. when the ignition module gets hot and the bike shuts off then you found the culprit. if not then aim the heat gun at the coil, if the bike dies then you found it. if not then aim it at the Ignition control module if the bike dies again you found it..
I did this sequence due to what fails more often to what fails least often.
Side note, when was the last time you changed your plugs?
oh, and checking the coil with an ohm meter is next to useless because brand new coils strait out of the box will fail spec but will run fine for years so that’s why I said to check it with a heat gun.
I know chevy had some issues with their pumps. The props in the housing would seize up once they started getting hot and then it wouldnt start until it cooled a little. So it might be a fuel pump. It sounds fuel related. Did u ever change the fuel filter on that thing when u did the plugs. Anyways i would look at fuel related issue and pump might be very likely.
My guess is a dead short at some point feeding your ignition. It’s robbing your ignition system of juice. Sending it to ground until causing the miss-firing and heating your main bi-metal circuit breaker to trip. When the bi-metal circuit breaker cools it makes contact again and the bike will fire again. When the bi-metal breaker trips you have nothing, no lights, no starter, no ignition.
Done anything to the bike? Taken the tank or seat off? Check there to see if a wire was pinched. Check at your coil wires or any other ignition sources to look for bare or touching, loose connections.
you might have a bad valve guide. this is one of the first tapes you will see if you become harley certified.
your valve steam to guide tolerance is wrong and it hangs up once its at full operating temp. thats the noise you hear and the open valve to back fire. when you let it set to cool it unhangs and the process starts again.
rebuild the heads.
also make sure the top end is getting oil.
sounds like the coil is bad a coil has oil in it if the plastic gets a crack in it it will heat up fast and cut out then will be fine when thy cool off