426 spitting fire

[zup88]

My 426ex has got me completely lost. When its cold, it will fire right up and idle with no problem. Once it starts to warm up, the idle will start to drop and eventually shut the motor off. If you give it gas trying to keep it running it will pop, backfire and spit flames sometimes. I am completely lost on this. It ran fire until recently and only acts up after running for about 3-4 minutes. It has an e-series slip on, stage 2 cam, k&n filter w/ no lid, and a 426 bore. The jetting is 155/42. Any help is greatly appreciated!!

[jasonwayne222]

first thing i would check when spittin fire is exhaust leaks, it always does this when u got a leak, check the header flange, u might need new crush washers. check ur plug to see if your running rich or lean, if your having idling problems then i would probly go ahead and pull the carb apart pull all the jets out and dipp it in carb dip for a day or two, it will clean the crap out of it and eliminate another problem.

[F-16Guy]

That jetting sounds way too lean for a 426 unless you're at 5000 feet or better. You may have gotten it hot and caused some internal damage. Do a compression test and see where you're at.

[zup88]

Im in NC so im about 500ft above sea level. My younger brother used the quad while i was gone with the military. He said it was running rough so he let it sit and idle for an hour to clear it out!! Not sure if that messed something in the motor up thus when it gets hot it wont run... Ill get a compression checker and do that hopefully this weekend. The carb has been cleaned numerous times with air and carb cleaner.

[F-16Guy]

Yeah, letting an air cooled engine idle for a long time probably isn't a good idea, especially after it's gotten hot. The symptoms sound like a lean condition to me. I would bump your main up to a 165 or 168, make sure your needle clip is in the 3rd groove from the top, and the fuel screw is about 2.5 turns out and see how it runs. You may also want to check your valve clearances and adjust if necessary. Valves that are too tight can be worse than loose valves, so make sure you check and adjust when the engine is completely cold and use a feeler guage. At this point, your priority should be getting the jetting close before you try to start it again. Once you get the jetting close and make sure your valve clearance is correct, you can fire it up and start troubleshooting any problems that might still exist.

[MidnightBlade]

not to be contraversial but i prefer to keep my jets at about 158-162 so try them and see if the idle does anything. also do you know how to check if it is running lean?
find a place to run it hard in 3rd or 4th gear the hit the kill switch and pull the clutch in at the same time then pull the saprk plug and see if it is black,white,or brown
if it is white your running too lean
black your running too rich
brown-tan your just right