1993 520h back firing

[grasscuts 0]

Hi, here's what happened. I changed out 9 pin moles plug...had issues tracter quit running and changed the plugs while I was at it....got plugs from auto store cross reference to ngk they said it was the same heat range and I check electrod  length with calipers ,same...tracter started right up and ran great for about 10 min. And started back firing and quit.....going to check it out tonite anybody have an idea?    

[stevasaurus 23,036]

Pull the plugs back out...what do they look like??  

[lynnmor 7,539]

You should have NGK # TR4/3754 spark plugs.

[grasscuts 0]

great news, opened up the hood spark plug wire off......iI was thinking doom and gloom.....put the boot on and fired right up!  daaaaa but happy.  I have ngk tr5ix7397 plugs in now.. per the auto store. thats diff. from what your suggesting Lynnmor so I need to now whats correct.........champion   rs14yc  is whats in the owners manual please chime in tks guys 

[Chestnut 315]

13 hours ago, lynnmor said:

You should have NGK # TR4/3754 spark plugs.

I installed the TR4/3754 plugs early this spring to replace a pair of the Champions. I was having hard starting problems and it starts much better with the NGK's, even though there were only a few hours on the plugs I took out. According to NGK's conversion chart the TR4 and Champion RS14 are the same heat range. TR5 is the next range colder. I don't have enough experience or knowledge to say how the Onan would respond to a colder plug. Most engines will tolerate one heat range up or down without issue. A hotter plug will burn off carbon better, and a colder plug will dissipate heat better. Something to be said for each with the Onan. They do build carbon, but the rear cylinder can also run hot. If it were mine and I'd already spent the $16 or so for a couple of Iridium plugs, I'd run them for mowing but make sure I ran full throttle. For snowblowing or other winter work I might switch back to the hotter plug.

The ix designates a modern fine-wire Iridium tip plug. The TR4/3754 and the Champion are old fashioned copper core plugs. 

https://www.ngk.com/ngk-7397-tr5ix-iridium-ix-spark-plug

https://www.ngk.com/heat-range-conversion-chart-2