It wasn't running to lean, I had been running it hard for a month and all day long since 8 am till 3:30 when it broke. It didn't overheat either, the rod broke because of high compression. The dynojet needles require much smaller makuni mains cause of the sharp taper.

 

Bigbubba the Dynojets shouldn't need a smaller main for the sharper taper. I guess thats why Dynojets say you can't MIX kits?? Dynojet requires you to use there needles with there MAINS.

 

IF it was running lean enough to break a rod, wouldn't his piston be SEVERLY damaged by it? I have a hard time beleiving his jetting caused the rod to snap. Why from heat? Wouldn't the aluminum piston have melted before the steel rod broke?

 

Ward.. I was thinking the same thing as I was reading through the posts!

Bubba... Way Sorry for your loss!!! I hate to see anyone have to go through a rebuild.. especially this soon after getting it together!!!

Good luck on getting your quad back together!

 

Running lean is as much about spikes in the flame front as it is overall temperature. The pressure spikes are what stress the rod.

 

But still wouldn't you be able to see piston dammage, and have a spot to start on pin pointing the cause?

 

Maybe with a cast piston, a forged piston is pretty tough. The kind of stress I'm imagining is a process, not exactly an event. If it was running real lean, he have found broken rings if he tore it down just before it blew. Dodge tried a "lean burn" concept for a few years in the late 70's to save fuel. They even redesigned the intake to push the air/fuel charge into the cylinder differently to help with pressure spikes, it didn't. Lots of 360s with rod knock until that idea died out.

In my 12:1 686, I'm running 190/195. I'd like to see a picture of Bubba's spark plug.

 

I'm no expert, and what your saying makes sense, but for the amount of time bubbas quad has been together I still don't know about the lean thing causing it. I would still be more prone to think it was the compression (stock rod just cant take it)... Not sure though.

 

How long did it hold together after it was jetted by DTR?

I agree that the stock rod appears to be a weak link that can be broken by a number of additional stresses.

 

Seeing this thread sure makes me glad that I upgraded to a Carrillo rod. Sorry for your loss Bubba.