canadian oddy wrote:
I would like to comment on jetting here.
This might be long winded but please bear with me.
In my opinion jetting has to be WAY out to cause major
Engine damage. The reason I say this is because of some of my experiences with oddy's. One of my oddy's (the one I ride) is stock except for a bigger carb. The other oddy (my brothers) is highly modified, pipe, carb, port work, cylinder milled. It has 180 psi compression and mine had 150 psi. On rare occasions we swap machines for one run up the mountain. We go from just above sea level to just over 5000' on one run up the hill. We do not re-jet and they run fine top to bottom. I noticed one day that my machine had lots of power. My brother couldn't pull me on the straights. He then rode mine and commented on the power. This went on almost all summer (half a dozen rides at least). Then one day near the top of the hill my Engine made a back fire and died. To shorten this long story I will tell you that my intake had a two inch break (slash) in it. I couldn't see it because it was on the bottom side. When I stripped the Engine I found that my rod bearing let go. It blew because of the lack of oiling because of the severe lean condition. This severe condition did not melt my piston. In fact that piston would have been useable if all of the metal from the bearing coming apart didn't embed itself in the piston and smash up the ring grooves. I was running AVGAS and it ran great to the end even with that severe lean condition. My machines have homemade liquid cooled heads and cylinders also. Basically what I am getting at is even if you are out a couple of jet sizes I have to call bullshyte when ever I hear "your jetting is out". No FN way will you blow an Engine if you are out a jet size or two. No way. My experience above is why I believe that. Others will argue the point but I know what I know through experience. We all have our own pet theories and beliefs. That's why we are all different. Some like red heads others blondes, it don't matter, they both cost alimoney.
As you said, everyone has their own ideas, and there's more than 1 way to skin a cat.
In your story here, there are things to consider.
http://www.jetsrus.com/FAQs/FAQ_rejet_e ... rature.htmYou're going up 5000'. According to this chart posted in that link, you're actually running fat or rich as you go up. I assume the temperature is dropping as you go higher as well. So that's going to need more fuel. So, in theory, you are only slightly fatter/richer than when you started at the base of the mountain. No worries with your poofkaboom there.
What do you think the chances are of you having a small pin hole leak in your intake manifold that was torn open from the Engine backfire?
Seems possible to me.
How familiar are you guys with watercraft carbs? There are no float bowls. There are no jet needles. You have a float chamber and diaphragm. Pop off pressure relates to when the needle lifts off the seat and allows fuel to flow through the carb.
It's not uncommon to have a burn down (piston melt) at only partial throttle. The reason being you have the most timing advance around 3/4 throttle. (generally the
CDI (Capacitor Discharge Ignition) (Capacitor Discharge Ignition) starts to retard timing as the RPM continues up to red line)
So, you may have sufficient fuel at idle and
WOT (Wide Open Throttle) (Wide Open Throttle), but if you're lean in between there, it's possible to have a melt down.
Since you never answered what carbs you're using, I'm going to assume you have the Mikuni Super BN's. Here's a manual that you might find useful.
http://www.mikuni.com/pdf/sbn_manual.pdfGood luck with your buggy
about a rotax or the carbs it uses.
Any comments I make are based on an oddy.
Not shooting down anyone's ideas as we are all guessing based on our experiences.
It's possible that I am wrong but then you have to prove it to me.
I reject all realities and substitute my own.