Banshee was running great until I get it to the dunes, then it won't pull itself

[racin69z]

I have a 2003 banshee that I just went through. New 64.25 pro x pistons fresh bore, midrange porting, fmf Fatty's, 19cc? (I think} cool head 130 psi compression, stock carbs pod filters with what I thought was optimized jetting for the combo. I think I am.at 330 main 35 pilot but I'd have to check. 

 

The thing was running great other than a hard first start of the day. Drive 600 miles to silver lake sand dunes ORV, and I won't even pull itself up the sand road to the dunes. Elevation is only 300 ft more than home, so I don't think that's enough for a major jet change. 

 

The right side plug is clean, left side plug gets wet. By feeling the exhaust output when I rev it, I can definitely tell the left side is not running as good as the right side. And the left side pipe doesn't get as hot. But it sounds like it's running on two cylinders and idles fine, just makes no power. 

 

Both cylinders have the same compression, right has 2% leak down, left has 3%. I don't think that's too far off.  Reeds look good,  Carb jets and passages all seem to be clear and open. I swapped plug wires side to side and there was no change. I am considering swapping carbs to see if the problem follows the carb, but otherwise I am out of ideas. Does anyone have any ideas?

 

[JerzOutlaw350]

  What’s your outside temperature and humidity? Sometimes just a little bit of change in elevation can make a difference as well. These 3 factors listed above play a huge part in your jetting.
 
   What are the current carburetor settings mains, pilots, clip on the needle and how many turns “OUT”on the air screw from the seated position? What type of fuel are you using and at what fuel/oil ratio are you using? 
 

Please report back with more detail information. 
 
 

 

[JerzOutlaw350]

Even though this is for link is for Keihin carburetors this will explain and help you properly jet your carburetors. When it comes to jetting your carburetors it takes a lot time and plenty of patiences to get them properly tuned. 

https://static1.squarespace.com/static/5be4d5b35ffd2095efa9bdff/t/5bf1a09b6d2a7391b5a84730/1542561947962/KeihinCarbJetting-2015.pdf

 

[racin69z]

I am at work today, and cannot get the carbs off to get the current settings.  The thing that is wierd to me is why the left side isn't running correctly, when the right is.  The cylinders have almost identical cranking compression and leakdown.  I am back home now where i jetted the bike to run originally.  I have a decent understanding of jetting, no where near an expert, but most of my experience is with Mikuni round slide carbs, so at least that is good.  The 2 stroke end of it is fairly new to me.  I was going to put a scope down in the plug hole to look at the tops of the pistons and see how the crowns looked, but haven't had a chance.

[racin69z]

I fooled with it last night, and figured out that the cool head o ring was leaking combustion pressure into the cooling system on the left side. Thanks for the suggestions

 

[Tedder]

Take a good look at things to determine why it blew the oring. We're going to Silver Lake soon from Northeast Ohio. Don't know what kind of riding you do at home but to power through the sand and up those hills it'll generally require a little richer jetting.

[racin69z]

It was a really good time even though I never got the banshee on the sand.  Lots of cools vehicles to watch.  We are planning a trip back, but now we want to take our trucks, and sxs, and bikes, so I need a semi truck and trailer lol.  I was unaward of the requirement for richer jetting, I appreciate the heads up.   I am not sure why the oring let go.  The head was on the bike when I got it.  It is a pro design head and the domes are in pretty rough shape.  I am ordering another set of domes and will go from there.  Right now, it has 21cc domes.  They cylinder has been ported, raising the exhaust port a bit loosing some compression.  With it only cranking at 130, I am considering going to a 20 or 19cc dome to get closer to 150 psi.  From what I have read, 150 seems to be the cutoff for pump 93 octane.