Banshee running rich all of a sudden

[racin69z]

I have a mild built banshee. Build consists of dune ported cylinders, FMF fattys, cool head 135 psi v force 4 reeds 30mm oko carbs with fuel inlet enlarged, uni filters.  Ran great all spring and summer. Drove 600 miles to silver lake and ran it for and hour running normally and all of a sudden it's popping and acting stupid rich. Altitude was within a few hundred feet, temp was the same as when I jetted back home. I did plug chops until the plug looked what I thought was good in the spring. Now it won't run clean enough to do a chop. Fouls borh plugs rich in seconds. I am very hesitant to jet down, because if whatever phenomenon caused it to go rich goes away, then it will probably burn up. 

 

I've replaced the coils and wires thinking they may have gotten weak with no change. I am going to try the stock carbs if I don't get any other suggestions. 

[rtg_61184]

What do the air filters look like? 

gas mixed same ratio?

Edited November 4, 2025 by rtg_61184

[racin69z]

Air filters mint. 32:1 super techoplate ever since it's built. Thanks for the ideas. 

[locogato11283]

Uni foam filters? Anyone have a set of KN you can try? I never cared for the Uni. They hold too much moisture, dirt and dust.

I'm betting the elevation and those filters are your problem. 

[racin69z]

I don't have any other filters, but I ran it without filters on the blacktop for a small stretch and it didn't change anything 

[locogato11283]

Chokes are off?

[racin69z]

Chokes are off. Haven't had a chance to fool with it lately but I'm starting to think it's ignition related and just showing up as rich in the plugs. My experience has always been ignition make plugs appear lean, but I just don't understand how it is rich all of a sudden. Up a silver lake I even turned the gas off and as it ran out of fuel, it still wouldn't rev, so I am going to dig into that if the stock carbs do the same thing these are

[gusto]

I’d do a compressions test next followed by a reed check. 
OKO’s have had issues with internals and people would upgrade those parts to Kehein  (probably not if)

If you can borrow a CDI for a few minutes that would cross that off the list 

you can ohm out a stator and I think there’s a vid on SouthTexas Banshee channel

[JerzOutlaw350]

What type of fuel are you using?  
 

 A few months ago I was working on a Banshee for a friend of one of guys that to that rides in our group. It was experiencing the same symptoms that you are describing. I went completely over the banshee from compression test to leak down test and exchanged carbs, reeds and even all the electrical part from an excellent running banshee and the symptoms were still there. It drove me absolutely nuts. I even drained the fuel to see if it was contaminated. It looked fine and so I put it back in and it still had the same symptoms. I then again drained all the fuel out and I even flushed the tank out and put some of my own fresh 32:1 pre-mix and the symptoms went away. So I talked with the owner and asked him what type of fuel he was using and he told me that he was running VP T2 fuel and mixing his fuel @ 32:1. He didn’t know that VP T2 comes already mixed @ 40:1 from VP racing. So he was adding 32:1 to fuel that was already pre-mixed @ 40:1. 

 So the problem could be with your fuel that you are using. A lot of states start right around August to switch to winter blend fuel and fuel at your local gas stations are loaded ethanol which is not good for anything other than your car depending on the percentage of ethanol. I have everything I own from my 1987 Buick GNX all the way down to my weed whacker is on an ethanol free diet. In my area I can get ethanol free 95 octane Sunoco Optima at the pump locally. 

[racin69z]

 

I am running pump 91-93 depending on what I can get. I'm not sure where that gas came from Missouri or Michigan. 

That's actually a great idea. I will buy a some fuel and try that. 

 

[racin69z]

I finally got around to working on this thing again. Changed to fresh gas, no change. Changed back to the stock carbs no change. Changed the stator and pickup coil, no change. It just will not run under power over 6k rpm. Anyone near southeast Missouri that has a CDI that I can borrow?  I tried 2 different Chinese CDIs and neither would even start the bike. I hate to buy an expensive name brand or OEM CDI and that not be the issue. 

[locogato11283]

Do you have Facebook?

If so, check with Preston Mason or Spencer Clipperton.

Both sell used Banshee parts. Preston is in Harrisonville, MO.

I bet it’s CDI. I’ve had the same tho my happen before and seen other bikes do the same thing.

[racin69z]

It was in fact the CDI. Runs great with a new one.