Jetting help!

5 replies to this topic
  • Danco

Posted September 03, 2002 - 04:13 AM


Hi all,

I just installed my White Bros. E-Series S-bend on my uncorked 01 BRP. It ran great with the cored out stock exhaust. Now I get a low speed stumble when the throttle is cracked. Once it gets going it screams. I have the 178 main jet, 68s pilot and the needle clip in the 4th position. Adjusting the pilot does not help it. I currently have it at 2.5 turns out. Removing 4 discs for a total of 8 helped some but not much. It's not really that bad but noticable. Any suggestions? Thanks.

  • needsprayer

Posted September 03, 2002 - 05:00 AM



Are you talking about cracking the throttle open from an idle or at a point above idle, but still below the 1/4 throttle range. The stock carb does not allow you to go from idle to WTO without a bog (or worse a stall). You must roll the throttle on from an idle.

If you are experiencing this bog from an above idle starting point it is best to start troubleshooting with a clean plate. I hope you have a manual. Put in a new plug, clean air filter, lube and inspect throttle cables for slack and return Pilot Screw to stock position. Adjust idle speed according to manual and then determine if problem persists. If so , make one change at a time. Start with simple stuff like checking the Pilot Jet for looseness. This will also allow you to inspect the float bowl for contaminants. If all is well try changing back to the stock (65) Pilot Jet.

Good luck

[ September 03, 2002, 08:45 AM: Message edited by: needsprayer ]

  • Danco

Posted September 03, 2002 - 05:19 AM


Thanks Needsprayer! It's only from a dead crack of the throttle. When I roll on - no problems. It seemed like it was not a problem with the stock exhaust. Maybe it's just me. My brother now tells me to drop the clip to the 5th postion which may solve the problem. I may call White Bros. to see what they have to say. Thanks.

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  • Potato

Posted September 05, 2002 - 03:46 PM


Do as your brother says play with the needle position you should be able to clean it up. Are you running a stock air filter? If so you'll need to get a good high flow filter.
Good luck!

  • motometal

Posted September 07, 2002 - 07:47 AM


wouldn't going to a leaner pilot jet (stock) make it worse???

  • needsprayer

Posted September 08, 2002 - 04:32 AM



I will try to explain my reasoning for giving the 65 Pilot another try.

My assumption was that if a bog (from a blip) persisted after the idle speed was properly adjusted with the 68s pilot jet then perhaps a rich condition existed.

This following is taken from a discussion about Constant Vaccum (CV) carburetors (I.e. Keihin) at

"Pilot circuit (zero to 1/8 throttle): The mixture is rich if the throttle is lightly 'blipped' and the idle speed drops below the set idle speed before rising up to the set speed." This is a bog condition.

Please bear with me, I am not a jetting expert. I am running the stock Pilot Jet (65) at 4500' altitude and find that I can blip the throttle (not WTO) without a bog. As I said before the Keihin carburetor wants the throttle to be rolled on from idle,not cracked WTO.

Lot's of people run the 68s. Of course elevation and temperature have an effect. I was suggesting a change based on what is working for me. :)

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