View Full Version : 16 discs and still fouling plugs?

chief john
03-14-2011, 08:43 AM
I have a a 1999 Indian with 88 c.i. S&S, Super E carb 2:1 exhaust. I wanted it a little louder so I now have 16 discs with open end cap. It was put on Dyno and they rejetted carb. I get average 100 miles before plugs foul. I like the way it sounds but should I try to add 2 more discs to start or have the carb jetted back? It runs great when it runs, lot of power. P.S. Super E says drag pipes will make carb malfunction, does this qualify? Thank you for any response.

03-15-2011, 07:04 AM
16 discs and an open end-cap on a 3" disc muffler is pretty much flowing the core assembly, there would be no benefit to adding discs. Even though your at about max flow for that pipe, I wouldn't consider the 2:1 merge pipe a "drag pipe" by any means. I'd talk to your tuner about potential jetting changes.

03-15-2011, 11:31 PM
Absolutely rejet.

I don't know how much you know about carb fuel circuits, but you may be rich on some or all of them. I'd start by finding out what your bike's stock jetting, jet needle, pilot jet, pilot air screw turns and float height were and compare them to what they are now. I'll bet your main & pilot jet are several sizes larger, your jet needle is potentially raised too high, your pilot air screw is turned 1/2 - 2.0 turns more than stock and your float height may be improperly set.

The fact that you are fouling plugs also means your bike, as powerful as you think it is, is actually less powerful than stock and is underperforming. It's underperforming because it's choking on fuel it cannot burn. If you reduce your jetting from the way it is jetted now, your engine's power output will increase. The way you can do this is by first setting the main jet correctly and working your way down. Factory Pro has a DIY procedure (http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,cv,high_rpm_engines.html) that you can follow to accomplish this and you don't need to buy a jet kit or pay a tune shop to accomplish the task. Just buy what you need from your HD dealer or anyone who sells jets for your carbs. It's how every carburetor can be tuned to the power characteristics you are after...after all, you'll be doing the jetting and recording the results.

http://justkdx.dirtrider.net/images/Smaller_PWK_highlow_speed_animation.gif (http://justkdx.dirtrider.net/printcarbtuning.html)

When you are done, I'd also recommend having your carburetors synchronized. That's especially important an a large displacement V-Twin, since it will set both carbs to flow identically; reducing vibration and increasing HP.