Marks exhuast low end stumble

[dodgediesel59]

So i got my bike all figured out which is bone stock for the motor. I put a marks exhaust on my buddies bike and did everything i did and he has a low end stumble from idle to about 3K. You can hear it kinda sputter and miss. Its an 04 with about 8,000 miles and ran great before. I shimmed needles .037 and tried pilot adjustments between 2-3 1/2 turns with no change in the stumble. Pulled plugs and the front right was just off white and the right rear was a gray color. If you guys could give me a little direction as what i can do here it would be much appreciated!

 

[KosRider]

Dodgediesel59,
my only suggestion is to check the float level of the carbs. Sounds like it might be rich. You can check the wet method (see the carb section of this forum for details) to see how close it is to the 17 mm they currently are. Anything over 15 mm should require disassembly of the carbs to adjust. My 06 from the factory was way above the 15mm mark; too rich. After adjusting to 17mm (took a couple times to get there) bike runs great with the Mark Pipes and the same changes you made.

 

[[email protected]]

Not sure how long it was between the bike running fine and the new marks were installed. Are you positive the pilot jets are clear? Pretty common for them to get plugged up from sitting for a period of time.

As mentioned, float level is very important and often overlooked.

When tuning my bike it ran terrible from idle up to around 4K rpm. It would surge and buck. Almost like the engine was cold but it never got any better after heating up. I raised the needle up 1 clip and it smoothed out and ran fine. Not saying for sure this is the problem. I think about .040 is all you can go with stock needles so it doesn't sound like you have much room left to adjust.

Are the carb vent hoses clear and routed properly routed? If not it will never run right. Is the air box, boots, carb boots, and vboost boots all installed properly with no leaks?

 

[SpecOps13]

Marshall, WI shows an average altitude of 879 feet. Your jetting will be a touch leaner than mine here at zero ft in Florida. Mark's 4-2 System. My plugs and bike run perfect: 152.5 Stock Mains, in fact, all carb jets are stock. Stock Needles are shimmed at 0,028 and the A/F Screws are 3 turns out. All of my plugs are running absolutely the same light golden tan on the insulator. Your friends plugs should be GTG. Only difference may be that I'm running Non Ethanol Fuel.... Ethanol would show up slightly leaner which is good because of your altitude...

Considering that you have 2 plugs that are not the same, you should compare all of them. One carb may be giving the problem you are seeing.

Good Luck,

 

[sdt354]

Exhaust leak a possibility? New gaskets? Diaphrams in right,o-ring in place?I like to go back and retighten everything after I ride it a little. I'm a one change at a time guy. Learned this the hardway .Do something,test ride ect.
Steve-o

 

[gamorg02]

you can try the a/f screws out to about 6 or 7 turns. i've seen them make a difference all the way out to 8 or so on a dyno.

if you're at the max of shimming your needle you may want to try a stg1 needle or a larger main. if you're running lean.

 

[dodgediesel59]

one of the needles wedged in the slide causing it to stick open. Found that the threaded in cap that holds the needle was pushing the needle tight and making it sit at a slight angle. I took about .020 off the bottom now it runs perfect. Thanks for all the help guys!

 

[dannymax]

Somebody just mentioned putting an o-ring under the shoulder on the threaded cap to allow for a little wiggle room for the needle. Seems like a good idea, or do what you did and remove a little material from the bottom.