All was well until I did the Nyroc pipe mod... I have a 03 Prairie 650 that I have added a twn air filter, black secondary spring, DG Snorkel, and a DynoJet Kit. With that setup, I noticed performance gains at mid and top end. Maybe I had more low end but couldn't really tell without some kind of performance metrics. So in my quest to try to get more out of it, and dtay ahead of my good friend FruitJacket and his Grizz 660, I tried the muffler mod. I drilled out 6 7/16" holes and cut out the end cap plus spark arrester. After that, based on some posts, I removed the DynoJet Mains and put in Keihn 142 in the front and put a 145.5 in the rear. I am at arond 800 to 1000 feet above sea level so I left the Dynojet needle in at the 5th notch. It started well, idled well, and seemed to accelerate nicely. The problem surfaced on the trail when it warmed up. I typically ride at around 1/4 throttle on the trails around here and when coming upon a corner slow a bit and goose it to take the corner. That is when I noticed a stumble. It starts at around 1/8 throttle and stops just a bit before 1/4 throttle. Plugs seem to be a bit black if I hold it there and check. DynoJet techies tell me to put the old snorkle on and go to the 4th notch on the needle... Even worse... Air Filter is newly cleaned as well. As it sits right now, I have the stock snorkle, stock needles and Jets and it doesn't need to be warm anymore to happen but the plugs are black... I am at a loss here. Anybody ever experianece anything like this? I am thinking about buying a stock pipe and going back to stock everything but the air filter just to get a baseline... Then go from there. Could there be anything else I missed??? How can the muffler mod make it more rich or too rich????

Thanks for any help
Java

 

Maybe you should try it with the dynojet mains again if it run good before and only adding the muffler mod. I tried the 145 and 142 and when it warmed up, it cut out bad when in higher rpm . Went back to stock and run pretty well at 1800' with the mods.

 

Java are you running premuim fuel?

Put the needle in the 5th notch

Start with the 134 f and the 138 r jets and jet down as needed until the stumble goes away.

Your plugs should be white with a light tan ring close to the electrod.

 

Java

Just something to check. Is the choke sticking? Mine got water and mud in the cable. It caused the choke to stick a little and caused mine to run rich. Can't beleive the muffler mod would cause a rich problem. If your luck is like mine, the rusty cable would show its face right when you are trying to figure out the jetting.LOL

 

When I did the same stuff I ran into the same problem. Drove me crazy it was my chock springs I must have got sand in the cable I did replace the springs only took the dj kit out thougt my be that was the problem but Im shur it was just the chokes hanging up GOOD LUCK!

 

Thanks guys,

Looks like the only way to check the choke properly is to pull the carb, right? I poked around a little without yanking it and can't seem to do anything with the choke...

Java

 

Well,

I yanked the carbs and took a look at the choke springs and all I found was a piece of hairlike fiber in one of the plungers. No mud or anything else. I put 'er all back together and still the same hesitation at off idle when it gets warm... It idles fine and at just before 1/4 throttle to full throttle, it seems to run fine. I guess I will buy a stock pipe and take everything back to stock to get a baseline and then start from there unless anyone else may have some ideas...

Thanks,
Java

 

You havent mentioned anything about the mixture screws and the pilot jets. Have you tried going leaner on the mixture screw? What happens then?
Usually a stumble is caused from a lean condition, but you say the plugs are black. Try doing a test drive, and just before you accelerate , thru the problem area, pull the choke on. If the conditions get better, then its lean.
Have you checked for vacumn leaks around the carb boots?

 

Hey HondaBuster, you are right about being lean. I can't explain the black plugs, but when I apply the choke it stops stumbling runs better. Then if I increase throttle to the point where it hesitates again and if I turn off the choke it runs better again. Not sure how to resolve this and it only started after I drilled out my pipe. I never had the problems with just a snorkle, twin air filter, and dynojet kit in it. How fo I richen it at off idle to 1/8 throttle? Do I put the Dyno Jet kit back in and go to the 6th notch? Any suggestions?

Thanks a bunch,
Java