I posted this same problem previously. I Grampsized my 800 and followed the instructions to the letter. Now, when I am running in 4th or 5th gear, and seems to have a strong headwind, the motor sputters and chokes. I had an idea to try to pull the choke lever while its sputtering, and the motor smooths out and seems to run better. If I release the choke lever and it retracts, the motor sputters again. I don't know if I am getting too much air and need to put a baffle back into the breather, or turn the adjusting screw further out to make the air/fuel mixture richer. I need someone to enlighted me if they have had this type of problem after Grampsizing a bike.
I'll have to defer this thread to another 800 rider I did not modify my airbox or anything to do with my fuel system.
Clearly, you are running too lean. What needle/jet combination are you running? Did you get a DynoJet kit and install that, as per instructions? Do you have a shim under the needle, and last of all, is the diaphragm in good condition? Rubber parts wear out, and the bike is how many years old???
Quote from: oldschool on January 21, 2017, 14:49:17 PM
I posted this same problem previously. I Grampsized my 800 and followed the instructions to the letter. Now, when I am running in 4th or 5th gear, and seems to have a strong headwind, the motor sputters and chokes. I had an idea to try to pull the choke lever while its sputtering, and the motor smooths out and seems to run better. If I release the choke lever and it retracts, the motor sputters again. I don't know if I am getting too much air and need to put a baffle back into the breather, or turn the adjusting screw further out to make the air/fuel mixture richer. I need someone to enlighted me if they have had this type of problem after Grampsizing a bike.
I have not grampsized mine (still have the stock air filter) but I have done a Dynojet mod to the carb because I don't have stock exhaust. I had pretty much the same symptoms you describe where I had to choke the bike especially in cold weather to make it run right. Troll is the one who said I need to do a carb rejet, so I deferred to his expertise and bought a Dynojet kit. Have you done that on your bike? I'm no expert but the problem you describe was what I was experiencing and rejetting my carb cured it.
I grampsized my 800 and did not have these problems. Whey you said you followed the instructions - there were more than one option given in the instructions -- What size jets did you use? Sounds like you need to increase the jet size, perhaps.
Update to choking issue......I backed out the adjustment screw on bottom of carb. took it for about 100 mile run this past weekend. I did not have the sputtering issue as before. I hope this has fixed the problem but time will tell. I appreciate your input on my problem and I will keep you guys posted.