Saturday afternoon I installed and emgo cone air filter to replaced the stock filter and box. I jetted up from 400 to 410.It installed right on the back of the 42mm flatside.The filter hurt the sport 400 more than it helped. It used to wheelie hard on the launch,now it seems the bottom end is dead, and I still have the mid range power loss. I lost a dirt drag to a 300ex several times. Anyone know of a manual that one could use to tune these machines. Mine is wickedly fast, just takes forever to get there. It seems everything I do to increase performance does the opposite.

98 sport 400L
rcr stage 1 pipe & silencer
hpd trailpiped/ported clutch kit
v force delta reed cage
hsp 42mm carb
Emgo cone airfilter

 

Biggin, Did you get your 42 from Hot Seat? If so, or, I guess it doesn't matter, but they sell a leaner cut slide and a richer needle for the 42. These two units really make a difference on the throttle response end. I would take some plug readings at your 1/4, 1/2, 3/4, and wot settings just to see where you're at.

Ken

 

biggin,

It sounds like it's too lean on the bottom. While you did the correct thing to upsize the main jet, the other jets are also working at full throttle too. If I read your post right, you are just having trouble on the bottom end.

 

I went to a friends today(he is a street bike man)and was bitc#ing about my quads problems. He told me of a local 2 stroke "Guru" who came of age when 2 strokes ruled. This man is has been in the bike repair for at least 12 years. I have been riding by his shop for years and never once thought of going in. My bud said 2 strokes are alomost a black magic when it comes to tuning for peak performance. I have read web sites on tuning but there are so many ifs, buts and other words that compound the tuning procedure to league out of my reach. The sport engine is a fresh rebuild so I know that is not the problem. It is the ficklest machine.I know that pipes play an important role in the engines performance but so does eveything else.I bought the carb from hotseat and besides the mainjet I have not adjusted it. Mr. Chero, the plug was wet and oily black when I changed it. I asked a guy on an ATC250R why I was back firing so much and he said to change the plug,so I did it and I did not back fire once Sunday.(it only back fired when I cranked it while it was warm)You said it is lean, but wouldn't that plug show other wise.I had been using a 400 main jet until I got the emgo, now I use a 410.The needle clip is in the middle position.My set up is at 300ft elevation:1)engine is stock(2) v force reed cage(3) hsp 42mm flatside with 410 main jet and needle clip in the middle(4) Emgo cone air filter(5) RCR top end pipe and silencer(6)clutching is 58g wieghts with orange primary and violet secondary(7) stock sprockets(8)Stock size tires(9) .029in gapped plug.
Long post and confused, should I just pay to have it tuned or can some body see the problem. It is like the sport is going on strike some days and running with the big dogs on others.SUnday I had no back firing with the fresh plug,but could not hang with a 300ex or a blaster. HELP!