Strange behavior...jetting help needed

[Blaster_Kart]

Well, we took the project blaster for its maiden voyage today. It is a stock engine except for an FMF SST pipe and an open clamp on K&N style filter. I started with a 290 main to be safe. Needle in the middle, 1.5 turns out on the pilot.

I want to say that I have read all the jetting threads, and I am having a hard time determining what the bike is doing.

I noticed a couple things. First, when you rev it in neutral, it takes a while to settle back down to idle. I hear this means lean. Well, turning the air screw doesnt seem to do too much, but I figured I would take it down the road to see what the main would do.

The thing kinda sputters a bit just off idle, and then cleans up and seems to "hit". It pulls fine through the midrange and then sputters/misses on top.

I figured its rich, and pulled the plug to find it black and sooty. I dropped down to a 280 main and tried again. Same thing. Wont pull clean to the top. Only place it seems right is midrange.

Then I put in a fresh plug and did a chop. TBH, the plug was hard to read. You could see a tan smoke haze on it, but it was not a "defined 2mm ring" like I hear you want to see. A few trips up and down the road, I come back, pull the plug, and its grey/black sooty again. So I figure I'm still just really rich. I drop to a 270 main.

I make another run up the road and it still wont pull cleanly through the top end. Now it kinda feels different. Like a surging as opposed to missing, but its hard to tell because I dont ride 2 strokes much and dont really know what Im listening/feeling for. Plug is still sooty grey/black.

Am I just that rich on the main? One thing I noticed is that if I short shift it, I can run at WOT, though once the RPMs climb enough, it starts to sputter/surge again.

My question is, should I keep dropping on the main? If it is lean on the main, how will it act? Its tough to tell if its falling on its face/surging lean, or blubbering rich... Plug tells me rich though.

Think I should try a 260 or drop the needle one clip? If its not raining I can get some video so you guys can hear all the things its doing tomorrow. I'll also get pics of the plugs.

Thanks for any help given to the jetting n00b.

 

[blasterman87]

put the needle clip in the middle and use a 290 again, maybe even bigger than that like a 310 and the clip a notch lower than the middle, your running lean

 

[Blaster_Kart]

Gotcha. I'll give that a shot. I think I have a 310 and a 315 to try.

 

[blasterman87]

yeah go with the 315, i have basically the same set up as you do intake/pipe wise and i have a 340 main with the needle in the middle

 

[Blaster_Kart]

Man that is so much larger than I see being suggested here normally. Usually you hear between 260-290 for a pipe and filter. Still I'll try going up as dropping down has not seemed to help.

 

[blasterman87]

yeah its larger as you have a clamp on filter, that makes a HUGE diffrence, not many people on here run a clamp on it has alot more flow than any airbox you can buy

 

[Outlawed Genetics]

if i didnt cross creeks regularly i'd have one but hell the creeks i cross usually leave me with a full air box with only a couple holes in the lid lol

 

[jeepinncreepin]

ive got a filter right on my carb stock pipes bored l40over im up to a 260 main and im thinking it might be to rich my plugs like a redish color still breaking it in

 

[Blaster_Kart]

Ok, I went with the largest jet I had which was actually a 310 and it was VERY rich. The symptoms got worse. Then just to be sure, I checked the needle and it turned out it was set one notch above the middle which made the needle one step leaner. I put it back in the middle(where I thought it was to begin with) and the 310 was still running horribly. Since I was out of ideas and jets, I said f*ck it and stuck a 260 in it. Now it pulls like mad. Seems to run really well. I did a plug chop with a fresh plug and it is looking a little lean though. Just a hint of mocha.

I think maybe the needle position was screwing me up during my first runs, so next weekend I will be trying the 270-290 again with the needle in the middle. I for sure cant run the 310 though. It wont pull anywhere in the range with that thing in there.

 

[Blaster_Kart]

You know, I do have a blue needle in this carb. From what I read it is a Vitos needle, and some say it has a different profile that makes it fatter up top than a normal needle. Is there any truth to that? Maybe that is why I am having trouble dialing it in...

 

[xjma]

I concur that with a clamp on filter you should be higher than that...but if it sputters and stuff the higher you go it must be rich....strange.

A non-stock needle would make a difference too. Usually needles are made to work with jet X through Y. That needle may not be made for the size jets your trying????

 

[blasterman87]

ask flotek about vitos needles, there not worthy of a tooth pick, toss it and get a stock needle

 

[Blaster_Kart]

Now we are getting somewhere. The Vitos needle was the problem. I bummed a stock needle from a pal of mine. Stuck it in there with a 290 and worked down to a 270. Pulls way better throughout the range, and doesn't do that rev limiter sputtery crap any more.

I would say its pretty darn close now. Maybe just a tad rich still. Here is a plug chop with the 270 main. Don't mind the redness, the cam was turning everything red tonight, even the grass. Must have been the lighting or my lack of camera skills.

 

[sev]

300 is way way to big if your on the stock mikuni move the clip to the middle and try a 270. that should do it for you if its just piped. but you just need to mess with it. eventually you'll get it.