unusual jetting question.

Hi guys,
I know ya'll hate to answer these kinds of jetting questions but this one is a little different. I just got my quad back from my mechanic where he was putting in dynojets to go with my k&n filter, modded airbox lid, and an fmf PC4Q silencer and a powerbong header. He told me he put in the needle clip on position 3 on the DYNOJET NEEDLE, a 170 DYNOJET main jet, and the air screw 3.5 turns out. I am at about 15-200 ft above sea level on long island, new york. I was wondering what you guys thought of this jetting and how the sizing goes on a DYNOJET main jet. Is a 170 DYNOJET main like a 155 or 158 keihin main?? I know that the DYNOJETS are numbered higher but how much?? how do you think i will like this setup? Will I be able to beat my friend that has a Pro circuit t-4 and header with only a larger main jet and a filter????

Thanks in advance!!! Peace out.

[400exJOE]

170 is too rich. Dynojet and kehin jets alike. I would try the 160 dynojet.

[VegasEx'r]

That's right per the directions from Dynojet. I believe that the dynojet jets are bigger (a 170 Dynojet main is larger than a 170 Kehin main), but I could be wrong. Those settings will probably be pretty close, if not dead on. Install it & go on a 5 minute ride. Get on it full throttle, then let off all the way. If while you are slowing down you hear any pops (like backfiring) from the exhaust, you may be lean. After you get back, pull the plug & look at it. If it is white, you are lean, black you are rich (not likely), but if it is tan, you are in good shape. If anything you might need to put the clip on the 4th slot & go up to a 175. If you do those, make sure to change only one thing at a time (& remember that the MJ is easier to change than the needle).

[Wheelie]

Step up to a #40 pilot jet, lower the clip on the needle one notch from stock, and set your air screw at 2- 2 1/2 turns.

IF the dynojet #'s and the keihin #'s are the same, go with a 155 or 158 main jet. From my experience, seat of the pants is the best way to jet your quad, the spark plug can give an inaccurate reading due to additives in the fuel.

FYI--If your quad pulls good in the lower gears and doesn't have the top end power that it should, you are too rich on the main jet circuit. If the quad lags in the bottom gears and pulls the top gears o.k. then you are too lean.

When I first got my pipe, I ran a 160 main jet, my quad wouldn't fully rev in fourth gear in the sand. Also, hill climbing sucked, it revved slow and didn't have the pull I knew it should. After reading the article that showed the information above, I stepped down to a 158, it ran better, then a 155mj. It now pulls the hills like it should, and it pulls fifth in the sand with no problem.

Sorry so long, I'm bored.

I hope this helps, Good Luck!!


2000 400ex--E-Series slip-on, 12 discs, K&N w/outerwear, no airbox lid, welds in header cleaned up, no snorkel, #40pj, #155mj, clip on needle lowered one notch, screw out 2 turns. 0-2000ft. elevation.

[SGA]

I've heard the dyno jets are bigger than the kehein jets. I ride 15-100 feet above sea level. My 400 likes a 160 kehein main, needle clip down one from stock, a 40 pilot and about 2-1/2 turns out on the air screw. I had a 165 main in it and it was too rich. Much better top end power with the 160 main. I use kehein jets and the stock needle. Run what the mechanic put in for awhile and see how it does. I bet its pretty close to what you need. It takes a little time for the plug color to adjust to the new settings. hope this helps.

[ChadEXer]

A 170 main will probably be just a little rich. I was running a 170 main in my 416 with removed choke and many other mods and it was still a little rich!

Ok thanks anyway even though no one really answered my question. I read the dynojet instructions and the mechanic installed the right main jet, put in the right needle position and turned the air screw correctly. You guys are thinking out Keihin jets when you are saying its too rich!! Keihin jets are numbered totally different than Dynojet ones!!!! All that I was wondering was what size a 170 dynojet main is in a kehin jet. I'm guessing it'll be like a 155 or 158. thanks anyway, and just try to be a little more sure of what you're talking about when you reply! by the way, the quad is still a little lean so i called dynojet and he said to turn the airscrew out 1/4 to a 1/2 a turn(just in case anyone is having the same problem as me).

You asked....
"I was wondering what you guys thought of this jetting and how the sizing goes on a DYNOJET main jet"

Vegas'EXr responded.......
"I believe that the dynojet jets are bigger (a 170 Dynojet main is larger than a 170 Kehin main), but I could be wrong."

Then you respond with....
"thanks anyway, and just try to be a little more sure of what you're talking about when you reply!"

First off you asking for peoples opinions which many folks here gave you.. Secondly you asked about the sizing in which from the above was answered.. So whats up!!!

[400exredrider]

i dont know anything but i called WB on my pipe and they said they used a 165 and stock pilot and needle position and mines still LEAN!