Problem with bottom end jetting

[SunDevil]

I just put a new piston (87mm JE 10.8:1) and Hot cam stg 2 in my quad and I am having trouble getting it jetted correctly. After reading this site for a while I went to a 42 main jet, moved the needle (Dyno Jet ) position down one and a main jet of 158 (keihn). Altittude that I tested it was at 4000 feet and temp was about 60 degrees. It idles fine but as I start to take off the quad sputters and chugs along with no power gain, and the as I get past 1/4 throttle the quad takes off and then run great after that. I run with no air box and white bros slip on. I have tried the mixture screw at 3 turns , 2 1/2 and 1 1/2 and there is no difference. It seems to idle better at 1 1/2. I can not figure out if it is getting to much fuel or not a enough. I pulled the plug and it was dark brown. Please help...Thanks

[Glamis400ex]

I think maybe a #42 pilot is too rich for 4000 ft. Try a #40. For what it's worth, I had a Dynojet needle in mine, and I went back to stock. Helped the jetting become easier to figure out.

Here's my set up.

168 main(keihin) a tad rich tho.
42 pilot
stock needle, 4th clip
2 and 1/2 turns out on air screw
no airbox lid
no choke

[SunDevil]

I also ride at Glamis and before I put the 416 kit on I could just change the main jet for the different altitude and not mess with anything else. The problem is I can't tell if it is running rich or lean.

[Glamis400ex]

I also had an air leak in the carb, so my prob I had that to contend with also. Does it speed up and then slowly die?

Glamis

[SunDevil]

when it is idling for a couple minutes it wll speed up for a few seconds then it will slow down to normal and then speed up again but not die.

[Glamis400ex]

You probalby have an air leak. Mine did the same thing, only more radical. Mine would speed up super fast, then die out. I tore the whole carb apart, shot out all the passages (main, pilot, throttle valve) with carb cleaner. The o-ring on the top of the carb wasn't seated 100% in the groove and that was causing the air leak.

Check the intake at the head and carb and if you moved your needle, check the cover on top of the carb and make sure that o-ring is in the groove, if it's even a tiny bit out, it leaks.

When its running take some starting fluid or carb cleaner and shoot a little at the connection of the head intake, the air boot to carb intake and the top of the carb cover. If it speeds up SUPER quick, that's your air leak.

Glamis

[cals400ex]

ever since i installed my stage 2 cam, mine never idled right. the idle fluctuates up and slowly goes down to almost nothing after the bike warms up. when the bike is cold, it idles just fine. i had to turn my fuel skrew in to 1.5 turns out with my 42 pilot jet. but i live at 625 ft above sea level. you will need it to be leaner. so, i would try the 40 pilot. it seems as if my jetting leaned out on the pilot jet/fuel skrew after installed my cam/piston. i have had my carb and exhaust off a couple of times so i don't think i have an air leak there. by the way, i don't know if if you are suppose to use dynojet needles with the stock mainjets?? just something to consider, but it may work fine.

[Glamis400ex]

Before I did my 416, I had a Dynojet needle with a stocker main jet. It was on the 3rd clip from top. So, it does work, but jetting gets a little tricky due to the fact that your trying to use 2 different ways of metering, in the same carb. I dunno

Ever since I put the carb back to stock, it's been easier to figure out the jetting and doesn't seem so "touchy" now.

Just my 2 cents...

Glamis

[zephead400ex]

Originally posted by SunDevil
I just put a new piston (87mm JE 10.8:1) and Hot cam stg 2 in my quad and I am having trouble getting it jetted correctly. After reading this site for a while I went to a 42 main jet, moved the needle (Dyno Jet ) position down one and a main jet of 158 (keihn). Altittude that I tested it was at 4000 feet and temp was about 60 degrees. It idles fine but as I start to take off the quad sputters and chugs along with no power gain, and the as I get past 1/4 throttle the quad takes off and then run great after that. I run with no air box and white bros slip on. I have tried the mixture screw at 3 turns , 2 1/2 and 1 1/2 and there is no difference. It seems to idle better at 1 1/2. I can not figure out if it is getting to much fuel or not a enough. I pulled the plug and it was dark brown. Please help...Thanks

If you still have the stock needle, I would put it back in and possibly drop it 1 more notch along with messing with the mixture screw. At 1/4 throttle the pilot jet and needle are the factors. The main jet is 3/4 to WOT, so that is probably not the problem.

hope this helps

later

[speedy400]

my jetting is about the same as yours....almost... also I use Dyno jets. well my jetting is-
DJ 175(from a ds650 jet kit)
DJ needle at the 3rd position with the clip under the clip
45 pilot
3 1/2 turns out on the fuel screw
mine still backfires but it somewhat gives you a better guess....-darren